- Y. W. Kim, M. T. Meyer, A. Berkovich, S. Subramanian, A. A. Iliadis, W. E. Bentley, and R. Ghodssi, "A surface acoustic wave biofilm sensor integrated with a treatment method based on the bioelectric effect," Sensors and Actuators A-Physical, 238, 140-149, 2016.
[Abstract]
Bacterial biofilms have an extensive impact on quality of life, ranging from severe infections in the clinical field to water facility contamination in environmental science. Biofilms are comprised of diverse bacteria that produce an extracellular matrix which prevents drug diffusion through them. Hence traditional antibiotic therapies require 500-5000 times the concentration used to eliminate non-biofilm-associated infections. Early biofilm detection is critical for effective eradication. Moreover, developing an alternative biofilm treatment method that utilizes low doses of antibiotics is desired. In this paper, a real-time microsystem is shown to detect growth of biofilms as well as their removal through integrated treatment. Detection of biofilms is achieved using a surface acoustic wave (SAW) sensor that monitors the total biomass by measuring the resonant frequency of the system. Biofilm treatment is based on the bioelectric effect (BE), a combination of low-dose antibiotics with application of both alternating and direct current signals. The detection limit of the SAW system is approximately 166 pg, corresponding to a bacterial population on the order of hundreds of bacteria. The system is used to observe an 80% reduction of total biomass when treated by the BE as compared to traditional antibiotics. Through system integration of the BE with the SAW sensor, simultaneous biofilm detection and treatment is achieved. The system consumes 194 mu W of power, with the sensor and treatment consuming 100 mu W and 94 mu W, respectively. The integrated sensing and treatment capabilities of this system advance the development of an innovative biofilm control method. (C) 2015 Elsevier B.V. All rights reserved.
- Y. W. Kim, M. P. Mosteller, S. Subramanian, M. T. Meyer, W. E. Bentley, and R. Ghodssi, "An optical microfluidic platform for spatiotemporal biofilm treatment monitoring," Journal of Micromechanics and Microengineering, 26 (1), 2016.
[Abstract]
Bacterial biofilms constitute in excess of 65% of clinical microbial infections, with the antibiotic treatment of biofilm infections posing a unique challenge due to their high antibiotic tolerance. Recent studies performed in our group have demonstrated that a bioelectric effect featuring low-intensity electric signals combined with antibiotics can significantly improve the efficacy of biofilm treatment. In this work, we demonstrate the bioelectric effect using sub-micron thick planar electrodes in a microfluidic device. This is critical in efforts to develop microsystems for clinical biofilm infection management, including both in vivo and in vitro applications. Adaptation of the method to the microscale, for example, can enable the development of localized biofilm infection treatment using microfabricated medical devices, while augmenting existing capabilities to perform biofilm management beyond the clinical realm. Furthermore, due to scale-down of the system, the voltage requirement for inducing the electric field is reduced further below the media electrolysis threshold. Enhanced biofilm treatment using the bioelectric effect in the developed microfluidic device elicited a 56% greater reduction in viable cell density and 26% further decrease in biomass growth compared to traditional antibiotic therapy. This biofilm treatment efficacy, demonstrated in a micro-scale device and utilizing biocompatible voltage ranges, encourages the use of this method for future clinical biofilm treatment applications.
- A. X. Lu, Y. J. Liu, H. Oh, A. Gargava, E. Kendall, Z. H. Nie, D. L. DeVoe, and S. R. Raghavan, "Catalytic Propulsion and Magnetic Steering of Soft, Patchy Microcapsules: Ability to Pick-Up and Drop-Off Microscale Cargo," ACS Applied Materials & Interfaces, 8 (24), 15676-15683, 2016.
[Abstract]
We describe the creation of polymeric micro capsules that can exhibit autonomous motion along defined trajectories. The capsules are made by cross-linking aqueous microdroplets of the biopolymer chitosan using glutaraldehyde. A coflow microfluidic tubing device is used to generate chitosan droplets containing nanoparticles (NPs) with an iron (Fe) core and a platinum (Pt) shell. The droplets are then incubated in a Petri dish with the cross-linking solution, and an external magnet is placed below the Petri dish to pull the NPs together as a collective "patch" on one end of each droplet. This results in cross-linked capsules (similar to 150 mu m in diameter) with an anisotropic (patchy) structure. When these capsules are placed in a solution of H2O2, the Pt shell of the NPs catalyzes the decomposition of H2O2 into O-2 gas, which is ejected from the patchy end in the form of bubbles. As a result, the capsules (which are termed micromotors) move in a direction opposite to the bubbles. Furthermore, the micromotors can be steered along specific paths by an external magnet (the magnetic response arises due to the Fe in the core of the NPs). A given micromotor can thus be directed to meet with and adhere to an inert capsule, i.e., a model cargo. Adhesion occurs due to the soft nature of the two structures. Once the cargo is picked up, the micromotor-cargo pair can be moved along a specific path to a destination, whereupon the cargo can be released from the micromotor. We believe these soft micromotors offer significant benefits over their existing hard counterparts because of their biocompatibility, biodegradability, and ability to encapsulate a variety of payloads.
- S. Subramanian, K. Gerasopoulos, M. Guo, H. O. Sintim, W. E. Bentley, and R. Ghodssi, "Autoinducer-2 analogs and electric fields - an antibiotic-free bacterial biofilm combination treatment," Biomedical Microdevices, 18 (5), 2016.
[Abstract]
Bacterial biofilms are a common cause of chronic medical implant infections. Treatment and eradication of biofilms by conventional antibiotic therapy has major drawbacks including toxicity and side effects associated with high-dosage antibiotics. Additionally, administration of high doses of antibiotics may facilitate the emergence of antibiotic resistant bacteria. Thus, there is an urgent need for the development of treatments that are not based on conventional antibiotic therapies. Presented herein is a novel bacterial biofilm combination treatment independent of traditional antibiotics, by using low electric fields in combination with small molecule inhibitors of bacterial quorum sensing autoinducer-2 analogs. We investigate the effect of this treatment on mature Escherichia coli biofilms by application of an alternating and offset electric potential in combination with the small molecule inhibitor for 24 h using both macro and micro-scale devices. Crystal violet staining of the macro-scale biofilms shows a 46 % decrease in biomass compared to the untreated control. We demonstrate enhanced treatment efficacy of the combination therapy using a high-throughput poly-dimethylsiloxane-based microfluidic biofilm analysis platform. This microfluidic flow cell is designed to reduce the growth variance of in vitro biofilms while providing an integrated control, and thus allows for a more reliable comparison and evaluation of new biofilm treatments on a single device. We utilize linear array charge-coupled devices to perform real-time tracking of biomass by monitoring changes in optical density. End-point confocal microscopy measurements of biofilms treated with the autoinducer analog and electric fields in the microfluidic device show a 78 % decrease in average biofilm thickness in comparison to the negative controls and demonstrate good correlation with real-time optical density measurements. Additionally, the combination treatment showed 76 % better treatment efficacy compared to conventional antibiotic therapy. Taken together these results suggest that the antibiotic-free combination treatment described here may provide an effective alternative to traditional antibiotic therapies against bacterial biofilm infections. Use of this combination treatment in the medical and environmental fields would alleviate side effects associated with high-dosage antibiotic therapies, and reduce the rise of antibiotic-resistant bacteria.
- M. S. Wiederoder, I. Misri, and D. L. Devoe, "Impedimetric immunosensing in a porous volumetric microfluidic detector," Sensors and Actuators B-Chemical, 234, 493-497, 2016.
[Abstract]
A sensitive and rapid impedemetric immunosensor is demonstrated utilizing porous volumetric microfluidic detection elements and silver enhanced gold nanoparticle probes. The porous detection elements significantly increase capture probe density and decrease diffusion length scales compared to conventional planar sensors to improve target capture efficiency and enhance impedance signal. In this work, a packed bed of silica beads functionalized with antibody probes serves as a porous sensor element within a thermoplastic microchannel, with an interdigitated gold electrode microarray used to measure impedance changes caused by the concentration dependent formation of silver aggregates. The measured impedance change is independent of electrode spacing, enabling a device with low resolution electrodes to achieve a sandwich immunoassay detection limit between 1 and 10 ng/mL with a 4-log dynamic range, with a total assay time of 75 min. (C) 2016 Elsevier B.V. All rights reserved.
- T. E. Winkler, H. Ben-Yoav, and R. Ghodssi, "Hydrodynamic focusing for microfluidic impedance cytometry: a system integration study," Microfluidics and Nanofluidics, 20 (9), 2016.
[Abstract]
We present the first in-depth system integration study of in-plane hydrodynamic focusing in a microfluidic impedance cytometry lab-on-a-chip. The method relies on constricting the detection volume with non-conductive sheath flows and characterizing particles or cells based on changes in impedance. This approach represents an avenue of overcoming current limitations in sensitivity with translating cytometers to the point of care for rapid, low-cost blood analysis. While examples of integrated devices are present in the literature, no systematic study of the interplay between hydrodynamics and electrodynamics has been carried out as of yet. We develop analytical and numerical models to describe the impedimetric response of the sensor as a function of cellular characteristics, physical flow properties, and device geometry. We fabricate a working prototype lab-on-a-chip for experimental validation using latex particles. We find that ionic diffusion can be a critical limiting factor even at high Peclet number. Moreover, we explore geometric variations, revealing that the ionic diffusion-related distance between the center of the hydrodynamic focusing junction and the impedance measurement electrodes plays a dominant role. With our device, we demonstrate over fivefold enhancement in impedance signals and population separation with in-plane hydrodynamic focusing. It is only through such in-depth system studies, in both models and experiments, that optimal utilization of microsystem capabilities becomes possible.
- C. J. Wolfram, G. W. Rubloff, and X. L. Luo, "Perspectives in flow-based microfluidic gradient generators for characterizing bacterial chemotaxis," Biomicrofluidics, 10 (6), 2016.
[Abstract]
Chemotaxis is a phenomenon which enables cells to sense concentrations of certain chemical species in their microenvironment and move towards chemically favorable regions. Recent advances in microbiology have engineered the chemotactic properties of bacteria to perform novel functions, but traditional methods of characterizing chemotaxis do not fully capture the associated cell motion, making it difficult to infer mechanisms that link the motion to the microbiology which induces it. Microfluidics offers a potential solution in the form of gradient generators. Many of the gradient generators studied to date for this application are flow-based, where a chemical species diffuses across the laminar flow interface between two solutions moving through a microchannel. Despite significant research efforts, flow-based gradient generators have achieved mixed success at accurately capturing the highly subtle chemotactic responses exhibited by bacteria. Here we present an analysis encompassing previously published versions of flow-based gradient generators, the theories that govern their gradient-generating properties, and new, more practical considerations that result from experimental factors. We conclude that flow-based gradient generators present a challenge inherent to their design in that the residence time and gradient decay must be finely balanced, and that this significantly narrows the window for reliable observation and quantification of chemotactic motion. This challenge is compounded by the effects of shear on an ellipsoidal bacterium that causes it to preferentially align with the direction of flow and subsequently suppresses the cross-flow chemotactic response. These problems suggest that a static, non-flowing gradient generator may be a more suitable platform for chemotaxis studies in the long run, despite posing greater difficulties in design and fabrication. Published by AIP Publishing.
- F. H. Zang, K. Gerasopoulos, X. Z. Fan, A. D. Brown, J. N. Culver, and R. Ghodssi, "Real-time monitoring of macromolecular biosensing probe self-assembly and on-chip ELISA using impedimetric microsensors," Biosensors & Bioelectronics, 81, 401-407, 2016.
[Abstract]
This paper presents a comprehensive study of the self-assembly dynamics and the biosensing efficacy of Tobacco mosaic virus-like particle (TMV VLP) sensing probes using an impedimetric microsensor platform. TMV VLPs are high surface area macromolecules with nanorod structures constructed from helical arrangements of thousands of identical coat proteins. Genetically modified TMV VLPs express both surface attachment-promoting cysteine residues and FLAG-tag antibody binding peptides on their coat protein outer surfaces, making them selective biosensing probes with self-assembly capability on sensors. The VLP self-assembly dynamics were studied by the continuous monitoring of impedance changes at 100 Hz using interdigitated impedimetric microsensors. Electrical impedance spectroscopy revealed VLP saturation on impedance sensor surface with the coverage of 68% in self-assembly process. The VLP-functionalized impedance sensors responded to 12 ng/ml to 1.2 mu g/ml of target anti-FLAG IgG antibodies in the subsequent enzyme-linked immunosorbent assays (ELISA), and yielded 18-35% total impedance increases, respectively. The detection limit of the target antibody is 9.1 ng/ml using the VLP-based impedimetric microsensor. These results highlight the significant potential of genetically modified VLPs as selective nanostructured probes for autonomous sensor functionalization and enhanced biosensing. (C) 2016 Elsevier B.V. All rights reserved.
- H. Ben-Yoav, P. H. Dykstra, W. E. Bentley, and R. Ghodssi, "A controlled microfluidic electrochemical lab-on-a-chip for label-free diffusion-restricted DNA hybridization analysis," Biosensors & Bioelectronics, 64, 579-585, 2015.
[Abstract]
Lab-on-a-chip (LOC) devices for electrochemical analysis of DNA hybridization events offer a technology for real-time and label-free assessment of biomarkers at the point-of-care. Here, we present a microfluidic LOC, with 3 x 3 arrayed electrochemical sensors for the analysis of DNA hybridization events. A new dual layer microfluidic valved manipulation system is integrated providing controlled and automated capabilities for high throughput analysis. This feature improves the repeatability, accuracy, and overall sensing performance (Fig. 1). The electrochemical activity of the fabricated microfluidic device is validated and demonstrated repeatable and reversible Nernstian characteristics. System design required detailed analysis of energy storage and dissipation as our sensing modeling involves diffusion-related electrochemical impedance spectroscopy. The effect of DNA hybridization on the calculated charge transfer resistance and the diffusional resistance components is evaluated. We demonstrate a specific device with an average cross-reactivity value of 27.5%. The device yields semilogarithmic dose response and enables a theoretical detection limit of 1 nM of complementary ssDNA target. This limit is lower than our previously reported non-valved device by 74% due to on-chip valve integration providing controlled and accurate assay capabilities. (C) 2014 Elsevier B.V. All rights reserved.
- H. Ben-Yoav, S. E. Chocron, T. E. Winkler, E. Kim, D. L. Kelly, G. F. Payne, and R. Ghodssi, "An Electrochemical Micro-System for Clozapine Antipsychotic Treatment Monitoring," Electrochimica Acta, 163, 260-270, 2015.
[Abstract]
Clozapine is the most effective antipsychotic medication for schizophrenia, but it is underutilized because of the inability to effectively monitor its treatment efficacy and side effects. In this work, we demonstrate the first analytical micro-system for real-time monitoring of clozapine serum levels. An electrochemical lab-on-a-chip is developed and integrated with a catechol-chitosan redox cycling system. The microfabricated device incorporates 4 electrochemical reaction chambers with the capability of analyzing microliter-volume samples. Integration of the catechol-chitosan film amplifies the clozapine oxidative signal and improves the signal-to-noise ratio, which addresses sensitivity and selectivity challenges. Optimization of the redox cycling system fabrication parameters and analysis of various electrochemical techniques and data processing approaches is implemented to maximize clozapine detection performance. The device is tested with buffer samples containing clozapine and demonstrates a sensitivity of 54 mu C mL cm (2) mu g (1) and a limit-of-detection of 0.8 mu g mL (1), a sensing performance similar to a counterpart macro-scale benchtop system. Importantly, the feasibility to differentiate between 0.33 mu g mL (1) and 3.27 mu g mL (1) clozapine concentrations in human serum without any preceding dilution or filtering procedures is demonstrated, a significant step towards utilizing point-of-care testing micro-systems for schizophrenia treatment management. With these micro-systems, we envision more effective and safe treatment that will enable fewer visits to the clinicians, decrease costs and patient burden. (C) 2015 Elsevier Ltd. All rights reserved.
- J. N. Culver, A. D. Brown, F. Zang, M. Gnerlich, K. Gerasopoulos, and R. Ghodssi, "Plant virus directed fabrication of nanoscale materials and devices," Virology, 479, 200-212, 2015.
[Abstract]
Bottom-up self-assembly methods in which individual molecular components self-organize to form functional nanoscale patterns are of long-standing interest in the field of materials sciences. Such self-assembly processes are the hallmark of biology where complex macromolecules with defined functions assemble from smaller molecular components. In particular, plant virus-derived nanoparticles (PVNs) have drawn considerable attention for their unique self-assembly architectures and functionalities that can be harnessed to produce new materials for industrial and biomedical applications. In particular, PVNs provide simple systems to model and assemble nanoscale particles of uniform size and shape that can be modified through molecularly defined chemical and genetic alterations. Furthermore, PVNs bring the added potential to "farm" such bio-nanomaterials on an industrial scale, providing a renewable and environmentally sustainable means for the production of nano-materials. This review outlines the fabrication and application of several PVNs for a range of uses that include energy storage, catalysis, and threat detection. (C) 2015 Elsevier Inc. All rights reserved.
- X. Z. Fan, L. Naves, N. P. Siwak, A. Brown, J. Culver, and R. Ghodssi, "Integration of genetically modified virus-like-particles with an optical resonator for selective bio-detection," Nanotechnology, 26 (20), 2015.
[Abstract]
A novel virus-like particle (TMV-VLP) receptor layer has been integrated with an optical microdisk resonator transducer for biosensing applications. This bioreceptor layer is functionalized with selective peptides that encode unique recognition affinities. Integration of bioreceptors with sensor platforms is very challenging due their very different compatibility regimes. The TMV-VLP nanoreceptor exhibits integration robustness, including the ability for self-assembly along with traditional top-down microfabrication processes. An optical microdisk resonator has been functionalized for antibody binding with this receptor, demonstrating resonant wavelength shifts of (Delta lambda(o)) of 0.79 nm and 5.95 nm after primary antibody binding and enzyme-linked immunosorbent assay (ELISA), respectively, illustrating label-free sensing of this bonding event. This demonstration of label-free sensing with genetically engineered TMV-VLP shows the flexibility and utility of this receptor coating when considering integration with other existing transducer platforms.
- J. Felder, E. Lee, and D. L. DeVoe, "Large Vertical Displacement Electrostatic Zipper Microstage Actuators," Journal of Microelectromechanical Systems, 24 (4), 896-903, 2015.
[Abstract]
An out-of-plane electrostatic microactuator delivering exceptionally high vertical displacements is described. The devices, based on an electrostatic zipper actuator design, employ composite Si/SiO2 beams with engineered stress gradients that result in large and controllable beam curvatures. The microactuators are fabricated in a silicon-on-insulator/deep reactive-ion etching process, with an additional oxidized silicon wafer serving as a bonded ground electrode. Simple cantilever Si/SiO2 zipper actuators are investigated and extended to a meander configuration with regions of variable curvature able to produce large tip deflections in a small on-chip footprint. An analytic model is presented and used to optimize deflection of the meander-shaped zipper actuators, followed by the implementation of a full microstage actuator employing parallel meanders connected to a moving silicon stage. Using this configuration, purely vertical actuation is realized. The static deflections of various actuator designs are characterized and shown to be in a good agreement with analytical predictions. Fabricated microstage actuators achieving deflections up to 60% of their in-plane dimensions are described, and reliable actuation over nearly 106 Hz is demonstrated.
- J. Feldman, B. M. Hanrahan, S. Misra, X. Z. Fan, C. M. Waits, P. D. Mitcheson, and R. Ghodssi, "Vibration-Based Diagnostics for Rotary MEMS," Journal of Microelectromechanical Systems, 24 (2), 289-299, 2015.
[Abstract]
This paper demonstrates the use of low-cost off-the-shelf (OTS) microelectromechanical system (MEMS) technology to perform vibration-based in situ monitoring, diagnostics, and characterization of a MEMS microball bearing supported radial air turbine platform. A multimodal software suite for platform automation and sensor monitoring is demonstrated using a three-level heuristic software suite and sensor network. The vibration diagnostic methods used in the platform have applications in rotary microsystems for the early detection of failure, fault diagnosis, and integrated diagnostic systems for feedback-based optimization to increase device performance, reliability, and operational lifetimes. The studied rotary microdevice used a dual OTS accelerometer configuration for dual range parallel redundant vibration analysis. The sensor suite has been used to monitor and detect multiple operational parameters measured optimally in time or frequency domains such as rotor instability, imbalance, wobble, and system resonance. This paper will lay the framework for active diagnostics in future MEMS devices through integrated systems.
- B. Hanrahan, S. Misra, C. M. Waits, and R. Ghodssi, "Wear mechanisms in microfabricated ball bearing systems," Wear, 326, 1-9, 2015.
[Abstract]
Microfabricated ball bearings have been demonstrated successfully in a number of microsystems, although a complete understanding of their tribological properties remains elusive. This paper investigates the wear mechanisms for a microfabricated ball bearing platform that includes silicon and thin-film coated silicon raceway/steel ball materials systems. Adhesion of ball material, found to be the primary wear mechanism, is universally present in all tested materials systems. Volumetric adhesive wear rates are observed between 4 x 10(-4) and 4 x 10(-5) mu m(3)/mN.rev. Pressured-induced phase changes take place in the contact areas of the bare silicon raceways, observed with Raman spectroscopy. An understanding of the wear mechanisms within microfabricated ball bearings will help optimize operational parameters and materials systems for long-term reliability. (C) 2015 Elsevier B.V. All rights reserved.
- R. R. Hood, T. Wyderko, and D. L. Devoe, "Programmable digital droplet microfluidics using a multibarrel capillary bundle," Sensors and Actuators B-Chemical, 220, 992-999, 2015.
[Abstract]
The integration of multibarrel glass capillaries into a microfluidic co-flow configuration is demonstrated for parallel production of nanoliter scale droplets. The multibarrel system supports the generation of a continuous stream of single-phase or dual-phase droplets with digital control over droplet content, enabling the formation of dynamically-programmable and tunable emulsions. The multibarrel capillary method allows simultaneous generation of multiple droplets from parallel droplet generators, with controlled switching between selected dispersed phase or continuous phase compositions. Individual phases emerging from each capillary outlet may be selected to yield merged droplets combining continuous phase emitted from one or more neighboring droplet generators. Because the capillary emitters are configured in a two dimensional array, the multibarrel system provides greater flexibility toward producing controlled interactions between multiple solutions and phases than conventional planar microfluidic droplet generators. Using a 7-barrel capillary configuration, the ability to regulate droplet composition and particle size of individual as well as combined single and merged water-in-oil droplets is explored, together with the use of two-dimensional spatial control within the multibarrel array to generate higher order emulsions. (C) 2015 Elsevier B.V. All rights reserved.
- K. Jiang, A. X. Lu, P. Dimitrakopoulos, D. L. DeVoe, and S. R. Raghavan, "Microfluidic generation of uniform water droplets using gas as the continuous phase," Journal of Colloid and Interface Science, 448, 275-279, 2015.
[Abstract]
Microfluidic schemes for forming uniform aqueous microdroplets usually rely on contacting the aqueous liquid (dispersed phase) with an immiscible oil (continuous phase). Here, we demonstrate that the oil can be substituted with gas (nitrogen or air) while still retaining the ability to generate discrete and uniform aqueous droplets. Our device is a capillary co-flow system, with the inner flow of water getting periodically dispersed into droplets by the external flow of gas. The droplet size and different formation modes can be tuned by varying the liquid and gas flow rates. Importantly, we identify the range of conditions that correspond to the "dripping mode", i.e., where discrete droplets are consistently generated with no satellites. We believe this is a significant development that will be beneficial for chemical and biological applications requiring clean and contaminant-free droplets, including DNA amplification, drug encapsulation, and microfluidic cell culture.
- K. Q. Jiang, A. X. Lu, P. Dimitrakopoulos, D. L. Devoe, and S. R. Raghavan, "Microfluidic generation of uniform water droplets using gas as the continuous phase," Journal of Colloid and Interface Science, 448, 275-279, 2015.
[Abstract]
Microfluidic schemes for forming uniform aqueous microdroplets usually rely on contacting the aqueous liquid (dispersed phase) with an immiscible oil (continuous phase). Here, we demonstrate that the oil can be substituted with gas (nitrogen or air) while still retaining the ability to generate discrete and uniform aqueous droplets. Our device is a capillary co-flow system, with the inner flow of water getting periodically dispersed into droplets by the external flow of gas. The droplet size and different formation modes can be tuned by varying the liquid and gas flow rates. Importantly, we identify the range of conditions that correspond to the "dripping mode", i.e., where discrete droplets are consistently generated with no satellites. We believe this is a significant development that will be beneficial for chemical and biological applications requiring clean and contaminant-free droplets, including DNA amplification, drug encapsulation, and microfluidic cell culture. (C) 2015 Elsevier Inc. All rights reserved.
- I. D. Jung, M. C. Lee, H. Lim, E. Smela, and J. S. Ko, "Microbumpers maintain superhydrophobicity of nano structured surfaces upon touch," Applied Surface Science, 349, 705-714, 2015.
[Abstract]
Because of their fragility, nanostructured surfaces have not been used in applications that require mechanical contact with the environment. This paper demonstrates the utility of an array of "microbumpers" in the form of pillars rising above a nanostructured surface to provide protection. Superhydrophobic surfaces with micro-pillar arrays of varying pitch were fabricated and subjected to repeated vertical touch with a PDMS finger replica under different applied forces, such as would be experienced by a touch screen display. For sufficiently small pitches, the microbumpers maintained the strong water repellency and low droplet adhesion, even after 1000 touch cycles, but if the pitch was too large the nanostructures were damaged and the superhydrophobicity lost. In comparison, surfaces comprising only nano structures lost superhydrophobicity almost immediately. To image surface wetting by the water droplets, a droplet freeze-fixing, resin-embedding (FFRE) technique was developed. The approach of decorating a surface with microbumpers to provide mechanical protection should be applicable to a wide range of substrates with coatings optimized for various functions. (C) 2015 Elsevier B.V. All rights reserved.
- E. L. Kendall, J. Y. Han, M. S. Wiederoder, A. Sposito, A. Wilson, O. D. Rahmanian, and D. L. DeVoe, "Soft lithography microfabrication of functionalized thermoplastics by solvent casting," Journal of Polymer Science Part B-Polymer Physics, 53 (18), 1315-1323, 2015.
[Abstract]
A soft lithographic method is described for casting functional thermoplastic devices with microscale features without the need for specialized tools or equipment. In the thermoplastic soft lithography process, termed solvent casting, low temperature supersaturated solutions of thermoplastic are poured over solvent permeable PDMS molds which allow omnidirectional solvent removal as they template functional microstructures into the thermoplastic layers. Rapid gelation of supersaturated solutions enables the deposition of multiple patterned layers of varying composition, with self-adhesion of the solvent-laden thermoplastic ensuring intimate bonding between adjacent layers. This latter feature is further used in this work to realize sealed thermoplastic microfluidic devices with high fidelity replication of microchannel features with negligible channel deformation. The incorporation of functional dopants into patterned thermoplastic layers allows the fabrication of thermoplastic devices with embedded fluorescent sensors and integrated conductive elements. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1315-1323
- E. Kim, Y. Xiong, Y. Cheng, H.-C. Wu, Y. Liu, B. H. Morrow, H. Ben-Yoav, R. Ghodssi, G. W. Rubloff, J. Shen, W. E. Bentley, X. Shi, and G. F. Payne, "Chitosan to Connect Biology to Electronics: Fabricating the Bio-Device Interface and Communicating Across This Interface," Polymers, 7 (1), 1-46, 2015.
[Abstract]
Individually, advances in microelectronics and biology transformed the way we live our lives. However, there remain few examples in which biology and electronics have been interfaced to create synergistic capabilities. We believe there are two major challenges to the integration of biological components into microelectronic systems: (i) assembly of the biological components at an electrode address, and (ii) communication between the assembled biological components and the underlying electrode. Chitosan possesses a unique combination of properties to meet these challenges and serve as an effective bio-device interface material. For assembly, chitosan's pH-responsive film-forming properties allow it to "recognize" electrode-imposed signals and respond by self-assembling as a stable hydrogel film through a cathodic electrodeposition mechanism. A separate anodic electrodeposition mechanism was recently reported and this also allows chitosan hydrogel films to be assembled at an electrode address. Protein-based biofunctionality can be conferred to electrodeposited films through a variety of physical, chemical and biological methods. For communication, we are investigating redox-active catechol-modified chitosan films as an interface to bridge redox-based communication between biology and an electrode. Despite significant progress over the last decade, many questions still remain which warrants even deeper study of chitosan's structure, properties, and functions.
- X. Long and M. Yu, "One to one nonlinear internal resonance of sensor diaphragm under initial tension," Journal of Vibration and Acoustics, 137 (3), 2015.
[Abstract]
In this paper, investigations into the nonlinear asymmetric vibrations of a pressure sensor diaphragm under initial tension are presented. A comprehensive mechanics model based on a plate with in-plane tension is presented and the effect of cubic nonlinearity is studied. Specifically, the nonlinear asymmetric response is investigated when the excitation frequency is close to the natural frequency of an asymmetric mode of the plate. The obtained results show that in the presence of an internal resonance, depending on the initial tension, the response can have not only the form of a standing wave but also the form of a traveling wave. In addition, damping can be used to reduce the nonlinear effect and avoid the nonlinear interactions. The results of this work will benefit the design of diaphragm-type structures used in microscale sensors including pressure sensors.
- X. L. Luo, C. Y. Tsao, H. C. Wu, D. N. Quan, G. F. Payne, G. W. Rubloff, and W. E. Bentley, "Distal modulation of bacterial cell-cell signalling in a synthetic ecosystem using partitioned microfluidics," Lab on a Chip, 15 (8), 1842-1851, 2015.
[Abstract]
The human gut is over a meter in length, liquid residence times span several hours. Recapitulating the human gut microbiome "on chip" holds promise to revolutionize therapeutic strategies for a variety of diseases, as well as for maintaining homeostasis in healthy individuals. A more refined understanding of bacterial-bacterial and bacterial-epithelial cell signalling is envisioned and such a device is a key enabler. Indeed, significant advances in the study of bacterial cell-cell signalling have been reported, including at length and time scales of the cells and their responses. Few reports exist, however, where signalling events that span physiologically relevant time scales are monitored and coordinated. Here, we employ principles of biofabrication to assemble, in situ, cell communities that are (i) spatially adjacent within partitioned microchannels for studying near communication and (ii) distally connected within longitudinal microfluidic networks so as to mimic long distance signalling among intestinal flora. We observed native signalling processes of the bacterial quorum sensing autoinducer-2 (AI-2) system among and between these communities. Cells in an upstream device successfully self-reported their activities and also secreted autoinducers that were carried downstream to the assembled networks of bacteria that reported on their presence. Furthermore, active signal modulation of among distal populations was demonstrated in a "programmed" manner where "enhancer" and "reducer" communities were assembled adjacent to the test population or "reporter" cells. The modulator cells either amplified or attenuated the cell-cell signalling between the distal, already communicating cell populations. Modulation was quantified with a bioassay, and the reaction rates of signal production and consumption were further characterized using a first principles mathematical model. Simulated distribution profiles of signalling molecules in the cell-gel composites agreed well with the observed cellular responses. We believe this simple platform and the ease by which it is assembled can be applied to other cell-cell interaction studies among various species or kingdoms of cells within well-regulated microenvironments.
- M. T. Meyer, S. Subramanian, Y. W. Kim, H. Ben-Yoav, M. Gnerlich, K. Gerasopoulos, W. E. Bentley, and R. Ghodssi, "Multi-depth valved microfluidics for biofilm segmentation," Journal of Micromechanics and Microengineering, 25 (9), 2015.
[Abstract]
Bacterial biofilms present a societal challenge, as they occur in the majority of infections but are highly resistant to both immune mechanisms and traditional antibiotics. In the pursuit of better understanding biofilm biology for developing new treatments, there is a need for streamlined, controlled platforms for biofilm growth and evaluation. We leverage advantages of microfluidics to develop a system in which biofilms are formed and sectioned, allowing parallel assays on multiple sections of one biofilm. A microfluidic testbed with multiple depth profiles was developed to accommodate biofilm growth and sectioning by hydraulically actuated valves. In realization of the platform, a novel fabrication technique was developed for creating multi-depth microfluidic molds using sequentially patterned photoresist separated and passivated by conformal coatings using atomic layer deposition. Biofilm thickness variation within three separately tested devices was less than 13% of the average thickness in each device, while variation between devices was 23% of the average thickness. In a demonstration of parallel experiments performed on one biofilm within one device, integrated valves were used to trisect the uniform biofilms with one section maintained as a control, and two sections exposed to different concentrations of sodium dodecyl sulfate. The technology presented here for multi-depth microchannel fabrication can be used to create a host of microfluidic devices with diverse architectures. While this work focuses on one application of such a device in biofilm sectioning for parallel experimentation, the tailored architectures enabled by the fabrication technology can be used to create devices that provide new biological information.
- M. Mosteller, M. Austin, R. Ghodssi, and S. A. Yang, "Platforms for Engineering Biomedical Experiments," IEEE Systems Journal, 9 (4), 1218-1228, 2015.
[Abstract]
Due to the highly stochastic nature of biological systems, the systematic design, validation, and verification of systems for biomedical experiments in laboratory and clinical applications are complex activities. This paper presents a platform framework for the modeling of these biological components in the context of system-level analysis. By integrating models of biological systems with those of physical engineering systems, one can obtain a set of potential architectures that satisfy the requirement specifications of the application. Such models can aid in the analysis of biomedical systems intended for applications in medical science, where the stochastic elements are the biological components themselves. A prototype application is presented that implements this platform framework for the development of a microfluidic assay device for the study of antibacterial treatments of bacterial biofilms. The results of our work indicate that looking forward, platforms will facilitate early validation and verification of biomedical devices, and enable the development of more efficient and effective experimental biomedical systems.
- O. D. Rahmanian and D. L. DeVoe, "Single-use thermoplastic microfluidic burst valves enabling on-chip reagent storage," Microfluidics and Nanofluidics, 18 (5-6), 1045-1053, 2015.
[Abstract]
A simple and reliable method for fabricating single-use normally closed burst valves in thermoplastic microfluidic devices is presented, using a process flow that is readily integrated into established workflows for the fabrication of thermoplastic microfluidics. An experimental study of valve performance reveals the relationships between valve geometry and burst pressure. The technology is demonstrated in a device employing multiple valves engineered to actuate at different inlet pressures that can be generated using integrated screw pumps. On-chip storage and reconstitution of fluorescein salt sealed within defined reagent chambers are demonstrated. By taking advantage of the low gas and water permeability of cyclic olefin copolymer, the robust burst valves allow on-chip hermetic storage of reagents, making the technology well suited for the development of integrated and disposable assays for use at the point of care.
- R. Q. Rudy, G. L. Smith, D. L. DeVoe, and R. G. Polcawich, "Millimeter-scale traveling wave rotary ultrasonic motors," Journal of Microelectromechanical Systems, 24 (1), 108-114, 2015.
[Abstract]
Bidirectional rotary motion of a millimeter-scale traveling wave ultrasonic motor is demonstrated using solution-deposited thin-film lead zirconate titanate and wafer-scale microelectromechanical system fabrication techniques. Rotation speeds of a motor 3 mm in diameter have been characterized up to 2000 r/min as a function of voltage, phase, and frequency, with power consumption less than 4 mW. Frequency characterization shows no nonlinear behavior, while phase characterization shows that motion can be generated with a single source drive. Furthermore, imprint in the piezoelectric response was exploited to achieve higher speeds, starting voltages lower than 4 V, and demonstration of a 2-mm diameter motor up to 1730 r/min. Design and fabrication of the motors are also presented. [2013-0032]
- N. P. Siwak, X. Z. Fan, and R. Ghodssi, "Fabrication challenges for indium phosphide microsystems," Journal of Micromechanics and Microengineering, 25 (4), 2015.
[Abstract]
From the inception of III-V microsystems, monolithically integrated device designs have been the motivating drive for this field, bringing together the utility of single-chip microsystems and conventional fabrication techniques. Indium phosphide (InP) has a particular advantage of having a direct bandgap within the low loss telecommunication wavelength (1550 nm) range, able to support passive waveguiding and optical amplification, detection, and generation depending on the exact alloy of In, P, As, Ga, or Al materials. Utilizing epitaxy, one can envision the growth of a substrate that contains all of the components needed to establish a single-chip optical microsystem, containing detectors, sources, waveguides, and mechanical structures. A monolithic InP MEMS system has, to our knowledge, yet to be realized due to the significant difficulties encountered when fabricating the integrated devices. In this paper we present our own research and consolidate findings from other research groups across the world to give deeper insight into the practical aspects of InP monolithic microsystem development: epitaxial growth of InP-based alloys, etching techniques, common MEMS structures realized in InP, and future applications. We pay special attention to shedding light on considerations that must be taken when designing and fabricating a monolithic InP MEMS device.
- D. Sritharan, A. S. Chen, P. Aluthgama, B. Naved, and E. Smela, "Bubble-free electrokinetic flow with propylene carbonate," Electrophoresis, 36 (20), 2622-2629, 2015.
[Abstract]
For electroosmotic pumping, a large direct-current (DC) electric field (10+ V/cm) is applied across a liquid, typically an aqueous electrolyte. At these high voltages, water undergoes electrolysis to form hydrogen and oxygen, generating bubbles that can block the electrodes, cause pressure fluctuations, and lead to pump failure. The requirement to manage these gases constrains system designs. This article presents an alternative polar liquid for DC electrokinetic pumping, propylene carbonate (PC), which remains free of bubbles up to at least 10 kV/cm. This offers the opportunity to create electrokinetic devices in closed configurations, which we demonstrate with a fully sealed microfluidic hydraulic actuator. Furthermore, the electroosmotic velocity of PC is similar to that of water in PDMS microchannels. Thus, water could be substituted by PC in existing electroosmotic pumps.
- L. Wang, Y. J. Liu, J. He, M. J. Hourwitz, Y. L. Yang, J. T. Fourkas, X. J. Han, and Z. H. Nie, "Continuous Microfluidic Self-Assembly of Hybrid Janus-Like Vesicular Motors: Autonomous Propulsion and Controlled Release," Small, 11 (31), 3762-3767, 2015.
[Abstract]
- M. S. Wiederoder, L. Peterken, A. X. Lu, O. D. Rahmanian, S. R. Raghavan, and D. L. Devoe, "Optical detection enhancement in porous volumetric microfluidic capture elements using refractive index matching fluids," Analyst, 140 (16), 5724-5731, 2015.
[Abstract]
Porous volumetric capture elements in microfluidic sensors are advantageous compared to planar capture surfaces due to higher reaction site density and decreased diffusion lengths that can reduce detection limits and total assay time. However a mismatch in refractive indices between the capture matrix and fluid within the porous interstices results in scattering of incident, reflected, or emitted light, significantly reducing the signal for optical detection. Here we demonstrate that perfusion of an index-matching fluid within a porous matrix minimizes scattering, thus enhancing optical signal by enabling the entire capture element volume to be probed. Signal enhancement is demonstrated for both fluorescence and absorbance detection, using porous polymer monoliths in a silica capillary and packed beds of glass beads within thermoplastic microchannels, respectively. Fluorescence signal was improved by a factor of 3.5x when measuring emission from a fluorescent compound attached directly to the polymer monolith, and up to 2.6x for a rapid 10 min direct immunoassay. When combining index matching with a silver enhancement step, a detection limit of 0.1 ng mL(-1) human IgG and a 5 log dynamic range was achieved. The demonstrated technique provides a simple method for enhancing optical sensitivity for a wide range of assays, enabling the full benefits of porous detection elements in miniaturized analytical systems to be realized.
- Z. Zhang, Y. Chen, H. Liu, H. Bae, D. A. Olson, A. K. Gupta, and M. Yu, "On-fiber plasmonic interferometer for multi-parameter sensing," Optics Express, 23 (8), 10732-10740, 2015.
[Abstract]
We demonstrate a novel miniature multi-parameter sensing device based on a plasmonic interferometer fabricated on a fiber facet in the optical communication wavelength range. This device enables the coupling between surface plasmon resonance and plasmonic interference in the structure, which are the two essential mechanisms for multi-parameter sensing. We experimentally show that these two mechanisms have distinctive responses to temperature and refractive index, rendering the device the capability of simultaneous temperature and refractive index measurement on an ultra-miniature form factor. A high refractive index sensitivity of 220 nm per refractive index unit (RIU) and a high temperature sensitivity of -60 pm/ degrees C is achieved with our device.
- W. Z. Bao, Z. Q. Fang, J. Y. Wan, J. Q. Dai, H. L. Zhu, X. G. Han, X. F. Yang, C. Preston, and L. B. Hu, "Aqueous Gating of van der Waals Materials on Bilayer Nanopaper," ACS Nano, 8 (10), 10606-10612, 2014.
[Abstract]
In this work, we report transistors made of van der Waals materials on a mesoporous paper with a smooth nanoscale surface. The aqueous transistor has a novel planar structure with source, drain, and gate electrodes on the same surface of the paper, while the mesoporous paper is used as an electrolyte reservoir. These transistors are enabled by an all-cellulose paper with nanofibrillated cellulose (NFC) on the top surface that leads to an excellent surface smoothness, while the rest of the microsized cellulose fibers can absorb electrolyte effectively. Based on two-dimensional van der Waals materials, including MoS2 and graphene, we demonstrate high-performance transistors with a large on-off ratio and low subthreshold swing. Such planar transistors with absorbed electrolyte gating can be used as sensors integrated with other components to form paper microfluidic systems. This study is significant for future paper-based electronics and biosensors.
- J. M. Burke, R. E. Zubajlo, E. Smela, and I. M. White, "High-throughput particle separation and concentration using spiral inertial filtration," Biomicrofluidics, 8 (2), 2014.
[Abstract]
A spiral inertial filtration (SIFT) device that is capable of high-throughput (1 ml/min), high-purity particle separation while concentrating recovered target particles by more than an order of magnitude is reported. This device is able to remove large fractions of sample fluid from a microchannel without disruption of concentrated particle streams by taking advantage of particle focusing in inertial spiral microfluidics, which is achieved by balancing inertial lift forces and Dean drag forces. To enable the calculation of channel geometries in the SIFT microsystem for specific concentration factors, an equivalent circuit model was developed and experimentally validated. Large particle concentration factors were then achieved by maintaining either the average fluid velocity or the Dean number throughout the entire length of the channel during the incremental removal of sample fluid. The SIFT device was able to separate MCF7 cells spiked into whole blood from the non-target white blood cells (WBC) with a recovery of nearly 100% while removing 93% of the sample volume, which resulted in a concentration enhancement of the MCF7 cancer cells by a factor of 14. (C) 2014 AIP Publishing LLC.
- J. Liu, B. Du, P. Zhang, M. Haleyurgirisetty, J. Zhao, V. Ragupathy, S. Lee, D. L. DeVoe, and I. K. Hewlett, "Development of a microchip Europium nanoparticle immunoassay for sensitive point-of-care HIV detection," Biosensors & Bioelectronics, 61, 177-183, 2014.
[Abstract]
Rapid, sensitive and specific diagnostic assays play an indispensable role in determination of HIV infection stages and evaluation of efficacy of antiretroviral therapy. Recently, our laboratory developed a sensitive Europium nanoparticle-based microtiter-plate immunoassay capable of detecting target analytes at subpicogram per milliliter levels without the use of catalytic enzymes and signal amplification processes. Encouraged by its sensitivity and simplicity, we continued to miniaturize this assay to a microchip platform for the purpose of converting the benchtop assay technique to a point-of-care test. It was found that detection capability of the microchip platform could be readily improved using Europium nanoparticle probes. We were able to routinely detect 5 pg/mL (4.6 attomoles) of HIV-1 p24 antigen at a signal-to-blank ratio of 1.5, a sensitivity level reasonably close to that of microtiter-plate Europium nanoparticle assay. Meanwhile, use of the microchip platform effectively reduced sample/reagent consumption 4.5 fold and shortened total assay time 2 fold in comparison with microtiter plate assays. Complex matrix substance in plasma negatively affected the microchip assays and the effects could be minimized by diluting the samples before loading. With further improvements in sensitivity, reproducibility, usability, assay process simplification, and incorporation of portable time-resolved fluorescence reader, Europium nanoparticle immunoassay technology could be adapted to meet the challenges of point-of-care diagnosis of HIV or other health-threatening pathogens at bedside or in resource-limited settings. (C) 2014 Elsevier B.V. All rights reserved.
- Y. C. Tang, C. Chen, A. Khaligh, I. Penskiy, and S. Bergbreiter, "An Ultracompact Dual-Stage Converter for Driving Electrostatic Actuators in Mobile Microrobots," IEEE Transactions on Power Electronics, 29 (6), 2991-3000, 2014.
[Abstract]
Electrostatic actuators are being widely investigated to convert electrical energy into mechanical deformation in a broad variety of microrobotic applications. Both electrostatic gap closing and comb drive actuators require high excitation voltages for high performance operation. In the majority of applications, external bulky and heavy power supplies are used to provide such high voltages, which inevitably bring limitations on autonomous operation. One of the major challenges toward enabling operation of these systems without a bulky external power source is the development of ultralight and high power density power electronic interfaces (PEIs) with large step-up gains. In this paper, a special circuit topology, controlled by a pulse frequency modulation scheme, is introduced to meet stringent electrical and drive voltage requirements of electrostatic actuators. An ultracompact 63 mg (excluding PCB mass), 31.5 mm(2), and 500 mW PEI has been designed and fabricated. Experimental validations have been carried out to verify the circuit's ability to drive an 110-V-input electrostatic inchworm motor at 1-kHz actuating frequency.
- R. Kempaiah and Z. H. Nie, "From nature to synthetic systems: shape transformation in soft materials," Journal of Materials Chemistry B, 2 (17), 2357-2368, 2014.
[Abstract]
Nature offers a plethora of astonishing examples of shapes and functions from the aspects of both simplicity and complexity. The creation of synthetic systems that can morph in a controlled manner as seen in nature is of paramount importance in many fields of fundamental and applied sciences. The tremendous interest in self-shaping materials stems from a wide range of applications for these materials, ranging from biomedical devices to aircraft design. This review article highlights recent advances in understanding and designing thin, sheet-like soft materials that can transform into complex three-dimensional structures in a controlled manner by modulating the internal stresses. We review the general principles underlying shape transformation phenomena in natural and synthetic systems, and the significant achievements in fabricating self-shaping of soft materials via representative examples. We conclude with a discussion on the challenges facing the field, and future directions from the perspective of theoretical and experimental methodology and interdisciplinary applications.
- B. Hanrahan, C. M. Waits, and R. Ghodssi, "Isotropic etching technique for three-dimensional microball-bearing raceways," Journal of Micromechanics and Microengineering, 24 (1), 2014.
[Abstract]
A multi-step plasma etching technique is developed to obtain deep-grooved micro-scale ball-bearing raceways and employed in the fabrication of multiple ball-bearing supported microturbines. Deep-groove geometry has been chosen for the microball-bearing systems because of the ability to handle mixed axial and radial loads, allowing for stable, high-speed operation compared to previous iterations of the microball-bearing raceways. The multi-step inductively coupled plasma-based process is optimized to obtain <2% deviation amongst intended raceway depth, width and curvature. Etching non-uniformity is measured to be 0.15% within the raceway of a single device. The bearing dynamics with the new deep-groove geometry have been simulated. The deep-groove raceway packed with off-the-shelf precision ball-bearings provided a stability improvement over previous demonstrations of high-performance rotary micromachines operating at high speeds.
- H. Ben-Yoav, P. H. Dykstra, T. Gordonov, W. E. Bentley, and R. Ghodssi, "A Microfluidic-based Electrochemical Biochip for Label-free DNA Hybridization Analysis," Jove-Journal of Visualized Experiments, (91), 2014.
[Abstract]
Miniaturization of analytical benchtop procedures into the micro-scale provides significant advantages in regards to reaction time, cost, and integration of pre-processing steps. Utilizing these devices towards the analysis of DNA hybridization events is important because it offers a technology for real time assessment of biomarkers at the point-of-care for various diseases. However, when the device footprint decreases the dominance of various physical phenomena increases. These phenomena influence the fabrication precision and operation reliability of the device. Therefore, there is a great need to accurately fabricate and operate these devices in a reproducible manner in order to improve the overall performance. Here, we describe the protocols and the methods used for the fabrication and the operation of a microfluidic-based electrochemical biochip for accurate analysis of DNA hybridization events. The biochip is composed of two parts: a microfluidic chip with three parallel micro-channels made of polydimethylsiloxane (PDMS), and a 3 x 3 arrayed electrochemical micro-chip. The DNA hybridization events are detected using electrochemical impedance spectroscopy (EIS) analysis. The EIS analysis enables monitoring variations of the properties of the electrochemical system that are dominant at these length scales. With the ability to monitor changes of both charge transfer and diffusional resistance with the biosensor, we demonstrate the selectivity to complementary ssDNA targets, a calculated detection limit of 3.8 nM, and a 13% cross-reactivity with other non-complementary ssDNA following 20 min of incubation. This methodology can improve the performance of miniaturized devices by elucidating on the behavior of diffusion at the micro-scale regime and by enabling the study of DNA hybridization events.
- T. Datta-Chaudhuri, P. Abshire, and E. Smela, "Packaging commercial CMOS chips for lab on a chip integration," Lab on a Chip, 14 (10), 1753-1766, 2014.
[Abstract]
Combining integrated circuitry with microfluidics enables lab-on-a-chip (LOC) devices to perform sensing, freeing them from benchtop equipment. However, this integration is challenging with small chips, as is briefly reviewed with reference to key metrics for package comparison. In this paper we present a simple packaging method for including mm-sized, foundry-fabricated dies containing complementary metal oxide semiconductor (CMOS) circuits within LOCs. The chip is embedded in an epoxy handle wafer to yield a level, large-area surface, allowing subsequent photolithographic post-processing and microfluidic integration. Electrical connection off-chip is provided by thin film metal traces passivated with parylene-C. The parylene is patterned to selectively expose the active sensing area of the chip, allowing direct interaction with a fluidic environment. The method accommodates any die size and automatically levels the die and handle wafer surfaces. Functionality was demonstrated by packaging two different types of CMOS sensor ICs, a bioamplifier chip with an array of surface electrodes connected to internal amplifiers for recording extracellular electrical signals and a capacitance sensor chip for monitoring cell adhesion and viability. Cells were cultured on the surface of both types of chips, and data were acquired using a PC. Long term culture (weeks) showed the packaging materials to be biocompatible. Package lifetime was demonstrated by exposure to fluids over a longer duration (months), and the package was robust enough to allow repeated sterilization and re-use. The ease of fabrication and good performance of this packaging method should allow wide adoption, thereby spurring advances in miniaturized sensing systems.
- R. R. Hood, W. N. Vreeland, and D. L. DeVoe, "Microfluidic remote loading for rapid single-step liposomal drug preparation," Lab on a Chip, 14 (17), 3359-3367, 2014.
[Abstract]
Microfluidic-directed formation of liposomes is combined with in-line sample purification and remote drug loading for single step, continuous-flow synthesis of nanoscale vesicles containing high concentrations of stably loaded drug compounds. Using an on-chip microdialysis element, the system enables rapid formation of large transmembrane pH and ion gradients, followed by immediate introduction of amphipathic drug for real-time remote loading into the liposomes. The microfluidic process enables in-line formation of drug-laden liposomes with drug : lipid molar ratios of up to 1.3, and a total on-chip residence time of approximately 3 min, representing a significant improvement over conventional bulk-scale methods which require hours to days for combined liposome synthesis and remote drug loading. The microfluidic platform may be further optimized to support real-time generation of purified liposomal drug formulations with high concentrations of drugs and minimal reagent waste for effective liposomal drug preparation at or near the point of care.
- R. R. Hood, D. L. DeVoe, J. Atencia, W. N. Vreeland, and D. M. Omiatek, "A facile route to the synthesis of monodisperse nanoscale liposomes using 3D microfluidic hydrodynamic focusing in a concentric capillary array," Lab on a Chip, 14 (14), 2403-2409, 2014.
[Abstract]
A novel microscale device has been developed to enable the one-step continuous flow assembly of monodisperse nanoscale liposomes using three-dimensional microfluidic hydrodynamic focusing (3D-MHF) in a concentric capillary array. The 3D-MHF flow technique displays patent advantages over conventional methods for nanoscale liposome manufacture (i.e., bulk-scale alcohol injection and/or sonication) through the on-demand synthesis of consistently uniform liposomes without the need for post-processing strategies. Liposomes produced by the 3D-MHF device are of tunable size, have a factor of two improvement in polydispersity, and a production rate that is four orders of magnitude higher than previous MHF methods, which can be attributed to entirely radially symmetric diffusion of alcohol-solvated lipid into an aqueous flow stream. Moreover, the 3D-MHF platform is simple to construct from low-cost, commercially-available components, which obviates the need for advanced microfabrication strategies necessitated by previous MHF nanoparticle synthesis platforms.
- H. J. Pandya, H. T. Kim, R. Roy, and J. P. Desai, "MEMS based low cost piezoresistive microcantilever force sensor and sensor module," Materials Science in Semiconductor Processing, 19, 163-173, 2014.
[Abstract]
In the present work, we report fabrication and characterization of a low-cost MEMS based piezoresistive micro-force sensor with SU-8 tip using laboratory made silicon-on-insulator (SOI) substrate. To prepare SOI wafer, silicon film (0.8 pm thick) was deposited on an oxidized silicon wafer using RF magnetron sputtering technique. The films were deposited in argon (Ar) ambient without external substrate heating. The material characteristics of the sputtered deposited silicon film and silicon film annealed at different temperatures (400-1050 degrees C) were studied using atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. The residual stress of the films was measured as a function of annealing temperature. The stress of the as-deposited films was observed to be compressive and annealing the film above 1050 degrees C resulted in a tensile stress. The stress of the film decreased gradually with increase in annealing temperature. The fabricated cantilevers were 130 mu m in length, 40 mu m wide and 1.0 mu m thick. A series of force-displacement curves were obtained using fabricated microcantilever with commercial AFM setup and the data were analyzed to get the spring constant and the sensitivity of the fabricated microcantilever. The measured spring constant and sensitivity of the sensor was 0.1488 N/m and 2.7 mV/N. The microcantilever force sensor was integrated with an electronic module that detects the change in resistance of the sensor with respect to the applied force and displays it on the computer screen. (C) 2013 Elsevier Ltd. All rights reserved.
- A. U. Andar, R. R. Hood, W. N. Vreeland, D. L. DeVoe, and P. W. Swaan, "Microfluidic Preparation of Liposomes to Determine Particle Size Influence on Cellular Uptake Mechanisms," Pharmaceutical Research, 31 (2), 401-413, 2014.
[Abstract]
This study investigates the cellular uptake and trafficking of liposomes in Caco-2 cells, using vesicles with distinct average diameters ranging from 40.6 nm to 276.6 nm. Liposomes were prepared by microfluidic hydrodynamic flow focusing, producing nearly-monodisperse populations and enabling size-dependent uptake to be effectively evaluated. Populations of PEG-conjugated liposomes of various distinct sizes were prepared in a disposable microfluidic device using a simple continuous-flow microfluidic technique. Liposome cellular uptake was investigated using flow cytometry and confocal microscopy. Liposome uptake by Caco-2 cells was observed to be strongly size-dependent for liposomes with mean diameters ranging from 40.6 nm to 276.6 nm. When testing these liposomes against endocytosis inhibitors, cellular uptake of the largest (97.8 nm and 162.1 nm in diameter) liposomes were predominantly subjected to clathrin-dependent uptake mechanisms, the medium-sized (72.3 nm in diameter) liposomes seemed to be influenced by all investigated pathways and the smallest liposomes (40.6 nm in diameter) primarily followed a dynamin-dependent pathway. In addition, the 40.6 nm, 72.3 nm, and 162.1 nm diameter liposomes showed slightly decreased accumulation within endosomes after 1 h compared to liposomes which were 97.8 nm in diameter. Conversely, liposome co-localization with lysosomes was consistent for liposomes ranging from 40.6 nm to 97.8 nm in diameter. The continuous-flow synthesis of nearly-monodisperse populations of liposomes of distinct size via a microfluidic hydrodynamic flow focusing technique enabled unique in vitro studies in which specific effects of particle size on cellular uptake were elucidated. The results of this study highlight the significant influence of liposome size on cellular uptake mechanisms and may be further exploited for increasing specificity, improving efficacy, and reducing toxicity of liposomal drug delivery systems.
- R. R. Hood, E. L. Kendall, M. Junqueira, W. N. Vreeland, Z. Quezado, J. C. Finkel, and D. L. Devoe, "Microfluidic-Enabled Liposomes Elucidate Size-Dependent Transdermal Transport," Plos One, 9 (3), 2014.
[Abstract]
Microfluidic synthesis of small and nearly-monodisperse liposomes is used to investigate the size-dependent passive transdermal transport of nanoscale lipid vesicles. While large liposomes with diameters above 105 nm are found to be excluded from deeper skin layers past the stratum corneum, the primary barrier to nanoparticle transport, liposomes with mean diameters between 31-41 nm exhibit significantly enhanced penetration. Furthermore, multicolor fluorescence imaging reveals that the smaller liposomes pass rapidly through the stratum corneum without vesicle rupture. These findings reveal that nanoscale liposomes with well-controlled size and minimal size variance are excellent vehicles for transdermal delivery of functional nanoparticle drugs.
- Z. J. Wei, Z. Jia, J. M. Athas, C. Y. Wang, S. R. Raghavan, T. Li, and Z. H. Nie, "Hybrid hydrogel sheets that undergo pre-programmed shape transformations," Soft Matter, 10 (41), 8157-8162, 2014.
[Abstract]
This communication describes a novel strategy to achieve programmable shape transformation of hybrid hydrogel sheets by modulating both the in-plane and out-of-plane mismatches in mechanical properties. Both our experimental and computational results demonstrate that the shape transformation of hybrid hydrogel sheets shows rich features (e.g., rolling direction, axis, chirality, etc.) and versatile tunability (e.g., via various external stimuli, material properties, pattern geometry, etc.). This work can provide guidance for designing soft materials that are able to undergo more precise and complex shape transformation.
- B. M. Hanrahan, S. Misra, M. I. Beyaz, J. H. Feldman, C. M. Waits, and R. Ghodssi, "An Adhesion-Dominated Rolling Friction Regime Unique to Micro-scale Ball Bearings," Tribology Letters, 56 (2), 215-221, 2014.
[Abstract]
We demonstrate that micro-scale rolling bearings exhibit friction and wear properties markedly different from their macro-scale counterparts. A microfabricated testing platform uses variable rolling element diameters or vapor-phase lubricated interfaces to independently test friction force with varying contact area and surface energy. A linear, consistent, relationship between friction force and contact area is observed among different rolling element diameters. When surface free energy is altered through the introduction of vapor-phase lubrication, an 83 % decrease in friction is observed. When coupled with observed ball material adhered to the raceway, there is strong evidence for adhesion-dominated rolling friction regime at the micro-scale.
- J. He, L. Wang, Z. J. Wei, Y. L. Yang, C. Y. Wang, X. J. Han, and Z. H. Nie, "Vesicular Self-Assembly of Colloidal Amphiphiles in Microfluidics," ACS Applied Materials & Interfaces, 5 (19), 9746-9751, 2013.
[Abstract]
Hydrodynamic flow in a microfluidic (MF) device offers a high-throughput platform for the continuous and controllable self-assembly of amphiphiles. However, the role of hydrodynamics on the assembly of colloidal amphiphiles (CAMs) is still not well understood. This Article reports a systematic study of the assembly of CAMs, which consist of Au nanoparticles (AuNPs) grafted with amphiphilic block copolymers, into vesicles with a monolayer of CAMs in the membranes using laminar flows in MF flow-focusing devices. Our experimental and simulation studies indicate that the transverse diffusion of solvents and colloids across the boundary of neighboring lamellar flows plays a critical role in the assembly of CAMs into vesicles. The dimension of the vesicles can be controlled in the range of 100-600 nm by tuning the hydrodynamic conditions of the flows. In addition, the diffusion coefficient of CAMs was also critical for their assembly. Under the same flow conditions, larger CAMs generated larger assemblies as a result of the reduced diffusion rate of large amphiphiles. This work could provide fundamental guidance for the preparation of nanoparticle vesicles with applications in bioimaging, drug delivery, and nano- and microreactors.
- S. H. Yazdi and I. M. White, "Multiplexed detection of aquaculture fungicides using a pump-free optofluidic SERS microsystem," Analyst, 138 (1), 100-103, 2013.
[Abstract]
In this work, an optofluidic SERS device optimized for on-site analytics in the field is utilized for the multiplexed detection of three fungicides that are highly regulated in aquaculture. The optofluidic SERS microsystemdoes not require a bulky pump for sample loading, which significantly improves its portability; the sample is simply loaded into the device by applying negative pressure using a pipette. Moreover, integrated fiber optic cables automate sample excitation and signal collection without the need for alignment on a traditional Raman microscope. The detection zone of the device consists of a porous matrix of packed silica microspheres that accumulates silver nanoparticles and adsorbed analyte molecules. This passive concentration matrix has been shown to boost the SERS signal by up to four orders of magnitude as compared to SERS in an open microfluidic channel. We were able to detect as low as 5 ppm methyl parathion, 0.1 ppb malachite green, and 5 ppb thiram simultaneously.
- W. W. Yu and I. M. White, "Chromatographic separation and detection of target analytes from complex samples using inkjet printed SERS substrates," Analyst, 138 (13), 3679-3686, 2013.
[Abstract]
In principle, surface enhanced Raman spectroscopy (SERS) is thought to provide unique identification of a target analyte, even in complex samples or in the presence of multiple analytes. In practice, however, this is not always true for real-world samples due to various forms of interference. In this report, we build upon our previous work on inkjet-printed SERS substrates by using paper and polymer membranes to integrate sample cleanup and analyte separation with SERS detection. Inkjet-printed paper SERS substrates provide a highly sensitive chemical detection platform of unprecedented cost and simplicity. In addition, paper inherently provides unique capabilities, such as capillary-actuated fluid transport and selective molecular retention. Utilizing these properties, we demonstrate two-dimensional chromatographic separation and SERS detection on inkjet-printed paper SERS substrates. Then, we leverage the separation properties of paper and polymer membranes for real applications that feature complex sample matrices, including the detection of down to 5 ppm melamine in infant formula, as well as the quantification of nanograms of heroin in samples contaminated with a highly fluorescent background. The results presented here demonstrate that inkjet-printed paper SERS devices not only provide advantages in terms of sensitivity and cost, but the paper provides inherently integrated sample cleanup capabilities that are not available in traditional SERS substrates and microfluidic SERS devices. These unique capabilities of paper SERS devices enable the identification of targeted analytes even in complex real-world samples.
- W. W. Yu and I. M. White, "Inkjet-printed paper-based SERS dipsticks and swabs for trace chemical detection," Analyst, 138 (4), 1020-1025, 2013.
[Abstract]
We demonstrate a paper-based surface swab and lateral-flow dipstick that includes an inkjet-printed surface-enhanced Raman spectroscopy (SERS) substrate for analyte detection. Due to capillary-action wicking of cellulose, the paper dipstick enables extremely simple and pump-free loading of liquid samples into the detection device, and in addition provides inherent analyte concentration within the detection volume. Furthermore, the flexible nature of the paper-based SERS device also enables it to act as a swab to collect analyte molecules directly from a large-area surface; the collected analyte molecules can then be focused into a small-volume SERS-active region by lateral-flow concentration. These capabilities are unseen in today's SERS substrates and microfluidic SERS devices. Using these novel lateral-flow paper SERS devices, we achieved detection limits as low as 95 fg of Rhodamine 6G (R6G), 413 pg of the organophosphate malathion, 9 ng of heroin, and 15 ng of cocaine. Moreover, the measurements show that the technique is quantitative and is repeatable across multiple swabs and dipsticks. The results reported here may lead to ultra-low-cost portable applications in trace chemical detection.
- S. Yang, S. T. Eshghi, H. Chiu, D. L. DeVoe, and H. Zhang, "Glycomic Analysis by Glycoprotein Immobilization for Glycan Extraction and Liquid Chromatography on Microfluidic Chip," Analytical Chemistry, 85 (21), 10117-10125, 2013.
[Abstract]
Glycosylation is one of the most common protein modifications and profoundly regulates many biological processes. Aberrant glycosylation is reported to associate with diseases such as cancers, human immunodeficiency virus, and immune disorders. It is considerably important to study protein glycosylation and the associated glycans for diagnostics and disease prognostics. Unlike other protein modifications, glycans attached to proteins are enormously complex. Therefore, the comprehensive analysis of glycans from biological or clinical samples is an unmet technical challenge. Development of the high-throughput method will facilitate the glycomics analysis. In this study, we developed a novel method for the high-throughput analysis of N-glycans from glycoproteins using glycoprotein immobilization for glycan extraction (GIG) coupled with liquid chromatography (LC) in an integrated microfluidic platform (chipLC). The separated glycans were then analyzed by mass spectrometry. Briefly, proteins were first immobilized on a solid support. Glycans on immobilized glycoproteins were modified on solid phase to increase the detection and structure analysis. N-Glycans were then enzymatically released and subsequentially separated by porous graphitized carbon particles packed in the same device. By applying the GIG-chipLC for glycomic analysis of human sera, we identified N-glycans with 148 distinct N-glycan masses. The platform was used to analyze N-glycans from mouse heart tissue and serum. The extracted N-glycans from tissues indicated that unique unsialylated N-glycans were detected in tissues that were missing from the proximal or distal serum, whereas common N-glycans from tissues and serum have mature and sialylated structures. The GIG-chipLC provides a simple and robust platform for glycomic analysis of complex biological and clinical samples.
- S. H. Yazdi, K. L. Giles, and I. M. White, "Multiplexed Detection of DNA Sequences Using a Competitive Displacement Assay in a Microfluidic SERRS-Based Device," Analytical Chemistry, 85 (21), 10605-10611, 2013.
[Abstract]
We demonstrate sensitive and multiplexed detection of DNA sequences through a surface enhanced resonance Raman spectroscopy (SERRS)-based competitive displacement assay in an integrated microsystem. The use of the competitive displacement scheme, in which the target DNA sequence displaces a Raman-labeled reporter sequence that has lower affinity for the immobilized probe, enables detection of unlabeled target DNA sequences with a simple single-step procedure. In our implementation, the displacement reaction occurs in a microporous packed column of silica beads prefunctionalized with probe reporter pairs. The use of a functionalized packed-bead column in a microfluidic channel provides two major advantages: (i) immobilization surface chemistry can be performed as a batch process instead of on a chip-by-chip basis, and (ii) the microporous network eliminates the diffusion limitations of a typical biological assay, which increases the sensitivity. Packed silica beads are also leveraged to improve the SERRS detection of the Raman-labeled reporter. Following displacement, the reporter adsorbs onto aggregated silver nanoparticles in a microfluidic mixer; the nanoparticle reporter conjugates are then trapped and concentrated in the silica bead matrix, which leads to a significant increase in plasmonic nanoparticles and adsorbed Raman reporters within the detection volume as compared to an open microfluidic channel. The experimental results reported here demonstrate detection down to 100 pM of the target DNA sequence, and the experiments are shown to be specific, repeatable, and quantitative. Furthermore, we illustrate the advantage of using SERFS by demonstrating multiplexed detection. The sensitivity of the assay, combined with the advantages of multiplexed detection and single-step operation with unlabeled target sequences makes this method attractive for practical applications. Importantly, while we illustrate DNA sequence detection, the SERBS-based competitive displacement assay is applicable to detection of a variety of biological macromolecules, including proteins and proteolytic enzymes.
- V. Roy, M. T. Meyer, J. A. I. Smith, S. Gamby, H. O. Sintim, R. Ghodssi, and W. E. Bentley, "AI-2 analogs and antibiotics: a synergistic approach to reduce bacterial biofilms," Applied Microbiology and Biotechnology, 97 (6), 2627-2638, 2013.
[Abstract]
Quorum sensing (QS), the process of autoinducer-mediated cell-cell signaling among bacteria, facilitates biofilm formation, virulence, and many other multicellular phenotypes. QS inhibitors are being investigated as antimicrobials because of their potential to reduce symptoms of infectious disease while slowing the emergence of resistant strains. Autoinducer-2 (AI-2) analogs have been shown to inhibit genotypic QS responses among many bacteria. We demonstrate for the first time, the ability of C1-alkyl AI-2 analog, isobutyl-DPD, to significantly inhibit the maturation of Escherichia coli biofilms grown in vitro. Using a novel microfluidic device that incorporates dynamic, real-time measurements of biofilm density, we also show that a combinatorial approach wherein isobutyl-DPD ((S)-4,5-dihydroxy-2,3-pentanedione) is used with the antibiotic gentamicin is quite effective in rendering near complete clearance of pre-existing E. coli biofilms. Similarly, another AI-2 analog, phenyl-DPD, also used in combination with near MIC levels of gentamicin, resulted in clearance of preformed Pseudomonas aeruginosa biofilms. Clearance of pre-existing biofilms has remained a significant health care challenge; these results warrant consideration of a new approach based on the combination of "quenching" QS signal transduction processes with traditional antibiotic treatment.
- X. W. Shi, L. Qiu, Z. Nie, L. Xiao, G. F. Payne, and Y. M. Du, "Protein addressing on patterned microchip by coupling chitosan electrodeposition and 'electro-click' chemistry," Biofabrication, 5 (4), 2013.
[Abstract]
Many applications in proteomics and lab-on-chip analysis require methods that guide proteins to assemble at surfaces with high spatial and temporal control. Electrical inputs are particularly convenient to control, and there has been considerable effort to discover simple and generic mechanisms that allow electrical inputs to trigger protein assembly on-demand. Here, we report the electroaddressing of a protein to a patterned surface by coupling two generic electroaddressing mechanisms. First, we electrodeposit the stimuli-responsive film-forming aminopolysaccharide chitosan to form a hydrogel matrix at the electrode surface. After deposition, the matrix is chemically functionalized with alkyne groups. Second, we "electro-click' an azide-tagged protein to the functionalized matrix using electrical signals to trigger conjugation by Huisgen 1,3-dipolar cycloadditions. Specifically, a cathodic potential is applied to the matrix-coated electrode to reduce Cu(II) to Cu(I) which is required for the click reaction. Using fluorescently-labeled bovine serum albumin as our model, we demonstrate that protein conjugation can be controlled spatially and temporally. We anticipate that the coupling of polysaccharide electrodeposition and electro-click chemistry will provide a simple and generic approach to electroaddress proteins within compatible hydrogel matrices.
- K. Saadin, J. M. Burke, N. P. Patel, R. E. Zubajlo, and I. M. White, "Enrichment of tumor-initiating breast cancer cells within a mammosphere-culture microdevice," Biomedical Microdevices, 15 (4), 645-655, 2013.
[Abstract]
We report for the first time a microdevice that enables the selective enrichment, culture, and identification of tumor-initiating cells on native polydimethylsiloxane (PDMS). For nearly a decade, researchers have identified tumor-initiating breast cancer cells within heterogeneous populations of breast cancer cells by utilizing low-attachment serum-free culture conditions, which lead to the formation of spheroidal colonies (mammospheres) that are enriched for tumor-initiating cells. However, the utility of this assay has been limited by difficulties in combining this culture-plate-based technique with other cellular and molecular analyses. Integrating the mammosphere technique into a microsystem can enable it to be combined directly with a number of functions, such as cell sorting, drug screens, and molecular assays. In this work, we demonstrate mammosphere culture within a PDMS microdevice. We first prove that a native hydrophobic PDMS surface is as effective as commercial low-attachment plates at selectively promoting the formation of mammospheres. We then experimentally assess the PDMS microdevice. Time-lapse images of mammosphere formation within the microdevice show that mammospheres form from single cells or small clusters of cells. Following formation of the mammospheres, it is desirable to evaluate the cells within the spheroids for enrichment of tumor initiating cells. To perform assays such as this (which require the loading and rinsing of reagents) without flushing the cells (which are in suspension) from the device, the culture chamber is separated from a reagent reservoir by a commercially available microporous membrane, and thus reagents are exchanged between the reservoir and the culture chamber by diffusion only. Using this capability, we verify that the mammospheres are enriched for tumor initiating cells by staining aldehyde dehydrogenase activity, a cancer stem cell marker. To the best of our knowledge, this is the first assay that enables the direct observation of tumor-initiating cells within a suspended mammosphere.
- K. Saadin and I. M. White, "Breast cancer stem cell enrichment and isolation by mammosphere culture and its potential diagnostic applications," Expert Review of Molecular Diagnostics, 13 (1), 49-60, 2013.
[Abstract]
Expert Rev. Mol. Diagn. 13(1), 49-60 (2013) Emerging knowledge about cancer stem cells (CSCs) is raising attention about the need to provide a more precise and complete diagnosis including the molecular profile of a patient's CSCs. As opposed to simply treating the bulk of the tumor, a more complete diagnosis can lead to treatment regimens designed to eradicate CSCs from a patient. In this review the authors detail the application of the mammosphere assay in the study of breast CSCs. The authors then describe the potential transition of the mammosphere assay from the research laboratory to the clinic by leveraging microsystems technology, which enables the integration Of multiple functions into a single automated device. To conclude the review, the authors project that future clinical devices will be capable of isolating circulating metastatic cells from patient blood, enriching the dangerous CSCs, and providing a molecular profile of the CSCs, thus arming physicians with the information to select a treatment program that combats CSCs.
- A. G. Banerjee and S. K. Gupta, "Research in Automated Planning and Control for Micromanipulation," IEEE Transactions on Automation Science and Engineering, 10 (3), 485-495, 2013.
[Abstract]
Manipulation of microscopic objects, especially biological objects and microelectromechanical systems (MEMS) components, has become an important area of robotics research over the past several years. Automation is necessary as it is challenging to manually control the microobjects due to the scaling effect of the surface forces, stochastic motion of objects in fluid media, and uncertainty associated with object state estimation. Automation requires real-time control of the position, orientation, and force applied by each of the operational manipulators, as governed by the system-level objectives of optimizing resource, time, and effort, by planning suitable actions for the manipulated objects. In this paper, we provide a survey of the research in planning and control of such automated micromanipulation operations. We present a broad taxonomy based on the underlying approach, and discuss the salient features and experimental success of each research effort. We also identify the major limitations and common trends across all the approaches, discuss the effectiveness of an approach depending on the operation characteristics, and outline promising future research directions.
- S. Chowdhury, P. Svec, C. L. Wang, K. T. Seale, J. P. Wikswo, W. Losert, and S. K. Gupta, "Automated Cell Transport in Optical Tweezers-Assisted Microfluidic Chambers," IEEE Transactions on Automation Science and Engineering, 10 (4), 980-989, 2013.
[Abstract]
In this paper, we present a physics-aware, planning approach for automated transport of cells in an optical tweezers-assisted microfluidic chamber. The approach can be used for making a uniform distribution of cells inside the chamber to allow the study of a variety of biological processes, including cell signaling. Fluid forces inside the chamber, modeled using computational fluid dynamics, are incorporated into the widely used Langevin equation to simulate the motion of cells. The developed simulator was used for building a map that contains probabilities of a cell successfully reaching one of the outlets of the chamber from different locations under the influence of the fluid flow. The developed planner not only generates collision-free paths that exploit the fluid flow inside the chamber but also utilizes the offline generated simulation data to decide suitable locations for releasing the cells. This ensures fast and robust cell transport, while minimizing the required laser power and operational time. The planner is based on the heuristic D-star Lite algorithm that employs a specific cost function for searching over a novel state-action space representation. The effectiveness of the planning algorithm is demonstrated using both simulation and physical experiments in a microfluidics-optical tweezers hybrid manipulation setup.
- C. Arya, J. G. Kralj, K. Jiang, M. S. Munson, T. P. Forbes, D. L. DeVoe, S. R. Raghavan, and S. P. Forry, "Capturing rare cells from blood using a packed bed of custom-synthesized chitosan microparticles," Journal of Materials Chemistry B, 1 (34), 4313-4319, 2013.
[Abstract]
We describe batch generation of uniform multifunctional chitosan microparticles for isolation of rare cells, such as circulating tumor cells (CTCs), from a sample of whole blood. The chitosan microparticles were produced in large numbers using a simple and inexpensive microtubing arrangement. The particles were functionalized through encapsulation of carbon black, to control autofluorescence, and surface attachment of streptavidin, to enable interactions with biotinylated antibodies. These large custom modified microparticles (approximate to 164 mu m diameter) were then packed into a microfluidic channel to demonstrate their utility in rare cell capture. Blood spiked with breast cancer (MCF-7) cells was first treated with a biotinylated antibody (anti-EpCAM, which is selective for cancer cells like MCF-7) and then pumped through the device. In the process, the cancer cells were selectively bound to the microparticles through non-covalent streptavidin-biotin interactions. The number density of captured cells was determined by fluorescence microscopy at physiologically relevant levels. Selective capture of the MCF-7 cells was characterized, and compared favorably with previous approaches. The overall approach using custom synthesized microparticles is versatile, and can allow researchers more flexibility for rare cell capture through simpler and cheaper methods than are currently employed.
- L. M. Sanchez, D. M. Potrepka, G. R. Fox, I. Takeuchi, K. Wang, L. A. Bendersky, and R. G. Polcawich, "Optimization of PbTiO3 seed layers and Pt metallization for PZT-based piezoMEMS actuators," Journal of Materials Research, 28 (14), 1920-1931, 2013.
[Abstract]
This work attempts to optimize past research results on lead zirconate titanate (PZT) using the fabrication processes at the U. S. Army Research Laboratory so as to achieve a high degree of {001} texture and improved piezoelectric properties. A comparative study was performed between Ti/Pt and TiO2/Pt bottom electrodes. The results indicate that the use of a highly oriented {100} rutile phase TiO2 led to highly textured {111} Pt which in turn improved both the PTO and PZT orientations. PZT (52/48) and (45/55) thin films with and without PTO seed layers were deposited and examined via x-ray diffraction (XRD) methods as a function of annealing temperature. The seed layer provides significant improvement in the {100} orientation generally, and in the {001} subset of planes specifically, while suppressing the {111} orientation of the PZT. Improvements in the Lotgering factor (f) were observed from an existing Ti/Pt/PZT process (f = 0.66) to samples using the PTO seed layer deposited onto the improved Pt electrodes, TiO2/Pt/PTO/PZT (f = 0.96).
- M. I. Beyaz, B. M. Hanrahan, J. Feldman, and R. Ghodssi, "An Integrated Permanent-Magnet Microturbogenerator Supported on Microball Bearings," Journal of Microelectromechanical Systems, 22 (3), 794-803, 2013.
[Abstract]
This paper presents the design, fabrication, and testing of an integrated microturbogenerator utilizing permanent magnets and microball bearings. The key components of this generator are the following: 1) a silicon microturbine rotor housing thick magnetic components; 2) encapsulated microball bearings providing a simple actuation scheme and a robust support structure; and 3) wafer-thick stator coils. The microturbogenerator was designed and fabricated to have a ten-pole rotor and a ten-pole three-turns-per-pole stator. The impedance of the stator coils was shown to be a purely resistive 220 Omega up to 10 kHz. The spin-down characterization of the rotor revealed a dynamic friction torque of 33 mu N . m at a rotational speed of 16 kilo rotations per minute (krpm), corresponding to 6% turbine efficiency. The maximum per-phase ac open-circuit voltage and power were measured to be 0.1 V and 5.6 mu W on a matched load at 23 krpm, respectively, in full agreement with theoretical analysis and performance estimations. The microturbogenerator presented in this paper provides a flexible design platform for further improvement and will lead to the development of next-generation integrated microturbogenerators offering high power, simple operation, and robust mechanics. [2012-0186]
- A. P. Gerratt and S. Bergbreiter, "Dielectric breakdown of PDMS thin films," Journal of Micromechanics and Microengineering, 23 (6), 2013.
[Abstract]
This note presents the data on the dielectric breakdown of polydimethylsiloxane (PDMS) thin films with thicknesses from 2 to 14 mu m between the silicon electrodes. The results demonstrate that there is a strong dependence of the breakdown field on both the electrode gap and shape. The breakdown fields range from 250 to 635 V mu m(-1), depending on the electrode geometry and gap, approaching 10x the breakdown fields for air gaps of the same size. The results are critical for understanding the performance limits of PDMS thin films used in the electromechanical microsystems.
- A. P. Gerratt, I. Penskiy, and S. Bergbreiter, "In situ characterization of PDMS in SOI-MEMS," Journal of Micromechanics and Microengineering, 23 (4), 2013.
[Abstract]
This paper presents the in situ characterization of microscale poly(dimethylsiloxane) (PDMS) springs using silicon-on-insulator-microelectromechanical systems (SOI-MEMS). PDMS samples that were 30 mu m long, 20 mu m thick, and 6 mu m wide were fabricated on-chip along with a test mechanism that included electrostatic comb drive actuators and silicon flexures. The test mechanism allowed for applying strains up to 65%. The in situ test results were compared with results of tests on macroscale samples performed using a dynamic mechanical analyzer. The results imply that the process steps during fabrication initially led to increased crosslinking of the PDMS but that the final release of the structure in buffered hydrofluoric acid decreased the crosslink density, thereby decreasing the stiffness of the PDMS. Several implications of the results on processing PDMS in MEMS are presented. The results of this work are important for the design of MEMS devices which incorporate PDMS as a mechanical material.
- M. Gnerlich, E. Pomerantseva, K. Gregorczyk, D. Ketchum, G. Rubloff, and R. Ghodssi, "Solid flexible electrochemical supercapacitor using Tobacco mosaic virus nanostructures and ALD ruthenium oxide," Journal of Micromechanics and Microengineering, 23 (11), 2013.
[Abstract]
An all-solid electrochemical supercapacitor has been developed using a nanostructured nickel and titanium nitride template that is coated with ruthenium oxide by atomic layer deposition (ALD). The electrode morphology was based on a high surface area biotemplate of genetically modified Tobacco mosaic virus. The biotemplate automatically self-assembles at room temperature in aqueous solution. Nafion (R) perfluorosulfonate ionomer dispersion was cast on the electrodes and used as a solid proton-conducting electrolyte. A 5.8 F g(-1) gravimetric capacity (578 mu F cm(-2) based on footprint) was achieved in Nafion electrolyte, and the device retained 80% of its capacity after 25 000 cycles. The technology presented here will enable thin, solid, flexible supercapacitors that are compatible with standard microfabrication techniques.
- R. J. Hergert, B. Hanrahan, R. Ghodssi, and A. S. Holmes, "Performance of integrated retainer rings in silicon micro-turbines with thrust style micro-ball bearings," Journal of Micromechanics and Microengineering, 23 (6), 2013.
[Abstract]
This work explores the performance of different silicon retainer ring designs when integrated into silicon micro-turbines (SMTs) incorporating thrust style bearings supported on 500 mu m diameter steel balls. Experimental performance curves are presented for SMTs with rotor diameters of 5 mm and 10 mm, each with five different retainer designs varying in mechanical rigidity, ball pocket shape and ball complement. It was found that the different retainer designs yielded different performance curves, with the closed pocket designs consistently requiring lower input power for a given rotation speed, and the most rigid retainers giving the best performance overall. Both 5 mm and 10 mm diameter devices have shown repeatable performance at rotation speeds up to and exceeding 20 000 RPM with input power levels below 2 W, and devices were tested for over 2.5 million revolutions without failure. Retainer rings are commonly used in macro-scale bearings to ensure uniform spacing between the rolling elements. The integration of retainers into micro-bearings could lower costs by reducing the number of balls required for stable operation, and also open up the possibility of 'smart' bearings with integrated sensors to monitor the bearing status.
- Y. S. Kim, N. G. Dagalakis, and S. K. Gupta, "Creating large out-of-plane displacement electrothermal motion stage by incorporating beams with step features," Journal of Micromechanics and Microengineering, 23 (5), 2013.
[Abstract]
Realizing out-of-plane actuation in micro-electro-mechanical systems (MEMS) is still a challenging task. In this paper, the design, fabrication methods and experimental results for a MEMS-based out-of-plane motion stage are presented based on bulk micromachining technologies. This stage is electrothermally actuated for out-of-plane motion by incorporating beams with step features. The fabricated motion stage has demonstrated displacements of 85 mu m with 0.4 mu m (mA)(-1) rates and generated up to 11.8 mN forces with stiffness of 138.8 N m(-1). These properties obtained from the presented stage are comparable to those for in-plane motion stages, therefore making this out-of-plane stage useful when used in combination with in-plane motion stages.
- I. Penskiy and S. Bergbreiter, "Optimized electrostatic inchworm motors using a flexible driving arm," Journal of Micromechanics and Microengineering, 23 (1), 2013.
[Abstract]
A new motor architecture that uses in-plane electrostatic gap-closing actuators along with a flexible driving arm mechanism to improve motor force density is introduced, optimized, manufactured, and tested. This motor operates similarly to other inchworm-based microactuators by accumulating small displacements from the actuators into much larger displacements in the motor. Using an analytical model of the inchworm motor based on the static force equilibrium condition, optimizations of a full motor design were performed to maximize motor force density. In addition, force losses from supporting flexures were included to calculate the theoretical motor efficiency for different motor designs. This force density optimization analysis of the gap-closing actuators and supporting motor structures provided the basis for designing and manufacturing inchworm motors with flexible driving arms and gap-closing actuators. The motor required only a single-mask fabrication and demonstrated robust performance, a maximum speed of 4.8 mm s(-1), and a maximum force on the shuttle of 1.88 mN at 110 V which corresponds to area force density of 1.38 mN mm(-2). In addition, instead of estimating motor force based on drawn or measured dimensions which often overestimates force, the demonstrated maximum motor force was measured using calibrated springs. The efficiency of the manufactured motor was measured at 8.75% using capacitance measurements and useful work output.
- E. Pomerantseva, H. Jung, M. Gnerlich, S. Baron, K. Gerasopoulos, and R. Ghodssi, "A MEMS platform for in situ, real-time monitoring of electrochemically induced mechanical changes in lithium-ion battery electrodes," Journal of Micromechanics and Microengineering, 23 (11), 2013.
[Abstract]
We report the first successful demonstration of an optical microelectromechanical systems (MEMS) sensing platform for the in situ characterization of electrochemically induced reversible mechanical changes in lithium-ion battery (LIB) electrodes. The platform consists of an array of flexible membranes with a reflective surface on one side and a thin-film LIB electrode on the other side. The membranes deflect due to the active battery material volume change caused by lithium intercalation (expansion) and extraction (contraction). This deflection is monitored using the Fabry-Perot optical interferometry principle. The active material volume change causes high internal stresses and mechanical degradation of the electrodes. The stress evolution observed in a silicon thin-film electrode incorporated into this MEMS platform follows a 'first elastic, then plastic' deformation scheme. Understanding of the internal stresses in battery electrodes during discharge/charge is important for improving the reliability and cycle lifetime of LIBs. The developed MEMS platform presents a new method for in situ diagnostics of thin-film LIB electrodes to aid the development of new materials, optimization of electrode performance, and prevention of battery failure.
- H. Therien-Aubin, Z. L. Wu, Z. H. Nie, and E. Kumacheva, "Multiple Shape Transformations of Composite Hydrogel Sheets," Journal of the American Chemical Society, 135 (12), 4834-4839, 2013.
[Abstract]
Soft materials undergoing shape transformations in response to changes in ambient environment have potential applications in tissue engineering, robotics and biosensing. Generally, stimulus-responsive materials acquire two stable shapes corresponding to the "on" and "off" states of the external trigger. Here, we report a simple, yet versatile approach to induce multiple shape transformations of a planar hydrogel sheet, each triggered by a particular, well-defined external stimulus. The approach is based on the integration of small-scale multiple polymer components with distinct compositions in the composite gel sheet. In response to different stimuli, the structural components undergo differential swelling or shrinkage, which creates internal stresses within the composite hydrogel sheet and transforms its shape in a specific manner.
- X. Z. Fan, E. Pomerantseva, M. Gnerlich, A. Brown, K. Gerasopoulos, M. McCarthy, J. Culver, and R. Ghodssi, "Tobacco mosaic virus: A biological building block for micro/nano/bio systems," Journal of Vacuum Science & Technology A, 31 (5), 2013.
[Abstract]
Tobacco mosaic virus (TMV) has the potential to be an ideal candidate for a building block of the next-generation micro/nano/bio systems. The TMV virion is a high-aspect ratio rigid nanotube that is robust and compatible with some conventional microfabrication processes. TMV can be chemically and genetically modified to enhance its physical properties and tailor them to specific applications. This review covers the use of TMV nanostructures in a wide range of micro/nano/bio systems. TMV has been utilized in the production of nanowires, nanostructured thin films, biomimetic surfaces, novel sensors, high performance microbatteries, solid-state electronics, and engineered biosystems. The work highlighted here is meant to give a perspective of the entire breadth of the properties of these virions, from their synthesis and functionalization to assembly and patterning, as well as feature works that represent key milestones in the field of biofabrication and biomaterial integration. The advantages already demonstrated by the integration of TMV nanostructures, even at this early stage of development, suggest that the applications for this micro/nano/bio systems building block will continue to grow. (C) 2013 American Vacuum Society.
- J. F. Betz, Y. Cheng, C. Y. Tsao, A. Zargar, H. C. Wu, X. L. Luo, G. F. Payne, W. E. Bentley, and G. W. Rubloff, "Optically clear alginate hydrogels for spatially controlled cell entrapment and culture at microfluidic electrode surfaces," Lab on a Chip, 13 (10), 1854-1858, 2013.
[Abstract]
We describe an innovation in the immobilization, culture, and imaging of cells in calcium alginate within microfluidic devices. This technique allows unprecedented optical access to the entirety of the calcium alginate hydrogel, enabling observation of growth and behavior in a chemical and mechanical environment favored by many kinds of cells.
- O. Rahmanian and D. L. DeVoe, "Pen microfluidics: rapid desktop manufacturing of sealed thermoplastic microchannels," Lab on a Chip, 13 (6), 1102-1108, 2013.
[Abstract]
A unique technique for the rapid fabrication of thermoplastic microfluidic chips is described. The method enables the realization of fully-sealed microchannels in around one hour while requiring only minimal infrastructure by taking advantage of a solvent swelling mechanism that allows raised features to be patterned on the surface of homogeneous thermoplastic materials. Patterning is achieved without photolithography by simply drawing the desired microchannel pattern onto the polymer surface using a suitable ink as a masking layer, either manually or under robotic control, followed by timed exposure to solvent vapor to yield a desired depth for the masked channel features. The channels are then permanently sealed through solvent bonding of the microchannel chip to a mating thermoplastic substrate. The process is demonstrated using cyclic olefin copolymer as a thermoplastic material, with fully operational microfluidic devices fabricated following a true desktop manufacturing model suitable for rapid prototyping.
- A. X. Lu, K. Jiang, D. L. DeVoe, and S. R. Raghavan, "Microfluidic Assembly of Janus-Like Dimer Capsules," Langmuir, 29 (44), 13624-13629, 2013.
[Abstract]
We describe the microfluidic assembly of soft dimer capsules by the fusion of individual capsules with distinct properties. Microscale aqueous droplets bearing the biopolymer chitosan are generated in situ within a chip and, as they travel downsteam, pairs of droplets are made to undergo controlled cross-linking and coalescence (due to a channel expansion) to form stable dimers. These dimers are very much like Janus particles: the size, shape, and functionality of each individual lobe within the dimer can be precisely controlled. Dimers with one lobe much shorter than the other resemble a bowling pin in their overall morphology, while dimers with nearly equal-sized lobes are akin to a snowman. To illustrate the diverse functionalities possible, we have prepared dimers wherein one lobe encapsulates paramagnetic Fe2O3 nanoparticles. The resulting dimers undergo controlled rotation in an external rotating magnetic field, much like a magnetic stir bar. The overall approach described here is simple and versatile: it can be easily adapted in numerous ways to produce soft structures with designed properties.
- E. Pomerantseva, K. Gerasopoulos, M. Gnerlich, P. Odenwald, J. Culver, and R. Ghodssi, "Using Tobacco mosaic virus template for the fabrication of three-dimensional hierarchical microbattery electrodes with high energy and high power density," Nanoepitaxy: Materials and Devices V, 8820, 2013.
[Abstract]
We present a novel approach for the fabrication of lithium-ion microbattery electrodes which deliver high energy and high power density. The key enabling technology is the use of self-assembled Tobacco mosaic virus (TMV) nanoforests as a template for active battery materials. The self-assembling TMV is a genetically modified biological nanorod with increased metal binding properties for enhanced manufacturability. High energy density is achieved due to the active surface area increase within a given footprint by combining TMV with three-dimensional (3D) microfabricated structures. The TMV nanostructure enables high power density through larger electrode/electrolyte contact area and faster charge transport. The electrodes consist of an array of electroplated gold micropillars. The pillars are coated with the self-assembled nanoscale TMV template and subsequently metalized in-place. Active battery material (V2O5) is conformally deposited using atomic layer deposition (ALD) on the hierarchical micro/nano network. Electrochemical testing of these electrodes indicates a 3-5 fold increase in energy density, compared to the TMV-templated electrodes without micropillars, without increasing footprint area or reducing rate performance. Further increase in energy density can be achieved by increasing surface area of 3D microelements as demonstrated by fabrication and electrochemical testing of the electrodes with hollow gold micropillars. Scaling up energy density by increasing active material thickness beyond 100 nm revealed some loss in surface area which highlighted the importance of nanoscale engineering for achieving maximum energy and power density in energy storage systems.
- Z. L. Wu, M. Moshe, J. Greener, H. Therien-Aubin, Z. H. Nie, E. Sharon, and E. Kumacheva, "Three-dimensional shape transformations of hydrogel sheets induced by small-scale modulation of internal stresses," Nature Communications, 4, 2013.
[Abstract]
Although Nature has always been a common source of inspiration in the development of artificial materials, only recently has the ability of man-made materials to produce complex three-dimensional (3D) structures from two-dimensional sheets been explored. Here we present a new approach to the self-shaping of soft matter that mimics fibrous plant tissues by exploiting small-scale variations in the internal stresses to form three-dimensional morphologies. We design single-layer hydrogel sheets with chemically distinct, fibre-like regions that exhibit differential shrinkage and elastic moduli under the application of external stimulus. Using a planar-to-helical three-dimensional shape transformation as an example, we explore the relation between the internal architecture of the sheets and their transition to cylindrical and conical helices with specific structural characteristics. The ability to engineer multiple three-dimensional shape transformations determined by small-scale patterns in a hydrogel sheet represents a promising step in the development of programmable soft matter.
- C. Pang, H. Bae, A. Gupta, K. Bryden, and M. Yu, "MEMS Fabry-Perot sensor interrogated by optical system-on-a-chip for simultaneous pressure and temperature sensing," Optics Express, 21 (19), 21829-21839, 2013.
[Abstract]
We present a micro-electro-mechanical systems (MEMS) based Fabry-Perot (FP) sensor along with an optical system-on-a-chip (SOC) interrogator for simultaneous pressure and temperature sensing. The sensor employs a simple structure with an air-backed silicon membrane cross-axially bonded to a 45 degrees polished optical fiber. This structure renders two cascaded FP cavities, enabling simultaneous pressure and temperature sensing in close proximity along the optical axis. The optical SOC consists of a broadband source, a MEMS FP tunable filter, a photodetector, and the supporting circuitry, serving as a miniature spectrometer for retrieving the two FP cavity lengths. Within the measured pressure and temperature ranges, experimental results demonstrate that the sensor exhibits a good linear response to external pressure and temperature changes. (c) 2013 Optical Society of America
- R. R. Hood, C. Shao, D. M. Omiatek, W. N. Vreeland, and D. L. DeVoe, "Microfluidic Synthesis of PEG- and Folate-Conjugated Liposomes for One-Step Formation of Targeted Stealth Nanocarriers," Pharmaceutical Research, 30 (6), 1597-1607, 2013.
[Abstract]
A microfluidic hydrodynamic flow focusing technique enabling the formation of small and nearly monodisperse liposomes is investigated for continuous-flow synthesis of poly(ethylene glycol) (PEG)-modified and PEG-folate-functionalized liposomes for targeted drug delivery. Controlled laminar flow in thermoplastic microfluidic devices facilitated liposome self-assembly from initial lipid compositions including lipid/cholesterol mixtures containing PEG-lipid and folate-PEG-lipid conjugates. Relationships among flow conditions, lipid composition, and liposome size were evaluated; their impact on PEG and folate incorporation were determined through a combination of UV-vis absorbance measurements and characterization of liposome zeta potential. PEG and folate were successfully incorporated into microfluidic-synthesized liposomes over the full range of liposome sizes studied. Efficiency of PEG-lipid incorporation was inversely correlated with liposome diameter. Folate-lipid was effectively integrated into liposomes at various flow conditions. Liposomes incorporating relatively large PEG-modified and folate-PEG-modified lipids were successfully synthesized using the microfluidic flow focusing platform, providing a simple, low cost, rapid method for preparing functionalized liposomes. Relationships between preparation conditions and PEG or folate-PEG functionalization have been elucidated, providing insight into the process and defining paths for optimization of the microfluidic method toward the formation of functionalized liposomes for pharmaceutical applications.
- A. P. Gerratt and S. Bergbreiter, "Incorporating compliant elastomers for jumping locomotion in microrobots," Smart Materials & Structures, 22 (1), 2013.
[Abstract]
Small insects and other animals use a multitude of materials to realize specific functions, including locomotion. This paper demonstrates application of the first microfabrication process to incorporate high aspect ratio compliant elastomer structures in-plane with traditional silicon microelectromechanical systems (MEMS). By incorporating these new materials, compact energy storage systems based on elastomer springs for small jumping robots have been demonstrated. Results include a 4 mm x 4 mm jumping mechanism that has reached heights of 32 cm, x 80 its own height, and an on-chip actuated mechanism that has been used to propel a 1.4 mg projectile over 7 cm.
- C. Pang, M. Yu, A. K. Gupta, and K. M. Bryden, "Investigation of smart multifunctional optical sensor platform and its application in optical sensor networks," Smart Structures and Systems, 12 (1), 23-39, 2013.
[Abstract]
In this article, a smart multifunctional optical system-on-a-chip (SOC) sensor platform is presented and its application for fiber Bragg grating (FBG) sensor interrogation in optical sensor networks is investigated. The smart SOC sensor platform consists of a superluminescent diode as a broadband source, a tunable microelectromechanical system (MEMS) based Fabry-Perot filter, photodetectors, and an integrated microcontroller for data acquisition, processing, and communication. Integrated with a wireless sensor network (WSN) module in a compact package, a smart optical sensor node is developed. The smart multifunctional sensor platform has the capability of interrogating different types of optical fiber sensors, including Fabry-Perot sensors and Bragg grating sensors. As a case study, the smart optical sensor platform is demonstrated to interrogate multiplexed FBG strain sensors. A time domain signal processing method is used to obtain the Bragg wavelength shift of two FBG strain sensors through sweeping the MEMS tunable Fabry-Perot filter. A tuning range of 46 nm and a tuning speed of 10 Hz are achieved. The smart optical sensor platform will open doors to many applications that require high performance optical WSNs.
- Y. Liu, B. Zhang, K. M. Gray, Y. Cheng, E. Kim, G. W. Rubloff, W. E. Bentley, Q. Wang, and G. F. Payne, "Electrodeposition of a weak polyelectrolyte hydrogel: remarkable effects of salt on kinetics, structure and properties," Soft Matter, 9 (9), 2703-2710, 2013.
[Abstract]
The electrodeposition of weak polyelectrolyte hydrogels involves an array of subtle interactions. We report that salt dramatically affects the kinetics of chitosan electrodeposition, and the structure and properties of deposited hydrogel films. The kinetics of film growth was measured using a microfluidic device which demonstrated that salt increases both the rate and extent of deposition. The structure of the deposited film was measured by atomic force microscopy which showed that salt addition to the deposition solution leads to films with greater surface roughness (consistent with the tendency of chitosan to aggregate at high salt concentrations). The properties of the deposited films were measured by quartz crystal microbalance with dissipation (QCM-D) which showed that salt addition to the deposition solution leads to films with substantially reduced moduli (over 3-orders-of-magnitude). These results illustrate the potential to tailor electrodeposition to meet specific requirements for the diverse applications in the life and medical sciences.
- K. Gerasopoulos, E. Pomerantseva, M. McCarthy, A. Brown, C. S. Wang, J. Culver, and R. Ghodssi, "Hierarchical Three-Dimensional Microbattery Electrodes Combining Bottom-Up Self-Assembly and Top-Down Micromachining," ACS Nano, 6 (7), 6422-6432, 2012.
[Abstract]
The realization of next-generation portable electronics and integrated microsystems is directly linked with the development of robust batteries with high energy and power density. Three-dimensional micro- and nanostructured electrodes enhance energy and power through higher surface area and thinner active materials, respectively. Here, we present a novel approach for the fabrication of hierarchical electrodes that combine benefits of both length scales. The electrodes consist of self-assembled, virus-templated nanostructures conformally coating three-dimensional micropillars. Active battery material (V2O5) is deposited using atomic layer deposition on the hierarchical micro/nanonetwork Electrochemical characterization of these electrodes indicates a 3-fold increase in energy density compared to nanostructures alone, in agreement with the surface area increase, while maintaining the high power characteristics of nanomaterials. Investigation of capacity scaling for varying active material thickness reveals underlying limitations in nanostructured electrodes and highlight the importance of our method in controlling both energy and power density with structural hierarchy.
- Y. Cheng, C. Y. Tsao, H. C. Wu, X. L. Luo, J. L. Terrell, J. Betz, G. F. Payne, W. E. Bentley, and G. W. Rubloff, "Electroaddressing Functionalized Polysaccharides as Model Biofilms for Interrogating Cell Signaling," Advanced Functional Materials, 22 (3), 519-528, 2012.
[Abstract]
Bacteria often reside at surfaces as complex biofilms in which an exopolysaccharide matrix entraps the population while allowing access to its chemical environment. There is a growing awareness that the biofilm structure and activity are integral to a wide array of properties important to health (the microbiome), disease (drug resistance) and technology (fouling). Despite the importance of bacterial biofilms, few experimental platforms and systems are available to assemble complex populations and monitor their activities. Here, a functionalized alginate composite material for creating in vitro model biofilms suitable for cell-cell signaling studies by entrapping bacterial cells in situ is reported. Biofilm assembly is achieved using device-imposed electrical signals to electrodeposit the stimuli-responsive polysaccharide alginate. This electrodeposition mechanism is versatile in that it allows control of the bacterial population density and distribution. For instance, it is demonstrated that a mixed population can be homogeneously distributed throughout the biofilm or can be assembled as spatially segregated populations within a stratified biofilm. The electroaddressable biofilms are visualized using both a planar 2D chip with patterned electrodes and a microfluidic bioMEMS device with sidewall electrodes. Specifically, it is observed that bacteria entrapped within the model biofilm recognize and respond to chemical stimuli imposed from the fluidic environment. Finally, reporter cells are used to demonstrate that bacteria entrapped within this model biofilm engage in intercellular quorum sensing. This work demonstrates the functionality of the stimuli-responsive polysaccharide by biofabricating pseudo-3D cell-gel biocomposites, mimicking the formation of biofilms, for interrogating phenotypes of E. coli bacterial populations. In addition to controlling assembly, the microfluidic device allows the biofilm to be monitored through the fluorescence methods commonly used in biological research. This platform technology should be able to be exploited for monitoring biofilm development, as well as for extending the understanding of the interactions between various bacterial species arranged in controlled patterns.
- J. Lankelma, Z. H. Nie, E. Carrilho, and G. M. Whitesides, "Paper-Based Analytical Device for Electrochemical Flow-Injection Analysis of Glucose in Urine," Analytical Chemistry, 84 (9), 4147-4152, 2012.
[Abstract]
This article describes a new design for a paper-based electrochemical system for flow injection analysis. Capillary wicking facilitates a gravity-driven flow of buffer solution continuously through paper and nitrocellulose, from a buffer reservoir at one end of the device to a sink at the other. A difference in height between the reservoir and the sink leads to a continuous and constant flow. The nitrocellulose lies horizontally on a working electrode, which consists of a thin platinum layer deposited on a solid support. The counter and reference electrodes are strategically positioned upstream in the buffer reservoir. A simple pipetting device was developed for reliable application of (sub)microliter volumes of sample without the need of commercial micropipets; this device did not damage the nitrocellulose membrane. Demonstration of the system for the determination of the concentration of glucose in urine resulted in a noninvasive, quantitative assay that could be used for diagnosis and monitoring of diabetes. This method does not require disposable test strips, with enzyme and electrodes, that are thrown away after each measurement Because of its low cost, this system could be used in medical environments that are resource-limited.
- S. H. Yazdi and I. M. White, "Optofluidic Surface Enhanced Raman Spectroscopy Microsystem for Sensitive and Repeatable On-Site Detection of Chemical Contaminants," Analytical Chemistry, 84 (18), 7992-7998, 2012.
[Abstract]
We demonstrate highly sensitive detection of real-world food and water contaminants using a portable and automated optofluidic surface enhanced Raman spectroscopy (SERS) microsystem. The optofluidic SEAS device utilizes a porous microfluiclic matrix formed by packed silica microspheres to concentrate silver nanoparticles and adsorbed analyte molecules, resulting in greatly improved SEAS detection performance. In addition, a passive micromixer that mixes silver nanoparticles into the sample solution is integrated into the device for improved automation. Furthermore, two optical fibers are integrated into the device and aligned to the detection volume to improve the automation as compared to confocal SERS, which requires focusing and alignment. The device exhibits up to 2 orders of magnitude improvement in SERS performance as compared to conventional microfluidic SEAS in an open channel. Using the optofluidic SEAS device, the food contaminant melamine was detected in low concentrations, with an estimated limit of detection (LOD) of 63 ppb, while the fungicide thiram was detected down to an estimated LOD of 50 ppt. In both cases, the reported results meet the U.S. federal requirements. Additionally, it is shown that the device continues to exhibit excellent performance even when mated to a commercially available portable spectrometer for the trace detection of thiram. This combination of the optofluidic SERS microsystem with a portable spectrometer will lead to highly sensitive and automated sensing systems for on-site detection of food and water contaminants in the field.
- X. J. Li, A. V. Valadez, P. Zuo, and Z. H. Nie, "Microfluidic 3D cell culture: potential application for tissue-based bioassays," Bioanalysis, 4 (12), 1509-1525, 2012.
[Abstract]
Current fundamental investigations of human biology and the development of therapeutic drugs commonly rely on 2D monolayer cell culture systems. However, 2D cell culture systems do not accurately recapitulate the structure, "function or physiology of living tissues, nor the highly complex and dynamic 3D environments in vivo. Microfluidic technology can provide microscale complex structures and well-controlled parameters to mimic the in vivo environment of cells. The combination of microfluidic technology with 3D cell culture offers great potential for in vivo-like tissue-based applications, such as the emerging organ-on-a-chip system. This article will review recent advances in the microfluidic technology for 3D cell culture and their biological applications.
- K. M. Gray, B. D. Liba, Y. F. Wang, Y. Cheng, G. W. Rubloff, W. E. Bentley, A. Montembault, I. Royaud, L. David, and G. F. Payne, "Electrodeposition of a Biopolymeric Hydrogel: Potential for One-Step Protein Electroaddressing," Biomacromolecules, 13 (4), 1181-1189, 2012.
[Abstract]
The electrodeposition of hydrogels provides a programmable means to assemble soft matter for various technological applications. We report an anodic method to deposit hydrogel films of the aminopolysaccharide chitosan. Evidence suggests the deposition mechanism involves the electrolysis of chloride to generate reactive chlorine species (e.g., HOCl) that partially oxidize chitosan to generate aldehydes that can couple covalently with amines (presumably through Schiff base linkages). Chitosan's anodic deposition is controllable spatially and temporally. Consistent with a covalent cross-linking mechanism, the deposited chitosan undergoes repeated swelling/deswelling in response to pH changes. Consistent with a covalent conjugation mechanism, proteins could be codeposited and retained within the chitosan film even after detergent washing. As a proof-of-concept, we electroaddressed glucose oxidase to a side-wall electrode of a microfabricated fluidic channel and demonstrated this enzyme could perform electrochemical biosensing functions. Thus, anodic chitosan deposition provides a reagentless, single-step method to electroaddress a stimuli-responsive and biofunctionalized hydrogel Film.
- X. L. Luo, H. C. Wu, C. Y. Tsao, Y. Cheng, J. Betz, G. F. Payne, G. W. Rubloff, and W. E. Bentley, "Biofabrication of stratified biofilm mimics for observation and control of bacterial signaling," Biomaterials, 33 (20), 5136-5143, 2012.
[Abstract]
Signaling between cells guides biological phenotype. Communications between individual cells, clusters of cells and populations exist in complex networks that, in sum, guide behavior. There are few experimental approaches that enable high content interrogation of individual and multicellular behaviors at length and time scales commensurate with the signal molecules and cells themselves. Here we present "biofabrication" in microfluidics as one approach that enables in-situ organization of living cells in microenvironments with spatiotemporal control and programmability. We construct bacterial biofilm mimics that offer detailed understanding and subsequent control of population-based quorum sensing (QS) behaviors in a manner decoupled from cell number. Our approach reveals signaling patterns among bacterial cells within a single biofilm as well as behaviors that are coordinated between two communicating biofilms. We envision versatile use of this biofabrication strategy for cell-cell interaction studies and small molecule drug discovery. (C) 2012 Elsevier Ltd. All rights reserved.
- J. M. Burke and E. Smela, "A novel surface modification technique for forming porous polymer monoliths in poly(dimethylsiloxane)," Biomicrofluidics, 6 (1), 2012.
[Abstract]
A new method of surface modification is described for enabling the in situ formation of homogenous porous polymer monoliths (PPMs) within poly(dimethylsiloxane) (PDMS) microfluidic channels that uses 365 nm UV illumination for polymerization. Porous polymer monolith formation in PDMS can be challenging because PDMS readily absorbs the monomers and solvents, changing the final monolith morphology, and because PDMS absorbs oxygen, which inhibits free-radical polymerization. The new approach is based on sequentially absorbing a non-hydrogen-abstracting photoinitiator and the monomers methyl methacrylate and ethylene diacrylate within the walls of the microchannel, and then polymerizing the surface treatment polymer within the PDMS, entangled with it but not covalently bound. Four different monolith compositions were tested, all of which yielded monoliths that were securely anchored and could withstand pressures exceeding the bonding strength of PDMS (40 psi) without dislodging. One was a recipe that was optimized to give a larger average pore size, required for low back pressure. This monolith was used to concentrate and subsequently mechanical lyse B lymphocytes. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3693589]
- S. H. Yazdi and I. M. White, "A nanoporous optofluidic microsystem for highly sensitive and repeatable surface enhanced Raman spectroscopy detection," Biomicrofluidics, 6 (1), 2012.
[Abstract]
We report the demonstration of an optofluidic surface enhanced Raman spectroscopy (SERS) device that leverages a nanoporous microfluidic matrix to improve the SERS detection performance by more than two orders of magnitude as compared to a typical open microfluidic channel. Although it is a growing trend to integrate optical biosensors into microfluidic channels, this basic combination has been detrimental to the sensing performance when applied to SERS. Recently, however, synergistic combinations between microfluidic functions and photonics (i.e., optofluidics) have been implemented that improve the detection performance of SERS. Conceptually, the simplest optofluidic SERS techniques reported to date utilize a single nanofluidic channel to trap nanoparticle-analyte conjugates as a method of preconcentration before detection. In this work, we leverage this paradigm while improving upon the simplicity by forming a 3D nanofluidic network with packed nanoporous silica microspheres in a microfluidic channel; this creates a concentration matrix that traps silver nanoclusters and adsorbed analytes into the SERS detection volume. With this approach, we are able to achieve a detection limit of 400 attomoles of Rhodamine 6G after only 2 min of sample loading with high chip-to-chip repeatability. Due to the high number of fluidic paths in the nanoporous channel, this approach is less prone to clogging than single nanofluidic inlets, and the loading time is decreased compared to previous reports. In addition, fabrication of this microsystem is quite simple, as nanoscale fabrication is not necessary. Finally, integrated multimode fiber optic cables eliminate the need for optical alignment, and thus the device is relevant for portable and automated applications in the field, including point-of-sample and point-of-care detection. To illustrate a relevant field-based application, we demonstrate the detection of 12 ppb of the organophosphate malathion in water using the nanofluidic SERS microsystem. (C) 2012 American Institute of Physics. [doi:10.1063/1.3677369]
- H. Ben-Yoav, P. H. Dykstra, W. E. Bentley, and R. Ghodssi, "A microfluidic-based electrochemical biochip for label-free diffusion-restricted DNA hybridization analysis," Biosensors & Bioelectronics, 38 (1), 114-120, 2012.
[Abstract]
DNA hybridization detection in microfluidic devices can reduce sample volumes, processing times, and can be integrated with other measurements. However, as device footprints decrease and their complexity increase, the signal-to-noise ratio in these systems also decreases and the sensitivity is thereby compromised. Device miniaturization produces distinct properties and phenomena with greater influence at the micro-scale than at the macro-scale. Here, a diffusion-restriction model was applied to a miniaturized biochip nanovolume reactor to accurately characterize DNA hybridization events that contribute to shifts in both charge transfer resistance and diffusional resistance. These effects are shown to play a significant role in electrochemical impedance spectroscopy (EIS) analyses at these length scales. Our highly functional microfluidic biosensor enables the detection of ssDNA targets selectively, with a calculated detection limit of 3.8 nM, and cross-reactivity of 13% following 20 min incubation with the target. This new biosensing approach can be further modeled and tested elucidating diffusion behavior in miniaturized devices and improving the performance of biosensors. (C) 2012 Elsevier B.V. All rights reserved.
- J. L. Terrell, T. Gordonov, Y. Cheng, H. C. Wu, D. Sampey, X. L. Luo, C. Y. Tsao, R. Ghodssi, G. W. Rubloff, G. F. Payne, and W. E. Bentley, "Integrated biofabrication for electro-addressed in-film bioprocessing," Biotechnology Journal, 7 (3), 428-439, 2012.
[Abstract]
Many recent advances in bioprocessing have been enabled by developments in miniaturization and microfluidics. A continuing challenge, however, is integrating multiple unit operations that require distinct spatial boundaries, especially with included labile biological components. We have suggested "biofabrication" as a means for organizing cells and biomolecules in complex configurations while preserving function of individual components. Polysaccharide films of chitosan and alginate that are assembled on-chip by electrodeposition are "smart" configurable interfaces that mediate communication between the biological systems and microfabricated devices. Here, we demonstrate the scalable performance of a production address, where incubated cells secrete antibodies, and a capture address, where secreted antibody is retained with specificity and subsequently assayed. The antibody exchange from one electro-address to another exemplifies integrated in-film bioprocessing, facilitated by the integrated biofabrication techniques used. This in-film approach enables complex processes without need for microfluidics and valving. Finally, we have shown scalability by reducing electrode sizes to a 1 mm scale without compromising film biofabrication or bioprocessing performance. The in situ reversible deposition of viable cells, productivity characterization, and capture of secreted antibodies could find use in bioprocessing applications such as clonal selection, run-to-run monitoring, initial scale-up, and areas including drug screening and biopsy analysis.
- Y. Cheng, X. L. Luo, G. F. Payne, and G. W. Rubloff, "Biofabrication: programmable assembly of polysaccharide hydrogels in microfluidics as biocompatible scaffolds," Journal of Materials Chemistry, 22 (16), 7659-7666, 2012.
[Abstract]
Because of their stimuli-responsiveness to chemical and pH gradients, polysaccharide hydrogels such as chitosan and alginate can be assembled as scaffolds for biomolecules or cells. Using the electrical and flow control available in microfluidic networks, in situ fabrication of 3D hydrogel scaffolds can be programmed in space and time to arrange biological components as an in vitro biochemically communicating system. Flexible in situ on-demand construction of a biocompatible scaffold within microfluidics holds promise for the assembly of biological components and systems for in vitro analysis and investigation. We foresee a wide spectrum applications ranging from replication of metabolic pathways as testbeds for drug discovery to identification of cell signaling mechanisms and observation of cellular response.
- W. A. Churaman, L. J. Currano, C. J. Morris, J. E. Rajkowski, and S. Bergbreiter, "The First Launch of an Autonomous Thrust-Driven Microrobot Using Nanoporous Energetic Silicon," Journal of Microelectromechanical Systems, 21 (1), 198-205, 2012.
[Abstract]
As the capability and complexity of robotic platforms continue to evolve from the macro to the micron scale, the challenge of achieving autonomy requires the development of robust, lightweight architectures. These architectures must provide a platform upon which actuators, control, sensing, power, and communication modules are integrated for optimal performance. In this paper, the first autonomous jumping microrobotic platform is demonstrated using a hybrid integration approach to assemble on-board control, sensing, power, and actuation directly onto a polymer chassis. For the purposes of this paper, jumping is defined as brief parabolic motion achieved via an actuation pulse at takeoff. In this paper, the actuation pulse comes from the rapid release of chemical energy to create propulsion. The actuation pulse lasts several microseconds and is achieved using a novel high-force/low-power thrust actuator, nanoporous energetic silicon, resulting in 250 mu J of kinetic energy delivered to the robot and a vertical height of approximately 8 cm. [2011-0030]
- P. Hareesh, I. Misri, S. Yang, and D. L. DeVoe, "Transverse Interdigitated Electrode Actuation of Homogeneous Bulk PZT," Journal of Microelectromechanical Systems, 21 (6), 1513-1518, 2012.
[Abstract]
A new method for achieving transverse bending-mode actuation of piezoelectric devices microfabricated from homogeneous layers of bulk lead zirconate titanate (PZT) is presented. The technique, which employs a set of interdigitated electrodes patterned on a single side of the piezoelectric substrate, takes advantage of an engineered electric field gradient within the PZT that can be optimized by selecting an appropriate electrode gap. Bulk PZT cantilevers have been fabricated by micropowder blasting, allowing the actuation technique to be evaluated experimentally and compared against analytical and finite-element-model results. Optimal poling conditions for the microfabricated cantilevers are reported, together with both quasi-static and resonant behaviors of the devices. The transverse interdigitated electrode topology provides a simple method for realizing high-performance bending-mode piezoelectric microactuators from a single homogeneous layer of bulk PZT using a simple two-mask process. [2012-0053]
- M. Dandin, P. Abshire, and E. Smela, "Polymer filters for ultraviolet-excited integrated fluorescence sensing," Journal of Micromechanics and Microengineering, 22 (9), 2012.
[Abstract]
Optical filters for blocking ultraviolet (UV) light were fabricated by doping various polymer hosts with a UV absorbing chromophore. The polymers were polydimethylsiloxane (PDMS), a silicone elastomer frequently used in microfluidics, SU-8, a photopatternable epoxy, and Humiseal 1B66, an acrylic coating used for moisture protection of integrated circuits. The chromophore was 2-(2'-hydroxy-5'-methylphenyl) benzotriazole (BTA), which has a high extinction coefficient between 300 nm and 400 nm. We demonstrate filters 5 mu m thick that exhibit high ultraviolet rejection (nearly -40 dB at 342 nm) yet pass visible light (near 0 dB above 400 nm), making them ideal for ultraviolet-excited fluorescence sensing within microsystems. The absorbance of the BTA depended on the host polymer. These filters are promising for integrated fluorescence spectroscopy in bioanalytical platforms because they can be patterned by dry etching, molding or exposure to ultraviolet light.
- A. Fox, D. R. Hines, and T. Li, "Probing the adhesion of submicron thin films fabricated on a polymer substrate via nano-transfer printing," Journal of Micromechanics and Microengineering, 22 (9), 2012.
[Abstract]
Determining the interfacial adhesion of ultrathin functional films in micro-electro-mechanical systems (MEMS) and nano-electro-mechanical systems (NEMS) becomes increasingly crucial for optimal design of MEMS/NEMS devices. However, direct measurement of adhesion properties of ultrathin films can be challenging, as the traditional metrology of adhesion at macroscopic scales becomes unsuitable in dealing with samples of extremely small dimension. In this paper, we present a feasible and robust approach combining nano-transfer printing (nTP) experiments and mechanics modeling to quantitatively determine the interfacial adhesion of submicron thin films. We show that the measurements of the interfacial adhesion of a submicron polycarbonate (PC) thin film on a PC substrate at multiple locations in multiple samples agree within 7.3%, demonstrating the accuracy and robustness of our approach. Given the versatility of the nTP process, the approach demonstrated in this paper is expected to be generally applicable to measure the adhesion of interfaces of other material combinations. In this sense, this study sheds light on better understanding of the adhesive properties of functional interfaces in MEMS and NEMS.
- Y. S. Kim, J. M. Yoo, S. H. Yang, Y. M. Choi, N. G. Dagalakis, and S. K. Gupta, "Design, fabrication and testing of a serial kinematic MEMS XY stage for multifinger manipulation," Journal of Micromechanics and Microengineering, 22 (8), 2012.
[Abstract]
In micro-electro-mechanical systems (MEMS) it is difficult to obtain a large range of motion with a small coupled error. This limitation was overcome by designing and fabricating a nested structure as a serial kinematic mechanism (SKM). In this paper, a MEMS-based XY stage is reported for multifinger manipulation application. The SKM MEMS XY stage is implemented by embedding a single degree-of-freedom (DOF) stage into another single DOF stage. The proposed MEMS XY stage is fabricated by deep reactive ion etching (DRIE) from both sides of a silicon-on-insulator (SOI) wafer. This SKM MEMS stage has the capability to generate more than 50 mu m displacements along each X- and Y-axes. This nested structure also suppressed the coupled motion error to 0.6% of the original actuation displacement. For the demonstration on the micro-particle manipulation, a 15 mu m sized polypropylene particle is manipulated and rotated by operating two individual fingers attached to proposed MEMS stages.
- I. Misri, P. Hareesh, S. Yang, and D. L. DeVoe, "Microfabrication of bulk PZT transducers by dry film photolithography and micro powder blasting," Journal of Micromechanics and Microengineering, 22 (8), 2012.
[Abstract]
A facile fabrication process for bulk PZT microsystems using dry film photoresist and micro powder blasting is presented. Bulk PZT and dry film photoresist etching characteristics are evaluated as a function of process parameters and mask dimensions using 127 mu m thick PZT substrates. The resulting process simplifies microscale patterning of bulk PZT compared with existing methods, with selection of suitable etching parameter providing excellent etch rate, selectivity and anisotropy. The technique is used to fabricate two different cantilever microactuator topologies based on piezoelectric d(31) and d(33) mode actuation, demonstrating the capabilities of the patterning method for applications in bulk PZT microelectromechanical systems (MEMS).
- H. S. Seo, B. Han, and Y. J. Kim, "Numerical Study on the Mixing Performance of a Ring-Type Electroosmotic Micromixer with Different Obstacle Configurations," Journal of Nanoscience and Nanotechnology, 12 (6), 4523-4530, 2012.
[Abstract]
A new type of electrokinetic micromixer with a ring-type channel is introduced for fast mixing. The proposed mixer takes two fluids from different inlets and combines them in a ring-type mixing chamber. The fluids enter two different inlets (inner radius: 25 mu m and outer radius: 50 mu m), respectively. The total channel length is 500 mu m, and four microelectrodes are positioned on the outer wall of the mixing chamber. The electric potentials on the four microelectrodes are sinusoidal with time, having various maximum values of voltage, zeta potential and frequency. Also, in order to compare the mixing performance with different obstacle configurations, we performed a numerical analysis using a commercial code, COMSOL. The concentration of the dissolved substances in the working fluid and the flow and electric fields in the channel were investigated and the results were graphically depicted for various flow and electric conditions.
- C. Shao, E. L. Kendall, and D. L. DeVoe, "Electro-optical BLM chips enabling dynamic imaging of ordered lipid domains," Lab on a Chip, 12 (17), 3142-3149, 2012.
[Abstract]
Studies of lipid rafts, ordered microdomains of sphingolipids and cholesterol within cell membranes, are essential in probing the relationships between membrane organization and cellular function. While in vitro studies of lipid phase separation are commonly performed using spherical vesicles as model membranes, the utility of these models is limited by a number of factors. Here we present a microfluidic device that supports simultaneous electrical measurements and confocal imaging of on-chip bilayer lipid membranes (BLMs), enabling real-time multi-domain imaging of membrane organization. The chips further support closed microfluidic access to both sides of the membrane, allowing the membrane boundary conditions to be rapidly changed and providing a mechanism for dynamically adjusting membrane curvature through application of a transmembrane pressure gradient. Here we demonstrate the platform through the study of dynamic generation and dissolution of ordered lipid domains as membrane components are transported to and from the supporting annulus containing solvated lipids and cholesterol.
- J. Y. Wang, Y. D. Hu, R. H. Deng, W. J. Xu, S. Q. Liu, R. J. Liang, Z. H. Nie, and J. T. Zhu, "Construction of multifunctional photonic crystal microcapsules with tunable shell structures by combining microfluidic and controlled photopolymerization," Lab on a Chip, 12 (16), 2795-2798, 2012.
[Abstract]
Holey photonic crystal (PC) microcapsules are generated through a combined technique of microfluidic- and controlled-photopolymerization. This versatile route allows the fine tuning of shell structure (from well-ordered nanoporous to single-hole structures with tailored hole size) by etching or by varying UV light intensity, and endowing the PC microcapsules with multifunctional properties.
- Z. J. Wei, P. K. Amponsah, M. Al-Shatti, Z. H. Nie, and B. C. Bandyopadhyay, "Engineering of polarized tubular structures in a microfluidic device to study calcium phosphate stone formation," Lab on a Chip, 12 (20), 4037-4040, 2012.
[Abstract]
This communication describes the formation of tubular structures with a circular cross-section by growing epithelial cells in a microfluidic (MF) device. Here we show for the first time that it is possible to form a monolayer of polarized cells, embedded within the MF device which can function as an in vivo epithelia. We showed: i) the overexpression of specific protein(s) of interest (i. e., ion channel and transport proteins) is feasible inside tubular structures in MFs; ii) the functional kinetic information of Ca2+ in cells can be measured by microflurometry using cell permeable Ca2+ probe under confocal microscope; and iii) calcium phosphate stones can be produced in real time in MFs with Ca2+ transporting epithelia. These data suggest that tubular structures inside this MF platform can be used as a suitable model to understand the molecular and pharmacological basis of calcium phosphate stone formation in the epithelial or other similar cellular micro environments.
- O. Rahmanian, C.-F. Chen, and D. L. DeVoe, "Microscale Patterning of Thermoplastic Polymer Surfaces by Selective Solvent Swelling," Langmuir, 28 (35), 12923-12929, 2012.
[Abstract]
A new method for the fabrication of microscale features in thermoplastic substrates is presented. Unlike traditional thermoplastic microfabrication techniques, in which bulk polymer is displaced from the substrate by machining or embossing, a unique process termed orogenic microfabrication has been developed in which selected regions of a thermoplastic surface are raised from the substrate by an irreversible solvent swelling mechanism. The orogenic technique allows thermoplastic surfaces to be patterned using a variety of masking methods, resulting in three-dimensional features that would be difficult to achieve through traditional microfabrication methods. Using cyclic olefin copolymer as a model thermoplastic material, several variations of this process are described to realize growth heights ranging from several nanometers to tens of micrometers, with patterning techniques include direct photoresist masking, patterned UV/ozone surface passivation, elastomeric stamping, and noncontact spotting. Orogenic microfabrication is also demonstrated by direct inkjet printing as a facile photolithography-free masking method for rapid desktop thermoplastic microfabrication.
- Y. Cheng, K. M. Gray, L. David, I. Royaud, G. F. Payne, and G. W. Rubloff, "Characterization of the cathodic electrodeposition of semicrystalline chitosan hydrogel," Materials Letters, 87, 97-100, 2012.
[Abstract]
We report the visualization of the electrodeposition of chitosan hydrogels and structural characterization of such materials. An electrode embedded microfluidic device is used to visualize the gel deposition process as a distinguishable sol-gel interface separating the clear electrolyte solution region and the orderly textured gel region. The crystalline structure and the nanostructure of the as-deposited gel is characterized with synchrotron X-ray scattering measurements, confirming the semicrystalline nature of the deposited chitosan gels by a neutralization process at the cathode. (C) 2012 Elsevier B.V. All rights reserved.
- I. M. White, S. H. Yazdi, and W. W. Yu, "Optofluidic SERS: synergizing photonics and microfluidics for chemical and biological analysis," Microfluidics and Nanofluidics, 13 (2), 205-216, 2012.
[Abstract]
Surface enhanced Raman spectroscopy (SERS) leverages the specificity of Raman scattering and the sensitivity provided by localized plasmonic effects for applications in chemical and biomolecular detection. However, nearly four decades after the first report of SERS, practical uses of the technique remain limited. Optofluidic SERS-the synergistic use of microfluidics to improve the performance of SERS-may finally lead to practical devices for chemical and biomolecular detection. In this review, we describe recent advances in optofluidic SERS microsystems that have been developed to improve the performance and applicability of SERS. These techniques include designs that improve the light-analyte interaction, that perform active or passive concentration of metal nanoparticles and/or analyte molecules, and that utilize microfluidic techniques to improve functionality. In addition, we present optofluidic SERS techniques that enable new applications that have not been possible before the advent of optofluidics. Finally, we project future advances in optofluidic SERS and present a vision for the disruptive technologies that will enable the translation of SERS from the research lab to practical uses.
- I. Chakraborty and B. Balachandran, "Near-grazing dynamics of base excited cantilevers with nonlinear tip interactions," Nonlinear Dynamics, 70 (2), 1297-1310, 2012.
[Abstract]
In this article, nonsmooth dynamics of impacting cantilevers at different scales is explored through a combination of analytical, numerical, and experimental efforts. For off-resonance and harmonic base excitations, period-doubling events close to grazing impacts are experimentally studied in a macroscale system and a microscale system. The macroscale test apparatus consists of a base excited aluminum cantilever with attractive and repulsive tip interactions. The attractive force is generated through a combination of magnets, one located at the cantilever structure's tip and another attached to a high-resolution translatory stage. The repulsive forces are generated through impacts of the cantilever tip with the compliant material that covers the magnet on the translatory stage. The microscale system is an atomic force microscope cantilever operated in tapping mode. In this mode, this microcantilever experiences a long-range attractive van der Waals force and a repulsive force as the cantilever tip comes close to the sample. The qualitative changes observed in the experiments are further explored through numerical studies, assuming that the system response is dominated by the fundamental cantilever vibratory mode. In both the microscale and macroscale cases, contact is modeled by using a quadratic repulsive force. A reduced-order model, which is developed on the basis of a single mode approximation, is employed to understand the period-doubling phenomenon experimentally observed close to grazing in both the macroscale and microscale systems. The associated near-grazing dynamics is examined by carrying out local analyses with Poincar, map constructions to show that the observed period-doubling events are possible for the considered nonlinear tip interactions. In the corresponding experiments, the stability of the observed grazing periodic orbits has been assessed by constructing the Jacobian matrix from the experimentally obtained Poincar, map. The present study also sheds light on the use of macroscale systems to understand near-grazing dynamics in microscale systems.
- C. Shao, B. Sun, D. L. DeVoe, and M. Colombini, "Dynamics of Ceramide Channels Detected Using a Microfluidic System," Plos One, 7 (9), 2012.
[Abstract]
Ceramide, a proapoptotic sphingolipid, has been shown to form channels, in mitochondrial outer membranes, large enough to translocate proteins. In phospholipid membranes, electrophysiological studies and electron microscopic visualization both report that these channels form in a range of sizes with a modal value of 10 nm in diameter. A hydrogen bonded barrel-like structure consisting of hundreds of ceramide molecules has been proposed for the structure of the channel and this is supported by electrophysiological studies and molecular dynamic simulations. To our knowledge, the mechanical strength and deformability of such a large diameter but extremely thin cylindrical structure has never been reported. Here we present evidence for a reversible mechanical distortion of the cylinder following the addition of La3+. A microfluidic system was used to repeatedly lower and then restore the conductance by alternatively perfusing La3+ and EDTA. Although aspects of the kinetics of conductance drop and recovery are consistent with a disassembly/diffusion/reassembly model, others are inconsistent with the expected time scale of lateral diffusion of disassembled channel fragments in the membrane. The presence of a residual conductance following La3+ treatment and the relationship between the residual conductance and the initial conductance were both indicative of a distortion/recovery process in analogy with a pressure-induced distortion of a flexible cylinder.
- K. Jiang, A. Sposito, J. Liu, S. R. Raghavan, and D. L. DeVoe, "Microfluidic synthesis of macroporous polymer immunobeads," Polymer, 53 (24), 5469-5475, 2012.
[Abstract]
This article describes the synthesis and characterization of a new type of discrete microparticle immunosensor employing macroporous methacrylate polymer microspheres. The microspheres are produced using a simple microfluidic tubing co-flow droplet generator to produce large populations of microparticles with exceptional size uniformity and controllable macroporosity. Subsequent grafting treatments are demonstrated to anchor immunoactive ligands on the porous surfaces, converting the microspheres into discrete immunosensor elements, with direct immunoassay tests demonstrating good detection limits and capturing specificity. This work demonstrates the adaptation of a traditional polymer monolith stationary phase material into a discrete microparticle immunosensor format using a synthesis and functionalization path with significant flexibility toward a diverse range of biological and chemical sensing applications. (C) 2012 Elsevier Ltd. All rights reserved.
- B. T. Han, "Measurements of True Leak Rates of MEMS Packages," Sensors, 12 (3), 3082-3104, 2012.
[Abstract]
Gas transport mechanisms that characterize the hermetic behavior of MEMS packages are fundamentally different depending upon which sealing materials are used in the packages. In metallic seals, gas transport occurs through a few nanoscale leak channels (gas conduction) that are produced randomly during the solder reflow process, while gas transport in polymeric seals occurs through the bulk material (gas diffusion). In this review article, the techniques to measure true leak rates of MEMS packages with the two sealing materials are described and discussed: a Helium mass spectrometer based technique for metallic sealing and a gas diffusion based model for polymeric sealing.
- A. P. Gerratt and S. Bergbreiter, "Microfabrication of compliant all-polymer MEMS thermal actuators," Sensors and Actuators A - Physical, 177, 16-22, 2012.
[Abstract]
This paper presents a fabrication process for compliant all-polymer MEMS actuators. This process allows high-aspect ratio conductive and non-conductive polymer features to be fabricated together in-plane. With this capability, robust all-polymer thermal actuators have demonstrated displacements as large at 100 mu m and forces as high as 55 mu N. The actuators are fabricated with elastomeric materials only, so they are very robust and can undergo large strains in both tension and bending and still operate once released. (C) 2011 Elsevier B.V. All rights reserved.
- C. Pang, M. Yu, X. M. Zhang, A. K. Gupta, and K. M. Bryden, "Multifunctional optical MEMS sensor platform with heterogeneous fiber optic Fabry-Perot sensors for wireless sensor networks," Sensors and Actuators A - Physical, 188, 471-480, 2012.
[Abstract]
A multifunctional optical sensor platform based on the microelectromechanical systems (MEMS) technology is developed with the aim of miniaturizing conventional bulky optical measurement systems for application in future optical wireless sensor networks (WSNs). Low-coherence interferometry is used as the sensing principle, which allows for high performance sensing with multiple heterogeneous sensors. The entire platform with the associated electric circuit has a footprint of 2 in. x 1.8 in. x 0.75 in., which are integrated with a conventional WSN module to form an optical WSN node. The multifunctionality of the platform is successfully demonstrated for simultaneous interrogation of a Fabry-Perot (FP) pressure sensor and a FP temperature sensor. To prove the optical sensor platform's multifunctionality, chemical sensing is also demonstrated with a FP sensor. The multifunctional optical sensor platform and the optical WSN node will enable optical WSNs, which are expected to impact many fronts including those space-constrained applications and monitoring in harsh environments. (C) 2012 Elsevier B.V. All rights reserved.
- G. L. Smith, R. Q. Rudy, R. G. Polcawich, and D. L. DeVoe, "Integrated thin-film piezoelectric traveling wave ultrasonic motors," Sensors and Actuators A - Physical, 188, 305-311, 2012.
[Abstract]
An integrated approach to the fabrication of thin-film piezoelectric traveling wave ultrasonic motors at the mm-scale is being developed for low power, high torque motors for small scale robotics, biomedical, and sensing applications. This paper describes the realization of ultrasonic motor stators ranging in diameter from 1 to 3 mm using wafer scale MEMS fabrication techniques with lead zirconate titanate (PZT) thin films. Using laser Doppler vibrometry (LDV), controlled traveling waves were demonstrated in the bulk silicon elastic medium of the stator and the standing wave behavior was characterized for control purposes. Furthermore, the resonant modes of the fabricated stators were modeled using finite element models, and experimental results agree well with this analysis. (C) 2011 Elsevier B.V. All rights reserved.
- E. L. Kendall, C. Shao, and D. L. DeVoe, "Visualizing the Growth and Dynamics of Liquid-Ordered Domains During Lipid Bilayer Folding in a Microfluidic Chip," Small, 8 (23), 3613-3619, 2012.
[Abstract]
A microfluidic platform enabling optical monitoring of bilayer lipid membrane formation by a new monolayer folding process is described. The thermoplastic chips integrate dried lipid films that are rehydrated by microfluidic perfusion, which enables delivery of lipid-laden air bubbles across a membrane-supporting aperture. As in traditional MontalMueller bilayer formation, lipid monolayers are delivered independently to each side of the aperture, thereby allowing asymmetric lipid composition in the resulting bilayer to be achieved. Confocal microscopy is used to image the monolayer folding process, and reveals the growth and dynamics of asymmetric liquid-ordered domains during bilayer stabilization.
- B. Balakrisnan, A. Nacev, J. M. Burke, A. Dasgupta, and E. Smela, "Design of compliant meanders for applications in MEMS, actuators, and flexible electronics," Smart Materials & Structures, 21 (7), 2012.
[Abstract]
Meandering beams, crenellated surfaces, and zigzag-shaped electrodes are employed as compliant elements in microscale applications ranging from springs attached to proof masses in microelectromechanical systems (MEMS) to stretchable electrodes in flexible electronics and dielectric elastomer actuators. An understanding of how the meander shape affects the stiffness of these structures would permit preliminary design without the necessity of fabricating or running simulations on each case. In this paper, we present general guidelines for designing meandering cantilevers, showing how the amplitude, angle, length, and thickness affect both the axial and bending stiffnesses. Simple analytical expressions are derived, and the results are compared with those from numerical simulations and experimental measurements. The more complex case of a stiff thin film overlying a crenellated elastomer is also simulated.
- K. Jiang, P. C. Thomas, S. P. Forry, D. L. DeVoe, and S. R. Raghavan, "Microfluidic synthesis of monodisperse PDMS microbeads as discrete oxygen sensors," Soft Matter, 8 (4), 923-926, 2012.
[Abstract]
We describe the creation of monodisperse microbeads of polydimethylsiloxane (PDMS) via a microfluidic approach. Using a flow-focusing configuration, a PDMS precursor solution is dispersed into microdroplets within an aqueous continuous phase. These droplets are collected and thermally cured off-chip into solid microbeads. Our microfluidic technique allows for direct integration of payloads into the PDMS microbeads. Specifically, we integrate an oxygen-sensitive porphyrin dye into the beads and show that the resulting structures can function as non-invasive and real-time oxygen microsensors utilizing a simple optical readout at the single-particle level.
- Y. F. Wang, Y. Liu, Y. Cheng, E. Kim, G. W. Rubloff, W. E. Bentley, and G. F. Payne, "Coupling Electrodeposition with Layer-by-Layer Assembly to Address Proteins within Microfluidic Channels," Advanced Materials, 23 (48), 5817-+, 2011.
[Abstract]
Two thin-film assembly methods are coupled to address proteins. Electrodeposition confers programmability and generates a template for layer-by-layer (LbL) assembly. LbL enables precise control of film thickness and the incorporation of labile biological components. The capabilities are demonstrated using glucose oxidase (GOx) based electrochemical biosensing within a microfabricated fluidic device.
- P. H. Dykstra, V. Roy, C. Byrd, W. E. Bentley, and R. Ghodssi, "Microfluidic Electrochemical Sensor Array for Characterizing Protein Interactions with Various Functionalized Surfaces," Analytical Chemistry, 83 (15), 5920-5927, 2011.
[Abstract]
We present a unique microfluidic platform to allow for quick and sensitive probing of protein adsorption to various functionalized surfaces. The ability to tailor a sensor surface for a specific analyte is crucial for the successful application of portable gas and fluid sensors and is of great interest to the drug screening community. However, choosing the correct surface chemistry to successfully passivate against nonspecific binding typically requires repeated trial and error experiments. The presented device incorporates an array of integrated electrochemical sensors for fast, sensitive, label-free detection of these binding interactions. The layout of the electrodes allows for loading various surface chemistries in one direction while sensing their interactions with particular compounds in another without any cross-contamination. Impedance data is collected for three commonly used passivation compounds (mercaptohexanol, polyethylene glycol, and bovine serum albumin) and demonstrates their interaction with three commonly studied proteins in genetic and cancer research (cAMP receptor protein, tumor necrosis factor a, and tumor necrosis factor)3). The ability to quickly characterize various surface interactions provides knowledge for selecting optimal functionalization for any biosensor.
- C. Shao, B. Sun, M. Colombini, and D. L. DeVoe, "Rapid Microfluidic Perfusion Enabling Kinetic Studies of Lipid Ion Channels in a Bilayer Lipid Membrane Chip," Annals of Biomedical Engineering, 39 (8), 2242-2251, 2011.
[Abstract]
There is growing recognition that lipids play key roles in ion channel physiology, both through the dynamic formation and dissolution of lipid ion channels and by indirect regulation of protein ion channels. Because existing technologies cannot rapidly modulate the local (bio)chemical conditions at artificial bilayer lipid membranes used in ion channel studies, the ability to elucidate the dynamics of these lipid-lipid and lipid-protein interactions has been limited. Here we demonstrate a microfluidic system supporting exceptionally rapid perfusion of reagents to an on-chip bilayer lipid membrane, enabling the responses of lipid ion channels to dynamic changes in membrane boundary conditions to be probed. The thermoplastic microfluidic system allows initial perfusion of reagents to the membrane in less than 1 s, and enables kinetic behaviors with time constants below 10 s to be directly measured. Application of the platform is demonstrated toward kinetic studies of ceramide, a biologically important lipid known to self-assemble into transmembrane ion channels, in response to dynamic treatments of small ions (La(3+)) and proteins (Bcl-x(L) mutant). The results reveal the broader potential of the technology for studies of membrane biophysics, including lipid ion channel dynamics, lipid-protein interactions, and the regulation of protein ion channels by lipid micro domains.
- H. Bhaskaran, M. Li, D. Garcia-Sanchez, P. Zhao, I. Takeuchi, and H. X. Tang, "Active microcantilevers based on piezoresistive ferromagnetic thin films," Applied Physics Letters, 98 (1), 2011.
[Abstract]
We report the piezoresistivity in magnetic thin films of Fe0.7Ga0.3 and their use for fabricating self-transducing microcantilevers. The actuation occurs as a consequence of both the ferromagnetic and magnetostrictive properties of Fe0.7Ga0.3 thin films, while the deflection readout is achieved by exploiting the piezoresistivity of these films. This self-sensing self-actuating micromechanical system involves a very simple bilayer structure, which eliminates the need for the more complex piezoelectric stack that is commonly used in active cantilevers. Thus, it potentially opens opportunities for remotely actuated cantilever-based sensors. (c) 2011 American Institute of Physics. [doi:10.1063/1.3533390]
- X. L. Luo, S. Buckhout-White, W. E. Bentley, and G. W. Rubloff, "Biofabrication of chitosan-silver composite SERS substrates enabling quantification of adenine by a spectroscopic shift," Biofabrication, 3 (3), 2011.
[Abstract]
Surface-enhanced Raman scattering (SERS) has grown dramatically as an analytical tool for the sensitive and selective detection of molecules adsorbed on nano-roughened noble metal structures. Quantification with SERS based on signal intensity remains challenging due to the complicated fabrication process to obtain well-dispersed nanoparticles and well-ordered substrates. We report a new biofabrication strategy of SERS substrates that enable quantification through a newly discovered spectroscopic shift resulting from the chitosan-analyte interactions in solution. We demonstrate this phenomenon by the quantification of adenine, which is an essential part of the nucleic acid structure and a key component in pathways which generate signal molecules for bacterial communications. The SERS substrates were fabricated simply by sequential electrodeposition of chitosan on patterned gold electrodes and electroplating of a silver nitrate solution through the chitosan scaffold to form a chitosan-silver nanoparticle composite. Active SERS signals of adenine solutions were obtained in real time from the chitosan-silver composite substrates with a significant concentration-dependent spectroscopic shift. The Lorentzian curve fitting of the dominant peaks suggests the presence of two separate peaks with a concentration-dependent area percentage of the separated peaks. The chitosan-mediated composite SERS substrates can be easily biofabricated on predefined electrodes within microfluidic channels for real-time detection in microsystems.
- N. D. Orloff, J. R. Dennis, M. Cecchini, E. Schonbrun, E. Rocas, Y. Wang, D. Novotny, R. W. Simmonds, J. Moreland, I. Takeuchi, and J. C. Booth, "Manipulating particle trajectories with phase-control in surface acoustic wave microfluidics," Biomicrofluidics, 5 (4), 2011.
[Abstract]
We present a 91 MHz surface acoustic wave resonator with integrated microfluidics that includes a flow focus, an expansion region, and a binning region in order to manipulate particle trajectories. We demonstrate the ability to change the position of the acoustic nodes by varying the electronic phase of one of the transducers relative to the other in a pseudo-static manner. The measurements were performed at room temperature with 3 mu m diameter latex beads dispersed in a water-based solution. We demonstrate the dependence of nodal position on pseudo-static phase and show simultaneous control of 9 bead streams with spatial control of -0.058 mu m/deg +/- 0.001 mu m/deg. As a consequence of changing the position of bead streams perpendicular to their flow direction, we also show that the integrated acoustic-microfluidic device can be used to change the trajectory of a bead stream towards a selected bin with an angular control of 0.008 deg/deg +/- 0.000(2) deg/deg. (C) 2011 American Institute of Physics. [doi:10.1063/1.3661129]
- I. J. Chen and I. M. White, "High-sensitivity electrochemical enzyme-linked assay on a microfluidic interdigitated microelectrode," Biosensors & Bioelectronics, 26 (11), 4375-4381, 2011.
[Abstract]
A novel enzyme-linked DNA hybridization assay on an interdigitated array (IDA) microelectrode integrated into a microfluidic channel is demonstrated with sub-nM detection limit. To improve the detection limit as compared to conventional electrochemical biosensors, a recyclable redox product, 4-aminophenol (PAP) is used with an IDA microelectrode. The IDA has a modest and easily fabricated inter-digit spacing of 10 mu m, yet we were able to demonstrate 97% recycling efficiency of PAP due to the integration in a microfluidic channel. With a 70 nL sample volume, the characterized detection limit for PAP of 1.0 x 10(-10) M is achieved, with a linear dynamic range that extends from 1.0 x 10(-9) to 1.0 x 10(-5) M. This detection limit, which is the lowest reported detection limit for PAP, is due to the increased sensitivity provided by the sample confinement in the microfluidic channel, as well as the increased repeatability due to perfectly static flow in the microchannel and an additional anti-fouling step in the protocol. DNA sequence detection is achieved through a hybridization sandwich of an immobilized complementary probe, the target DNA sequence, and a second complementary probe labeled with beta-galactosidase (beta-GAL); the beta-GAL converts its substrate, 4-aminophenyl-D-galactopyranoside (PAPG), into PAP. In this report we present the lowest reported observed detection limit (1.0 x 10(-10) M) for an enzyme-linked DNA hybridization assay using an IDA microelectrode and a redox signaling paradigm. Thus, we have demonstrated highly sensitive detection of a targeted DNA sequence using a low-cost easily fabricated electrochemical biosensor integrated into a microfluidic channel. (C) 2011 Elsevier B.V. All rights reserved.
- Y. Liu, X. W. Shi, E. Kim, L. M. Robinson, C. K. Nye, R. Ghodssi, G. W. Rubloff, W. E. Bentley, and G. F. Payne, "Chitosan to electroaddress biological components in lab-on-a-chip devices," Carbohydrate Polymers, 84 (2), 704-708, 2011.
[Abstract]
Chitosan offers a unique set of properties that suggest its potential for interfacing biological components into electronic devices for lab-on-a-chip (LOC) applications. Specifically, chitosan's pH-responsive film-forming properties allow it to be electrodeposited as a stable thin film in response to localized cathodic signals. In addition, the electrodeposited chitosan film can be electrochemically activated for protein conjugation by applying an anodic potential to the chitosan-coated electrode while it is immersed in an aqueous solution containing NaCl. Together electrodeposition and electrochemical protein conjugation allow proteins to be electroaddressed to electrode surfaces quickly and without the need for reactive reagents. On-going efforts aim to extend protein electroaddressing from patterned chips to microfluidic LOC devices. Additional efforts are beginning to show the potential for integrating chitosan with sensor technology to transduce chemical and biological events (e.g., molecular recognition) into device-compatible optical, electrical and mechanical signals. Highlights of the progress in using chitosan as the bio-device interface are reviewed. (C) 2010 Elsevier Ltd. All rights reserved.
- E. Tumarkin, J. Il Park, Z. H. Nie, and E. Kumacheva, "Temperature mediated generation of armoured bubbles," Chemical Communications, 47 (47), 12712-12714, 2011.
[Abstract]
This communication describes a novel strategy for the continuous microfluidic generation of highly monodispersed particle-coated microbubbles using temperature-dependent dissolution of carbon dioxide.
- L. Q. Wu, W. E. Bentley, and G. F. Payne, "Biofabrication with biopolymers and enzymes: Potential for constructing scaffolds from soft matter," International Journal of Artificial Organs, 34 (2), 215-224, 2011.
[Abstract]
Purpose: Regenerative medicine will benefit from technologies capable of fabricating soft matter to have appropriate architectures and that provide the necessary physical, chemical and biological cues to recruit cells and guide their development. The goal of this report is to review an emerging set of biofabrication techniques and suggest how these techniques could be applied for the fabrication of scaffolds for tissue engineering. Methods: Electrical potentials are applied to submerged electrodes to perform cathodic and anodic reactions that direct stimuli-responsive film-forming polysaccharides to assemble into hydrogel films. Standard methods are used to microfabricate electrode surfaces to allow the electrical signals to be applied with spatial and temporal control. The enzymes mushroom tyrosinase and microbial transglutaminase are used to catalyze macromolecular grafting and crosslinking of proteins. Results: Electrodeposition of the polysaccharides chitosan and alginate allow hydrogel films to be formed in response to localized electrical signals. Co-deposition of various components (e.g., proteins, vesicles and cells), and subsequent electrochemical processing allow the physical, chemical and biological activities of these films to be tailored. Enzymatic processing allows for the generation of stimuli-responsive protein conjugates that can also be directed to assemble in response to imposed electrical signals. Further, enzyme-catalyzed crosslinking of gelatin allows replica molding of soft matter to create hydrogel films with topological structure. Conclusions: Biofabrication with biological materials and mechanisms provides new approaches for soft matter construction. These methods may enable the formation of tissue engineering scaffolds with appropriate architectures, assembled cells, and spatially organized physical, chemical and biological cues.
- X. Z. Fan, N. Siwak, and R. Ghodssi, "An adaptive feedback circuit for MEMS resonators," Journal of Micromechanics and Microengineering, 21 (4), 2011.
[Abstract]
The first adaptive feedback circuit capable of detecting resonant frequencies for a wide range of MEMS resonators is presented. The feedback system presented implements a hill-climbing algorithm that sweeps actuation frequencies, locking onto the resonance condition at maximum cantilever amplitude response without limitations on the frequency range. To demonstrate its adaptability, a circuit implementation of this feedback algorithm was used to detect the resonant frequency of eight different cantilever-based sensors (width (W) = 1.4 mu m, length (L) = 40-75 mu m, and thickness (T) = 1.8 mu m), resonating at 201.0 to 592.1 kHz. Additionally, the same circuit was used to track resonant frequency shifts due to isopropanol adsorption on three different chemical sensors with no modifications. The feedback electronics integrated with these resonator sensors provide a mass resolution limit of 123 femptograms. The realization of this system will enable real-time chip-scale sensor systems, providing an alternative to external instrumentation modules that perform sensor control and monitoring.
- M. T. Meyer, V. Roy, W. E. Bentley, and R. Ghodssi, "Development and validation of a microfluidic reactor for biofilm monitoring via optical methods," Journal of Micromechanics and Microengineering, 21 (5), 2011.
[Abstract]
We present the design, fabrication, and verification of a microfluidic platform for optical monitoring of bacterial biofilms. Biofilm formation characterizes the majority of infections caused by bacteria that are developing increased resistance to traditional antibiotic treatment, necessitating the development of reliable tools not only for study of biofilm growth, but also for in situ examination of the response to applied stimuli. The presented platform was used to continuously and non-invasively observe the dependence of Escherichia coli biofilm formation on bacterial signaling by monitoring the change in biofilm optical density over the growth period. Results were corroborated by measurement of biofilm morphological properties via confocal microscopy, and statistical analysis was applied to verify the repeatability of observed optical and morphological differences in the biofilms formed. The presented platform will be used to characterize biofilm formation and response in drug discovery applications.
- I. Penskiy, A. P. Gerratt, and S. Bergbreiter, "Friction, adhesion and wear properties of PDMS films on silicon sidewalls," Journal of Micromechanics and Microengineering, 21 (10), 2011.
[Abstract]
This paper demonstrates the first tests of friction, adhesion and wear properties of thin poly(dimethylsiloxane) (PDMS) films on the sidewalls of silicon-on-insulator structures. The test devices were individually calibrated using a simple method that included optical and electrical measurements. The static coefficient of friction versus normal pressure curves were obtained for PDMS-PDMS, PDMS-silicon and silicon-silicon sidewall interfaces. The effects of aging on friction and adhesion properties of PDMS were also evaluated. The results of friction tests showed that the static coefficient of friction follows the JKR contact model, which means that the friction force depends on the apparent area of contact. The wear tests showed high resistance of PDMS to abrasion over millions of cycles.
- R. Probst and B. Shapiro, "Three-dimensional electrokinetic tweezing: device design, modeling, and control algorithms," Journal of Micromechanics and Microengineering, 21 (2), 2011.
[Abstract]
We show how to extend electrokinetic tweezing (which can manipulate any visible particles and has more favorable force scaling than optical actuation enabling manipulation of nanoscale objects to nanoscopic precision) from two-dimensional control to the third dimension (3D). A novel and practical multi-layer device is presented that can create both planar and vertical flow and electric field modes. Feedback control algorithms are developed and demonstrated in realistic simulations to show 3D manipulation of one and two particles independently. The design and control results presented here are the essential next step to go from current 2D manipulation capabilities to an experimental demonstration of nano-precise 3D electrokinetic tweezing in a microfluidic system. Doing so requires integration with vision-based nano-precise 3D particle imaging, a capability that has been shown in the literature and which we are now combining with the 3D actuation and control methods demonstrated here.
- A. P. Lisiewski, H. J. Liu, M. Yu, L. Currano, and D. Gee, "Fly-ear inspired micro-sensor for sound source localization in two dimensions," Journal of the Acoustical Society of America, 129 (5), E166-E171, 2011.
[Abstract]
Inspired by the hearing organ of the fly Ormia ochracea, a miniature sound localization sensor is developed, which can be used to pinpoint a sound source in two dimensions described by the azimuth and elevation angles. The sensor device employs an equilateral triangle configuration consisting of three mechanically coupled circular membranes whose oscillations are detected by a fiber-optic system. The experimental results indicate that significant amplification of the directional cues and directional sensitivity can be achieved with the fly-ear inspired sensor design. This work can provide a basis for the development of miniature sound localization sensors in two dimensions. (C) 2011 Acoustical Society of America
- Y. Cheng, X. L. Luo, C. Y. Tsao, H. C. Wu, J. Betz, G. F. Payne, W. E. Bentley, and G. W. Rubloff, "Biocompatible multi-address 3D cell assembly in microfluidic devices using spatially programmable gel formation," Lab on a Chip, 11 (14), 2316-2318, 2011.
[Abstract]
Programmable 3D cell assembly under physiological pH conditions is achieved using electrodeposited stimuli-responsive alginate gels in a microfluidic device, with parallel sidewall electrodes enabling direct observation of the cell assembly. Electrically triggered assembly and subsequent viability of mammalian cells is demonstrated, along with spatially programmable, multi-address assembly of different strains of E. coli cells. Our approach enables in vitro study of dynamic cellular and inter-cellular processes, from cell growth and stimulus/response to inter-colony and inter-species signaling.
- E. Tumarkin, Z. H. Nie, J. I. Park, M. Abolhasani, J. Greener, B. Sherwood-Lollar, A. Gunther, and E. Kumacheva, "Temperature-controlled 'breathing' of carbon dioxide bubbles," Lab on a Chip, 11 (20), 3545-3550, 2011.
[Abstract]
We report a microfluidic (MF) approach to studies of temperature mediated carbon dioxide (CO(2)) transfer between the gas and the liquid phases. Micrometre-diameter CO(2) bubbles with a narrow size distribution were generated in an aqueous or organic liquid and subsequently were subjected to temperature changes in the downstream channel. In response to the cooling-heating-cooling cycle the bubbles underwent corresponding contraction-expansion-contraction transitions, which we term 'bubble breathing'. We examined temperature-controlled dissolution of CO(2) in four exemplary liquid systems: deionized water, a 0.7 M aqueous solution of NaCl, ocean water extracted from Bermuda coastal waters, and dimethyl ether of poly(ethylene glycol), a solvent used in industry for absorption of CO(2). The MF approach can be extended to studies of other gases with a distinct, temperature-dependent solubility in liquids.
- X. D. Fan and I. M. White, "Optofluidic microsystems for chemical and biological analysis," Nature Photonics, 5 (10), 591-597, 2011.
[Abstract]
Optofluidics - the synergistic integration of photonics and microfluidics - is a new analytical field that provides a number of unique characteristics for enhancing the sensing performance and simplifying the design of microsystems. This Review describes various optofluidic architectures developed over the past five years, emphasizes the mechanisms by which optofluidics enhances biological/chemical analytic capabilities, including sensing and the precise control of biological micro- and nanoparticles, and also highlights new research directions to which the field of optofluidics may lead.
- K. Jiang, C. Xue, C. Arya, C. Shao, E. O. George, D. L. DeVoe, and S. R. Raghavan, "A New Approach to In-Situ "Micromanufacturing": Microfluidic Fabrication of Magnetic and Fluorescent Chains Using Chitosan Microparticles as Building Blocks," Small, 7 (17), 2470-2476, 2011.
[Abstract]
An in situ microfluidic assembly approach is described that can both produce microsized building blocks and assemble them into complex multiparticle configurations in the same microfluidic device. The building blocks are microparticles of the biopolymer chitosan, which is intentionally selected because its chemistry allows for simultaneous intraparticle and interparticle linking. Monodisperse chitosan-bearing droplets are created by shearing off a chitosan solution at a microfluidic T-junction with a stream of hexadecane containing a nonionic detergent. These droplets are then interfacially crosslinked into stable microparticles by a downstream flow of glutaraldehyde (GA). The functional properties of these robust microparticles can be easily varied by introducing various payloads, such as magnetic nanoparticles and/or fluorescent dyes, into the chitosan solution. The on-chip connection of such individual particles into well-defined microchains is demonstrated using GA again as the chemical "glue" and microchannel confinement as the spatial template. Chain flexibility can be tuned by adjusting the crosslinking conditions: both rigid chains and semiflexible chains are created. Additionally, the arrangement of particles within a chain can also be controlled, for example, to generate chains with alternating fluorescent and nonfluorescent microparticles. Such microassembled chains could find applications as microfluidic mixers, delivery vehicles, microscale sensors, or miniature biomimetic robots.
- K. Jiang, C. Xue, C. Arya, C. Shao, E. O. George, D. L. Devoe, and S. R. Raghavan, "Microfluidics: a new approach to in-situ "micromanufacturing": microfluidic fabrication of magnetic and fluorescent chains using chitosan microparticles as building blocks (small 17/2011)," Small (Weinheim an der Bergstrasse, Germany), 7 (17), 2469-2469, 2011.
[Abstract]
The image illustrates an in-situ dynamic microassembly on an integrated microfluidic platform that both produces microsized building blocks and also assembles them into complex multiparticle configurations. The building blocks used originate from microparticles produced microfluidically, with unprecedented control over particle size, geometry, and functional properties, while microfluidic channels serve as perfect spatial templates to accommodate building blocks into designed, highordered patterns. Advantages of this method include the simple chemistry for both interparticle curing and intraparticle linkage, and the facile control over subunit arrangement and microstructure flexibility. This microfluidic microassembly method conceptually envisions an integrated manufacturing platform where subunit generation and connection are accomplished on the same chip.
- Y. Cheng, X. L. Luo, J. Betz, G. F. Payne, W. E. Bentley, and G. W. Rubloff, "Mechanism of anodic electrodeposition of calcium alginate," Soft Matter, 7 (12), 5677-5684, 2011.
[Abstract]
Stimuli-responsive polysaccharides that can undergo a sol-gel transition in response to localized electrical signals provide a unique opportunity to electroaddress biological components at device interfaces. Most polysaccharide electroaddressing mechanisms use electrochemical reactions to generate pH gradients that can locally neutralize the polysaccharide and induce its reversible sol-gel transition to form a hydrogel film adjacent to the electrode surface. The calcium-responsive polysaccharide alginate is an exception; it may electrodeposit without requiring extreme pH gradients and thus may provide a means to electroaddress pH-sensitive biological components. Here, we use a novel device to characterize the mechanism for the anodic electrodeposition of a calcium alginate hydrogel. This device consists of a transparent fluidic channel with built-in sidewall electrodes that allows Ca-alginate electrodeposition to be directly measured by non-destructive optical and spectroscopic methods. We hypothesize a 3-step mechanism for calcium-alginate electrodeposition: (i) water is electrolyzed to locally generate protons (or hydronium ions); (ii) these protons are consumed by reacting with suspended CaCO(3) particles and this "buffering'' reaction generates a gradient in soluble Ca(2+); and (iii) the locally generated Ca(2+) ions interact with alginate to induce its sol-gel transition. We verified this electrodeposition mechanism using pH-responsive dyes to observe the local pH gradients during gel formation, Ca(2+) indicator dyes to observe the Ca(2+) gradient, and in situ Raman spectroscopy to demonstrate a strong interaction between soluble Ca(2+) and alginate. Importantly, these results demonstrate electrodeposition without the need for a substantial pH excursion from neutrality. Thus, calcium alginate appears especially well-suited for electroaddressing labile biological components for applications in biosensors, biofabrication and BioMEMS.
- P. Dykstra, V. Roy, W. E. Bentley, and R. Ghodssi, "A Microfluidic Electrochemical Sensor Array for Characterizing Protein Interactions with Various Surface Chemistries," 2010 IEEE Sensors, 2486-2489, 2010.
[Abstract]
We present a unique microfluidic platform to allow for quick and sensitive probing of protein adsorption to various functionalized surfaces. The ability to tailor a sensor surface for a specific analyte is crucial for the successful application of portable gas and fluid sensors and is of great interest to the drug screening community. However, choosing the correct surface chemistry to either block or bind biomolecules typically requires repeated trial and error experiments. The presented device incorporates an array of integrated electrochemical sensors for fast, sensitive, label-free detection of these binding interactions. The layout of the electrodes allows for loading various surface chemistries in one direction while sensing their interactions with particular compounds in another without any cross contamination. Impedance data is collected for two commonly used surface assembled monolayer (SAM) compounds, and demonstrates their interaction with a common bacterial gene regulator, cyclic adenosine monophosphate (cAMP) receptor protein (CRP). The ability to quickly characterize various surface interactions provides knowledge for selecting optimal functionalization for any biosensor.
- M. T. Meyer, V. Roy, W. E. Bentley, and R. Ghodssi, "A Microfluidic Platform for Optical Absorbance Monitoring of Bacterial Biofilms," 2010 IEEE Sensors, 2291-2294, 2010.
[Abstract]
Through intercellular molecular signaling, many types of bacteria form biofilms, pathogenic matrices that characterize many clinical infections. A microfluidic platform for optical monitoring of biofilms was developed and tested. The platform was used to observe the dependence of Escherichia coli biofilm formation on bacterial signaling by monitoring the change in biofilm optical density over the growth period. After 60 hours of growth at 10 mu L/hr, wild-type biofilms were approximately 275% more optically dense than biofilms formed by non-communicating bacteria. Communication was restored by extracellular addition of signaling molecules to non-communicating bacteria. Results were corroborated by measurement of biofilm morphological properties via confocal microscopy. The presented platform presents the unique capability of continuous optical monitoring of unlabeled samples, and will be used to characterize
- A. Jahn, S. M. Stavis, J. S. Hong, W. N. Vreeland, D. L. Devoe, and M. Gaitan, "Microfluidic Mixing and the Formation of Nanoscale Lipid Vesicles," ACS Nano, 4 (4), 2077-2087, 2010.
[Abstract]
We investigate the formation of unilamellar lipid vesicles (liposomes) with diameters of tens of nanometers by controlled microfluidic mixing and nanoparticle determination (COMMAND). Our study includes liposome synthesis experiments and numerical modeling of our microfluidic implementation of the batch solvent injection method. We consider microfluidic liposome formation from the perspective of fluid interfaces and convective-diffusive mixing, as we find that bulk fluid flow parameters including hydrodynamically focused alcohol stream width, final alcohol concentration, and shear stress do not primarily determine the vesicle formation process. Microfluidic device geometry in conjunction with hydrodynamic flow locusing strongly influences vesicle size distributions, providing a coarse method to control liposome size, while total flow rate allows fine-tuning the vesicle size in certain focusing regimes. Although microfluidic liposome synthesis is relatively simple to implement experimentally, numerical simulations of the mixing process reveal a complex system of fluid flow and mass transfer determining the formation of nonequilibrium vesicles. These results expand our understanding of the microfluidic environment that controls liposome self-assembly and yield several technological advances for the on-chip synthesis of nanoscale lipid vesicles.
- W. W. Yu and I. M. White, "Inkjet Printed Surface Enhanced Raman Spectroscopy Array on Cellulose Paper," Analytical Chemistry, 82 (23), 9626-9630, 2010.
[Abstract]
A novel, ultra low-cost surface enhanced Raman spectroscopy (SERS) substrate has been developed by modifying the surface chemistry of cellulose paper and patterning nanoparticle arrays, all with a consumer inkjet printer Micro/nanofabrication of SERS substrates for on-chip chemical and biomolecular analysis has been under intense investigation However, the high cost of producing these substrates and the limited shelf life severely limit their use, especially for routine laboratory analysis and for point-of-sample analysis in the field Paper-based microfluidic biosensing systems have shown great potential as low cost disposable analysis tools In this work, this concept is extended to SERS-based detection Using an inexpensive consumer inkjet printer, cellulose paper substrates are modified to be hydrophobic in the sensing regions Synthesized silver nanoparticles are printed onto this hydrophobic paper substrate with microscale precision to form sensing arrays The hydrophobic surface prevents the aqueous sample from spreading throughout the paper and thus concentrates the analyte within the sensing region A SERS fingerprint signal tor Rhodamine 6G dye was observed for samples with as low as 10 femtomoles of analyte in a total sample volume of 1 mu L This extraordinarily simple technique can be used to construct SERS microarrays immediately before sample analysis, enabling ultra low-cost chemical and biomolecular detection in the lab as well as in the field at the point of sample collection
- A. Q. Jian, X. M. Zhang, W. M. Zhu, and M. Yu, "Optofluidic refractometer using resonant optical tunneling effect," Biomicrofluidics, 4 (4), 2010.
[Abstract]
This paper presents the design and analysis of a liquid refractive index sensor that utilizes a unique physical mechanism of resonant optical tunneling effect (ROTE). The sensor consists of two hemicylindrical prisms, two air gaps, and a microfluidic channel. All parts can be microfabricated using an optical resin NOA81. Theoretical study shows that this ROTE sensor has extremely sharp transmission peak and achieves a sensitivity of 760 nm/refractive index unit (RIU) and a detectivity of 85 000 RIU-1. Although the sensitivity is smaller than that of a typical surface plasmon resonance (SPR) sensor (3200 nm/RIU) and is comparable to a 95% reflectivity Fabry-Perot (FP) etalon (440 nm/RIU), the detectivity is 17 000 times larger than that of the SPR sensor and 85 times larger than that of the FP etalon. Such ROTE sensor could potentially achieve an ultrahigh sensitivity of 10(-9) RIU, two orders higher than the best results of current methods. (C) 2010 American Institute of Physics. [doi:10.1063/1.3502671]
- Y. X. Liu and M. A. Yu, "Optical manipulation and binding of microrods with multiple traps enabled in an inclined dual-fiber system," Biomicrofluidics, 4 (4), 2010.
[Abstract]
We present experimental demonstrations of optical manipulation and optical binding of microscopic glass rods using the multiple traps created by a dual-fiber optical trapping system. Trapping, alignment, rotation, and stacking of glass rods were realized. To the best of our knowledge, this is the first time that cylindrical particles are optically trapped and bound by an optical fiber-based system. The optical manipulation of rods is also investigated through numerical simulations, which are used to quantitatively explain the experimental results. The ability of manipulating multiple particles of different shapes, as well as the integrable nature of the fiber-based setup, bestows the system the potential to be used in microfluidic systems for versatile particle manipulations. (C) 2010 American Institute of Physics. [doi:10.1063/1.3504716]
- J. Liu, C.-F. Chen, C.-W. Chang, and D. L. DeVoe, "Flow-through immunosensors using antibody-immobilized polymer monoliths," Biosensors & Bioelectronics, 26 (1), 182-188, 2010.
[Abstract]
High-sensitivity and rapid flow-through immunosensors based on photopolymerized surface-reactive polymer monoliths are investigated. The porous monoliths were synthesized within silica capillaries from glycidyl methacrylate and ethoxylated trimethylolpropane triacrylate precursors, providing a tortuous pore structure with high surface area for the immobilization of antibodies or other biosensing ligands The unique morphology of the monolith ensures efficient mass transport and interactions between solvated analyte molecules and covalently immobilize antibodies anchored to the monolith surface, resulting in rapid immunorecognition The efficacy of this approach is demonstrated through a direct immunoassay model using anti-IgG as a monolith-bound capture antibody and fluorescein-labeled IgG as an antigen. In situ antigen measurements exhibited a linear response over a concentration range between 0 1 and 50 ng/mL with 5 min assay times, while controllable injection of 1 mu L volumes of antigen through the monolith elements yielded a mass detection limit of 100 pg (similar to 700 amol) These results suggest that porous monolith supports represent a flexible and promising material for the fabrication of rapid and sensitive immunosensors suitable for integration into capillary or microfluidic devices (C) 2010 Elsevier B V All rights reserved
- A. J. Dick, B. Balachandran, and C. D. Mote, "Localization in Microresonator Arrays: Influence of Natural Frequency Tuning," Journal of Computational and Nonlinear Dynamics, 5 (1), 2010.
[Abstract]
Intrinsic localized modes are localization events caused by intrinsic nonlinearities within an array of perfectly periodic coupled oscillators. Recent developments in microscale fabrication techniques have allowed for the studies of this phenomenon in micro-electromechanical systems. Studies have also identified a relationship between the spatial profiles of intrinsic localized modes and forced nonlinear vibration modes, as well as a potential sensitivity to fundamental frequency relationships of one-to-one and three-to-one between adjacent oscillators. For the system considered, the one-to-one frequency relationship is determined to provide nonideal conditions for studying intrinsic localized modes. The influence of the three-to-one frequency relationship on the behavior of the intrinsic localized modes is studied with analytical methods and numerical simulations by tuning the fundamental frequencies of the oscillators. While the perfect tuning condition is not determined to produce a unique phenomenon, the number and energy concentration of the localization events are found to increase with the increased frequency ratio, which results in a decrease in the effective coupling stiffness within the array.
- C. M. Waits, M. McCarthy, and R. Ghodssi, "A Microfabricated Spiral-Groove Turbopump Supported on Microball Bearings," Journal of Microelectromechanical Systems, 19 (1), 99-109, 2010.
[Abstract]
The development of a microfabricated turbopump that is capable of delivering liquid fuel with the flow rates and pressures required for portable power generation is reported. The device is composed of a spiral-groove viscous pump driven by a radial in-flow microturbine and supported using a newly developed encapsulated microball bearing. A planar-contact bearing raceway is employed using 285-mu m-diameter 440C stainless steel microballs. A modification to the raceway geometry, as compared to previous designs, has enabled repeatable operation of the microturbine at speeds up to 87 000 r/min, showing negligible variations in performance for over 6 h and 3.8 million revolutions. Pumping has been demonstrated with water as the working fluid for flow rates of 10-80 mL/h and pressures rises of up to 8.2 kPa. This is the first application to incorporate an encapsulated microball bearing support mechanism, to achieve rotational speeds in excess of 50 000 r/min using a contact bearing, and to demonstrate reliable operation of more than 1 million revolutions. [2009-0123]
- A. P. Gerratt, I. Penskiy, and S. Bergbreiter, "SOI/elastomer process for energy storage and rapid release," Journal of Micromechanics and Microengineering, 20 (10), 2010.
[Abstract]
A new SOI/elastomer fabrication process that integrates a soft elastomer in-plane with silicon features has been developed, characterized and demonstrated. The simple three-mask process uses deep reactive ion etching of trenches in a silicon-on-insulator wafer to pattern high-aspect-ratio silicon and elastomer features from 2 mu m to hundreds of micrometers in width. The elastic and adhesive properties of the fabricated elastomer have been characterized. A Young's modulus of 1.4 MPa was measured at moderate strains up to 75%, and nonlinear strain was observed beyond that. The SOI/elastomer process has been used to fabricate micromechanical thrusters to repeatedly store and release 1.3 mu J to propel a 2 mg 1.6 mm by 0.8 mm by 0.45 mm projectile 1.35 cm.
- R. Ghodssi, C. Livermore, and D. Arnold, "Selected papers from the 9th International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2009)," Journal of Micromechanics and Microengineering, 20 (10), 2010.
[Abstract]
- R. Fernandes, X. L. Luo, C. Y. Tsao, G. F. Payne, R. Ghodssi, G. W. Rubloff, and W. E. Bentley, "Biological nanofactories facilitate spatially selective capture and manipulation of quorum sensing bacteria in a bioMEMS device," Lab on a Chip, 10 (9), 1128-1134, 2010.
[Abstract]
The emergence of bacteria that evade antibiotics has accelerated research on alternative approaches that do not target cell viability. One such approach targets cell-cell communication networks mediated by small molecule signaling. In this report, we assemble biological nanofactories within a bioMEMS device to capture and manipulate the behavior of quorum sensing (QS) bacteria as a step toward modifying small molecule signaling. Biological nanofactories are bio-inspired nanoscale constructs which can include modules with different functionalities, such as cell targeting, molecular sensing, product synthesis, and ultimately self-destruction. The biological nanofactories reported here consist of targeting, sensing, synthesis and, importantly, assembly modules. A bacteria-specific antibody constitutes the targeting module while a genetically engineered fusion protein contains the sensing, synthesis and assembly modules. The nanofactories are assembled on chitosan electrodeposited within a microchannel of the bioMEMS device; they capture QS bacteria in a spatially selective manner and locally synthesize and deliver the "universal" small signaling molecule autoinducer-2 (AI-2) at the captured cell surface. The nanofactory based AI-2 delivery is demonstrated to alter the progression of the native AI-2 based QS response of the captured bacteria. Prospects are envisioned for utilizing our technique as a test-bed for understanding the AI-2 based QS response of bacteria as a means for developing the next generation of antimicrobials.
- S. T. Koev, P. H. Dykstra, X. Luo, G. W. Rubloff, W. E. Bentley, G. F. Payne, and R. Ghodssi, "Chitosan: an integrative biomaterial for lab-on-a-chip devices," Lab on a Chip, 10 (22), 3026-3042, 2010.
[Abstract]
Chitosan is a naturally derived polymer with applications in a variety of industrial and biomedical fields. Recently, it has emerged as a promising material for biological functionalization of microelectromechanical systems (bioMEMS). Due to its unique chemical properties and film forming ability, chitosan serves as a matrix for the assembly of biomolecules, cells, nanoparticles, and other substances. The addition of these components to bioMEMS devices enables them to perform functions such as specific biorecognition, enzymatic catalysis, and controlled drug release. The chitosan film can be integrated in the device by several methods compatible with standard microfabrication technology, including solution casting, spin casting, electrodeposition, and nanoimprinting. This article surveys the usage of chitosan in bioMEMS to date. We discuss the common methods for fabrication, modification, and characterization of chitosan films, and we review a number of demonstrated chitosan-based microdevices. We also highlight the advantages of chitosan over some other functionalization materials for micro-scale devices.
- J. Liu, C.-F. Chen, S. Yang, C.-C. Chang, and D. L. DeVoe, "Mixed-mode electrokinetic and chromatographic peptide separations in a microvalve-integrated polymer chip," Lab on a Chip, 10 (16), 2122-2129, 2010.
[Abstract]
A cycloolefin polymer chip supporting the concatenation of isoelectric focusing (IEF) and reversed-phase liquid chromatography (RPLC) is demonstrated for high throughput two dimensional peptide separations. A unique benefit of the mixed-mode platform is the ability of IEF to act as a highly concentrating electrokinetic separation mode for effective isolation of sample components prior to RPLC. The thermoplastic chip contains integrated high pressure microvalves, enabling uniform sample transfer from the IEF channel to multiple parallel RPLC channels, gradient elution from each RPLC column, and hydrodynamic isolation between the separation dimensions. The reusable system is shown to provide efficient 2-D separations together with facile interfacing with MALDI-MS, suggesting a new path towards effective peptide analysis from complex samples.
- X. L. Luo, D. L. Berlin, J. Betz, G. F. Payne, W. E. Bentley, and G. W. Rubloff, "In situ generation of pH gradients in microfluidic devices for biofabrication of freestanding, semi-permeable chitosan membranes," Lab on a Chip, 10 (1), 59-65, 2010.
[Abstract]
We report the in situ generation of pH gradients in microfluidic devices for biofabrication of freestanding, semi-permeable chitosan membranes. The pH-stimuli-responsive polysaccharide chitosan was enlisted to form a freestanding hydrophilic membrane structure in microfluidic networks where pH gradients are generated at the converging interface between a slightly acidic chitosan solution and a slightly basic buffer solution. A simple and effective pumping strategy was devised to realize a stable flow interface thereby generating a stable, well-controlled and localized pH gradient. Chitosan molecules were deprotonated at the flow interface, causing gelation and solidification of a freestanding chitosan membrane from a nucleation point at the junction of two converging flow streams to an anchoring point where the two flow streams diverge to two output channels. The fabricated chitosan membranes were about 30-60 mu m thick and uniform throughout the flow interface inside the microchannels. A T-shaped membrane formed by sequentially fabricating orthogonal membranes demonstrates flexibility of the assembly process. The membranes are permeable to aqueous solutions and are removed by mildly acidic solutions. Permeability tests suggested that the membrane pore size was a few nanometres, i.e., the size range of antibodies. Building on the widely reported use of chitosan as a soft interconnect for biological components and microfabricated devices and the broad applications of membrane functionalities in microsystems, we believe that the facile, rapid biofabrication of freestanding chitosan membranes can be applied to many biochemical, bioanalytical, biosensing applications and cellular studies.
- C. Jang, B. D. Youn, P. F. Wang, B. Han, and S. J. Ham, "Forward-stepwise regression analysis for fine leak batch testing of wafer-level hermetic MEMS packages," Microelectronics Reliability, 50 (4), 507-513, 2010.
[Abstract]
An advanced regression scheme is proposed to analyze fine leak batch testing data of multiple MEMS packages. The scheme employs the forward-stepwise regression method to infer the information of leaky packages from a batch test data. The analysis predicts the number of leaky packages and the true leak rate of each leaky package in a progressive manner. The scheme is implemented successfully using an actual batch test data obtained from wafer-level hermetic MEMS packages. An error analysis is followed to define the applicable domain of the scheme. Advanced formulations are also suggested to extend the applicable domain. (C) 2009 Elsevier Ltd. All rights reserved.
- C.-W. Tsao, S. Tao, C.-F. Chen, J. Liu, and D. L. DeVoe, "Interfacing microfluidics to LDI-MS by automatic robotic spotting," Microfluidics and Nanofluidics, 8 (6), 777-787, 2010.
[Abstract]
We developed a method of interfacing microfluidics with mass spectrometry (MS) using a robotic spotting system to automate the contact spotting process. We demonstrate that direct and automated spotting of analyte from multichannel microfluidic chips to a custom microstructured MALDI target plate was a simple, robust, and high-throughput method for interfacing parallel microchannels using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Using thermoplastic cyclic olefin copolymer (COC) polymer microfluidic chips containing eight parallel 100 mu m x 46 mu m microchannels connected to a single input port, spotting volume repeatability and MALDI-MS signal uniformity are evaluated for a panel of sample peptides. The COC microfluidic chips were fabricated by hot embossing and solvent bonding techniques followed by chip dicing to create open ends for MS interfacing. Using the automatic robotic spotting approach, microfluidic chip-based reversed-phase liquid chromatography (RPLC) separations were interfaced with electrochemically etched nanofilament silicon (nSi) target substrate, demonstrating the potential of this approach toward chip-based microfluidic separation coupled with matrix-free laser desorption/ionization mass spectrometry.
- K. Gerasopoulos, M. McCarthy, P. Banerjee, X. Fan, J. N. Culver, and R. Ghodssi, "Biofabrication methods for the patterned assembly and synthesis of viral nanotemplates," Nanotechnology, 21 (5), 2010.
[Abstract]
This paper reports on novel methodologies for the patterning and templated synthesis of virus-structured nanomaterials in two-and three-dimensional microfabricated architectures using the Tobacco mosaic virus (TMV). The TMV is a high aspect ratio biological molecule which can be engineered to include amino acids with enhanced binding properties. These modifications facilitate self-assembly of the TMV onto various substrates and enable its use as a template for the synthesis of nanostructured materials. This work focuses on the combination of this bottom-up biologically inspired fabrication method with standard top-down micromachining processes that allow direct integration of the virus-structured materials into batch-fabricated devices. Photolithographic patterning of uncoated as well as nickel-coated TMV nanostructures has been achieved using a lift-off process in both solvent and mild basic solutions and their assembly onto three-dimensional polymer and silicon microstructures is demonstrated. In addition to these patterning techniques, in situ formation of metal oxide TMV coatings in patterned microfabricated environments is shown using atomic layer deposition directly on the nickel-coated viruses. The biofabrication 'process toolbox' presented in this work offers a simple and versatile alternative for the hierarchical patterning and incorporation of biotemplated nanomaterials into micro/nanofabrication schemes.
- J. D. Suter, W. Lee, D. J. Howard, E. Hoppmann, I. M. White, and X. D. Fan, "Demonstration of the coupling of optofluidic ring resonator lasers with liquid waveguides," Optics Letters, 35 (17), 2997-2999, 2010.
[Abstract]
Optofluidic lasers are of particular interest for lab-on-a-chip-type devices, with broad spectral tunability, convenient microfluidic integration, and a small footprint. Optofluidic ring resonator (OFRR) lasers are advantageous in terms of size but typically generate nondirectional emission that is of minimal practical use. We introduce two unique geometries for soft-lithography-based OFRR lasers-side-coupled rings and spiral rings-both of which can be produced in polydimethyl siloxane substrates with contact molding. These rings utilize evanescent and direct butt-coupling, respectively, to effectively couple the OFRR laser emission into microfluidic channels. A laser threshold of a few to tens of mu J/mm(2) is achieved. (C) 2010 Optical Society of America
- L. J. Currano, M. Yu, and B. Balachandran, "Latching in a MEMS shock sensor: Modeling and experiments," Sensors and Actuators A - Physical, 159 (1), 41-50, 2010.
[Abstract]
Modeling, numerical, and experimental efforts undertaken to develop a fundamental understanding of latching in a MEMS shock sensor are presented. A two degree-of-freedom model is developed and numerical studies are conducted with this model. These studies, which help shed light on difficult to observe experimental aspects, are used to examine the interaction forces between the shock sensor mass and latch, bounce effects, and loss of contact between the mass and the latch. High-speed video images of the shock sensor motions collected during a latching event are shown, and these results are used to verify the model predictions. Parametric studies conducted to examine the sensitivity of the design to friction and the effects of the latch mass and stiffness properties on the latch bounce are presented and discussed. Published by Elsevier B.V.
- S. T. Koev, W. E. Bentley, and R. Ghodssi, "Interferometric readout of multiple cantilever sensors in liquid samples," Sensors and Actuators B - Chemical
146 (1), 245-252, 2010.
[Abstract]
Microcantilever sensors in the static mode are a promising technology for chemical and biological detection in liquid phase. However, despite their potential for arrayed operation, most demonstrations to date have been performed with single devices due to the limitations of current methods for measuring cantilever displacement. We report a new readout technique using a curved semitransparent SU-8 cantilever on a reflective substrate. The displacement is measured by analyzing the interference pattern in microscope images of the device. Multiple cantilevers are read out with a single microscope by translating the stage to image each device before and after a chemical sample is introduced. Since the images are precisely aligned in software, the position of the stage is not critical, and the image acquisition is rapid. As a proof of principle, the cantilever displacement caused by pH variations or binding of homocysteine is measured. The experiments are performed with 3, 5, or 8 parallel devices exposed either to the same solution or to different sample concentrations. The minimal detectable displacement was determined to be on the order of 1 nm. The presented design and readout method can potentially be adapted for applications such as DNA hybridization assays or immunoassays in array format. (c) 2010 Elsevier B.V. All rights reserved.
- Y. Cheng, X. L. Luo, J. Betz, S. Buckhout-White, O. Bekdash, G. F. Payne, W. E. Bentley, and G. W. Rubloff, "In situ quantitative visualization and characterization of chitosan electrodeposition with paired sidewall electrodes," Soft Matter, 6 (14), 3177-3183, 2010.
[Abstract]
We report the first in situ quantitative visualization and characterization of electro-induced chitosan hydrogel growth in an aqueous environment. This was enabled with a pair of sidewall electrodes within a transparent fluidic system, which allowed us to resolve the electrogelling mechanism and interpret the dominant causes responsible for the formation and density distribution of the deposited hydrogel. The pH and the time-dependent growth profiles of the chitosan hydrogel were directly visualized, analyzed, and characterized. The results indicate that the gelation and immobilization of chitosan onto the cathode at a pH above its pK(a) value (similar to 6.3) are due to the electrochemically generated concentration gradient of reactant OH(-) ions, and their subsequent neutralization of the NH(3)(+) groups of chitosan chains in solution near the cathode. The increased gel density around the fringes of the electrodes was demonstrated and correlated with the electrophoretic migration of chitosan cations during deposition. Simulation of the electric potential/field distribution, together with the corresponding dry film topography confirmed the non-uniform, electric field-dependent density distribution of deposited hydrogel. This report provides fundamental understanding towards the mechanism and the kinetics of the electro-induced chitosan gel formation. It also provides important guidelines for pursuing its application in bio-components integrated microsystems. The method in use exemplifies a simple, effective and non-destructive approach for in situ characterization of electro-responsive biopolymers in an aqueous environment.
- J. Liu, C.-F. Chen, C.-W. Tsao, C.-C. Chang, C.-C. Chu, and D. L. DeVoe, "Polymer Microchips Integrating Solid-Phase Extraction and High-Performance Liquid Chromatography Using Reversed-Phase Polymethacrylate Monoliths," Analytical Chemistry, 81 (7), 2545-2554, 2009.
[Abstract]
Polymer microfluidic chips employing in situ photopolymerized polymethacrylate monoliths for high-performance liquid chromatography separations of peptides is described. The integrated chip design employs a 15 cm long separation column containing a reversed-phase polymethacrylate monolith as a stationary phase, with its front end seamlessly coupled to a 5 mm long methacrylate monolith which functions as a solid-phase extraction (SPE) element for sample cleanup and enrichment, serving to increase both detection sensitivity and separation performance. In addition to sample concentration and separation, solvent splitting is also performed on-chip, allowing the use of a conventional LC pump for the generation of on-chip nanoflow solvent gradients. The integrated platform Likes advantage of solvent bonding and a novel high-pressure needle interface which together enable the polymer chips to withstand internal pressures above 20 MPa (similar to 2900 psi) for efficient pressure-driven HPLC separations. Gradient reversed-phase separation of fluorescein-labeled model peptides and BSA tryptic digest are demonstrated using the microchip HPLC system. Online removal of free fluorescein and enrichment of labeled proteins are simultaneously achieved using the on-chip SPE column, resulting in a 150-fold improvement in sensitivity and a 10-fold reduction in peak width in the following microchip gradient LC separation.
- A. Goswami, B. Han, S. J. Ham, and B. G. Jeong, "Quantitative Characterization of True Leak Rate of Micro to Nanoliter Packages Using Helium Mass Spectrometer," IEEE Transactions on Advanced Packaging, 32 (2), 440-447, 2009.
[Abstract]
We propose a method to quantify the true leak rate of micro to nano-liter packages using the helium mass spectrometer. A new concept called "preprocessing time" is introduced to take into account 1) the instability of the helium mass spectrometer during the initial part of its operation and 2) the contribution of viscous conduction to the total conduction. The proposed method utilizes the complete profile of the apparent leak rate measured by the mass spectrometer and determines the true leak rate by performing a nonlinear regression analysis. The method is implemented successfully to measure the true leak rate of micro-electromechanical system packages. The validity of the proposed scheme is corroborated experimentally.
- S. T. Koev, R. Fernandes, W. E. Bentley, and R. Ghodssi, "A Cantilever Sensor With an Integrated Optical Readout for Detection of Enzymatically Produced Homocysteine," IEEE Transactions on Biomedical Circuits and Systems, 3 (6), 415-423, 2009.
[Abstract]
Microcantilever sensors have been recognized as a promising sensor platform for various chemical and biological applications. One of their major limitations is that the measurement of cantilever displacement typically involves elaborate off-chip setups with free-space optics. An improved device, known as the optical cantilever, has been proposed recently to eliminate the external optics. The response of the optical cantilever is measured on-chip through integrated waveguides. However, this method has been previously demonstrated only for devices operating in air, whereas most chemical and biological samples are in solution state. We present the first optical cantilever capable of operation in liquid. We test it with the detection of homocysteine with a minimal concentration of 10 mu M. The minimal measurable cantilever displacement and surface stress are 5 nm and 1 mN/m, respectively. The presented device will be used in studies of a homocysteine-producing bacterial pathway for the purpose of drug discovery. It can also be extended to various other chemical- or biological-sensing applications by selecting an appropriate surface coating.
- S. B. Prakash and P. Abshire, "A Fully Differential Rail-to-Rail CMOS Capacitance Sensor With Floating-Gate Trimming for Mismatch Compensation," IEEE Transactions on Circuits and Systems I-Regular Papers, 56 (5), 975-986, 2009.
[Abstract]
This paper presents a fully differential capacitance sensor employing the CBCM technique to map differential input capacitances into rail-to-rail differential output voltages. The circuit has been designed for measuring capacitances in the +/- 25-fF range, appropriate for sensing live cells using on-chip microelectrodes. An array architecture based on a shielded current routing bus has been developed for incorporating the capacitance measurement circuit into sensor arrays, with each pixel comprising four minimum-size digital transistors, enabling high-density integration. In addition to improving spatial resolution, the shielded current bus also eliminates the need for individual pixel calibration, conserves sensor evaluation speed, and provides protection from junction leakage. The sensor employs a 3-phase clocking scheme that enables on-chip gain tuning. The paper also presents a modified version of the sensor circuit incorporating floating-gate transistors for mismatch compensation and output offset cancellation, performed using a combination of impact-ionized channel hot electron injection and Fowler-Nordheim tunneling mechanisms. Chips comprising both versions of the sensor circuits in test arrays employing the shielded current routing bus were fabricated in a commercially available 2-poly, 3-metal, 0.5-mu m CMOS process. The sensor operation was demonstrated by measuring on-chip test capacitances comprising single and interdigitated metal electrodes, configured using different capacitance compensation schemes. The differential sensor in combination with the shielded current bus exhibits a maximum sensitivity of 200 mV/fF, a resolution of 15 aF, and an output dynamic range of 65 dB.
- C. S. Jang, A. Goswami, and B. Han, "Hermeticity Evaluation of Polymer-Sealed MEMS Packages by Gas Diffusion Analysis," Journal of Microelectromechanical Systems, 18 (3), 577-587, 2009.
[Abstract]
A gas transport mechanism is studied to characterize the hermetic behavior of polymer-sealed microelectromechanical systems packages. Diffusion-based governing equations, which are fundamentally different from the conduction-based governing equations used for metallic seals, are proposed to predict a change in cavity pressure. An effective numerical scheme is developed to implement the governing equations. The validity of the governing equations is corroborated by the optical leak test. The verified gas diffusion model is utilized to investigate the effect of the diffusion properties and geometries of polymeric seals on the gas leak behavior. [2008-0264]
- M. McCarthy, C. M. Waits, and R. Ghodssi, "Dynamic Friction and Wear in a Planar-Contact Encapsulated Microball Bearing Using an Integrated Microturbine," Journal of Microelectromechanical Systems, 18 (2), 263-273, 2009.
[Abstract]
The demonstration and characterization of a novel planar-contact encapsulated microball bearing using a radial inflow microturbine are presented. Stable operation of the air-driven silicon microturbine is shown for over 1000 000 revolutions at speeds, pressure drops, and flow rates of up to 10000 r/min, 0.45 lbf/in(2), and 3.5 slm, respectively. Incorporation of a gas thrust plenum using a novel packaging scheme has enabled comprehensive spin-down friction characterization of the encapsulated microball bearing. An empirical power-law model for dynamic friction has been developed for speeds of 250-5000 r/min and loads of 10-50 mN, corresponding to torques of 0.0625-2.5 mu N . m and friction torque constants of 2.25-5.25 x 10(-4) mu N . m/r/min. The onset and effect of wear and wear debris have been studied, showing negligible wear in the load bearing surfaces for the operating conditions considered.
- L. Mosher, C. M. Waits, B. Morgan, and R. Ghodssi, "Double-Exposure Grayscale Photolithography," Journal of Microelectromechanical Systems, 18 (2), 308-315, 2009.
[Abstract]
A double-exposure grayscale photolithography technique is developed and demonstrated to produce three-dimensional (3-D) structures with a high vertical resolution. Pixelated grayscale masks often suffer from limited vertical resolution due to restrictions on the mask fabrication. The double-exposure technique uses two pixelated grayscale mask exposures before development and dramatically increases the vertical resolution without altering the mask fabrication process. An empirical calibration technique was employed for mask design and was also applied to study the effects of exposure time and mask misalignment on the photoresist profile. This technology has been demonstrated to improve the average step between photoresist levels from 0.19 to 0.02 mu m and the maximum step from 0.43 to 0.2 mu m compared to a single pixelated exposure using the same mask design.
- N. Siwak, X. Z. Fan, D. Hines, S. Kanakaraju, N. Goldsman, and R. Ghodssi, "Indium Phosphide MEMS Cantilever Resonator Sensors Utilizing a Pentacene Absorption Layer," Journal of Microelectromechanical Systems, 18 (1), 103-110, 2009.
[Abstract]
We report a microelectromechanical system cantilever waveguide resonator sensing platform utilizing a novel optical readout scheme and the organic semiconductor pentacene as a surface absorbing layer. In this paper, the measurement of isopropyl alcohol and ethanol vapors by way of mass induced frequency shift using a cantilever microbalance is demonstrated. Vapor was introduced to the system through a custom built environmental chamber. A frequency shift due to a mass absorption of 65 Hz was measured, corresponding to a measurement of 6.92 +/- 1.1 x 10(-14) g with a minimum detectable mass of 5.09 x 10(-15) g for the devices presented. The pentacene absorbing layer in this paper shows it for the first time, functioning as a mass absorbing layer. These results are also the first demonstration of repeatable mass sensing performed using the integrated indium phosphide cantilever waveguide sensor platform. [2008-0134]
- B. Balakrisnan, S. Patil, and E. Smela, "Patterning PDMS using a combination of wet and dry etching," Journal of Micromechanics and Microengineering, 19 (4), 2009.
[Abstract]
PDMS films of 10 mu m thickness can be patterned within 30 min by combining dry etching to achieve substantially vertical sidewalls with wet etching to achieve high etch rates and to protect the underlying substrate from attack. Dry etching alone would have taken 5 h, and wet etching alone would produce severe undercutting. In addition, using either technique alone produces undesirable surface morphologies. The mask used during etching is critical to a successful patterning outcome. E-beam evaporated Al was found to work well, adhering strongly to oxygen-plasma-treated PDMS and holding up well during both dry and wet etching. To prevent wrinkling of the PDMS, a fast deposition rate should be used.
- S. Bergbreiter, D. Mahajan, and K. S. J. Pister, "A reusable micromechanical energy storage/quick release system with assembled elastomers," Journal of Micromechanics and Microengineering, 19 (5), 2009.
[Abstract]
A reusable, elastomer-based energy storage/quick release system for MEMS has been designed, built and tested. Microrubber bands have been fabricated from silicone using two different methods, laser cut and molded, and assembled into silicon microstructures fabricated in a two-mask silicon-on-insulator (SOI) process. Using silicon hooks and force gauges designed in this process, these microrubber bands have been characterized as to their energy storage potential and efficiency by stretching them with a probe tip. These tests showed recovered energy efficiencies up to 92% at strains over 200% with a maximum stored energy over 19 mu J. In addition, a fully integrated micromechanical energy storage system to both store and release energy has been demonstrated using an electrostatic inchworm motor to stretch the elastomer band and release it. Using the inchworm motor, an estimated 4.9 nJ of energy was stored in the elastomer spring and quickly released.
- M. McCarthy, C. M. Waits, M. I. Beyaz, and R. Ghodssi, "A rotary microactuator supported on encapsulated microball bearings using an electro-pneumatic thrust balance," Journal of Micromechanics and Microengineering, 19 (9), 2009.
[Abstract]
The development of a rotary microactuator supported on encapsulated microball bearings and driven by electro-pneumatic actuation is reported. The encapsulated bearing provides full support to an encased rotor, while an electro-pneumatic thrust balance is used to minimize rotor normal load. By minimizing normal load, bearing friction is reduced leading to increased speed and performance. Experimental results show that the microactuator is capable of repeatable operation and continuous 360 degrees motion at speeds of 5-2000 rpm. This is the first demonstration of a ball bearing supported electrostatic microactuator with a fully encased rotor, capable of direct mechanical attachment or reliable interaction with external media.
- C. S. Jang, A. Goswami, B. T. Han, and S. J. Ham, "In situ measurement of gas diffusion properties of polymeric seals used in MEMS packages by optical gas leak testing," Journal of Micro-Nanolithography MEMS and MOEMS, 8 (4), 2009.
[Abstract]
A novel inverse approach is proposed for in situ measurement of gas diffusion properties of polymeric seals used in microelectromechanical systems (MEMS) packages. The cavity pressure evolution of a polymer-sealed MEMS package subjected to a constant bombing pressure is documented as a function of time using classical interferometry, and the diffusion properties of the polymeric seal are subsequently determined from the measured pressure history. A comprehensive numerical procedure for the inverse analysis is established considering three diffusion regimes that characterize the leak behavior through a polymeric seal. The method is implemented to determine the helium diffusivity and solubility of a polymeric seal. (C) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3227904]
- M. Armani, J. Rodriguez-Canales, J. Gillespie, M. Tangrea, H. Erickson, M. R. Emmert-Buck, B. Shapiro, and E. Smela, "2D-PCR: a method of mapping DNA in tissue sections," Lab on a Chip, 9 (24), 3526-3534, 2009.
[Abstract]
A novel approach was developed for mapping the location of target DNA in tissue sections. The method combines a high-density, multi-well plate with an innovative single-tube procedure to directly extract, amplify, and detect the DNA in parallel while maintaining the two-dimensional (2D) architecture of the tissue. A 2D map of the gene glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was created from a tissue section and shown to correlate with the spatial area of the sample. It is anticipated that this approach may be easily adapted to assess the status of multiple genes within tissue sections, yielding a molecular map that directly correlates with the histology of the sample. This will provide investigators with a new tool to interrogate the molecular heterogeneity of tissue specimens.
- C. F. Chen, J. Liu, L. P. Hromada, C. W. Tsao, C. C. Chang, and D. L. DeVoe, "High-pressure needle interface for thermoplastic microfluidics," Lab on a Chip, 9 (1), 50-55, 2009.
[Abstract]
A robust and low dead volume world-to-chip interface for thermoplastic microfluidics has been developed. The high pressure fluidic port employs a stainless steel needle inserted into a mating hole aligned to an embedded microchannel, with an interference fit used to increase pressure resistance. Alternately, a self-tapping threaded needle screwed into a mating hole is also demonstrated. In both cases, the flat bottom needle ports seat directly against the microchannel substrate, ensuring low interfacial dead volumes. Low dispersion is observed for dye bands passing the interfaces. The needle ports offer sufficient pull-out forces for applications such as liquid chromatography that require high internal fluid pressures, with the epoxy-free interfaces compatible with internal microchannel pressures above 40 MPa.
- C.-F. Chen, J. Liu, C.-C. Chang, and D. L. DeVoe, "High-pressure on-chip mechanical valves for thermoplastic microfluidic devices," Lab on a Chip, 9 (24), 3511-3516, 2009.
[Abstract]
A facile method enabling the integration of elastomeric valves into rigid thermoplastic microfluidic chips is described. The valves employ discrete plugs of elastomeric polydimethylsiloxane (PDMS) integrated into the thermoplastic substrate and actuated using a threaded stainless steel needle. The fabrication process takes advantage of poly(ethylene glycol) (PEG) as a sacrificial molding material to isolate the PDMS regions from the thermoplastic flow channels, while yielding smooth contact surfaces with the PDMS valve seats. The valves introduce minimal dead volumes, and provide a simple mechanical means to achieve reproducible proportional valving within thermoplastic microfluidic systems. Burst pressure tests reveal that the valves can withstand pressures above 12 MPa over repeated open/close cycles without leakage, and above 24 MPa during a single use, making the technology well suited for applications such as high performance liquid chromatography. Proportional valve operation is demonstrated using a multi-valve chemical gradient generator fabricated in cyclic olefin polymer.
- S. Yang, J. Liu, C. S. Lee, and D. L. DeVoe, "Microfluidic 2-D PAGE using multifunctional in situ polyacrylamide gels and discontinuous buffers," Lab on a Chip, 9 (4), 592-599, 2009.
[Abstract]
A two-dimensional microfluidic system is presented for intact protein separations combining isoelectric focusing (IEF) and sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) employing in situ photopolymerized polyacrylamide (PAAm) gels. The PAAm gels are used for multiple functions. In addition to serving as a highly-resolving separation medium for gel electrophoresis, discrete polyacrylamide gel plugs are used to enable the efficient isolation of different on-chip media including anolyte, catholyte, and sample/ampholyte solutions for IEF. The gel plugs are demonstrated as on-chip reagent containers, holding defined quantities of SDS for on-chip SDS protein complexation, and enabling the use of a discontinuous buffer system for sample band sharpening during SDS-PAGE. The 2-D chip also employs several unique design features including an angled isoelectric focusing channel to minimize sample tailing, and backbiasing channels designed to achieve uniform interdimensional sample transfer. Separation results using E. coli cell lysate are presented using a 10-channel chip with and without the discontinuous buffer system, with resolving power more than doubled in the former case. Further improvements in separation resolution are demonstrated using a 20-channel chip design.
- C.-W. Tsao and D. L. DeVoe, "Bonding of thermoplastic polymer microfluidics," Microfluidics and Nanofluidics, 6 (1), 1-16, 2009.
[Abstract]
Thermoplastics are highly attractive substrate materials for microfluidic systems, with important benefits in the development of low cost disposable devices for a host of bioanalytical applications. While significant research activity has been directed towards the formation of microfluidic components in a wide range of thermoplastics, sealing of these components is required for the formation of enclosed microchannels and other microfluidic elements, and thus bonding remains a critical step in any thermoplastic microfabrication process. Unlike silicon and glass, the diverse material properties of thermoplastics opens the door to an extensive array of substrate bonding options, together with a set of unique challenges which must be addressed to achieve optimal sealing results. In this paper we review the range of techniques developed for sealing thermoplastic microfluidics and discuss a number of practical issues surrounding these various bonding methods.
- Y. X. Liu and M. A. Yu, "Multiple traps created with an inclined dual-fiber system," Optics Express, 17 (24), 21680-21690, 2009.
[Abstract]
Multiple optical traps allow one to manipulate multiple particles simultaneously, to characterize interactions in colloidal systems, and to assemble particles into complex structures. Most of the current multiple optical traps are realized with microscope objective-based optical tweezers, which are bulky in size. In this article, we created multiple optical traps with an inclined dual-fiber optical tweezers setup. One 3D trap and two 2D traps were formed at different vertical levels with adjustable separations and positions. We demonstrated that this fiber-based trapping system can be used as a simple block to perform multiple functions, such as particle grouping, separation, and stacking. Moreover, we found that multiple beads can be trapped and stacked up in three dimensions. Compared with those formed with objective-based optical tweezers, the multiple traps presented here are small in size and independent of the objective or the substrate, and hence hold the promise to be integrated in microfluidic systems. This fiber-based multiple traps can be used for on-chip parallel manipulation, particle separation, and characterization of interactions of colloidal and biological systems. (C) 2009 Optical Society of America
- Y. X. Liu and M. Yu, "Investigation of inclined dual-fiber optical tweezers for 3D manipulation and force sensing," Optics Express, 17 (16), 13624-13638, 2009.
[Abstract]
Optical tweezers provide a versatile tool in biological and physical researches. Optical tweezers based on optical fibers are more flexible and ready to be integrated when compared with those based on microscope objectives. In this paper, the three-dimensional (3D) trapping ability of an inclined dual-fiber optical tweezers is demonstrated. The trapping efficiency with respect to displacement is experimentally calibrated along two dimensions. The system is studied numerically using a modified ray-optics model. The spring constants obtained in the experiment are predicted by simulations. It is found both experimentally and numerically that there is a critical value for the fiber inclination angle to retain the 3D trapping ability. The inclined dual-fiber optical tweezers are demonstrated to be more robust to z-axis misalignment than the counter-propagating fiber optical tweezers, which is a special case of the former when the fiber inclination angle is 90 degrees. This inclined dual-fiber optical tweezers can serve as both a manipulator and a force sensor in integrated systems, such as microfluidic systems and lab-on-a-chip systems. (C) 2009 Optical Society of America
- X. M. Zhang, Y. X. Liu, H. Bae, C. Pang, and M. Yu, "Phase modulation with micromachined resonant mirrors for low-coherence fiber-tip pressure sensors," Optics Express, 17 (26), 23965-23974, 2009.
[Abstract]
This letter presents a simple phase modulation scheme for interrogation of low-coherence interferometry based fiber-tip pressure sensors to enable real-time monitoring and miniaturization of the entire sensor system. The key idea is to introduce a sinusoidal modulation signal and retrieve the sensing cavity length change using a simple algorithm, without resorting to any time information. In experiments, phase modulation has been achieved by using a silicon-micromachined tunable Fabry-Perot interferometer, which is integrated with a light source and a photodiode onto a single chip. Compared with the conventional interrogation methods, this scheme possesses the merits of being less susceptible to disturbance, easy control and easy miniaturization, making it particularly suitable for sensing in constrained spaces and harsh environments. (C) 2009 Optical Society of America
- M. I. Beyaz, M. McCarthy, N. Ghalichechian, and R. Ghodssi, "Closed-loop control of a long-range micropositioner using integrated photodiode sensors," Sensors and Actuators A - Physical, 151 (2), 187-194, 2009.
[Abstract]
Closed-loop control of an electrostatically actuated micropositioner using integrated feedback sensors is reported. A photodiode-based position sensing mechanism has been incorporated into a variable-capacitance micromotor supported on microball bearings with a range of 4 mm and a resolution of 120 mu m. Accurate and reliable positioning has been demonstrated using a proportional controllaw and the effect of the proportionality constant has been investigated for various stepping distances and actuation voltages. A minimum settling time of 0.1s was achieved for a 1 mm step at 150V. Closed-loop excitation has enabled sustained synchronous motion and a maximum speed of 20.4 mm/s. This is a noted improvement compared to open-loop excitation, which exhibits erratic motion and a maximum speed of 7.2 mm/s. Using feedback control, two critical functions for robust positioning have been demonstrated; the micropositioner can establish a necessary frame of reference and autonomously respond to arbitrary disturbances. The closed-loop position control system presented in this work illustrates the feasibility and functionality of smart microsystems using integrated feedback sensors. (C) 2009 Elsevier B.V. All rights reserved.
- P. Dykstra, J. J. Hao, S. T. Koev, G. F. Payne, L. L. Yu, and R. Ghodssi, "An optical MEMS sensor utilizing a chitosan film for catechol detection," Sensors and Actuators B - Chemical
138 (1), 64-70, 2009.
[Abstract]
Catechol is a widely studied phenol that is a common byproduct of factory waste. The presence of catechol in drinking water and food poses a safety concern due to its toxic and possibly carcinogenic effects. We report the successful fabrication and testing of an optical MEMS sensor for the detection of catechol. Studies on catechol detection have shown that byproducts from catechol oxidation will react with a chitosan film and induce a significant absorbance change in the UV and near UV range. Our reported sensor takes advantage of this unique absorbance property to detect catechol by measuring the change in light intensity at 472 nm through an electrodeposited film of chitosan on a transparent. conductive film of indium tin oxide. This optical detection technique eliminates the nonspecific response from the common antioxidant, ascorbic acid, which does not cause an absorbance change. Absorbance measurements were performed over 10 min while applying an oxidizing current density of 4 A/m(2). We observed a considerable response even for our lowest measured concentration (1 mM) while the detection limit of the device is found to be about 0.2 mM for a 10 min reaction time. (C) 2009 Elsevier B.V. All rights reserved.
- M. E. Piyasena, R. Newby, T. J. Miller, B. Shapiro, and E. Smela, "Electroosmotically driven microfluidic actuators," Sensors and Actuators B - Chemical
141 (1), 263-269, 2009.
[Abstract]
A prototype electroactive polymer actuator has been developed based on electroosmotic (EO) Pumping to create hydraulic pressure. The actuator was fabricated from poly(dimethylsiloxane) (PDMS) with embedded micro-scale channels, reservoirs, and electrodes Surmounted by a membrane. An applied voltage caused one reservoir to expand as fluid was pumped into it, and the other reservoir to contract, with the membrane above the expansion reservoir rising by 400 mu m within a few seconds. Since the prototype was made from PDMS. which is an elastomer, the device was entirely flexible. The actuator performance was characterized, and it agreed well with predicted Values. Furthermore, the calculations indicate that. once optimized, such actuators could have high stress as well as high strain and high speed. By combining unit cells Such as these into a material and actuating them individually via independently controlled flexible electrodes, one Could realize smart materials that could change shape. Other future applications may include micro-valves, micro-positioners. soft robots, and active camouflage layers. (C) 2009 Elsevier B.V. All rights reserved.
- S. L. Buckhout-White and G. W. Rubloff, "Spatial resolution in chitosan-based programmable biomolecular scaffolds," Soft Matter, 5 (19), 3677-3681, 2009.
[Abstract]
The polysaccharide chitosan is a versatile scaffold for assembly and conjugation of biomolecules, including nucleic acids, proteins, and viruses. It provides unique value in bioMEMS in that it can be electrodeposited on demand at specific locations in closed microfluidic systems, enabling spatial and temporal programmability of biomolecular binding and reaction sites in bio-microfluidic networks. In anticipating the scaling of such systems to smaller dimensions, we have investigated the spatial resolution which the chitosan electrodeposition process can achieve, using micron-scale electrode patterns coupled with fluorescence and Raman microscopies to assess the fidelity and edge sharpness of the resulting chitosan patterns. These show that electrodeposited chitosan scaffolds can be defined to an edge sharpness of 0.5-1.0 mu m, compatible with the vast majority of microfluidics and bioMEMS applications, where microfluidic channel dimensions in the range of 10s or 100s of micrometers are common.
- H. Y. Zhu, I. M. White, J. D. Suter, M. Zourob, and X. D. Fan, "Opto-fluidic micro-ring resonator for sensitive label-free viral detection," Analyst, 133 (3), 356-360, 2008.
[Abstract]
We have demonstrated sensitive label-free virus detection using the opto-fluidic ring resonator (OFRR) sensor. The OFRR is a novel sensing platform that integrates the microfluidics and photonic sensing technology with a low detection limit and small volume. In our experiment,. lamentous bacteriophage M13 was used as a safe model system. Virus samples were. owed through the OFRR whose surface was coated with M13-specific antibodies. We studied the sensor performance by monitoring in real-time the virus and antibody interaction. It is shown that OFRR can detect M13 with high specificity and sensitivity. The detection limit is approximately 2.3 x 103 pfu mL(-1) and the detection dynamic range spanned seven orders of magnitude. Theoretical analysis was also carried out to confirm the experimental results. Our study will lead to development of novel OFRR-based, sensitive, rapid, and low-cost micro total analysis devices for virus detection.
- J. R. Hattrick-Simpers, D. Hunter, C. M. Craciunescu, K. S. Jang, M. Murakami, J. Cullen, M. Wuttig, I. Takeuchi, S. E. Lofland, L. Benderksy, N. Woo, R. B. Van Dover, T. Takahashi, and Y. Furuya, "Combinatorial investigation of magnetostriction in Fe-Ga and Fe-Ga-Al," Applied Physics Letters, 93 (10), 2008.
[Abstract]
A high-throughput high-sensitivity optical technique for measuring magnetostriction of thin-film composition-spread samples has been developed. It determines the magnetostriction by measuring the induced deflection of micromachined cantilever unimorph samples. Magnetostriction measurements have been performed on as-deposited Fe-Ga and Fe-Ga-Al thin-film composition spreads. The thin-film Fe-Ga spreads display a similar compositional variation of magnetostriction as bulk. A previously undiscovered peak in magnetostriction at low Ga content was also observed and attributed to a maximum in the magnetocrystalline anisotropy. Magnetostrictive mapping of the Fe-Ga-Al ternary system reveals the possibility of substituting up to 8 at. % Al in Fe(70)Ga(30) without significant degradation of magnetostriction. (C) 2008 American Institute of Physics.
- X. Luo, D. L. Berlin, S. Buckhout-White, W. E. Bentley, G. F. Payne, R. Ghodssi, and G. W. Rubloff, "Design optimization for bioMEMS studies of enzyme-controlled metabolic pathways," Biomedical Microdevices, 10 (6), 899-908, 2008.
[Abstract]
Biological microelectromechanical systems (bioMEMS) provide an attractive approach to understanding and modifying enzymatic pathways by separating and interrogating individual reaction steps at localized sites in a microfluidic network. We have previously shown that electrodeposited chitosan enables immobilization of an enzyme at a specific site while maintaining its catalytic activity. While promising as a methodology to replicate metabolic pathways and search for inhibitors as drug candidates, these investigations also revealed unintended (or parasitic) effects, including products generated by the enzyme either (1) in the homogeneous phase (in the liquid), or (2) nonspecifically bound to microchannel surfaces. Here we report on bioMEMS designs which significantly suppress these parasitic effects. To reduce homogeneous reactions we have developed a new packaging and assembly strategy which eliminates fluid reservoirs that are commonly used for fluidic interconnects with external tubing. To suppress reactions by nonspecifically bound enzyme on microchannel walls we have implemented a cross-flow microfluidic network design so that enzyme flow for assembly and substrate/product for reaction share only the region where the enzyme is immobilized at the intended reaction site. Our results show that the signal-to-background ratio of sequential enzymatic reactions increases from 0.72 to 1.28 by eliminating the packaging reservoirs, and increases to 2.43 by separating the flow direction of enzymatic reaction from that of enzyme assembly step. These techniques can be easily applied to versatile microfluidic devices to minimize parasitic reactions in sequential biochemical reactions.
- J. D. Suter, I. M. White, H. Y. Zhu, H. D. Shi, C. W. Caldwell, and X. D. Fan, "Label-free quantitative DNA detection using the liquid core optical ring resonator," Biosensors & Bioelectronics, 23 (7), 1003-1009, 2008.
[Abstract]
We demonstrated quantitative real-time label-free detection of DNA sequences using the liquid core optical ring resonator (LCORR) sensor. The LCORR is a recently developed sensing platform that integrates microfluidics and photonic sensing technology with low detection limit and sub-nanoliter detection volume. We analyzed experimentally and theoretically the LCORR response to a variety of DNA samples that had different strand lengths (25-100 bases), number of base- mismatches (1-5), and concentrations (10 pM to 10 mu M) to evaluate the LCORR sequence detection capability. In particular, we established the linear correlation between the LCORR sensing signal and the molecule density, which allows us to accurately calculate the molecule density on the surface. It is found that the probe surface coverage was 26-51% and the extent of hybridization was 40-50%. The titration curve for 25-base probe and 25-base target DNA yields a dissociation constant of 2.9 nM. With a 37.1 nm/RIU LCORR, detection of 10 pM bulk DNA concentration was demonstrated. The mass detection limit was estimated to be 4 pg/mm(2) corresponding to a density of 10(10) molecules/cm(2) on the surface. We also showed that the LCORR was sensitive enough to differentiate DNA with only a few base-mismatches based on the raw sensing signal and kinetic analysis. Our work will provide important insight into the light-DNA interaction at the ring resonator surface and lay a foundation for future LCORR-based DNA label-free microarray development. (C) 2007 Elsevier B.V. All rights reserved.
- A. T. Lewandowski, H. M. Yi, X. L. Luo, G. F. Payne, R. Ghodssi, G. W. Rubloff, and W. E. Bentley, "Protein assembly onto patterned microfabricated devices through enzymatic activation of fusion pro-tag," Biotechnology and Bioengineering, 99 (3), 499-507, 2008.
[Abstract]
We report a versatile approach for covalent surface-assembly of proteins onto selected electrode patterns of pre-fabricated devices. Our approach is based on electro-assembly of the aminopolysaccharide chitosan scaffold as a stable thin film onto patterned conductive surfaces of the device, which is followed by covalent assembly of the target protein onto the scaffold surface upon enzymatic activation of the protein's "pro-tag." For our demonstration, the model target protein is green fluorescent protein (GFP) genetically fused with a pentatyrosine pro-tag at its C-terminus, which assembles onto both two-dimensional chips and within fully packaged microfluidic devices in situ and under flow. Our surface- assembly approach enables spatial selectivity and orientational control under mild experimental conditions. We believe that our integrated approach harnessing genetic manipulation, in situ enzymatic activation, and electro-assembly makes it advantageous for a wide variety of bioMEMS and biosensing applications that require facile "biofunctionalization" of microfabricated devices.
- A. T. Lewandowski, W. E. Bentley, H. M. Yi, G. W. Rubloff, G. F. Payne, and R. Ghodssi, "Towards Area-Based In Vitro Metabolic Engineering: Assembly of Pfs Enzyme onto Patterned Microfabricated Chips," Biotechnology Progress, 24 (5), 1042-1051, 2008.
[Abstract]
We report an approach for spatially selective assembly of an enzyme onto selected patterns of microfabricated chips. Our approach is based on electrodeposition of the aminopolysaccharide chitosan onto selected electrode patterns and covalent conjugation of a target enzyme to chitosan upon biochemical activation of a genetically fused "pro-tag." We report assembly of S-adenosylhomocysteine nucleosidase (Pfs) fused with a C-terminal pentatyrosine pro-tag. Pfs is a member of the bacterial autoinducer-2 biosynthesis pathway, catalyzing the irreversible cleavage of S-adenosylhomocysteine. The assembled Pfs retains its catalytic activity and structure, as demonstrated by retained antibody recognition. Assembly is controlled by the electrode area, resulting in reproducible rates of catalytic conversion for a given area, and thus allowing for area-based manipulation of catalysis and small molecule biosynthesis. Our approach enables optimization of small molecule biosynthesis 1-step as well as multistep enzymatic reactions, including entire metabolic pathways, and we envision a wide variety of potential applications.
- J. Liu, S. Yang, C. S. Lee, and D. L. DeVoe, "Polyacrylamide gel plugs enabling 2-D microfluidic protein separations via isoelectric focusing and multiplexed sodium dodecyl sulfate gel electrophoresis," Electrophoresis, 29 (11), 2241-2250, 2008.
[Abstract]
In situ photopolymerized polyacrylamide (PAAm) gel plugs are used as hydrodynamic flow control elements in a multidimensional microfluidic system combining IEF and parallel SDS gel electrophoresis for protein separations. The PAAm gel plugs offer a simple method to reduce undesirable bulk flow and limit reagent/sample crosstalk without placing unwanted constraints on the selection of separation media, and without hindering electrokinetic ion migration in the complex microchannel network. In addition to improving separation reproducibility, the discrete gel plugs integrated into critical regions of the chip enable the use of a simple pressure-driven sample injection method which avoids electrokinetic injection bias. The gel plugs also serve to greatly simplify operation of the spatially multiplexed system by eliminating the need for complex external fluidic interfaces. Using an FITC-labeled Escherichia coli cell lysate as a model system, the use of gel plugs is shown to significantly enhance separation reproducibility in a chip containing five parallel CGE channels, with an average variance in peak elution time of only 4.1%.
- N. Ghalichechian, A. Modafe, M. I. Beyaz, and R. Ghodssi, "Design, fabrication, and characterization of a rotary micromotor supported on microball bearings," Journal of Microelectromechanical Systems, 17 (3), 632-642, 2008.
[Abstract]
We report the design, fabrication, and characterization of a rotary micromotor supported on microball bearings. This is the first demonstration of a rotary micromachine with a robust mechanical support provided by microball-bearing technology. A six-phase bottom-drive variable-capacitance mi cromotor (phi = 14 mm) is designed and simulated using the finite-element (FE) method. The stator and the rotor are fabricated separately on silicon substrates and assembled with the microballs. Three layers of low-k benzocyclobutene polymer, two layers of gold, and a silicon microball housing are fabricated on the stator. Microball housing and salient structures (poles) are etched in the rotor and are coated with a silicon carbide film that reduces the friction without which the operation was not possible. A top angular velocity of 517 r/min, corresponding to the linear tip velocity of 324 mm/s, is measured at +/- 150-V and 800-Hz excitation. This is 44 times higher than the velocity previously demonstrated for linear micromotors supported on the microball bearings. A noncontact method is developed to extract the torque and the bearing coefficient of friction through dynamic response measurements. The torque is indirectly measured to be -5.62 +/- 0.5 mu N.m at +/- 150-V excitation which is comparable with the FE simulation results predicting -6.75 mu N.m. The maximum output mechanical power at +/- 150 V and 517 r/min was calculated to be 307 mu W. The bearing coefficient of friction is measured to be 0.02 +/- 0.002 which is in good agreement with the previously reported values. The rotary micromotor developed in this paper is a platform technology for centrifugal micropumps used for fuel-delivery and cooling applications.
- B. Morgan and R. Ghodssi, "Vertically-shaped tunable MEMS resonators," Journal of Microelectromechanical Systems, 17 (1), 85-92, 2008.
[Abstract]
We report the development of tunable comb-resonators that use vertically-shaped comb-fingers as electrostatic springs. By restricting our design modifications to the vertical dimension, the tunability is achieved without increasing the device footprint. Three-dimensional finite element analysis was used to evaluate the effects of geometry and design on electrostatic spring strength and linearity. All structural components were fabricated using gray-scale technology, simultaneously defining all vertical levels using a single lithography and dry-etching step. Subsequent testing achieved bidirectional resonant frequency tuning (> 17%) through the creation of electrostatic spring constants as high as 1.06 N/m (at 70 V) and 1.45 N/m (at 120 V). While the current resonant devices show evidence of nonlinear stiffness coefficients at large oscillation amplitudes (> 10 mu m), multiple design options are introduced and simulated as potential solutions.
- K. Gerasopoulos, M. McCarthy, E. Royston, J. N. Culver, and R. Ghodssi, "Nanostructured nickel electrodes using the Tobacco mosaic virus for microbattery applications," Journal of Micromechanics and Microengineering, 18 (10), 2008.
[Abstract]
The development of nanostructured nickel-zinc microbatteries utilizing the Tobacco mosaic virus (TMV) is presented in this paper. The TMV is a high aspect ratio cylindrical plant virus which has been used to increase the active electrode area in MEMS- fabricated batteries. Genetically modifying the virus to display multiple metal binding sites allows for electroless nickel deposition and self-assembly of these nanostructures onto gold surfaces. This work focuses on integrating the TMV deposition and coating process into standard MEMS fabrication techniques as well as characterizing nickel-zinc microbatteries based on this technology. Using a microfluidic packaging scheme, devices with and without TMV structures have been characterized. The TMV modified devices demonstrated charge-discharge operation up to 30 cycles reaching a capacity of 4.45 mu Ah cm(-2) and exhibited a six-fold increase in capacity during the initial cycle compared to planar electrode geometries. The effect of the electrode gap has been investigated, and a two- fold increase in capacity is observed for an approximately equivalent decrease in electrode spacing.
- C.-W. Tsao, J. Liu, and D. L. Devoe, "Droplet formation from hydrodynamically coupled capillaries for parallel microfluidic contact spotting," Journal of Micromechanics and Microengineering, 18 (2), 2008.
[Abstract]
The generation of liquid droplets at the exits of multiple capillaries coupled to a single flow source is evaluated for application to multiplexed microfluidic contact spotting. Using a simple analytic model and an iterative numerical model, relationships between applied flow rates and the number of channels which produce full droplets at their exits are determined for arbitrarily large arrays. Experimental validation is performed using eight-channel arrays fabricated in cyclic olefin copolymer chips, with good agreement between experimental and predicted data. Improvements in spotting repeatability and uniformity are achieved for microchannel arrays containing in situ porous methacrylate monoliths, particularly for individual channel flow rates below 1 mu L min(-1), revealing contact spotting as an appropriate interface between multiplexed microfluidic liquid chromatography and off-chip analysis.
- M. Urdaneta and E. Smela, "The design of dielectrophoretic flow-through sorters using a figure of merit," Journal of Micromechanics and Microengineering, 18 (1), 2008.
[Abstract]
Dielectrophoretic (DEP) forces produced by a pair of electrodes are used for such applications as particle sorting in microfluidic systems. In order to allow quantitative comparison of different DEP systems, we introduce a new figure of merit: dimensionless characteristic velocity corresponding to the maximum flow that can be used while still successfully deflecting the desired particles. This avoids the necessity of performing numerical simulations in order to compare designs and allows one to focus on general system design questions. The maximum deflection velocity is evaluated versus a characteristic length for four different sorter configurations, yielding curves that can be used as tools to design DEP sorters. Maximum flow predictions are compared with previously published theoretical and experimental results.
- C. L. Edwards, B. G. Boone, W. S. Levine, and C. C. Davis, "First principles jitter characterization of two-axis MEMS mirrors," Journal of Micro-Nanolithography MEMS and MOEMS, 7 (2), 2008.
[Abstract]
Recently developed MEMS micromirror technology provides an opportunity to replace macroscale actuators for laser beamsteering in lidar and free-space optical communication systems. Precision modeling of mirror pointing and its dynamics are critical to the design of MEMS beamsteerers. Beam jitter ultimately limits MEMS mirror pointing, with consequences for bit error rate and overall optical system performance. Sources of jitter are platform vibration, control voltage noise, and Brownian motion noise. This work relates the random jitter of the mirror facet to its originating sources via a multidimensional first-order Taylor expansion of a first-principles-derived analytic expression for the actuating torque. The input torque, consisting of deterministic and stochastic components, is related to the 2-D jitter through a pair of coupled damped harmonic oscillator differential equations. The linearized 2-D jitter model for the mirror is simulated using Matlab, while the full nonlinear torque model was simulated using Simulink. The work describes an experimental setup and methodology that is used to make precise micromirror measurements. Experimental measurements are in agreement with the jitter model, i.e., the linearized model is able to predict mirror facet jitter based on the measured power spectral densities for the sources of jitter. c 2008 Society of Photo-Optical Instrumentation Engineers.
- A. Jahn, J. E. Reiner, W. N. Vreeland, D. L. DeVoe, L. E. Locascio, and M. Gaitan, "Preparation of nanoparticles by continuous-flow microfluidics," Journal of Nanoparticle Research, 10 (6), 925-934, 2008.
[Abstract]
We review a variety of micro- and nanoparticle formulations produced with microfluidic methods. A diverse variety of approaches to generate microscale and nanoscale particles has been reported. Here we emphasize the use of microfluidics, specifically microfluidic systems that operate in a continuous flow mode, thereby allowing continuous generation of desired particle formulations. The generation of semiconductor quantum dots, metal colloids, emulsions, and liposomes is considered. To emphasize the potential benefits of the continuous-flow microfluidic methodology for nanoparticle generation, preliminary data on the size distribution of liposomes formed using the microfluidic approach is compared to the traditional bulk alcohol injection method.
- L. P. Hromada, B. J. Nablo, J. J. Kasianowicz, M. A. Gaitan, and D. L. DeVoe, "Single molecule measurements within individual membrane-bound ion channels using a polymer-based bilayer lipid membrane chip," Lab on a Chip, 8 (4), 602-608, 2008.
[Abstract]
The measurement of single poly(ethylene glycol) (PEG) molecules interacting with individual bilayer lipid membrane-bound ion channels is presented. Measurements were performed within a polymer microfluidic system including an open-well bilayer lipid membrane formation site, integrated Ag/AgCl reference electrodes for on-chip electrical measurements, and multiple microchannels for independent ion channel and analyte delivery. Details of chip fabrication, bilayer membrane formation, and alpha-hemolysin ion channel incorporation are discussed, and measurements of interactions between the membrane-bound ion channels and single PEG molecules are presented.
- X. L. Luo, A. T. Lewandowski, H. M. Yi, G. F. Payne, R. Ghodssi, W. E. Bentley, and G. W. Rubloff, "Programmable assembly of a metabolic pathway enzyme in a pre-packaged reusable bioMEMS device," Lab on a Chip, 8 (3), 420-430, 2008.
[Abstract]
We report a biofunctionalization strategy for the assembly of catalytically active enzymes within a completely packaged bioMEMS device, through the programmed generation of electrical signals at spatially and temporally defined sites. The enzyme of a bacterial metabolic pathway, S-adenosylhomocysteine nucleosidase (Pfs), is genetically fused with a pentatyrosine "pro-tag" at its C-terminus. Signal responsive assembly is based on covalent conjugation of Pfs to the aminopolysaccharide, chitosan, upon biochemical activation of the pro-tag, followed by electrodeposition of the enzyme-chitosan conjugate onto readily addressable sites in microfluidic channels. Compared to traditional physical entrapment and surface immobilization approaches in microfluidic environments, our signal-guided electrochemical assembly is unique in that the enzymes are assembled under mild aqueous conditions with spatial and temporal programmability and orientational control. Significantly, the chitosan-mediated enzyme assembly can be reversed, making the bioMEMS reusable for repeated assembly and catalytic activity. Additionally, the assembled enzymes retain catalytic activity over multiple days, demonstrating enhanced enzyme stability. We envision that this assembly strategy can be applied to rebuild metabolic pathways in microfluidic environments for antimicrobial drug discovery.
- M. Urdaneta and E. Smela, "Parasitic trap cancellation using multiple frequency dielectrophoresis, demonstrated by loading cells into cages," Lab on a Chip, 8 (4), 550-556, 2008.
[Abstract]
This paper presents a method of using multiple frequencies to counteract electric field distortions that interfere with the dielectrophoretic (DEP) manipulation of particles or cells. To demonstrate the technique, simulations were performed for a scenario in which cells were to be loaded into a cage whose walls created parasitic trapping sites that prevented cells from entering it. By employing negative DEP on one electrode in conjunction with positive DEP on another, these traps could be almost completely cancelled. The model predictions were validated experimentally: multiple frequency DEP was used to load many cells into a cage in a matter of seconds in fluid flows of up to 300 mu m s(-1), which could not be done with single frequency DEP. Actively cancelling field distortions permits the presence of features that would otherwise be prohibited near regions of dielectrophoretic manipulation, significantly expanding the environments in which dielectrophoresis can be used.
- S. Yang, J. Liu, and D. L. DeVoe, "Optimization of sample transfer in two-dimensional microfluidic separation systems," Lab on a Chip, 8 (7), 1145-1152, 2008.
[Abstract]
Multidimensional microfluidic separation systems combining a first dimension microchannel with an array of parallel second dimension microchannels can suffer from non-uniform sample transfer between the dimensions, sample leakage, and injection plug tailing within the second dimension array. These factors can significantly reduce overall two-dimensional separation performance. In this paper, numerical and analytical models reveal an optimized chip design which combines multidimensional backbiasing and an angled channel geometry to ensure leakage-free and uniform interdimensional sample transfer, while also minimizing injected sample plug lengths. The optimized design is validated experimentally using a multidimensional chip containing five second dimension channels.
- E. Smela, "Conjugated polymer actuators," MRS Bulletin, 33 (3), 197-204, 2008.
[Abstract]
Conjugated polymer artificial muscles fill a unique niche in the electroactive polymer portfolio. They combine high strength, low voltage, and reasonable speed with versatile fabrication and design. This article reviews the actuation mechanism in these materials and presents some of the designs that have been developed for applications such as Braille displays, catheters, and bioMEMS devices.
- A. J. Dick, B. Balachandran, and C. D. Mote, "Intrinsic localized modes in microresonator arrays and their relationship to nonlinear vibration modes," Nonlinear Dynamics, 54 (1-2), 13-29, 2008.
[Abstract]
Intrinsic Localized Modes (ILMs) are defined as localizations due to strong intrinsic nonlinearity within an array of perfect, periodically repeating oscillators. Such nonlinear phenomena have been studied for a number of years in the solid-state physics literature. Energy can become localized at a specific location in a discrete system as a result of the nonlinearity of the system and not due to any defects or impurities within the considered systems. Here, such mode localization is studied in the context of microcantilever arrays and microresonator arrays, and it is explored if an ILM can be realized as a forced nonlinear normal mode or nonlinear vibration mode. The method of multiple scales and methods to construct nonlinear normal modes are used to study nonlinear vibrations of microresonator arrays. Investigations reported in this article suggest that it is possible to realize an ILM as a forced nonlinear vibration mode. These results are believed to be important for future designs of microresonator arrays intended for signal processing, communication, and sensor applications.
- S. T. Koev and R. Ghodssi, "Advanced interferometric profile measurements through refractive media," Review of Scientific Instruments, 79 (9), 2008.
[Abstract]
Optical profilers are valuable tools for the characterization of microelectromechanical systems (MEMSs). They use phase sifting interferometry (PSI) or vertical scanning interferometry to measure the topography of microscale structures with nanometer resolution. However, for many emerging MEMS applications, the sample needs to be imaged while placed in a liquid or in a package with a glass window. The increased refractive index of the transparent medium degrades the interference image contrast and prevents any measurement of the sample. We report on the modification of a Veeco NT1100 optical profiler to enable PSI measurements through refractive media. This approach can be applied to any other optical profiler with PSI capability. The modification consists in replacing the original illumination source with a custom-built narrow linewidth source, which increases the coherence length of the light and the contrast of the interference image. We present measurements taken with the modified configuration on samples covered with 3 mm water or 500 mu m glass, and we compare them to measurements of uncovered samples. We show that the measurement precision is only slightly reduced by the water and glass, and that it is still sufficiently high for typical MEMS applications. The described method can be readily used for measuring through other types and thicknesses of refractive materials. c 2008 American Institute of Physics. [DOI: 10.1063/1.2979006]
- L. J. Currano, S. Bauman, W. Churaman, M. Peckerar, J. Wienke, S. Kim, M. Yu, and B. Balachandran, "Latching ultra-low power MEMS shock sensors for acceleration monitoring," Sensors and Actuators A - Physical, 147 (2), 490-497, 2008.
[Abstract]
A microelectromechanical shock sensor, which uses a latching mechanism to record a shock event above a specified threshold level, is discussed in this article. The fabrication process for the shock sensor, which includes wafer-level vacuum packaging, is detailed along with the design features. These features include a reset actuator for reuse of the sensor, a no-power operation scheme when the reset actuator is not activated, and a control circuit to minimize power used to unlatch the sensor. In order to describe the shock-sensor dynamics and interaction with the latch mechanism, a preliminary non-linear model has been developed. Experimental results are presented and compared with model predictions. Published by Elsevier B.V.
- H. Li, B. Piekarski, D. L. DeVoe, and B. Balachandran, "Nonlinear oscillations of piezoelectric microresonators with curved cross-sections," Sensors and Actuators A - Physical, 144 (1), 194-200, 2008.
[Abstract]
Nonlinear oscillations of microelectromechanical resonators with curved cross-sections are studied in this effort. The resonators are fabricated as clamped-clamped composite structures, and these structures have both lengthwise and widthwise curvatures induced by residual stresses. Harmonic piezoelectric actuations of these structures were considered in experiments and the spatial responses of these structures were studied. The spatial responses observed for different resonance excitations could not be explained by a previous model of these composite microresonators, where stepwise non-uniform properties along the length and rectangular cross-sections were considered. Here, a curved cross-section model is adopted to refine the previous model and the resulting predictions are found to compare better with the experimental observations. The results show that the cross-section curvature significantly affects the structural stiffness and response, and this is important to consider in system modeling. Published by Elsevier B.V.
- S. B. Prakasha, M. Urdaneta, M. Christophersen, E. Smela, and P. Abshire, "In situ electrochemical control of electroactive polymer films on a CMOS chip," Sensors and Actuators B - Chemical
129 (2), 699-704, 2008.
[Abstract]
The paper reports, for the first time, an integrated potentiostat for driving electrochemical actuation reactions on a CMOS chip. The integrated microsystem comprised on-chip working, counter, and quasi-reference electrodes fabricated on top of the necessary control circuitry. To demonstrate its capability, the potentiostat chip was used to electrodeposit films of polypyrrole/dodecylbenzenesulfonate, PPy(DBS), in situ onto the working electrodes. It was also used to cycle PPy(DBS) films between the fully oxidized and fully reduced states. This was confirmed by video recordings of the distinctive electrochromic changes, as well as by the shapes of the cyclic voltammograms. Both showed good repeatability. The demonstrated approach of integrating driver circuitry along with actuation electrodes on a common CMOS substrate eliminates the need for an external potentiostat instrument, and can be widely employed for the fabrication and control of electrochemical microactuators in integrated lab-on-a-chip systems. (C) 2007 Elsevier B.V. All rights reserved.
- G. M. Yang, I. M. White, and X. D. Fan, "An opto-fluidic ring resonator biosensor for the detection of organophosphorus pesticides," Sensors and Actuators B - Chemical
133 (1), 105-112, 2008.
[Abstract]
We developed a novel label-free opto-fluidic ring resonator (OFRR) biosensor for detection of an organophosphorus (OP) pesticide. The OFRR is based on a micro-sized glass capillary whose circular wall forms a ring resonator that supports the whispering gallery modes (WGMs). The WGMs has an evanescent field in the capillary core and interacts with the analyte flowing in the capillary. We used parathion-methyl as a model system to investigate the OFRR sensing performance in terms of bulk refractive index sensitivity, surface activation for affinity property, detection limit, and reproducibility. The performance of the OFRR was further compared with that of the Biacore 3000 SPR system. Our results show that the detection limit of 3.8 x 10(-11) M for parathion-methyl was achieved with an analysis time of about 0.5 min, 10 times faster than the surface plasmon resonance (SPR) system. Furthermore, the OFRR biosensor demonstrated excellent reproducibility (R.S.D. = 3.5%, n = 5). The OFRR offers optical label-free detection mechanism with integrated microfluidics. It is a promising technology platform for development of portable multi-channel biosensors with high sensitivity, quick detection time, and sub-nanoliter detection volume. (C) 2008 Elsevier B.V. All rights reserved.
- H. Y. Zhu, I. M. White, J. D. Suter, M. Zourob, and X. D. Fan, "Integrated refractive index optical ring resonator detector for capillary electrophoresis," Analytical Chemistry, 79 (3), 930-937, 2007.
[Abstract]
We developed a novel miniaturized and multiplexed, on-capillary, refractive index (RI) detector using liquid core optical ring resonators (LCORRs) for future development of capillary electrophoresis (CE) devices. The LCORR employs a glass capillary with a diameter of similar to 100 mu m and a wall thickness of a few micrometers. The circular cross section of the capillary forms a ring resonator along which the light circulates in the form of the whispering gallery modes (WGMs). The WGM has an evanescent field extending into the capillary core and responds to the RI change due to the analyte conducted in the capillary, thus permitting label-free measurement. The resonating nature of the WGM enables repetitive light-analyte interaction, significantly enhancing the LCORR sensitivity. This LCORR architecture achieves dual use of the capillary as a sensor head and a CE fluidic channel, allowing for integrated, multiplexed, and noninvasive on-capillary detection at any location along the capillary. In this work, we used electro-osmotic flow and glycerol as a model system to demonstrate the fluid transport capability of the LCORRs. In addition, we performed flow speed measurement on the LCORR to demonstrate its flow analysis capability. Finally, using the LCORR's label-free sensing mechanism, we accurately deduced the analyte concentration in real time at a given point on the capillary. A sensitivity of 20 nm/RIU (refractive index units) was observed, leading to an RI detection limit of 10(-6) RIU. The LCORR marries photonic technology with microfluidics and enables rapid on-capillary sample analysis and flow profile monitoring. The investigation in this regard will open a door to novel high-throughput CE devices and lab-on-a-chip sensors in the future.
- P. Kumar, S. Kanakaraju, and D. L. Devoe, "Sacrificial etching of AlxGa1-xAs for III-V MEMS surface micromachining," Applied Physics A, 88 (4), 711-714, 2007.
[Abstract]
A study of AlxGa1-xAs as a sacrificial film for surface micromachining is presented. AlxGa1-xAs etch rate and selectivity are measured over a range of aluminum mole fractions and HF etchant concentrations during the release of structural features up to 500 mu m in width. The etch process is found to be diffusion limited, with an inverse power law relationship between etch depth and etch rate. Excellent selectivity greater than 10(5) stop is achieved between sacrificial AlAs and structural GaAs, even for long etches up to 250 mu m in length. Compared with previous studies of AlxGa1-xAs etching for epitaxial liftoff processing, measured etch rates for surface micromachining are approximately an order of magnitude lower, primarily due to the longer effective etch lengths required. However, unlike epitaxial liftoff, AlxGa1-xAs surface micromachining is compatible with higher HF concentrations which can provide comparable overall etch rates, with important implications for AlGaAs MEMS fabrication.
- I. M. White, J. Gohring, Y. Sun, G. Yang, S. Lacey, and X. Fan, "Versatile waveguide-coupled optofluidic devices based on liquid core optical ring resonators," Applied Physics Letters, 91 (24), 2007.
[Abstract]
A versatile waveguide-coupled optofluidic device using the liquid core optical ring resonator (LCORR) that can be operated with liquid of any refractive index (RI) is theoretically analyzed and experimentally demonstrated. The results confirm the confinement of resonant modes for all sample RIs, and reveal that confined modes in a high-RI core are excited by an external waveguide by resonant tunneling through the LCORR wall. It is further found that a thin wall must be used for effective interaction between the core mode and the waveguide. The results have important applications in optofluidic devices, including sensors, microfluidic lasers, and nonlinear optics. (C) 2007 American Institute of Physics.
- W. M. Zhu, T. Zhong, A. Q. Liu, X. M. Zhang, and M. Yu, "Micromachined optical well structure for thermo-optic switching," Applied Physics Letters, 91 (26), 2007.
[Abstract]
This letter demonstrates the thermo-optic switching function using an adjustable optical well structure, which is constructed by a thin air gap sandwiched between two micromachined hemicylindrical prisms. The device is etched on a silicon-on-insulator wafer within a footprint of 400x400 mu m(2). In experiment, it measures an extinction ratio of 30.2 dB and a switching time of 2.2 mu s. Compared with the other demonstrated switches that have optical barrier structures, this device is unique in the working principle and optical design, and shows various merits such as high extinction ratio, fast speed, low power consumption, and small size. (c) 2007 American Institute of Physics.
- J. C. Marshall, D. L. Herman, P. T. Vernier, D. L. DeVoe, and M. Gaitan, "Young's modulus measurements in standard ICCMOS processes using MEMS test structures," IEEE Electron Device Letters, 28 (11), 960-963, 2007.
[Abstract]
This letter(1) presents a method to measure the Young's moduli of individual thin-film layers in a commercial integrated circuit (IC) foundry process. The method is based on measuring the resonance frequency of an array of micromachined cantilevers and using the presented optimization analysis to determine the elastic modulus of each layer. Arrays of cantilever test structures were fabricated in a commercial CMOS IC process and were released using XeF2 as a postprocessing etch. A piezoelectric transducer placed under the test chip was used to excite the cantilevers to resonance, and the resonance frequency was measured using a laser Doppler vibrometer. It is reported that excellent agreement for values of Young's modulus is observed for cantilevers between 200 and 400 pm in length, with average standard deviation being 4.07 GPa.
- I. M. White, H. Y. Zhu, J. D. Suter, N. M. Hanumegowda, H. Oveys, M. Zourob, and X. D. Fan, "Refractometric sensors for lab-on-a-chip based on optical. ring resonators," IEEE Sensors Journal, 7 (1-2), 28-35, 2007.
[Abstract]
We demonstrate refractive index measurement of liquids using two sensor system designs, both based on microring resonators. Evanescent sensors based on microrings utilize the resonating nature of the light to dramatically decrease the required size and sample consumption volume, which are requirements of lab-on-a-chip sensor systems. The first design, which utilizes an optical microsphere, exhibits a sensitivity of 30 nm/RIU and a resulting detection limit on the order of 10(-7) RIU. The second approach is a novel design called a liquid core optical ring resonator (LCORR). This concept uses a quartz capillary as the fluidics and as the ring resonator and achieves a sensitivity of 16.1 nm/RIU. The detection limit of this system is around 5 x 10(-6) RIU. Both of these systems have the potential to be incorporated with advanced microfluidic systems for lab-on-a-chip applications. In particular, the LCORR combines high sensitivity, performance stability, and microfluidic compatibility, making it an excellent choice for lab-on-a-chip development.
- K. Deng, P. Kumar, L. Li, and D. L. DeVoe, "Piezoelectric disk resonators based on epitaxial AlGaAs films," Journal of Microelectromechanical Systems, 16 (1), 155-162, 2007.
[Abstract]
A new design for anisotropic piezoelectric disk resonators is demonstrated using single-crystal Al0.3Ga0.7As films. The shape of the disk resonator is based on the velocity propagation profile of the elastic wave in the plane of the piezoelectric film, with lateral dimensions scaled to the half wavelength of the desired resonance frequency. The resonators are designed with supports which emulate free-free boundary conditions. Prototype resonators are fabricated using a three-layer Al0.3Ga0.7As heterostructure containing silicon-doped electrodes and an undoped piezoelectric Al0.3Ga0.7As layer. Quality factors as high as 11200 are measured in air for a 23.25 MHz fundamental resonant mode, with a corresponding motional resistance of 1.67 k Omega. A finite-element model for the resonator design is also described. Simulation results agree well with both theoretical calculations and experimental data.
- S. Moghaddam, K. T. Kiger, A. Modafe, and R. Ghodssi, "A novel benzocyclobutene-based device for studying the dynamics of heat transfer during the nucleation process," Journal of Microelectromechanical Systems, 16 (6), 1355-1366, 2007.
[Abstract]
A novel microelectromechanical device has been developed to study the details of the heat transfer mechanisms involved at the nucleation site for the nucleate boiling process. This device enables quantifying the magnitude, time period of activation, and specific areas of influence of different mechanisms of heat transfer from the surface with a resolution several times greater than previously reported. This is achieved through the use of an array of embedded temperature sensors within a carefully designed dual-layer (silicon and benzocyclobutene) wall which allows for the accurate calculation of local heat flux, circumventing difficulties encountered when using existing methods. The sensors are radially distributed around the nucleation site. Heat is supplied to the wall by a thin film heater fabricated on the outer nonwetted surface. Single bubbles are generated at the center of the array while the temperatures and the bubble images are recorded with a sampling frequency of 8 kHz. The temperature data provided the necessary thermal boundary conditions to numerically calculate the surface heat flux with an unprecedented radial resolution of 22-40 mu m. Fabrication, characterization, and the ability of the developed device to elucidate the heat transfer aspects of the nucleation process are demonstrated.
- B. Morgan, J. McGee, and R. Ghodssi, "Automated two-axes optical fiber alignment using grayscale technology," Journal of Microelectromechanical Systems, 16 (1), 102-110, 2007.
[Abstract]
In this paper, we report a new method for actuating an optical fiber in two axes. This device enables in package active alignment of an optical fiber towards reducing the time and cost of optoelectronic packaging by eliminating the need for expensive and slow macroalignment machines. Opposing comb-drive actuators with integrated three-dimensional (3-D) wedges (fabricated using grayscale technology) create a dynamic v-groove to alter the horizontal and vertical alignment of an optical fiber cantilever. All structural components are fabricated in silicon using a single lithography and dry-etching step, making the system conducive to batch fabrication, an essential element to minimize the cost of including in-package alignment capabilities. Actuation of a cleaved fiber tip greater than 30 mu m in each direction is demonstrated, with automated fiber alignment times on the order of 10 s, comparable to those achieved using macroalignment systems. Alignment tolerances are held below 1.25 mu m over a 20-by-20-mu m actuation area for the first time. The influences of alignment target location, actuation parameters, and alignment algorithm on total alignment time are also presented.
- D. Yashar, P. A. Domanski, and D. L. DeVoe, "A microfabricated flow controller for refrigerant expansion," Journal of Microelectromechanical Systems, 16 (5), 1106-1112, 2007.
[Abstract]
A flow controller for refrigerant expansion is reported. Devices are fabricated using a micromolding technique that is developed for thick nickel electrodeposition. The device consists of a short-tube restrictor with an integrated normally open valve, which, when actuated, presents a controllable blockage into the flow passage to obstruct the flow. Fabricated devices are evaluated with compressed air, with up to 22% reduction in mass flow rate at maximum actuation of the restrictor. The devices are also evaluated in an R134a vapor compression system of 1.5-2 kW, with the ability to control mass flow that is found to be greatly influenced by the vapor compression cycle's operational parameters. After the inlet pressure, the level of subcooling proved to be the most important parameter. For a cycle operating between 29 degrees C and 4 degrees C, saturation temperatures in the condenser and evaporator, respectively, actuation of the device reduced the refrigerant mass flow rate by 3.5 % with 0.6 degrees C subcooling and up to 10.8% with 5 degrees C subcooling.
- W. H. Chuang, R. K. Fettig, and R. Ghodssi, "Nano-scale fatigue study of LPCVD silicon nitride thin films using a mechanical-amplifier actuator," Journal of Micromechanics and Microengineering, 17 (5), 938-944, 2007.
[Abstract]
This paper describes a nano-scale tensile test to study the fatigue properties of LPCVD silicon nitride thin films using a novel electrostatic actuator design. Mechanical-amplifier devices made in silicon nitride thin films can apply controllable tensile stress (2.0-7.8 GPa) to test structures with relatively low actuation voltages (5.7-35.4 V-RMS) at the resonant frequencies of the devices. The test devices are fabricated using a surface micromachining technique in combination with deep reactive ion etching and ion milling. With the recently developed experimental techniques inside a focused-ion-beam system, in situ fatigue measurements are performed on silicon nitride test structures with beam widths of 200 nm. The silicon nitride test structures are found to exhibit time-delayed failures with continuous increases in their compliance. By reducing the applied tensile stress to 3.8 GPa, the test structures can survive cyclic loadings up to 10(8) cycles.
- C. M. Waits, B. Geil, and R. Ghodssi, "Encapsulated ball bearings for rotary micro machines," Journal of Micromechanics and Microengineering, 17 (9), S224-S229, 2007.
[Abstract]
We report on the first encapsulated rotary ball bearing mechanism using silicon microfabrication and stainless steel balls. The method of capturing stainless steel balls within a silicon race to support a silicon rotor both axially and radially is developed for rotary micro machines and MEMS ball bearing tribology studies. Initial demonstrations show speeds up to 6.8 krpm without lubrication, while speeds up to 15.6 krpm with lubrication are possible. Qualitative analysis is used to explain start-up behavior and investigate the wear of the stainless steel ball and silicon race.
- C. L. Edwards, B. G. Boone, W. S. Levine, and C. C. Davis, "Analytic torque model for two-axis microelectromechanical system mirrors," Journal of Micro-Nanolithography MEMS and MOEMS, 6 (4), 2007.
[Abstract]
The availability of recently developed microelectromechanical system (MEMS) micro-mirror technology provides an opportunity to replace macroscale actuators for free-space laser beam steering in light detection and ranging and communication systems. Precision modeling of mirror pointing and its dynamics are critical to the design and control of MEMS beam steerers. Beginning with Hornbeck's torque approach, we present a first-principles, analytically closed-form torque model for an electrostatically actuated two-axis (tip-tilt) MEMS mirror structure. The torque expression is a function of the mirror's physical parameters, such as angles, voltages, and size. An Euler dynamic equation formulation describes the gimballed motion as a pair of damped harmonic oscillators with a coupled torsion function. Static physical parameters such as MEMS mirror dimensions and voltages are inputs to the model as well as dynamic harmonic oscillator parameters, such as damping and restoring constants, which are calculated or fitted to measurements. A Taylor series expansion of the torque function provides insights into MEMS behavior, including operational sensitivities near "pull-in." MATLAB and SIMULINK simulations illustrate performance sensitivities, controllability, physical limitations, and other important considerations in the design of precise pointing systems. Commercial-off-the-shelf micromirror measurements confirm the model's validity in steady state and dynamic scanning operations. (C) 2007 Society of Photo-Optical Instrumentation Engineers.
- Y. Liu, Q. Gan, S. Baig, and E. Smela, "Improving PPy adhesion by surface roughening," Journal of Physical Chemistry C, 111 (30), 11329-11338, 2007.
[Abstract]
Conjugated polymers have found applications as "artificial muscles" because they undergo significant volume change upon electrochemical cycling. However, this large repeated strain also leads them to delaminate from the underlying electrode. Two methods of improving the adhesion of polypyrrole films to Au electrodes during extended electrochemical cycling were quantitatively characterized. Both involved roughening the Au surface, the first by electroplating and the second by etching. The extent of delamination was quantified using a tape test at regular intervals during switching between the fully oxidized and reduced states in an aqueous electrolyte, and the surfaces were characterized by scanning electron microscopy. Untreated smooth control surfaces were simultaneously monitored the same way. Without surface treatment, 3000 angstrom thick polypyrrole films doped with dodecylbenzenesulfonate, PPy( DBS), delaminated unpredictably between 1 cycle and 20 000 cycles, with almost half the samples failing before 3000 cycles. Electroplating even a thin layer of 1000 angstrom of Au in a low-concentration plating bath consistently improved lifetimes to at least 10 000 cycles. Thicker plating produced even better adhesion, and a 1 Am thick layer of electroplated Au virtually eliminated delamination, extending the lifetime beyond 60 000 cycles. However, this Au roughness is thicker than the PPy film itself, and is not useful for microactuator work. Etching also improved adhesion, with the best results obtained for the shortest etch times. With a roughness of only 700 angstrom, an undercut surface morphology was produced that allowed good mechanical interlocking of the PPy. This process is appropriate for use with thin films; however, it will be sensitive to the grain structure of the original Au film. On surfaces with no delamination, it was possible to measure the oxidative degradation of the PPy( DBS) in the aqueous electrolyte. The electroactivity decreased steadily over time, with 20% loss after 10 000 cycles, 50% at 35 000, and virtually no electroactivity by 60 000 cycles.
- M. Dandin, P. Abshire, and E. Smela, "Optical filtering technologies for integrated fluorescence sensors," Lab on a Chip, 7 (8), 955-977, 2007.
[Abstract]
Numerous approaches have been taken to miniaturizing fluorescence sensing, which is a key capability for micro-total-analysis systems. This critical, comprehensive review focuses on the optical hardware required to attenuate excitation light while transmitting fluorescence. It summarizes, evaluates, and compares the various technologies, including filtering approaches such as interference filters and absorption filters and filterless approaches such as multicolor sensors and light-guiding elements. It presents the physical principles behind the different architectures, the state-of-the-art micro-fluorometers and how they were microfabricated, and their performance metrics. Promising technologies that have not yet been integrated are also described. This information will permit the identification of methods that meet particular design requirements, from both performance and integration perspectives, and the recognition of the remaining technological challenges. Finally, a set of performance metrics are proposed for evaluating and reporting spectral discrimination characteristics of integrated devices in order to promote side-by-side comparisons among diverse technologies and, ultimately, to facilitate optimized designs of micro-fluorometers for specific applications.
- S. T. Koev, M. A. Powers, H. Yi, L. Q. Wu, W. E. Bentley, G. W. Rubloff, G. F. Payne, and R. Ghodssi, "Mechano-transduction of DNA hybridization and dopamine oxidation through electrodeposited chitosan network," Lab on a Chip, 7 (1), 103-111, 2007.
[Abstract]
While microcantilevers offer exciting opportunities for mechano-detection, they often suffer from limitations in either sensitivity or selectivity. To address these limitations, we electrodeposited a chitosan film onto a cantilever surface and mechano-transduced detection events through the chitosan network. Our first demonstration was the detection of nucleic acid hybridization. In this instance, we electrodeposited the chitosan film onto the cantilever, biofunctionalized the film with oligonucleotide probe, and detected target DNA hybridization by cantilever bending in solution (static mode) or resonant frequency shifts in air (dynamic mode). In both detection modes, we observed a two-order of magnitude increase in sensitivity compared to values reported in literature for DNA immobilized on self-assembled monolayers. In our second demonstration, we coupled electrochemical and mechanical modes to selectively detect the neurotransmitter dopamine. A chitosan-coated cantilever was biased to electrochemically oxidize dopamine solution. Dopamine's oxidation products react with the chitosan film and create a tensile stress of approximately 1.7 MPa, causing substantial cantilever bending. A control experiment was performed with ascorbic acid solution. It was shown that the electrochemical oxidation of ascorbic acid does not lead to reactions with chitosan and does not change cantilever bending. These results suggest that chitosan can confer increased sensitivity and selectivity to microcantilever sensors.
- C. W. Tsao, L. Hromada, J. Liu, P. Kumar, and D. L. DeVoe, "Low temperature bonding of PMMA and COC microfluidic substrates using UV/ozone surface treatment," Lab on a Chip, 7 (4), 499-505, 2007.
[Abstract]
The use of UV/ozone surface treatments for achieving low temperature bonds between PMMA and COC microfluidic substrates is evaluated. Low temperature bond strengths, approaching those of native polymer substrates bonded above their glass transition temperatures, are demonstrated for both thermoplastics. To evaluate the effects of the UV/O-3 surface treatment on the operation of bonded microfluidic devices, the relationship between UV/O-3 exposure and polymer hydrophilicity and surface chemistry are measured. Post-treatment surface chemistry is evaluated by XPS(X-ray photoelectron spectroscopy) analysis, and the stability of the treated surfaces following solvent exposure is reported. Electroosmotic flow within fabricated microchannels with modified wall surfaces is also characterized. Overall, UV/O-3 treatment is found to enable strong low temperature bonds between thermoplastic microfluidic substrates using a simple, low cost, and high throughput fabrication technology.
- A. Jahn, W. N. Vreeland, D. L. DeVoe, L. E. Locascio, and M. Gaitan, "Microfluidic directed formation of liposomes of controlled size," Langmuir, 23 (11), 6289-6293, 2007.
[Abstract]
A new method to tailor liposome size and size distribution in a microfluidic format is presented. Liposomes are spherical structures formed from lipid bilayers that are from tens of nanometers to several micrometers in diameter. Liposome size and size distribution are tailored for a particular application and are inherently important for in vivo applications such as drug delivery and transfection across nuclear membranes in gene therapy. Traditional laboratory methods for liposome preparation require postprocessing steps, such as sonication or membrane extrusion, to yield formulations of appropriate size. Here we describe a method to engineer liposomes of a particular size and size distribution by changing the flow conditions in a microfluidic channel, obviating the need for postprocessing. A stream of lipids dissolved in alcohol is hydrodynamically focused between two sheathed aqueous streams in a microfluidic channel. The laminar flow in the microchannel enables controlled diffusive mixing at the two liquid interfaces where the lipids self-assemble into vesicles. The liposomes formed by this self-assembly process are characterized using asymmetric flow field-flow fractionation combined with quasi-elastic light scattering and multiangle laser-light scattering. We observe that the vesicle size and size distribution are tunable over a mean diameter from 50 to 150 nm by adjusting the ratio of the alcohol-to-aqueous volumetric flow rate. We also observe that liposome formation depends more strongly on the focused alcohol stream width and its diffusive mixing with the aqueous stream than on the sheer forces at the solvent-buffer interface.
- C. Zhu, L. Q. Wu, X. Wang, J. H. Lee, D. S. English, R. Ghodssi, S. R. Raghavan, and G. F. Payne, "Reversible vesicle restraint in response to spatiotemporally controlled electrical signals: A bridge between electrical and chemical signaling modes," Langmuir, 23 (1), 286-291, 2007.
[Abstract]
Microelectronic devices employ electrons for signaling whereas the nervous system signals using ions and chemicals. Bridging these signaling differences would benefit applications that range from biosensing to neuroprosthetics. Here, we report the use of localized electrical signals to perform an operation common to chemical signaling in the nervous system. Specifically, we employ electrical signals to restrain vesicles reversibly. We perform this operation using the stimuli-responsive aminopolysaccharide chitosan that is able to electrodeposit onto cathode surfaces in response to localized electrical stimuli. We show that surfactant-vesicles and liposomes can be co-deposited with chitosan and are entrapped (i.e., restrained) within the deposited film's matrix. Vesicle co-deposition could be controlled spatially and temporally using microfabricated wafers with independent electrode addresses. Finally, we show that vesicles restrained within the deposited chitosan matrix can be mobilized under mildly acidic conditions (pH < 6.5) that resolubilize chitosan. Potentially, the ability to restrain and mobilize chemical signals that are segregated within vesicles may allow microfluidic systems to access the rich diversity offered by chemical signaling.
- S. Lacey, I. M. White, Y. Sun, S. I. Shopova, J. M. Cupps, P. Zhang, and X. D. Fan, "Versatile opto-fluidic ring resonator lasers with ultra-low threshold," Optics Express, 15 (23), 15523-15530, 2007.
[Abstract]
We develop a versatile integrated opto- fluidic ring resonator (OFRR) dye laser that can be operated regardless of the refractive index (RI) of the liquid. The OFRR is a micro-sized glass capillary with a wall thickness of a few micrometers. When the liquid in the core has an RI lower than that of the capillary wall (n= 1.45), the capillary circular cross- section forms the ring resonator and supports the whispering gallery modes (WGMs) that interact evanescently with the gain medium in the core. When the core RI is higher than that of the wall, the WGMs exist at the core/ wall interface. In both cases, the WGMs can have extremely high Q-factor (> 10(9)), providing excellent optical feedback for low- threshold lasing. In this paper, we analyze the OFRR laser for various core RI's and then we demonstrate the R6G laser when the dye is in ethanol ( n= 1.36), chloroform (n= 1.445), and quinoline (n= 1.626). The lasing threshold of 25 nJ/ mm(2) is achieved, two to three orders of magnitude lower than the previous work in microfluidic lasers. We further show that the laser emission can be efficiently out- coupled via an optical waveguide in touch with the OFRR for both high and low RI liquid core, allowing for easy guiding and delivery of the laser light. (c) 2007 Optical Society of America.
- I. M. White, J. Gohring, and X. D. Fan, "SERS-based detection in an optofluidic ring resonator platform," Optics Express, 15 (25), 17433-17442, 2007.
[Abstract]
The development of surface enhanced Raman scattering (SERS) detection has made Raman spectroscopy relevant for highly sensitive lab-on-a-chip bio/chemical sensors. Despite the tremendous benefit in specificity that a Raman-based sensor can deliver, development of a lab-on-a-chip SERS tool has been limited thus far. In this work, we utilize an optofluidic ring resonator (OFRR) platform to develop a SERS-based detection tool with integrated microfluidics. The liquid core optical ring resonator (LCORR) serves both as the microfluidic sample delivery mechanism and as a ring resonator, exciting the metal nanoclusters and target analytes as they pass through the channel. Using this OFRR approach and R6G as the analyte, we have achieved a measured detection limit of 400 pM. The measured Raman signal in this case is likely generated by only a few hundred R6G molecules, which foreshadows the development of a SERS-based lab-on-a-chip bio/chemical sensor capable of detecting a low number of target analyte molecules. (c) 2007 Optical Society of America.
- N. Ghalichechian, A. Modafe, J. H. Lang, and R. Ghodssi, "Dynamic characterization of a linear electrostatic micromotor supported on microball bearings," Sensors and Actuators A - Physical, 136 (2), 496-503, 2007.
[Abstract]
We report the dynamic characterization of a six-phase, bottom-drive, linear, variable-capacitance micromotor (B-LVCM) supported on microball bearings. The B-LVCM was fabricated and tested using a new test-bed. The motion of the micromotor was captured using low- and high-speed video cameras, tracked using image processing software, and analyzed to obtain the instantaneous velocity (11 mm/s), acceleration (1.9 m/s(2)), and net force (0.19 mN) (all in amplitude) from the position data. The predicted (simulated) and measured net forces at different applied voltages are in good agreement. The micromotor was then modeled as a mass-spring-dashpot system and the lumped parameters were extracted from position measurement. This characterization methodology provides an understanding of the dynamic behavior of both the variable-capacitance micromachines and the microball bearings on which they are supported. (C) 2006 Elsevier B.V. All rights reserved.
- S. Li, J. C. Day, J. J. Park, C. P. Cadou, and R. Ghodssi, "A fast-response microfluidic gas concentrating device for environmental sensing," Sensors and Actuators A - Physical, 136 (1), 69-79, 2007.
[Abstract]
This paper describes the design, fabrication and characterization of a microfluidic gas centrifuge for separating dilute gas mixtures based on the molecular weights of their constituents. The principal advantage of this approach is its fast response time compared to other methods that are based on permeation or adsorption/desorption. This would allow it to serve as a real-time preconcentrator for improving the sensitivity of miniature chemical sensors. Devices with nozzle throat widths as small as 3.6 Rm have been fabricated using photolithography, deep reactive ion etching (DRIE) and silicon-glass anodic bonding. Measurements of the device's performance show that a single stage can achieve a two-fold enrichment of an initially 1% mixture of SF6 in N-2 in 0.01 ms. These experimental findings are consistent with the results of two-dimensional numerical simulations of the flow through the device. The simulations suggest that the performance of a single stage could be improved significantly by changing the geometry of the entrance flow. Further improvements in performance could be achieved by cascading the devices. (C) 2006 Elsevier B.V. All rights reserved.
- L. Zhu, D. Meier, Z. Boger, C. Montgomery, S. Semancik, and D. L. DeVoe, "Integrated microfluidic gas sensor for detection of volatile organic compounds in water," Sensors and Actuators B - Chemical
121 (2), 679-688, 2007.
[Abstract]
A polymer microfluidic system for monitoring of volatile organic compounds diluted in water is presented. The sensor platform employs silicon-based microhotplate gas sensors as active detection elements, using a silicon-in-plastic microfabrication technology to enable integration of individual sensor chips into a larger polymer microfluidic substrate. The fabrication process provides seamless fluidic and electrical interconnects between the silicon and polymer substrates. The chemical monitoring system is designed to sample a water source, extract solvent present within the aqueous sample into the vapor phase, and direct the solvent vapor past the integrated gas sensor for analysis. Design, fabrication, and characterization of a prototype system is described, and results from illustrative measurements performed using methanol, toluene, and 1,2-dichloroethane in water are presented. (c) 2006 Elsevier B.V. All rights reserved.
- G. F. Payne and S. R. Raghavan, "Chitosan: a soft interconnect for hierarchical assembly of nano-scale components," Soft Matter, 3 (5), 521-527, 2007.
[Abstract]
Traditional microfabrication has tremendous capabilities for imparting order to hard materials (e.g., silicon wafers) over a range of length scales. However, conventional microfabrication does not provide the means to assemble pre-formed nano-scale components into higher-ordered structures. We believe the aminopolysaccharide chitosan possesses a unique set of properties that enable it to serve as a length-scale interconnect for the hierarchical assembly of nano-scale components into macro-scale systems. The primary amines (atomic length scale) of the glucosamine repeating units (molecular length scale) provide sites to connect pre-formed or self-assembled nano-scale components to the polysaccharide backbone (macromolecular length scale). Connections to the backbone can be formed by exploiting the electrostatic, nucleophilic, or metal-binding capabilities of the glucosamine residues. Chitosan's film-forming properties provide the means for assembly at micron-to-centimetre lengths (supramolecular length scales). In addition to interconnecting length scales, chitosan's capabilities may also be uniquely-suited as a soft component-hard device interconnect. In particular, chitosan's film formation can be induced under mild aqueous conditions in response to localized electrical signals that can be imposed from microfabricated surfaces. This capability allows chitosan to assemble soft nano-scale components (e.g., proteins, vesicles, and virus particles) at specific electrode addresses on chips and in microfluidic devices. Thus, we envision the potential that chitosan may emerge as an integral material for soft matter (bio) fabrication.
- D. L. DeVoe and C. S. Lee, "Microfluidic technologies for MALDI-MS in proteomics," Electrophoresis, 27 (18), 3559-3568, 2006.
[Abstract]
The field of microfluidics continues to offer great promise as an enabling technology for advanced analytical tools. For biomolecular analysis, there is often a critical need to couple on-chip microfluidic sample manipulation with back-end MS. Though interfacing microfluidics to MS has been most often reported through the use of direct ESI-MS, there are compelling reasons for coupling microfluidics to MALDI-MS as an alternative to ESI-MS for both online and offline analysis. The intent of this review is to provide a summary of recent developments in the integration of microfluidic systems with MALDI-MS, with an emphasis on applications in proteomics. Key points are summarized, followed by a review of relevant technologies and a discussion of outlook for the field.
- S. Chaudhary and B. Shapiro, "Arbitrary steering of multiple particles independently in an electro-osmotically driven microfluidic system," IEEE Transactions on Control Systems Technology, 14 (4), 669-680, 2006.
[Abstract]
We demonstrate how to use feedback control of microflows to steer multiple particles independently in planar microfluidic systems driven by electro-osmotic actuation. This technique enables the handling of biological materials, such as cells, bacteria, DNA, and drug packets, in a hand-held format using simple and easy-to-fabricate actuators. The feedback loop consists of a vision system which identifies the positions of the particles in real-time, a control algorithm that computes the actuator (electrode) inputs based on information received from the vision system, and a set of electrodes (actuators) that create the required flow through electro-osmotic forces to steer all the particles along their desired trajectories and correct for particle position errors and thermal noise. Here, we focus on the development of control algorithms to achieve the steering of particles: vision system implementation, fabrication of devices, and experimental validation is addressed in other publications. In particular, steering of a single (yeast cell) particle has been demonstrated experimentally in our prior research and we have recently demonstrated experimental steering of three particles independently. In this paper, we develop the control algorithms for steering multiple particles independently and we validate our control techniques using simulations with realistic sources of initial position errors and thermal noise. In this study, we assume perfect measurement and actuation.
- X. B. Tan, A. Modafe, and R. Ghodssi, "Measurement and modeling of dynamic rolling friction in linear microball bearings," Journal of Dynamic Systems Measurement and Control-Transactions of the Asme, 128 (4), 891-898, 2006.
[Abstract]
In prior work of the authors and co-workers, a vision-based system was developed for characterizing the tribological behavior of silicon-micromachined linear microball bearings. Plain difference methods introduce amplitude and/or phase distortion in computing the derivative signals (e.g., velocity and acceleration) based on the position snapshots. In this paper frequency-dependent amplitude and phase compensation algorithms are developed for both the forward difference and the central difference methods to retrieve without distortion the friction and the relative velocity between bearing elements. Processing of experimental data with these techniques reveals nonlinear viscous frictional behavior in the bearing. A viscoelastic model based on a continuum of mass-spring-damper elements is then proposed for the ball-groove interaction. Numerical results show that this model captures the nonlinear velocity dependence of the rolling friction observed in experiments.
- N. Sergeev, M. Distler, M. Vargas, V. Chizhikov, K. E. Herold, and A. Rasooly, "Microarray analysis of Bacillus cereus group virulence factors," Journal of Microbiological Methods, 65 (3), 488-502, 2006.
[Abstract]
Bacillus cereus, B. thuringiensis and B. anthracis are closely related medically and economically important bacterial species that belong to the B. cereus group. Members of the B. cereus group carry genes encoding several important virulence factors, including enterotoxins, phospholipases and exotoxins. Since it is difficult to differentiate among B. cereus group members, and because Bacillus virulence factors are very important for pathogenesis, we explored the use of microarray-based detection of virulence factor genes as a tool for strain identification and for determining virulence. Our method requires an initial multiplex PCR amplification step, followed by identification of the PCR amplicons by hybridization to an oligonucleotide microarray containing genes for all three types of Bacillus virulence factors including B. anthracis virulence factors. The DNA chip described here contains 21 identical arrays used for analysis of seven samples in triplicates. Using the arrays, we found that virulence factors are present in several combinations in the strains analyzed. This work also demonstrates the potential of oligonucleotide microarrays for medical, food safety and biodefense analysis of microbial pathogens. Published by Elsevier B.V.
- M. D. Armani, S. V. Chaudhary, R. Probst, and B. Shapiro, "Using feedback control of microflows to independently steer multiple particles," Journal of Microelectromechanical Systems, 15 (4), 945-956, 2006.
[Abstract]
In this paper, we show how to combine microfluidics and feedback control to independently steer multiple particles with micrometer accuracy in two spatial dimensions. The particles are steered by creating a fluid flow that carries all the particles from where they are to where they should be at each time step. Our control loop comprises sensing, computation, and actuation to steer particles along user-input trajectories. Particle locations are identified in real-time by an optical system and transferred to a control algorithm that then determines the electrode voltages necessary to create a flow field to carry all the particles to their next desired locations. The process repeats at the next time instant. Our method achieves inexpensive steering of particles by using conventional electroosmotic actuation in microfluidic channels. This type of particle steering does not require optical traps and can noninvasively steer neutral or charged particles and objects that cannot be captured by laser tweezers. (Laser tweezers cannot steer reflective particles, or particles where the index of refraction is lower than (or for more sophisticated optical vortex holographic tweezers does not differ substantially from) that of the surrounding medium.) We show proof-of-concept PDMS devices, having four and eight electrodes, with control algorithms that can steer one and three particles, respectively. In particular, we demonstrate experimentally that it is possible to use electroosmotic flow to accurately steer and trap multiple particles at once.
- R. Delille, M. G. Urdaneta, S. J. Moseley, and E. Smela, "Benchtop polymer MEMS," Journal of Microelectromechanical Systems, 15 (5), 1108-1120, 2006.
[Abstract]
Loctite photopatternable adhesives 3108, 3340, and 3525 are introduced for microelectromechanical systems (MEMS) applications. These materials are patterned within minutes by exposure to ultraviolet (UV) light followed by rinsing with a solvent; no further processing is required. Because the uncured fluid is relatively insensitive to room light, this can be done on any lab bench without the requirement for a clean room. The materials can be spin-coated to obtain films, or cast between spacers for layers up to 1 cm thick, and the cured polymers range from elastomeric to rigid. These adhesives are of interest for rapid, inexpensive fabrication of relatively low-resolution features (tens to hundreds of micrometers) by photocuring. They can alternatively be molded, like polydimethylsiloxane (PDMS), to achieve high resolution, as well as irreversibly bonded after an 02 plasma treatment. In addition, like SU8, they can be used as molds for patterning PDMS. Initial characterization of resolution, swelling, and biocompatibility were performed. One of the polymers, 3340, can be used for packaging bioMEMS-on-complementary-metal-oxide-semiconductor (CMOS) chips, exploiting its biocompatibility and its photopatternability at thicknesses of 1500 mu m to cover the bond wires while exposing the chip surface. As further demonstrations of the versatility of these materials, multilevel, interconnected channel structures were fabricated with a gelatin sacrificial layer, and magnetic films were prepared, since the polymers remain patternable even with additives.
- H. Li and B. Balachandran, "Buckling and free oscillations of composite microresonators," Journal of Microelectromechanical Systems, 15 (1), 42-51, 2006.
[Abstract]
Free oscillations of piezoelectric, microelectromechanical resonators are considered in this effort. These resonators are modeled as clamped-clamped composite structures, with stepwise varying properties across the length of the resonator. The different features of the model development are discussed, and buckling in these resonators is studied. A nonlinear analysis conducted to study oscillations about a buckled position is presented. The results of the analysis are found to compare well with the experimental observations.
- L. H. Li, P. Kumar, L. Calhoun, and D. L. DeVoe, "Piezoelectric Al0.3Ga0.7As longitudinal mode bar resonators," Journal of Microelectromechanical Systems, 15 (3), 465-470, 2006.
[Abstract]
This paper reports the modeling, fabrication, and experimental characterization of piezoelectric longitudinal mode bar resonators based on thin film single crystal Al0.3Ga0.7 As. Fabricated resonators with lengths ranging from 1000 mu m to 100 mu m have been characterized for operation in their first five odd longitudinal modes. Resonance frequencies range from 2.5 to 75 MHz, with quality factors up to 25 390 at 21.8 MHz in vacuum. Power handling capacity as high as -2.6 dBm is demonstrated at 18.8 MHz. Motional resistance and temperature stability of the resonators are also evaluated.
- S. W. Walker and B. Shapiro, "Modeling the fluid dynamics of electrowetting on dielectric (EWOD)," Journal of Microelectromechanical Systems, 15 (4), 986-1000, 2006.
[Abstract]
This paper discusses the modeling and simulation of a parallel-plate Electrowetting On Dielectric (EWOD) device that moves fluid droplets through surface tension effects. We model the fluid dynamics by using Hele-Shaw type equations with a focus on including the relevant boundary phenomena. Specifically, we show that contact angle saturation and hysteresis are needed to predict the correct shape and time scale of droplet motion. We demonstrate this by comparing our simulation to experimental data for a splitting droplet. Without these boundary effects, the simulation shows the droplet splitting into three pieces instead of two and the motion is over 15 times faster than the experiment. We then show how including the saturation characteristics of the device, and a simple model of contact angle hysteresis, allows the simulation to better predict the splitting experiment. The match is not perfect and suffers mainly because contact line pinning is not included. This is followed by a comparison between our simulation, whose parameters are now frozen, and a new experiment involving bulk droplet motion. Our numerical implementation uses the level set method, is fast, and is being used to design algorithms for the precise control of microdroplet motion, mixing, and splitting.
- A. J. Dick, B. Balachandran, D. L. DeVoe, and C. D. Mote, Jr., "Parametric identification of piezoelectric microscale resonators," Journal of Micromechanics and Microengineering, 16 (8), 1593-1601, 2006.
[Abstract]
Piezoelectrically actuated and sensed microscale resonators have been widely studied for filtering, communication and sensing applications. In this effort, to characterize these resonators, the nonlinear frequency-response behavior of these resonators is examined and parametric identification is carried out. A nonlinear beam model is used with a single-mode approximation to produce a forced Duffing oscillator. Nonlinear analysis is used to obtain the frequency-response equation, and this equation is used along with a least-squares minimization scheme to identify the linear and nonlinear parameter values in oscillator models describing the microscale structures. A linearized analytical model of the stepwise axially varying resonator is also used to obtain additional system parameters. The experimentally identified parameter values are found to be in agreement with predicted values obtained from a nonlinear beam model. Parameter values obtained from multiple sets of data for PZT and AlGaAs microresonators are used to observe trends with respect to a variety of operating conditions.
- H. Li, S. Preidikman, B. Balachandran, and C. D. Mote, "Nonlinear free and forced oscillations of piezoelectric microresonators," Journal of Micromechanics and Microengineering, 16 (2), 356-367, 2006.
[Abstract]
Free and forced oscillations of piezoelectric, microelectromechanical resonators fabricated as clamped-clamped composite structures are studied in this effort. Piezoelectric actuation is used to excite these structures on the input side and piezoelectric sensing is carried out on the output side. A refined integro-partial differential model is developed for a clamped-clamped composite beam structure and used for studying the nonlinear transverse vibrations of these resonators. This model accounts for the longitudinal extension due to transverse vibrations, distributed actuation and axially varying properties across the length of the structure. Free oscillations about a post-buckled position are studied, and for weak damping and weak forcing, the method of multiple scales is used to obtain an approximate solution for the response to a harmonic forcing. Analytical predictions are also compared with experimental observations. The model development and the analysis can serve as a basis for analysing the responses of other composite microresonators.
- L. Li, P. Kumar, S. Kanakraju, and D. L. Devoe, "Piezoelectric AlGaAs bimorph microactuators," Journal of Micromechanics and Microengineering, 16 (5), 1062-1066, 2006.
[Abstract]
Piezoelectric bimorph cantilever microactuators based on single-crystal Al0.3Ga0.7As are demonstrated. Fabricated devices are characterized for their quasistatic and resonant behavior when driven in both unimorph and bimorph configurations. Quasistatic actuator behavior is compared with a simple analytic model. Measured unimorph and bimorph tip deflections match well with the model, with deviations resulting from imperfections in device geometry and electrical resistivity of the electrodes. The effects of bimorph actuation on linearity and structural damping at resonance are also evaluated.
- A. Modafe, N. Ghalichechian, A. Frey, J. H. Lang, and R. Ghodssi, "Microball-bearing-supported electrostatic micromachines with polymer dielectric films for electromechanical power conversion," Journal of Micromechanics and Microengineering, 16 (9), S182-S190, 2006.
[Abstract]
This paper presents our latest research activities toward the development of electrostatic micromotors/microgenerators with a microball-bearing support mechanism and benzocyclobutene (BCB) low-k polymer insulating layers. The primary applications of these devices are long-range, high-speed micropositioning, high-speed micro pumping and micro power generation. In this paper, we present the development of the first generation of microball-bearing-supported micromachines. This device is a 6-phase, bottom-drive, linear, variable-capacitance micromotor. The design and fabrication of the linear micromotor, and characterization of the motor capacitance, force and motion in 3-phase and 6-phase excitation modes are presented. The micromotor consists of a silicon stator, a silicon slider and four stainless-steel microballs. The aligning force profile of the micromotor was extracted from simulated and measured capacitances of all phases. An average total aligning force of 0.27 mN with a maximum of 0.41 mN at 100 V dc was measured. The ac operation of the micromotor was verified by applying square-wave voltages and characterizing the slider motion. An average slider speed of 7.32 mm s(-1) at 40 Hz and 120 V P-P was reached without losing the synchronization. The design, fabrication and characterization methods presented in this paper can be used as a technology platform for developing rotary micromachines.
- S. Preidikman and B. Balachandran, "A semi-analytical tool based on geometric nonlinearities for microresonator design," Journal of Micromechanics and Microengineering, 16 (3), 512-525, 2006.
[Abstract]
In this paper, a computational mechanics model specifically tailored for composite microresonators with piezoelectric actuation and piezoelectric sensing is developed and used as a design tool for these microresonators. The developed model accounts for the structural properties and the electromechanical coupling effect through finite-element analysis. It is assumed that the deflection is large and that the geometric nonlinearity must be included. The dynamic admittance model is derived by combining the linear piezoelectric constitutive equations with the modal transfer function of the multi-layered microresonator structure. The resonator receptance matrix is constructed through modal summation by considering a limited number of dominant modes. The electromechanical coupling determination at the input and output ports makes use of converse and direct piezoelectric effects. In the development of the finite-element models, the boundary conditions, the shapes of electrodes and distributed parameters such as varying elastic modulus across the length of the structure have been taken into account. The developed semi-analytical tool can be used to carry out parametric studies with respect to the following: (i) the resonator beam thickness and length, (11) the influence of constant axial forces oil the transverse vibrations of clamped-clamped microresonators, (iii) the geometry of the drive and sense electrodes and (iv) imperfect boundary conditions due to mask imperfections and fabrication procedure. The semi-analytical development has been validated by comparing model predictions with prior results available in the literature for clamped-clamped resonators and experimental measurements. A detailed discussion of modeling considerations is also presented.
- M. W. Pruessner, N. Siwak, K. Amarnath, S. Kanakaraju, W. H. Chuang, and R. Ghodssi, "End-coupled optical waveguide MEMS devices in the indium phosphide material system," Journal of Micromechanics and Microengineering, 16 (4), 832-842, 2006.
[Abstract]
We demonstrate electrostatically actuated end-coupled optical waveguide devices in the indium phosphide (InP) material system. The design of a suitable layer structure and fabrication process for actuated InP-based waveguide micro-electro-mechanical systems (MEMS) is reviewed. Critical issues for optical design, such as coupling losses, are discussed and their effect on device performance is evaluated. Several end-coupled waveguide devices are demonstrated, including 1x2 optical switches and resonant sensors with integrated optical readout. The 1x2 optical switches exhibit low-voltage operation (<7 V), low crosstalk (-26 dB), reasonable loss (3.2 dB) and switching speed suitable for network restoration applications (140 mu s, 2 ms settling time). Experimental characterization of the integrated cantilever waveguide resonant sensors shows high repeatability and accuracy, with a standard deviation as low as sigma=50 Hz (0.027%) for f(resonant)=184.969 kHz. By performing focused-ion beam (FIB) milling on a sensor, a mass sensitivity of Delta m/Delta f=5.3x10(-15) g Hz(-1) was measured, which is competitive with other sensors. Resonant frequencies as high as f=1.061 MHz (Q(effective)=159.7) have been measured in air with calculated sensitivity Delta m/Delta f=1.1x10(-16) g Hz(-1). Electrostatic tuning of the resonator sensors was also examined. The prospect of developing InP MEMS devices monolithically integrated with active optical components (lasers, LEDs, photodetectors) is discussed.
- J. J. Park, X. L. Luo, H. M. Yi, T. M. Valentine, G. F. Payne, W. E. Bentley, R. Ghodssi, and G. W. Rubloff, "Chitosan-mediated in situ biomolecule assembly in completely packaged microfluidic devices," Lab on a Chip, 6 (10), 1315-1321, 2006.
[Abstract]
We report facile in situ biomolecule assembly at readily addressable sites in microfluidic channels after complete fabrication and packaging of the microfluidic device. Aminopolysaccharide chitosan's pH responsive and chemically reactive properties allow electric signal-guided biomolecule assembly onto conductive inorganic surfaces from the aqueous environment, preserving the activity of the biomolecules. A transparent and nonpermanently packaged device allows consistently leak-free sealing, simple in situ and ex situ examination of the assembly procedures, fluidic input/outputs for transport of aqueous solutions, and electrical ports to guide the assembly onto the patterned gold electrode sites within the channel. Both in situ fluorescence and ex situ profilometer results confirm chitosan-mediated in situ biomolecule assembly, demonstrating a simple approach to direct the assembly of biological components into a completely fabricated device. We believe that this strategy holds significant potential as a simple and generic biomolecule assembly approach for future applications in complex biomolecular or biosensing analyses as well as in sophisticated microfluidic networks as anticipated for future lab-on-a-chip devices.
- L. Zhu, C. S. Lee, and D. L. DeVoe, "Integrated microfluidic UV absorbance detector with attomol-level sensitivity for BSA," Lab on a Chip, 6 (1), 115-120, 2006.
[Abstract]
An integrated UV absorbance detection system employing a novel silicon-in-plastic technology to seamlessly integrate bare UV photodiode chips into polymer microfluidic systems has been developed. Detection platforms fabricated using this approach exhibit exceptionally low concentration and mass detection limits down to 15 nM and 9.8 amol, respectively, for bovine serum albumin (BSA) as a model protein. In addition to providing high sensitivity, sub-nanoliter detection volumes are enabled by the use of direct photodiode integration. The fabrication methodology is detailed, and system performance metrics including detection limits, detection volume, dynamic range, and linearity are reported.
- C. Zhu, J. H. Lee, S. R. Raghavan, and G. F. Payne, "Bioinspired vesicle restraint and mobilization using a biopolymer scaffold," Langmuir, 22 (7), 2951-2955, 2006.
[Abstract]
Biology employs vesicles to package molecules (e.g., neurotransmitters) for their targeted delivery in response to specific spatiotemporal stimuli. Biology is also capable of employing localized stimuli to exert an additional control on vesicle trafficking; intact vesicles can be restrained (or mobilized) by association with (or release from) a cytoskeletal scaffold. We mimic these capabilities by tethering vesicles to a biopolymer scaffold that can undergo (i) stimuli-responsive network formation (for vesicle restraint) and (ii) enzyme-catalyzed network cleavage (for vesicle mobilization). Specifically, we use the aminopolysaccharide chitosan as our scaffold and graft a small number of hydrophobic moieties onto its backbone. These grafted hydrophobes can insert into the bilayer to tether vesicles to the scaffold. Under acidic conditions. the vesicles are not restrained by the hydrophobically modified chitosan (hm-chitosan) because this scaffold is soluble. Increasing the pH to neutral or basic conditions allows chitosan to form interpolymer associations that yield a strong, insoluble restraining network. Enzymatic hydrolysis of this scaffold by chitosanase cleaves the network and mobilizes intact vesicles. Potentially. this approach will provide a controllable means to store and liberate vesicle-based reagents/therapeutics for microfluidic/medical applications.
- M. Christophersen, B. Shapiro, and E. Smela, "Characterization and modeling of PPy bilayer microactuators - Part 1. Curvature," Sensors and Actuators B - Chemical
115 (2), 596-609, 2006.
[Abstract]
Bilayer actuators of gold and polypyrrole doped with dodecylbenzenesulfonate, PPy(DBS), were microfabricated with lengths and thicknesses that varied over two orders of magnitude. The actuators were connected to rigid plates. The curvature of the bilayers was examined as a function of PPy and Au layer thicknesses to enable a determination of the actuation strain and Young's modulus of the PPy(DBS). Four different An thicknesses were tested, and maximum curvature was obtained in all cases at a PPy:Au thickness ratio of 5: 1. The data could not be fit with a constant value for the actuation strain; in addition, the PPy film bent even in the absence of an Au layer. Therefore, a model was developed that included strain and modulus variations along the direction of film thickness. The experimental data were fit with an exponential variation in actuation strain, starting at 20% at the surface of the PPy and decreasing to 3% at the gold interface in thicker films. The Young's modulus was found to be constant between 0.08 and 0.20 GPa in the oxidized state. These values differ significantly from thick-film values. With this information, micro-actuators can now be designed to achieve a specified radius of curvature. (c) 2005 Elsevier B.V. All rights reserved.
- L. Q. Wu, R. Ghodssi, Y. A. Elabd, and G. F. Payne, "Biomimetic pattern transfer," Advanced Functional Materials, 15 (2), 189-195, 2005.
[Abstract]
Biological systems routinely use phenols to construct complex materials with diverse functions. Typically, these phenolic materials are generated using oxidative enzymes to initiate a cascade of uncatalyzed reactions. We mimic these processes to micro-pattern films of aminopolysaccharide chitosan. Specifically, we microfabric silicon wafers to have gold patterns, cast a chitosan film onto the patterned wafers, and commence pattern transfer by polarizing the underlying gold surfaces to electro-chemically initiate the phenol reaction cascade. The electrochemically initiated reactions lead to modification of the chitosan film's chemistry, structure, and fluorescence. Further, electrochemically initiated modification of the chitosan film is localized to the interfacial region between the film and the anode, with resolution in the lateral direction of at least 20 mum. These results demonstrate that electrochemical pattern transfer provides a promising new method for micropatterning flexible films.
- H. M. Yi, L. Q. Wu, W. E. Bentley, R. Ghodssi, G. W. Rubloff, J. N. Culver, and G. F. Payne, "Biofabrication with chitosan," Biomacromolecules, 6 (6), 2881-2894, 2005.
[Abstract]
The traditional motivation for integrating biological components into microfabricated devices has been to create biosensors that meld the molecular recognition capabilities of biology with the signal processing capabilities of electronic devices. However, a different motivation is emerging; biological components are being explored to radically change how fabrication is achieved at the micro- and nanoscales. Here we review biofabrication, the use of biological materials for fabrication, and focus on three specific biofabrication approaches: directed assembly, where localized external stimuli are employed to guide assembly; enzymatic assembly, where selective biocatalysts are enlisted to build macromolecular structure; and self-assembly, where information internal to the biological material guides its own assembly. Also reviewed are recent results with the aminopolysaccharide chitosan, a material that offers a combination of properties uniquely suited for biofabrication. In particular, chitosan can be directed to assemble in response to locally applied electrical signals, and the chitosan backbone provides sites that can be employed for the assembly of proteins, nucleic acids, and virus particles.
- Y. X. Wang, Y. Zhou, B. M. Balgley, J. W. Cooper, C. S. Lee, and D. L. DeVoe, "Electrospray interfacing of polymer microfluidics to MALDI-MS," Electrophoresis, 26 (19), 3631-3640, 2005.
[Abstract]
The off-line coupling of polymer microfluidics to MALDI-MS is presented using electrospray deposition. Using polycarbonate microfluidic chips with integrated hydrophobic membrane electrospray tips, peptides and proteins are deposited onto a stainless steel target followed by MALDI-MS analysis. Microchip electrospray deposition is found to yield excellent spatial control and homogeneity of deposited peptide spots, and significantly improved MALDI-MS spectral reproducibility compared to traditional target preparation methods. A detection limit of 3.5 fmol is demonstrated for angiotensin. Furthermore, multiple electrospray tips on a single chip provide the ability to simultaneously elute parallel sample streams onto a MALDI target for high-throughput multiplexed analysis. Using a three-element electrospray, tip array with 150 mu m spacing, the simultaneous deposition of bradykinin, fibrinopeptide, and angiotensin is achieved with no cross talk between deposited samples. In addition, in-line proteolytic digestion of intact proteins is successfully achieved during the electrospray process by binding trypsin within the electrospray membrane, eliminating the need for on-probe digestion prior to MALDI-MS. The technology offers promise for a range of microfluidic platforms designed for high-throughput multiplexed proteomic analyses in which simultaneous on-chip separations require an effective interface to MS.
- M. Armani, S. Chaudhary, R. Probst, S. Walker, and B. Shapiro, "Control of microfluidic systems: Two examples, results, and challenges," International Journal of Robust and Nonlinear Control, 15 (16), 785-803, 2005.
[Abstract]
This paper describes results and challenges in feedback control of microfluidic systems. Results are provided for two representative examples: control of liquid droplets by electrically actuated surface tension forces and steering of many particles at once by micro flow control. Common themes and challenges are outlined based on the authors' research programs and on the results of the March 2004 NSF workshop on 'Control and System Integration of Micro- and Nano-Scale Systems' organized by the author. Copyright (c) 2005 John Wiley & Sons, Ltd.
- L. G. Frechette, S. A. Jacobson, K. S. Breuer, F. F. Ehrich, R. Ghodssi, R. Khanna, C. W. Wong, X. Zhang, M. A. Schmidt, and A. H. Epstein, "High-speed microfabricated silicon turbomachinery and fluid film bearings," Journal of Microelectromechanical Systems, 14 (1), 141-152, 2005.
[Abstract]
A single-crystal silicon micromachined air turbine supported on gas-lubricated bearings has been operated in a controlled and sustained manner at rotational speeds greater than 1 million revolutions per minute, with mechanical power levels approaching 5 W. The device is formed from a fusion bonded stack of five silicon wafers individually patterned on both sides using deep reactive ion etching (DRIE). It consists of a single stage radial inflow turbine on a 4.2-mm diameter rotor that is supported on externally pressurized hydrostatic journal and thrust bearings. This paper presents the design, fabrication, and testing of the first microfabricated rotors to operate at circumferential tip speeds up to 300 m/s, on the order of conventional high performance turbomachinery. Successful operation of this device motivates the use of silicon micromachined high-speed rotating machinery for power microelectromechanical systems (MEMS) applications such as portable energy conversion, micropropulsion, and microfluidic pumping and cooling.
- S. Hollar, A. Flynn, S. Bergbreiter, and K. S. J. Pister, "Robot leg motion in a planarized-SOI, two-layer poly-Si process," Journal of Microelectromechanical Systems, 14 (4), 725-740, 2005.
[Abstract]
With the ultimate goal of creating autonomous microrobots, we developed a five-mask process that combines two polysilicon structural layers with 50-mu m-thick SOI structures and a backside substrate etch. The polysilicon layers provide three-dimensional (3-D) hinged structures, high compliance structures, and electrical wiring. The SOI structural layer yields much stronger structures and large-force actuators. This process was developed as a part of a three-chip solution for a solar-powered 10-mg silicon robot. Here, we describe the fabrication of this planarized-SOI, two-layer poly-Si process (henceforth called the SOI/poly process), basic modules in the design of robot legs in this process, and lastly, the results of fabricated robot legs. In designing the leg structures, we developed guidelines and test structures to provide a better understanding of the robot leg performance. These guidelines include understanding the relationship between the lateral etch depth to the actuator spacing and performing static friction tests of polysilicon flaps to more accurately model the frictional forces of the linkages. Last, we report on the performance of the robot legs and inchworm motors. On an 8 mm x 3 mm robot, we have demonstrated a 1 degree-of-freedom (DOF) robot leg, I turn in length, which demonstrates up to 60 mu N of vertical leg force with an angular deflection of almost 30 degrees. A two-DOF robot leg, also 1 mm in length, operated with at least 90 degrees of angular deflection, and each inchworm motor demonstrated a shuttle displacement of 400 mu m with speeds up to 6.8 mm/s. In addition to robot legs, a bidirectional inchworm motor that produces equivalent forces in both directions was also fabricated in this SOI/poly process. This motor uses an additional set of gap-closing-actuator (GCA) arrays to prebias the drive frame.
- J. Liu, L. Fan, and D. L. DeVoe, "Microfabricated sequential-leaf time-delay mechanisms," Journal of Microelectromechanical Systems, 14 (5), 1051-1060, 2005.
[Abstract]
Arrays of micromechanical sequential-leaf time-delay mechanisms based on SOI/DRIE technology have been designed, fabricated, and characterized. The devices were designed as elements of a larger fuzing system for rifled munitions, in which a passive timing mechanism triggers at a predetermined rotational speed, followed by a desired delay time before the next element of the munition fuzing train is activated. Analytical models for the micromechanical timing mechanisms have been developed, and a variety of designs were simulated from the linear and nonlinear models, and using dynamics simulation software. Fabricated mechanism arrays designed to initiate switching at centrifugal accelerations from 44 to 263 g were characterized using a high-speed camera, with delay times of between 0.67 and 0.95 ms achieved for single elements within the arrays. Measured delay times and switching accelerations follow predicted trends based on analytical and numerical models.
- S. E. Nagle, C. Livermore, L. G. Frechette, R. Ghodssi, and J. H. Lang, "An electric induction micromotor," Journal of Microelectromechanical Systems, 14 (5), 1127-1143, 2005.
[Abstract]
This paper presents the analysis, design, fabrication, and testing of a planar electric induction micromotor. The micromotor is a 6-phase motor with 131 pole pairs distributed on a stator having a 4 mm outer diameter. The axial air gap is 3 mu m. With a 90 V stator excitation, applied at a 300-kHz slip frequency, the motor produces a torque of 2 mu N center dot m. Special attention is paid to the limitations that microfabrication places on the design of the motor.
- M. W. Pruessner, K. Amarnath, M. Datta, D. P. Kelly, S. Kanakaraju, P. T. Ho, and R. Ghodssi, "InP-Based optical waveguide MEMS switches with evanescent coupling mechanism," Journal of Microelectromechanical Systems, 14 (5), 1070-1081, 2005.
[Abstract]
An optical waveguide MEMS switch fabricated on an indium phosphide (InP) substrate for operation at 1550 mn wavelength is presented. Compared to other MEMS optical switches, which typically use relatively large mirrors or long end-coupled waveguides, our device uses a parallel switching mechanism. The device utilizes evanescent coupling between two closely-spaced waveguides fabricated side by side. Coupling is controlled by changing the gap and the coupling length between the two waveguides via electrostatic pull-in. This enables both optical switching and variable optical coupling at voltages below 10 V. Channel isolation as high as -47 dB and coupling efficiencies of up to 66% were obtained with switching losses of less than 0.5 dB. We also demonstrate voltage-controlled variable optical coupling over a 17.4 dB dynamic range. The devices are compact with 2 mu m x 2 mu m core cross section and active area as small as 500 mu m x 5 mu m. Due to the small travel range of the waveguides, fast operation is obtained with switching times as short as 4 mu s. Future devices can be scaled down to less than 1 mu m x 1 mu m waveguide cross-sectional area and device length less than 100 mu m without significant change in device design.
- J. S. Buch, F. Rosenberger, W. E. Highsmith, C. Kimball, D. L. DeVoe, and C. S. Lee, "Denaturing gradient-based two-dimensional gene mutation scanning in a polymer microfluidic network," Lab on a Chip, 5 (4), 392-400, 2005.
[Abstract]
An integrated two-dimensional (2-D) DNA separation platform, combining standard gel electrophoresis with temperature gradient gel electrophoresis (TGGE) on a polymer microfluidic chip, is reported. Rather than sequentially sampling DNA fragments eluted from standard gel electrophoresis, size-resolved fragments are simultaneously electrokinetically transferred into an array of orthogonal microchannels and screened for the presence of sequence heterogeneity by TGGE in a parallel and high throughput format. A bulk heater assembly is designed and employed to externally generate a temporal temperature gradient along an array of TGGE channels. Extensive finite element modeling is performed to determine the optimal geometries of the microfluidic network for minimizing analyte band dispersion caused by interconnected channels in the network. A pH-mediated on-chip analyte stacking strategy is employed prior to the parallel TGGE separations to further reduce additional band broadening acquired during the electrokinetic transfer of DNA fragments between the first and second separation dimensions. A comprehensive 2-D DNA separation is completed in less than 5 min for positive detection of single-nucleotide polymorphisms in multiplex PCR products that vary in size and sequence.
- M. A. Powers, S. T. Koev, A. Schleunitz, H. M. Yi, V. Hodzic, W. E. Bentley, G. F. Payne, G. W. Rubloff, and R. Ghodssi, "A fabrication platform for electrically mediated optically active biofunctionalized sites in BioMEMS," Lab on a Chip, 5 (6), 583-586, 2005.
[Abstract]
We report a new approach for microfluidic optical bioanalysis that is based on the electrically driven assembly of biocomponents on a transparent sidewall and the optical detection of the assembled components using planar waveguides. This allows localized electrical signals for bio-assembly and optical signals for bio-detection that can easily be applied in MEMS systems. We demonstrate a BioMEMS design incorporating this scheme and its output signal when using fluorescent detection.
- I. Treise, N. Fortner, B. Shapiro, and A. Hightower, "Efficient energy based modeling and experimental validation of liquid filling in planar micro-fluidic components and networks," Lab on a Chip, 5 (3), 285-297, 2005.
[Abstract]
This paper presents a model that describes how liquid flow fills micro-fluidic components and networks. As an alternative to computational fluid dynamic (CFD) simulations, we use a constrained energy minimization approach. This approach is based on two assumptions that hold in many micro-fluidic devices: (i) The length scales are small, and we consider slow filling rates, hence fluid momentum and viscous terms are small compared to surface tension forces, consequently the liquid/gas interfaces can be viewed as a succession of quasi-steady equilibrium configurations. (ii) Any equilibrium configuration corresponds to a surface tension energy minima which is constrained by the device shape and the volume of liquid in the device. The model is developed for planar micro-fluidic devices, is based on a fundamental physical principle, and shows accurate agreement with experimental data. It takes us only a few minutes to evaluate the model for a planar component of any shape using the Surface Evolver software, and this is significantly less then the computer run time required for CFD simulations. Moreover, once a library of component models has been created ( which takes less than an hour of computer time) it then takes only seconds to simulate different network architectures with thousands of components. This fast 'reconfigure the network and simulate in seconds' capability is essential for the design of truly complex networks that will enable the next generation of passive, micro-fluidic, lab-on-a-chip systems.
- S. Walker and B. Shapiro, "A control method for steering individual particles inside liquid droplets actuated by electrowetting," Lab on a Chip, 5 (12), 1404-1407, 2005.
[Abstract]
An algorithm is developed that allows steering of individual particles inside electrowetting systems by control of actuators already present in these systems. Particles are steered by creating time varying flow fields that carry the particles along their desired trajectories. Results are demonstrated using an experimentally validated model developed in ref. 1. We show that the current UCLA electro-wetting-on-dielectric (EWOD) system 2 contains enough control authority to steer a single particle along arbitrary trajectories and to steer two particles, at once, along simple paths. Particle steering is limited by contact angle saturation and by the small number of actuators that are available to actuate the flow in practical electrowetting systems.
- A. Ludwig, J. Cao, J. Brugger, and I. Takeuchi, "MEMS tools for combinatorial materials processing and high-throughput characterization," Measurement Science & Technology, 16 (1), 111-118, 2005.
[Abstract]
Using the combinatorial material synthesis approach, materials libraries can be produced in one experiment that contain up to several thousand samples on a single substrate. In order to identify optimized materials in an efficient way using screening methods, adequate automated material characterization tools have to be designed and applied. Microsystems (micro-electromechanical systems: MEMS) offer powerful tools for the fabrication and processing of materials libraries as well as for accelerated material characterization on planar substrates such as Si wafers. MEMS can be used for parallel materials processing, either as passive devices such as shadow mask structures, or as active devices such as micro-hotplates. Microstructured wafers, which incorporate sensor or actuator structures such as electrode or cantilever arrays, can be used to identify materials properties in an efficient way.
- A. Modafe, N. Ghalichechian, M. Powers, M. Khbeis, and R. Ghodssi, "Embedded benzocyclobutene in silicon: An integrated fabrication process for electrical and thermal isolation in MEMS," Microelectronic Engineering, 82 (2), 154-167, 2005.
[Abstract]
This paper reports a novel fabrication process to develop planarized isolated islands of benzocyclobutene (BCB) polymer embedded in a silicon substrate. Embedded BCB in silicon (EM) can be used as an alternative to silicon dioxide in fabrication of electrostatic micromotors, microgenerators, and other microelectromechanical devices. EBiS takes advantage of the low dielectric constant and thermal conductivity of BCB polymers to develop electrical and thermal isolation integrated in silicon. The process involves conventional microfabrication techniques such as photolithography, deep reactive ion etching, and chemical mechanical planarization (CMP). We have characterized CMP of BCB polymers in detail since CMP is a key step in EM process. Atomic force microscopy (AFM) and elipsometry of blanket BCB films before and after CMP show that higher polishing down force pressure and speed lead to higher removal rate at the expense of higher surface roughness, non-uniformity, and scratch density. This is expected since BCB is a softer material compared to inorganic films such as silicon dioxide. We have observed that as the cure temperature of BCB increases beyond 200 degrees C, the CMP removal rate decreases drastically. The results from optical microscopy, scanning electron microscopy, and optical profilometry show excellent planarized surfaces on the EM islands. An average step height reduction of more than 95% was achieved after two BCB deposition and three CMP steps. (c) 2005 Elsevier B.V. All rights reserved.
- B. Morgan, X. F. Hua, T. Iguchi, T. Tornioka, G. S. Oehrlein, and R. Ghodssi, "Substrate interconnect technologies for 3-D MEMS packaging," Microelectronic Engineering, 81 (1), 106-116, 2005.
[Abstract]
We report the development of 3-dimensional silicon substrate interconnect technologies, specifically for reducing the package size of a MOSFET relay. The ability to interconnect multiple chips at different elevations on a single substrate can significantly improve device performance and size. We present the process development of through-hole interconnects fabricated using deep reactive ion etching (DRIE), with an emphasis on achieving positively tapered, smooth sidewalls to ease deposition of a seed layer for subsequent Cu electroplating. Gray-scale technology is integrated on the same substrate to provide smooth inclined surfaces between multiple vertical levels (> 100 mu m apart), enabling interconnection between the two levels via simple metal evaporation and lithography. The developments discussed for each technique may be used together or independently to address future packaging and integration needs. (c) 2005 Elsevier B.V. All rights reserved.
- W. H. Chuang, T. Luger, R. Ghodssi, and R. K. Fettig, "A cryogenic measurement setup for microelectromechanical systems used in space applications," Review of Scientific Instruments, 76 (4), 2005.
[Abstract]
We present a cryogenic measurement setup installed inside a focused-ion-beam (FIB) system to characterize and microrepair microelectromechanical systems (MEMS) for space applications. The setup allows testing of MEMS devices under vacuum condition of 10(-6) Torr at variable temperatures ranging from 298 to 20 K. In the experiment, a lead-zirconate-titanate translator powered by a function generator and a dc voltage is utilized as an actuator, and a thin-film thermo-resistor fabricated with test devices is used as an integrated temperature sensor. Additionally, a motorized x-y-z stage is installed to achieve highly accurate positioning function. Resonant techniques and bending tests based on the designed setup are developed to measure the mechanical properties of silicon nitride thin films at cryogenic temperatures. Combined with the functions of the FIB system, this setup also demonstrates the capability to microrepair microshutter arrays, programmable field selectors in the NASA James Webb Space Telescopes. The presented test setup exhibits its feasibility to test MEMS devices needed for the space applications and can be extended to other cryogenic applications. (C) American Institute of Physics.
- W. H. Chuang, R. K. Fettig, and R. Ghodssi, "An electrostatic actuator for fatigue testing of low-stress LPCVD silicon nitride thin films," Sensors and Actuators A - Physical, 121 (2), 557-565, 2005.
[Abstract]
An electrostatic actuator and mechanical-amplifier (MA) device has been designed and fabricated to study fatigue properties of low-stress LPCVD silicon nitride thin films. The device consists of two resonators connected serially with a common torsion bar. When pumping electrostatic energy into the first resonator, the energy is transferred to the second resonator via the common torsion bar. The mechanical movement of the second resonator is thus amplified, introducing high stress levels (up to 7.7 GPa) when actuated at its first resonant mode. All devices were tested inside a focused-ion-beam (FIB) system with pressure of 10(-6) Torr at room temperature (23 +/- 1 degrees C), and the test duration ranged from 5 s to 8.5 h, 10(5) to 10(9) cycles, respectively. An ANSYS finite-element-analysis (FEA) model was built to determine the maximum operating stress of the devices. From the experiment, no failure of low-stress LPCVD silicon nitride thin films has been found even up to 109 cycles when testing at stress amplitude below 5.8 GPa with a load ratio of 0.03. The presented device design and experimental technique can be used to characterize fatigue properties of different microelectromechanical systems (MEMS) materials, and the test results are utilized in the design of microshutter arrays, programmable field selectors in the NASA James Webb Space Telescopes (JWST). (c) 2005 Elsevier B.V. All rights reserved.
- A. T. Ferguson, L. Li, V. T. Nagaraj, B. Balachandran, B. Piekarski, and D. L. DeVoe, "Modeling and design of composite free-free beam piezoelectric resonators," Sensors and Actuators A - Physical, 118 (1), 63-69, 2005.
[Abstract]
A model is presented and experimentally validated for the design of asymmetrically layered piezoelectric free-free beam micromechanical resonators. The thin film resonators are composed of quad-symmetric torsional anchors connected to the nodal points of a free-free beam vibrating in its fundamental bending mode. The model provides analytical approximations for the resonance frequencies of the composite anchors and the free-free beam. Since dissipation in these devices is minimized when the mechanical impedances of the coupled structures are matched at resonance, i.e. when bending beam and torsional anchor resonance frequencies are equal, the model may be used to design resonators with optimized mechanical quality factors. The model is shown to successfully predict resonance frequencies in agreement with the results of finite element analysis and experimental results obtained for multi-layered lead zirconate titanate (PZT) piezoelectric microresonators with first natural frequencies in the range of 448 kHz to 1.1 MHz. The model is also validated as a tool for optimizing resonator quality factor. (C) 2004 Published by Elsevier B.V.
- C. M. Waits, B. Morgan, M. Kastantin, and R. Ghodssi, "Microfabrication of 3D silicon MEMS structures using gray-scale lithography and deep reactive ion etching," Sensors and Actuators A - Physical, 119 (1), 245-253, 2005.
[Abstract]
Micromachinina arbitrary 3D silicon structures for micro-electromechanical systems can be accomplished using gray-scale lithography along with dry anisotropic etching. In this study, we have investigated the use of deep reactive ion etching (DRIE) and the tailoring of etch selectivity for precise fabrication. Silicon loading, the introduction of an O-2 step, wafer electrode power, and wafer temperature are evaluated and determined to be effective for coarsely controlling etch selectivity in DRIE. The non-uniformity and surface roughness characteristics are evaluated and found to be scaled by the etch selectivity when the 3D profile is transferred into the silicon. A micro-compressor is demonstrated using gray-scale lithography and DRIE showing that etch selectivity can be successfully tailored for a specific application. (c) 2004 Elsevier B.V. All rights reserved.
- J. S. Buch, C. Kimball, F. Rosenberger, W. E. Highsmith, D. L. DeVoe, and C. S. Lee, "DNA mutation detection in a polymer microfluidic network using temperature gradient gel electrophoresis," Analytical Chemistry, 76 (4), 874-881, 2004.
[Abstract]
A miniaturized system for DNA mutation analysis, utilizing temperature gradient gel electrophoresis (TGGE) in a polycarbonate (PC) microfluidic device, is reported. TGGE reveals the presence of sequence heterogeneity in a given heteroduplex sample by introducing a thermal denaturing gradient that results in differences between the average electrophoretic mobilities of DNA sequence variants. Bulk heater assemblies are designed and employed to externally generate temperature gradients in spatial and temporal formats along the separation channels. TGGE analyses of model mutant DNA fragments, each containing a single base substitution, are achieved using both single- and 10-channel parallel measurements in a microfluidic platform. Additionally, a comprehensive polymer microfluidic device containing an integrated microheater and sensor array is developed and demonstrated for performing spatial TGGE for DNA mutation analysis. The device consists of two PC modular substrates mechanically bonded together. One substrate is embossed with micro-channels, and the other contains a tapered microheater, lithographically patterned along with an array of temperature sensors. Compared with the external heating approaches, the integrated platform provides significant reduction in power requirement and thermal response time while establishing more accurate and highly effective control of the temperature gradient for achieving improved separation resolution.
- Y. Li, J. S. Buch, F. Rosenberger, D. L. DeVoe, and C. S. Lee, "Integration of isoelectric focusing with parallel sodium dodecyl sulfate gel electrophoresis for multidimensional protein separations in a plastic microfludic network," Analytical Chemistry, 76 (3), 742-748, 2004.
[Abstract]
An integrated protein concentration/separation system, combining non-native isoelectric focusing (IEF) with sodium dodecyl sulfate (SDS) gel electrophoresis on a polymer microfluidic chip, is reported. The system provides significant analyte concentration and extremely high resolving power for separated protein mixtures. The ability to introduce and isolate multiple separation media in a plastic microfluidic network is one of two key requirements for achieving multidimensional protein separations. The second requirement lies in the quantitative transfer of focused proteins from the first to second separation dimensions without significant loss in the resolution acquired from the first dimension. Rather than sequentially sampling protein analytes eluted from IEF, focused proteins are electrokinetically transferred into an array of orthogonal microchannels and further resolved by SDS gel electrophoresis in a parallel and high-throughput format Resolved protein analytes are monitored using noncovalent, environment-sensitive, fluorescent probes such as Sypro Red. In comparison with covalently labeling proteins, the use of Sypro staining during electrophoretic separations not only presents a generic detection approach for the analysis of complex protein mixtures such as cell lysates but also avoids additional introduction of protein microheterogeneity as the result of labeling reaction. A comprehensive 2-D protein separation is completed in less than 10 min with an overall peak capacity of similar to1700 using a chip with planar dimensions of as small as 2 cm x 3 cm. Significant enhancement in the peak capacity can be realized by simply raising the density of microchannels in the array, thereby increasing the number of IEF fractions further analyzed in the size-based separation dimension.
- N. J. Sniadecki, C. S. Lee, P. Sivanesan, and D. L. DeVoe, "Induced pressure pumping in polymer microchannels via field-effect flow control," Analytical Chemistry, 76 (7), 1942-1947, 2004.
[Abstract]
Microfluidic field-effect flow control (FEFC) modifies the xi potential of electroosmotic flow using a transverse electric field applied through the microchannel wall. Previously demonstrated in silicon-based and glass microsystems, FEFC is presented here as an elegant method for flow control in polymer-based microfluidics with a simple and low-cost fabrication process. In addition to direct FEFC flow modulation, independent transverse electric fields in connected microchannels are demonstrated to produce a differential pumping rate between the microchannels. The different electroosmotic pumping rates formed by local potential control induce an internal pressure at the microchannel intersection, resulting in hydrodynamic pumping through an interconnecting fieldfree microchannel. Modulation of the voltages applied to the gate electrodes adjusts the magnitude and direction of the bidirectional pressure pumping, with fine resolution volume flow rates from -2 to 2 nL/min in the field-free microchannel demonstrated.
- D. P. Kelly, M. W. Pruessner, K. Amarnath, M. Datta, S. Kanakaraju, L. C. Calhoun, and R. Ghodssi, "Monolithic suspended optical waveguides for InP MEMS," IEEE Photonics Technology Letters, 16 (5), 1298-1300, 2004.
[Abstract]
We present a novel waveguide design for InP microelecromechanical systems. The substrate is removed from underneath the waveguide by sacrificial etching, and the suspended waveguide is supported by lateral tethers. This allows segments of the waveguide to be moved and prevents substrate leakage loss in the fixed segments of the waveguides. A single-mask fabrication process is developed that can be extended to more complex devices employing electrostatic actuation. Fabricated suspended waveguides exhibit a loss of 2.2 dB/cm and tether pairs exhibit 0.25-dB additional loss.
- A. Modafe, N. Ghalichechian, B. Kleber, and R. Ghodssi, "Electrical characterization of benzocyclobutene polymers for electric micromachines," IEEE Transactions on Device and Materials Reliability, 4 (3), 495-508, 2004.
[Abstract]
An approach using interdigitated capacitors for electrical characterization of CYCLOTENE, a spin-on low-k benzocyclobutene (BCB)-based polymer is introduced and the effect of moisture uptake is investigated. The dielectric constant of CYCLOTENE is extracted from capacitance measurements with a systematic error less than 0.1%, giving an average value of 2.49 with a standard deviation of 1.5%. The dielectric constant increases by 1.2% after a humidity stress of 85% RH at 85degreesC. The I-V characteristics of CYCLOTENE show a dependency of breakdown strength and leakage current on the geometrical dimensions of the device under test. A breakdown strength of 225 V/mum and 320 V/mum for 2-mum and 3-mum finger spacing, respectively, and a leakage current of a few to tens of pA are measured. The I-V characteristics degrade drastically after the humidity stress, showing a breakdown strength of 100 V/mum and 180 V/mum for 2-mum and 3-mum finger spacing, respectively, and a maximum increase in the leakage current as large as one order of magnitude. The maximum performance and long-term reliability of an electric micromachine are adversely affected by the degradation of the breakdown voltage and the leakage current after moisture absorption. It is expected, however, that the electrical efficiency is improved using BCB-based polymers with negligible dependency on moisture absorption.
- T. W. Lin, A. Modafe, B. Shapiro, and R. Ghodssi, "Characterization of dynamic friction in MEMS-Based microball bearings," IEEE Transactions on Instrumentation and Measurement, 53 (3), 839-846, 2004.
[Abstract]
Rolling element hearing. is a well-known concept in macroscale machinery applications. They are prospective candidates for friction reduction in microelectromechanical system (MEMS), as well as for providing stable, robust support for moving micromechanisms. The characteristics of rolling element bearings need to be investigated to facilitate their applications in MEMS. It is well understood that the measured data on the macroscale cannot be directly applied to the microscale. This paper presents an in-situ noncontact experimental system to characterize the friction behavior of microball bearings on the microscale. The methodology presented in this paper provides a useful template to study the dynamical behavior of linear microball bearings with a variety. of materials, geometries, and surface qualities. The system, actuated by a motor, affords wide ranges of motion for measuring the dynamic friction using a vision system. It allows the determination of the coefficient of friction (COF) without any interference due to the measurement system. With careful optimization, the error in measurement has been reduced to 2%. Different designs of microball bearings are proposed to achieve lower friction. The studied microball bearings demonstrated an average static COF of 0.01 and an average dynamic COF of 0.007 between stainless-steel and silicon-micromachined contacting surfaces at 27 degreesC and 40% relative humidity.
- W. H. Chuang, T. Luger, R. K. Fettig, and R. Ghodssi, "Mechanical property characterization of LPCVD silicon nitride thin films at cryogenic temperatures," Journal of Microelectromechanical Systems, 13 (5), 870-879, 2004.
[Abstract]
T-shape, LPCVD silicon nitride cantilevers are fabricated to determine Young's modulus and fracture strength of silicon nitride thin films at room and cryogenic temperatures. A helium-cooled measurement setup is developed and installed inside a focused-ion-beam (FIB) system. A lead-zirconate-titanate (PZT) translator powered by a function generator and a dc voltage is utilized as an actuator, and a silicon diode is used as a temperature sensor in this setup. Resonant frequencies of identical cantilevers with different "milling masses" are measured to obtain thickness and Young's modulus of the silicon nitride thin films, while a bending test is performed to obtain fracture strength. From the experiment, the average Young's modulus of low-pressure chemical-vapor deposition (LPCVD) silicon nitride thin films varies from 260.5 GPa at room temperature (298 K) to 266.6 GPa at 30 K, and the average fracture strength ranges from 6.9 GPa at room temperature to 7.9 GPa at 30 K. The measurement setup and technique presented here can be used to characterize the mechanical properties of different MEMS materials at cryogenic temperatures.
- B. Morgan, C. M. Waits, J. Krizmanic, and R. Ghodssi, "Development of a deep silicon phase Fresnel lens using gray-scale lithography and deep reactive ion etching," Journal of Microelectromechanical Systems, 13 (1), 113-120, 2004.
[Abstract]
We report the first fabrication and development of a deep phase Fresnel lens (PFL) in silicon through the use of gray-scale lithography and deep-reactive ion etching (DRIE). A Gaussian tail approximation is introduced as a method of predicting the height of photoresist gray levels given the relative amount of transmitted light through a gray-scale optical mask. Device mask design is accomplished through command-line scripting in a CAD tool to precisely define the millions of pixels required to generate the appropriate profile in photoresist. Etch selectivity during DRIE pattern transfer is accurately controlled to produce the desired scaling factor between the photoreist and silicon profiles. As a demonstration of this technology, a 1.6-mm diameter PFL is etched 43 mum into silicon with each grating profile designed to focus 8.4 keV photons a distance of 118 m.
- J. M. Maloney, D. S. Schreiber, and D. L. DeVoe, "Large-force electrothermal linear micromotors," Journal of Micromechanics and Microengineering, 14 (2), 226-234, 2004.
[Abstract]
Electrothermal linear micromotors fabricated by deep reactive ion etching of silicon-on-insulator wafers are presented. These high-aspect-ratio motors are powered by thermal actuator arrays with a height of 50 mum. Synchronized arrays, each containing ten actuators connected by a midpoint yoke, are used to advance a slider through frictional contact. Forces of 6.7 mN have been demonstrated at a voltage of 12 V using motors measuring 2.5 mm by 2.1 mm. Unidirectional motors have been successfully operated at speeds of up to I mm s(-1) over a range in excess of 2 mm. Motors are found to be well suited for positioning compliant mechanisms and similar applications requiring large forces and displacements at low drive voltages.
- N. Ghalichechian, A. Modafe, R. Ghodssi, P. Lazzeri, V. Micheli, and M. Anderle, "Integration of benzocyclobutene polymers and silicon micromachined structures using anisotropic wet etching," Journal of Vacuum Science & Technology B, 22 (5), 2439-2447, 2004.
[Abstract]
Integration of thick, low-k dielectric benzocyclobutene (BCB) film with deep etched structures in silicon allows the fabrication of microelectromechanical systems (MEMS) devices with low parasitic loss. A fabrication process is developed for integration of 1-mum-thick BCB low-k dielectric film and 200-mum-deep anisotropically etched grooves in silicon with potassium hydroxide (KOH). In order to protect the low-k film during the highly corrosive, long, high-temperature KOH etching process, gold (Au) is used as an etch mask. Chromium (Cr) is used to improve the adhesion of Au to the underlying BCB layer. Metal-BCB adhesion is the key parameter in this masking design. Partial cure of BCB at 210degreesC for 40 min with appropriate surface treatment (adhesion promoter) prior to metallization and full cure at 250degreesC for 1 h after metallization, together with Cr/Au sputtering at 200degreesC, improves the adhesion dramatically. The adhesion strength of metal films to BCB was experimentally verified in a qualitative manner. V grooves were etched into silicon in 20 wt%, 80degreesC KOH solution for 8 h in the presence of 1 mum BCB film. BCB was protected and kept intact with an Au mask layer during the etch process. In order to understand the mechanism of the adhesion improvement, the interface between BCB and the Cr/Au layer was studied using secondary ion mass spectroscopy and Auger electron spectroscopy. Adhesion improvement which is mainly due to cure management and use of adhesion promoter is associated with (1) the diffusion of silicon and carbon from the polymer structure into the Cr layer, and (2) the chemical interaction of BCB and Cr at the interface mainly in the form of the oxidation of Cr. The integration of BCB and the KOH etching process which was obtained by improving the adhesion of metal etch mask to the BCB film, together with the study of the interfaces, allow us to use thick low dielectric constant BCB film for fabrication of MEMS devices with very low parasitic loss. (C) 2004 American Vacuum Society.
- Y. X. Wang, J. W. Cooper, C. S. Lee, and D. L. DeVoe, "Efficient electrospray ionization from polymer microchannels using integrated hydrophobic membranes," Lab on a Chip, 4 (4), 363-367, 2004.
[Abstract]
A simple process for realizing stable and reliable electrospray ionization (ESI) tips in polymer microfluidic systems is described. The process is based on the addition of a thin hydrophobic membrane at the microchannel exit to constrain lateral dispersion of the Taylor cone formed during ESI. Using this approach, ESI chips are shown to exhibit well-defined Taylor cones at flow rates as low as 80 nL min(-1) through optical imaging. Furthermore, stable electrospray current has been measured for flow rates as low as 10 nL min(-1) over several hours of continuous operation. Characterization of the electrospray process by optical and electrical monitoring of fabricated ESI chips is reported, together with mass spectrometry validation using myoglobin as a model protein. The novel process offers the potential for low-cost, direct interfacing of disposable polymer microfluidic separation platforms to mass spectrometry.
- O. O. Famodu, J. Hattrick-Simpers, M. Aronova, K. S. Chang, M. Murakami, M. Wuttig, T. Okazaki, Y. Furuya, L. A. Knauss, L. A. Bendersky, F. S. Biancaniello, and I. Takeuchi, "Combinatorial investigation of ferromagnetic shape-memory alloys in the Ni-Mn-Al ternary system using a composition spread technique," Materials Transactions, 45 (2), 173-177, 2004.
[Abstract]
Using a thin-film composition spread technique, we have mapped the phase diagram of the Ni-Mn-Al ternary system in search of ferromagnetic shape-memory alloys (FMSA). A characterization technique that allows detection of martensitic transitions by visual inspection using micromachined cantilever arrays was combined with quantitative magnetization mapping using scanning superconducting quantum interference device (SQUID) microscopy. A large compositional region in the Al deficient part of the phase diagram was found to be ferromagnetic and reversibly martensitic at room temperature. In addition, in the Al rich region, a new compositional range that displays marked ferromagnetism was found.
- P. Kumar, L. H. Li, L. Calhoun, P. Boudreaux, and D. DeVoe, "Fabrication of piezoelectric Al0.3Ga0.7As microstructures," Sensors and Actuators A, 115 (1), 96-103, 2004.
[Abstract]
A process has been developed for the fabrication of single crystal AlGaAs-based MEMS to exploit the inherent piezoelectric transduction of this material for microsensors and microactuation. The process combines molecular beam epitaxial growth of a three-layer single-crystal Al0.3Ga0.7As heterostructure on a GaAs substrate, inductively coupled plasma reactive-ion etching, and selective wet etching of GaAs to produce released Al0.3Ga0.7As beams with integrated electrodes and piezoelectric layers. The process has been validated through the fabrication of both cantilever and doubly clamped beam test structures ranging from 80 to 120 mum in length, up to 15 mum in width, and oriented at angles ranging from 5degrees to 90degrees relative to the (1 1 0) plane. The transverse piezoelectric coupling coefficient d(31) has been measured in released devices as a function of beam orientation using both quasistatic and resonance matching methods, with good agreement to theoretical predictions. (C) 2004 Published by Elsevier B.V.
- M. Datta, M. W. Pruessner, D. P. Kelly, and R. Ghodssi, "Design of MEMS-tunable novel monolithic optical filters in InP with horizontal bragg mirrors," Solid-State Electronics, 48 (10-11), 1959-1963, 2004.
[Abstract]
This paper presents the theoretical design and analysis of a tunable Fabry-Perot resonant microcavity filter realized by movable-waveguide-based integrated optical MEMS technology in InP. Wide-bandwidth, high-reflectivity horizontal InP/air-gap distributed bragg reflector (DBR) mirrors monolithically integrated with the waveguides have been proposed. The filter can be tuned by moving one of the high-reflectivity mirrors axially with on-chip MEMS electrostatic actuation. Spectral performance of the filter is numerically simulated taking into account the diffraction effects. Finite element mechanical modeling of the parallel-plate capacitive microactuator, consisting of a micromachined suspension beam and fixed electrodes, predicts a wide wavelength tuning range (1250-1650 nm) achievable by low actuation voltage (<7 V). (C) 2004 Elsevier Ltd. All rights reserved.
- L. Q. Wu and G. F. Payne, "Biofabrication: using biological materials and biocatalysts to construct nanostructured assemblies," Trends in Biotechnology, 22 (11), 593-599, 2004.
[Abstract]
Emerging opportunities are placing greater demands on device fabrication: next-generation microelectronics will need minimum features of less than 100 nm, high-throughput drug screening will require facile methods to incorporate sensitive biological components into microelectromechanical systems (MEMS), and implantable devices will need to be built from biocompatible materials. Increasingly, these emerging demands are being addressed by combining traditional microfabrication methods with 'biofabrication': namely, the use of biologically derived materials and biocatalysts. Recent fabrication techniques are using biological construction materials as process aids or structural components, and enzymes are being considered for their potential to fabricate devices with high selectivity under mild conditions. If incompatibilities between biology and microfabrication can be eliminated, then biofabrication will be poised to emerge as the standard for nanoscale construction.
- B. Piekarski, M. Dubey, E. Zakar, R. Polcawich, D. DeVoe, and D. Wickenden, "Sol-gel PZT for MEMS applications," Integrated Ferroelectrics, 42, 25-37, 2002.
[Abstract]
Thin-film piezoelectric materials offer an alternative transduction mechanism to electrostatic actuation and capacitive sensing with many attractive advantages for applications in microelectromechanical systems (MEMS). Researchers at the U.S. Army Research Laboratory are utilizing sot-gel deposited lead zirconate titanate (PZT) thin-films in developing several new MEMS technologies, including high frequency filters, magnetometers, micropumps, and pressure sensors. The fabrication procedure and an overview of the technologies being developed are reported.
- B. Baidya, S. K. Gupta, and T. Mukherjee, "An extraction-based verification methodology for MEMS," Journal of Microelectromechanical Systems, 11 (1), 2-11, 2002.
[Abstract]
Micromachining techniques are being increasingly used to develop miniaturized sensor and actuator systems. These system designs tend to be captured as layout, requiring extraction of the equivalent microelectromechanical circuit as a necessary step for design verification. This paper presents an extraction methodology to (re-)construct a circuit schematic representation from the layout, enabling the designer to use micro electromechanical circuit simulators to verify the functional behavior of the layout. This methodology uses a canonical representation of the given layout on which feature-based and graph-based recognition algorithms are applied to generate the equivalent extracted schematic. Extraction can be performed to either the atomic level or the functional level representation of the reconstructed circuit. The choice of level in hierarchy is governed by the trade off between simulation time and simulation accuracy of the extracted circuit. The combination of the MEMS layout extraction and lumped-parameter circuit simulation provides MEMS designers with VLSI-like tools enabling faster design cycles, and improved design productivity.
- L. Q. Wu, A. P. Gadre, H. M. Yi, M. J. Kastantin, G. W. Rubloff, W. E. Bentley, G. F. Payne, and R. Ghodssi, "Voltage-dependent assembly of the polysaccharide chitosan onto an electrode surface," Langmuir, 18 (22), 8620-8625, 2002.
[Abstract]
We examined the assembly of the amine-rich polysaccharide chitosan from solution onto electrode surfaces as a result of voltage bias on the electrode. Chitosan is positively charged and water soluble under mildly acidic conditions and is uncharged and insoluble under basic conditions. We observed that chitosan is deposited from acidic solution onto the surface of a negative electrode and the thickness of the deposited layer is on the order of a micron. The thickness of the deposited layer was observed to be dependent upon the deposition time the applied voltage, and the chitosan concentration, No deposition was observed on the positive electrode or on an "electrode" that had no applied voltage. Once deposited and neutralized, the chitosan layer can be retained on the electrode surface without the need for an applied voltage. Infrared (FT-IR) and electrospray mass spectrometry confirmed that the deposited material was chitosan. These results demonstrate that chitosan can be deposited and retained on electrode surfaces, and the potential advantages for applications in microfabricated devices are discussed.
- J. S. Buch, P. C. Wang, D. L. DeVoe, and C. S. Lee, "Field-effect flow control in a polydimethylsiloxane-based microfluidic system," Electrophoresis, 22 (18), 3902-3907, 2001.
[Abstract]
The application of the field-effect for direct control of electroosmosis in a polydimethyl- siloxane (PDMS)-based microfluidic system, constructed on a silicon wafer with a 2.0 mum electrically insulating layer of silicon dioxide, is demonstrated. This microfluidic system consists of a 2.0 cm open microchannel fabricated on a PDMS slab, which can reversibly adhere to the silicon wafer to form a hybrid microfluidic device. Aside from mechanically serving as a robust bottom substrate to seal the channel and support the microfluidic system, the silicon wafer is exploited to achieve field-effect flow control by grounding the semiconductive silicon medium. When an electric field is applied through the channel, a radial electric potential gradient is created across the silicon dioxide layer that allows for direct control the zeta (zeta) potential and the resulting electroosmotic flow (EOF). By configuring this microfluidic system with two power supplies at both ends of the microchannel, the applied electric potentials can be varied for manipulating the polarity and the magnitude of the radial electric potential gradient across the silicon dioxide layer. At the same time, the longitudinal potential gradient through the microchannel, which is used to induce EOF, is held constant. The. results of EOF control in this hybrid microfluidic system are presented for phosphate buffer at pH 3 and pH 5 It is also demonstrated that EOF control can be performed at higher solution pH of 6 and 7.4 by modifying the silicon wafer surface with cetyltrimethylammonium bromide (CTAB) prior to assembly of the hybrid microfluidic system. Results of EOF control from this study are compared with those reported in the literature involving the use of other microfluidic devices under comparable solution conditions.
- P. C. Wang, D. L. DeVoe, and C. S. Lee, "Integration of polymeric membranes with microfluidic networks for bioanalytical applications," Electrophoresis, 22 (18), 3857-3867, 2001.
[Abstract]
The concept of microfluidics has significantly influenced the design and the implementation of modern bioanalytical systems due to the fact that these miniaturized devices of Mechanical can handle and manipulate samples in a much more efficient way than conventional instruments. In an analogy to the development of microelectronics, increasingly sophisticated devices with greater functionalities have become one of the major goals being pursued in the area of micrototal analysis systems. The incorporation of polymeric membranes into microfluidic networks has therefore been employed in an effort to enhance the functionalities of these microfabricated devices. These commercially available membranes are porous, flexible, mechanically robust and compatible with plastic microfluidic networks. The large surface area-to-volume ratio of porous membrane media is particularly important for achieving rapid buffer exchange during microdialysis and obtaining ultrahigh concentration of adsorbed enzymes for various biochemical reactions. Furthermore, the membrane pore diameter in the sub-mum range eliminates the constraints of diffusional mass-transfer resistance for performing chiral separation using adsorbed protein as the chiral stationary phase. A review on the recent advancement in the integration of polymeric membranes with microfluidic networks is presented for their widespread applications in bioanalytical chemistry.
- D. L. DeVoe, "MEMS and microsystems technology: Opportunities and challenges in experimental mechanics," Experimental Techniques, 25 (6), 1-+, 2001.
[Abstract]
- J. Darabi, M. M. Ohadi, and D. DeVoe, "An electrohydrodynamic polarization micropump for electronic cooling," Journal of Microelectromechanical Systems, 10 (1), 98-106, 2001.
[Abstract]
This paper presents the design, fabrication, and characterization of an innovative microcooling de,ice far microelectronics applications. The device incorporates an active evaporative cooling surface, a polarization micropump, and temperature sensors into a single chip. The micropump provides the required pumping action to bring the working fluid to the evaporating surface, allowing the effective heat transfer coefficient through a thin-film evaporation/boiling process. The device is based on VLSI microfabrication technology, allowing the electrohydrodynamic (EHD) electrodes to be integrated directly onto the cooling surface. Since the EHD electrodes are fabricated using the same technology as the electronic systems themselves, the proposed microelectronic cooling system in the form of an integrated microchip is very suitable for mass production. The prototype devices demonstrated a maximum cooling capacity of 65 W/cm2 with a corresponding pumping head of 250 Pa. The results of this investigation will assist in the development of future microcooling devices capable of operating at high power levels.
- D. L. DeVoe and A. P. Pisano, "Surface micromachined piezoelectric accelerometers (PiXLs)," Journal of Microelectromechanical Systems, 10 (2), 180-186, 2001.
[Abstract]
The design, fabrication, and characterization of surface micromachined piezoelectric accelerometers are presented in this paper. The thin-film aecelerometers employ zinc oxide (ZnO) as the active piezoelectric material, with different designs using either polysilicon or ZnO bimorph substrates, Sensitivity analyses are presented for two specific sensor designs. Guidelines for design optimization are derived by combining expressions for device sensitivity and resonant frequency. Two microfabrication techniques based on SiO2 and Si sacrificial etching are outlined. Techniques for residual stress compensation in both fabrication processes are discussed. Accelerometers based on both processes have been fabricated and characterized. A sensitivity of 0.95 fC/g and resonant frequency of 3.3 kHz has been realized for a simple cantilever accelerometer fabricated using the sacrificial SiO2 process. Sensors fabricated in the sacrificial Si process with discrete proof masses have exhibited sensitivities of 13.3 fC/g and 44.7 fC/g at resonant frequencies of 2.23 kHz and 1.02 kHz, respectively.
- R. J. Jackman, T. M. Floyd, R. Ghodssi, M. A. Schmidt, and K. F. Jensen, "Microfluidic systems with on-line UV detection fabricated in photodefinable epoxy," Journal of Micromechanics and Microengineering, 11 (3), 263-269, 2001.
[Abstract]
This paper describes a method for fabricating microfluidic devices in a photodefinable epoxy (SU-8). This technique is compatible with, and complementary to, conventional fabrication techniques. It allows microstructures formed in SU-8 to be bonded to produce sealed microfluidic channels. A micromixer fabricated entirely in SU-8, using this technique, for performing liquid-phase reactions is shown to be suitable for visible spectroscopy. This fabrication method also allows the incorporation of materials that are often difficult to integrate. By fabricating hybrid devices that incorporate quartz windows, we demonstrate that these devices are compatible with organic solvents and that in situ ultraviolet detection in a microfluidic system is possible.
- B. Panchapakesan, D. L. DeVoe, M. R. Widmaier, R. Cavicchi, and S. Semancik, "Nanoparticle engineering and control of tin oxide microstructures for chemical microsensor applications," Nanotechnology, 12 (3), 336-349, 2001.
[Abstract]
The use of metal nanoparticles as seed layers for controlling the microstructures of tin oxide (SnO2) films on temperature controllable micromachined platforms has been investigated. The study is focused on SnO2 due to its importance in the field of chemical microsensors. Nanoparticle seeds of iron, cobalt, nickel, copper and silver were formed by vapour deposition on the microhotplates followed by annealing at 500 degreesC prior to self-aligned SnO2 deposition. Significant control of SnO2 grain sizes, ranging between 20 and 121 nm, was achieved depending on the seed-layer type. A correlation was found between decreasing the SnO2 grain size and increasing the melting temperature of the seed-layer metals, suggesting the use of high temperature metals as being appropriate choices as seed layers for obtaining a smaller SnO2 grain structure. Smaller grain diameters resulted in high sensitivity in 90 ppm ethanol illustrating the benefits of nanoparticle seeding for chemical sensing. The initial morphology, particle size and distribution of the seed layers was found to dictate the final SnO2 morphology and grain size. This paper not only demonstrates the possibility of depositing nanostructured oxide materials for chemical microsensor applications, but also demonstrates the feasibility of conducting combinatorial research into nanoparticle growth using temperature controllable microhotplate platforms. This paper also demonstrates the possibility of using multi-element arrays to form a range of different types of devices that could be used with suitable olfactory signal processing techniques in order to identify a variety of gases.
- P. Abshire and A. G. Andreou, "Capacity and energy cost of information in biological and silicon photoreceptors," Proceedings of the IEEE, 89 (7), 1052-1064, 2001.
[Abstract]
We outline a theoretical framework to analyze information processing in biological sensory organs and in engineered microsystems. We employ the mathematical tools of communication theory and model natural or synthetic physical structures as microscale communication networks, studying them under physical constraints at two different levels of abstraction. At the functional levels we examine the operational and task specification. while at the physical level, we examine the material specification and realization. Both levels of abstraction are characterized by Shannon's channel capacity as determined bi, the channel bandwidth, the signal power, and the noise power he link between the functional level and the physical level of abstraction is established through models for transformations on the signal, physical constraints on the system, and noise that degrades the signal. As a specific example, we present a comparative study of information capacity (in bits per second) versus energy cost of information (in joules per bit) in a biological and in a silicon adaptive photoreceptor The communication channel model for each of the two systems is a cascade of linear bandlimiting sections followed by additive noise. We model the filters and the noise from first principles whenever possible and phenomenologically otherwise. The parameters for the blowfly model are determined from biophysical data available in the literature. and the parameters of the silicon model are determined from our experimental data. This comparative study is a first step toward a fundamental and quantitative understanding of the tradeoffs between system performance and associated costs such as size, reliability, and energy requirements for natural and engineered sensory microsystems.
- Z. X. Liu and D. L. DeVoe, "Micromechanism fabrication using silicon fusion bonding," Robotics and Computer-Integrated Manufacturing, 17 (1-2), 131-137, 2001.
[Abstract]
Silicon fusion bonding is studied as an enabling technology for the fabrication of microrobotic mechanisms. The effects of both surface activation technique and annealing temperature on bond strength are considered using a crack-opening technique. As part of the study, the relationship between patterned silicon feature size and the resulting bond strength is explored. Based on the experimental results, recommendations for an optimal silicon fusion bonding process for micromechanism fabrication are presented. The experimental results indicate that bulk silicon bonding strength can be achieved independent of feature size at temperatures as low as 300 degreesC, with positive implications for micromechanism fabrication. (C) 2001 Elsevier Science Ltd. All rights reserved.
- B. Piekarski, D. DeVoe, M. Dubey, R. Kaul, and J. Conrad, "Surface micromachined piezoelectric resonant beam filters," Sensors and Actuators A, 91 (3), 313-320, 2001.
[Abstract]
Piezoelectric actuation and sensing of suspended single-beam microelectromechanical system (MEMS) resonant filters is demonstrated. Resonant frequencies between 171 kHz and 9.2 MHz were observed for resonators with dimensions of 6-20 mum wide and 25-400 mum long. Operation was demonstrated from a vacuum pressure of 20 mTorr to atmospheric with drive voltages as low as 2.5 mV and a dynamic range of greater than 40 dB. Loaded quality factors (Q(s)) greater than 1000 resulted at 9.2 MHz and a 20 mTorr pressure. A 20 kHz tuning range resulting from the piezoelectric poling conditions and a 75 ppm/K frequency temperature dependency was observed. The resonators utilize a clamped-clamped beam design with sol-gel lead zirconate titanate (PZT) as the piezoelectric actuator and sensor, PECVD silicon dioxide as the resonant beam structure, and platinum as the top and bottom electrode. The effects of operating temperature, operating pressure, poling condition, and drive voltage are reported. (C) 2001 Elsevier Science B.V. All rights reserved.
- X. Zhang, K. S. Chen, R. Ghodssi, A. A. Ayon, and S. M. Spearing, "Residual stress and fracture in thick tetraethylorthosilicate (TEOS) and silane-based PECVD oxide films," Sensors and Actuators A - Physical, 91 (3), 373-380, 2001.
[Abstract]
This paper reports residual stress measurements and fracture analysis in thick tetraethylorthosilicate (TEOS) and silane-based plasma enhanced chemical vapor deposition (PECVD) oxide films. The measured residual stress depended strongly on thermal process parameters; dissolved hydrogen gases played an important role in governing intrinsic stress. The tendency to form cracks was found to be a strong function of film thickness and annealing temperature. Critical cracking temperature was predicted using mixed mode fracture mechanics, and the predictions provide a reasonable match to experimental observations. Finally, engineering solutions were demonstrated to overcome the problems caused by wafer bow and film cracks. The results of this study should be able to provide important insights for the design of fabrication processes for MEMS devices requiring high temperature processing of films. (C) 2001 Elsevier Science B.V. All rights reserved.
- S. Semancik, R. E. Cavicchi, M. C. Wheeler, J. E. Tiffany, G. E. Poirier, R. M. Walton, J. S. Suehle, B. Panchapakesan, and D. L. DeVoe, "Microhotplate platforms for chemical sensor research," Sensors and Actuators B, 77 (1-2), 579-591, 2001.
[Abstract]
This paper describes the development and use of microdevices and microarrays in chemical sensor research. The surface-micromachined "microhotplate" structure common within the various platforms included here was originally designed for fabricating conductometric gas microsensor prototypes. Microhotplate elements include functionality for measuring and controlling temperature, and measuring the electrical properties of deposited films. As their name implies, they are particularly well-suited for examining temperature-dependent phenomena on a micro-scale, and their rapid heating/cooling characteristics has led to the development of low power sensors that can be operated in dynamic temperature programmed modes. Tens or hundreds of the microhotplates can be integrated within arrays that serve as platforms for efficiently producing processing/performance correlations for sensor materials. The microdevices also provide a basis for developing new types of sensing prototypes and can be used in investigations of proximity effects and surface transient phenomena. Published by Elsevier Science B.V.
- E. W. H. Jager, E. Smela, and O. Inganas, "Microfabricating conjugated polymer actuators," Science, 290 (5496), 1540-1545, 2000.
[Abstract]
Conjugated polymer actuators can be operated in aqueous media, which makes them attractive for laboratories-on-a-chip and applications under physiological conditions. One of the most stable conjugated polymers under these conditions is polypyrrole, which can be patterned by means of standard photolithography. Polypyrrole-gold bilayer actuators that bend out of the plane of the wafer have been microfabricated in our laboratory. These can be used to move and position other microcomponents. Here we review the current status of these microactuators, outlining the methods used to fabricate them. We describe the devices that have been demonstrated as well as some potential future applications.
- Y. Kaminorz, E. Smela, T. Johansson, L. Brehmer, M. R. Andersson, and O. Inganas, "Characteristics of polythiophene surface light emitting diodes," Synthetic Metals, 113 (1-2), 103-114, 2000.
[Abstract]
Surface light emitting diodes (SLEDs), in which previously microfabricated electrodes were coated with a conjugated polymer, were made with greatly different electrode spacings (250 nm and 10 or 20 mu m) and with different electrode material combinations. The fabrication process allowed us to compare several electrode materials. The SLED structures also enabled imaging of the light emission zone with fluorescence video microscopy. Conventional sandwich structures were also made for comparison (electrode separation 50 nm). In this study, the emitting layer was poly[3-(2',5'-bis(1'',4",7" trioxaoctyl)phenyl)-2,2'-bithiophene] (EO-PT), a conjugated polymer based on polythiophene with oligo(ethyleneoxide) side chains. The current-voltage (I(V)) and light-voltage (L(V)) characteristics of the SLEDs were largely insensitive to electrode separation except at high voltages, at which the current in the devices with the largest separations was limited. Sandwich structures had the same light output at a given current. Light could be obtained in forward and reverse bias from indium tin oxide (ITO)-aluminum, gold silicide-aluminum, and gold silicide-gold SLEDs, but the turn-on voltages were lowest with the ITO-aluminum devices, and these were also the brightest and most reliable. Adding salt to the EO-PT increased the current and brightness, decreased the turn-on voltages, and made the I(V) characteristics symmetric; thus, a device with an electrode separation of 10 mu m had the extraordinarily low turn-on voltage of 6 V. The location of the light emission was at the electron-injecting contact. (C) 2000 Elsevier Science S.A. All rights reserved.
- E. Smela, "A microfabricated movable electrochromic "pixel" based on polypyrrole," Advanced Materials, 11 (16), 1343-1345, 1999.
[Abstract]
- E. Smela and N. Gadegaard, "Surprising volume change in PPy(DBS): An atomic force microscopy study," Advanced Materials, 11 (11), 953-+, 1999.
[Abstract]
Communication: Conjugated polymers such as polypyrrole (PPy) have potential use as artificial muscles or in microsystems such as valves for micro-fluid handling. One of the most important parameters in such uses is the magnitude of volume change during associated redox processes; however, until now estimates have varied greatly. Atomic force microscopy is reported here as allowing direct measurement of the in situ thickness change during oxidation and reduction of thin films of PPy doped with dodecylbenzenesulfonate.
- H. R. Last, M. Deeds, D. Garvick, R. Kavetsky, P. A. Sandborn, E. B. Magrab, and S. K. Gupta, "Nano-to-millimeter scale integrated systems," IEEE Transactions on Components and Packaging Technologies, 22 (2), 338-343, 1999.
[Abstract]
- B. Piekarski, M. Dubey, D. Devoe, E. Zakar, R. Zeto, J. Conrad, R. Piekarz, and M. Ervin, "Fabrication of suspended piezoelectric microresonators," Integrated Ferroelectrics, 24 (1-4), 147-154, 1999.
[Abstract]
A new process for realizing piezoelectric microdevices has been developed. Suspended piezoelectric clamped-clamped beam resonators have been fabricated using sol-gel deposited lead zirconate titanate (PZT) films as the piezoelectric material, platinum (Pt) as the top and bottom electrode, and silicon dioxide for the supporting beam structure. A five-mask process was used to fabricate the suspended resonators. The process flow included sol-gel PZT deposition, Pt sputter deposition, Pt and PZT argon ion milling, PZT wet and reactive ion etching (RTE), silicon deep reactive ion etching (DRIE), and oxide RIE. Both single- and triplebeam resonators were fabricated with beam widths of 15, 20, and 30 mu m and lengths of 200 and 400 mu m. Testing of the resonators produced resonant frequencies between 100 kHz and 1.2 MHz, depending on beam geometry.
- E. Smela, M. Kallenbach, and J. Holdenried, "Electrochemically driven polypyrrole bilayers for moving and positioning bulk micromachined silicon plates," Journal of Microelectromechanical Systems, 8 (4), 373-383, 1999.
[Abstract]
The conjugated polymer polypyrrole undergoes a volume change of several percent when its oxidation state is changed electrochemically by the application of voltages between 0 and -1 V (versus Ag/AgCl), This volume change is due to ion movements in or out of the polymer film, Bilayers of polypyrrole and gold undergo a large bending and can deliver high force. They can thus function as hinges to lift rigid components, In this work, we demonstrate that silicon plates produced by reactive ion etching can be lifted by such PPy/Au hinges. The strength and efficiency of these bilayers are also determined. [419].
- E. Smela, "Microfabrication of PPy microactuators and other conjugated polymer devices," Journal of Micromechanics and Microengineering, 9 (1), 1-18, 1999.
[Abstract]
Conjugated polymers have a number of interesting properties that can be exploited in microfabricated sensors and actuators. For example, polypyrrole is a conjugated polymer that can change volume to deliver significant stresses and strains. These materials can be patterned using conventional microfabrication techniques. The procedures for doing this are described in this paper, focusing on the microfabrication of polypyrrole microactuators. in addition, other methods for the deposition and patterning of conjugated polymers are reviewed. A special technique for releasing actuators, differential adhesion, is also detailed.
- E. W. H. Jager, E. Smela, and O. Inganas, "On-chip microelectrodes for electrochemistry with moveable PPy bilayer actuators as working electrodes," Sensors and Actuators B - Chemical
56 (1-2), 73-78, 1999.
[Abstract]
We present electrochemical microactuators which have all the electrodes necessary for the actuation-the working, counter, and reference electrodes-on-chip. This is a first step towards an all-polymer system, i.e., a system that does not require a liquid electrolyte. The microactuators' performance was as good as when standard, off-chip counter and reference electrodes were used. Specifically, the speed of actuation was the same. In addition, we obtained;a good cyclic voltammogram, although the oxidation and reduction peaks were shifted and some noise was present. Apart from application in an all-polymer system, we will also use these microactuators for studies on the effect of mechanical stimulation of living cells. (C) 1999 Elsevier Science S.A. All rights reserved.
- E. W. H. Jager, E. Smela, O. Inganas, and I. Lundstrom, "Polypyrrole microactuators," Synthetic Metals, 102 (1-3), 1309-1310, 1999.
[Abstract]
The doping and undoping of conjugated polymers is accompanied by a volume change. This volume change can be used to make micro-actuators, We have built polypyrrole (PPy) gold bilayer structures. The volume change of PPy induces a bending of the bilayer. We have made micro-actuators based on this principle, which have been examined with video-microscopy. Some applications for these micro-actuators are proposed, including opening and closing boxes for cell biology and nanoliter chemistry and micro-robotics.
- D. Pede, E. Smela, T. Johansson, M. Johansson, and O. Inganas, "A general-purpose conjugated-polymer device array for imaging," Advanced Materials, 10 (3), 233-+, 1998.
[Abstract]
Communication: Optical and chemical "cameras" are possible using the general purpose device array geometry presented. The device consists of an array of bridge pixels covered by a conjugated polymer layer suitable for sensing of optical or chemical stimuli. In this geometry the polymer is directly exposed to the environment, which allows the array to be used not only to read optical images but also to detect the distribution of chemical species or even to drive an optical display. Microfabricated arrays are demonstrated, and it is shown that these bridge arrays can perform as well as standard photodiode sandwich arrays.
- E. Smela, Y. Kaminorz, O. Inganas, and L. Brehmer, "Planar microfabricated polymer light-emitting diodes," Semiconductor Science and Technology, 13 (4), 433-439, 1998.
[Abstract]
Conjugated polymers are organic semiconducting materials that can emit light. These polymers have the advantages of being light, cheap and easy to process, and in addition the band gap can be tailored. We report the microfabrication of surface light-emitting diodes (SLEDs) on silicon substrates in which the electrodes are underneath the organic electroluminescent layer. Patterned electrodes are separated by a 2500 Angstrom thick insulating layer of silicon oxide or are interdigitated with a separation of 10 or 20 mu m; the luminescent polymer is spin coated or solvent cast on top of the electrodes. This fabrication method is completely compatible with conventional silicon processing because the polymer is deposited last and the light is emitted from the upper surface of the diodes. Despite the large spacing between electrodes, and despite the absence of an evaporated top contact, the Voltages required for light emission were not much greater than those used in conventional sandwich-type structures.
- D. L. DeVoe and A. P. Pisano, "Modeling and optimal design of piezoelectric cantilever microactuators," Journal of Microelectromechanical Systems, 6 (3), 266-270, 1997.
[Abstract]
A novel model is described for predicting the static behavior of a piezoelectric cantilever actuator with an arbitrary configuration of elastic and piezoelectric layers, The model is compared to deflection measurements obtained from 500-mu m-long ZnO cantilever actuators fabricated by surface micromachining, Modeled and experimental results demonstrate the utility of the model for optimizing device design, A discussion of design considerations and optimization of device performance is presented.
- E. Smela, O. Inganas, and I. Lundstrom, "Controlled folding of micrometer-size structures," Science, 268 (5218), 1735-1738, 1995.
[Abstract]
Several types of microactuators have been fabricated, from simple paddles to self-assembling and -disassembling cubes. Conducting bilayers made of a layer of polymer and a layer of gold were used as hinges to connect rigid plates to each other and to a silicon substrate. The bending of the hinges was electrically controlled and reversible, allowing precise three-dimensional positioning of the plates. The structures were released from the substrate with a technique based on differential adhesion. This method, which avoids the use of a sacrificial layer and allows the actuators to pull themselves off the surface, may have general applications in micromachining. Possibilities include the manufacture of surfaces whose light reflection or chemical properties can be switched.
- E. Smela, O. Inganas, Q. B. Pei, and I. Lundstrom, "Electrochemical muscles- micromachining fingers and corkscrews," Advanced Materials, 5 (9), 630-632, 1993.
[Abstract]
Millimeter-scale polymer ''fingers'' are reported, in which the volume changes of the conjugated polymer polypyrrole that occur in response to electrochemical reduction or oxidation are used to create electrically controlled mechanical actuators. The short bilayer gold and polypyrrole fingers in the Figure can be made to curl by reducing the polypyrrole. The primitive fabrication technique used to make these fingers points the way to the microminiaturization of these artificial muscles.
- R. Ghodssi, D. D. Denton, A. A. Seireg, and B. Howland, "Rolling friction in a linear microactuator," Journal of Vacuum Science & Technology A, 11 (4), 803-807, 1993.
[Abstract]
In order to design a precise and repeatable microelectromechanical system, friction and wear must be minimized in the surfaces of the microstructure. Rolling bearings are known to exhibit lower friction over sliding contact bearings in precision macromechanical systems. Rolling friction can be characterized on a microscale to facilitate the design of precision microelectromechanical systems. We have designed a test specimen utilizing stainless steel microballs (285 mum in diameter) in contact with silicon micromachined v-groove surfaces (310 mum wide, 163 mum deep, 10 000 mum long). Different thin films are deposited on the surface of the silicon v grooves and their frictional properties are investigated experimentally. We have shown that at zero applied normal force, the adhesion is dominant and as the applied normal force is increased, the friction coefficient reaches an asymptotic value below 0.01. The measured frictional forces represent the total resistance at the onset of rolling motion for the bearing which is generated at all the contacting surfaces. The measured values for the coefficient of friction will allow designers to select optimum lubricant surfaces to be used in microroller bearings using microballs and silicon micromachined V-groove surfaces.