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Dec 2009

Volume 3, Issue 4, Articles (04xxxx)

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Study on surface properties of PDMS microfluidic chips treated with albumin

Walter Schrott, Zdeněk Slouka, Petr Červenka, Jiří Ston, Marek Nebyla, Michal Přibyl, and Dalimil Šnita

Biomicrofluidics 3, 044101 (2009); http://dx.doi.org/10.1063/1.3243913 (15 pages) | Cited 8 times

Online Publication Date: 12 October 2009

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Electrokinetic properties and morphology of PDMS microfluidic chips intended for bioassays are studied. The chips are fabricated by a casting method followed by polymerization bonding. Microchannels are coated with 1% solution of bovine serum albumin (BSA) in Tris buffer. Albumin passively adsorbs on the PDMS surface. Electrokinetic characteristics (electro-osmotic velocity, electro-osmotic mobility, and zeta potential) of the coated PDMS channels are experimentally determined as functions of the electric field strength and the characteristic electrolyte concentration. Atomic force microscopy (AFM) analysis of the surface reveals a “peak and ridge” structure of the protein layer and an imperfect substrate coating. On the basis of the AFM observation, several topologies of the BSA-PDMS surface are proposed. A nonslip mathematical model of the electro-osmotic flow is then numerically analyzed. It is found that the electrokinetic characteristics computed for a channel with the homogeneous distribution of a fixed electric charge do not fit the experimental data. Heterogeneous distribution of the fixed electric charge and the surface roughness is thus taken into account. When a flat PDMS surface with electric charge heterogeneities is considered, the numerical results are in very good agreement with our experimental data. An optimization analysis finally allowed the determination of the surface concentration of the electric charge and the degree of the PDMS surface coating. The obtained findings can be important for correct prediction and possibly for robust control of behavior of electrically driven PDMS microfluidic chips. The proposed method of the electro-osmotic flow analysis at surfaces with a heterogeneous distribution of the surface electric charge can also be exploited in the interpretation of experimental studies dealing with protein-solid phase interactions or substrate coatings.
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87.80.Ek Mechanical and micromechanical techniques
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
47.85.Np Fluidics

Concurrent droplet charging and sorting by electrostatic actuation

Byungwook Ahn, Kangsun Lee, Romain Louge, and Kwang W. Oh

Biomicrofluidics 3, 044102 (2009); http://dx.doi.org/10.1063/1.3250303 (8 pages) | Cited 10 times

Online Publication Date: 13 October 2009

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This paper presents a droplet-based microfluidic device for concurrent droplet charging and sorting by electrostatic actuation. Water-in-oil droplets can be charged on generation by synchronized electrostatic actuation. Then, simultaneously, the precharged droplets can be electrostatically steered into any designated laminar streamline, thus they can be sorted into one of multiple sorting channels one by one in a controlled fashion. In this paper, we studied the size dependence of the water droplets under various relative flow rates of water and oil. We demonstrated the concurrent charging and sorting of up to 600 droplets/s by synchronized electrostatic actuation. Finally, we investigated optimized voltages for stable droplet charging and sorting. This is an essential enabling technology for fast, robust, and multiplexed sorting of microdroplets, and for the droplet-based microfluidic systems.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
87.80.Ek Mechanical and micromechanical techniques
47.55.D- Drops and bubbles
47.85.Np Fluidics

Design and optimization of a double-enzyme glucose assay in microfluidic lab-on-a-chip

Yegermal Tesfaw Atalay, Daan Witters, Steven Vermeir, Nicolas Vergauwe, Pieter Verboven, Bart Nicolaï, and Jeroen Lammertyn

Biomicrofluidics 3, 044103 (2009); http://dx.doi.org/10.1063/1.3250304 (14 pages) | Cited 12 times

Online Publication Date: 19 October 2009

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An electrokinetic driven microfluidic lab-on-a-chip was developed for glucose quantification using double-enzyme assay. The enzymatic glucose assay involves the two-step oxidation of glucose, which was catalyzed by hexokinase and glucose-6-phosphate dehydrogenase, with the concomitant reduction of NADP+ to NADPH. A fluorescence microscopy setup was used to monitor the different processes (fluid flow and enzymatic reaction) in the microfluidic chip. A two-dimensional finite element model was applied to understand the different aspects of design and to improve the performance of the device without extensive prototyping. To our knowledge this is the first work to exploit numerical simulation for understanding a multisubstrate double-enzyme on-chip assay. The assay is very complex to implement in electrokinetically driven continuous system due to the involvement of many species, which has different transport velocity. With the help of numerical simulation, the design parameters, flow rate, enzyme concentration, and reactor length, were optimized. The results from the simulation were in close agreement with the experimental results. A linear relation exists for glucose concentrations from 0.01 to 0.10 g l−1. The reaction time and the amount of enzymes required were drastically reduced compared to off-chip microplate analysis.
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87.80.Ek Mechanical and micromechanical techniques
87.14.ej Enzymes
87.15.R- Reactions and kinetics
87.10.Kn Finite element calculations
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Dielectrophoretic field-flow method for separating particle populations in a chip with asymmetric electrodes

Ciprian Iliescu, Guillaume Tresset, and Guolin Xu

Biomicrofluidics 3, 044104 (2009); http://dx.doi.org/10.1063/1.3251125 (10 pages) | Cited 12 times

Online Publication Date: 21 October 2009

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This paper presents a field-flow method for separating particle populations in a dielectrophoretic (DEP) chip with asymmetric electrodes under continuous flow. The structure of the DEP device (with one thick electrode that defines the walls of the microfluidic channel and one thin electrode), as well as the fabrication and characterization of the device, was previously described. A characteristic of this structure is that it generates an increased gradient of electric field in the vertical plane that can levitate the particles experiencing negative DEP. The separation method consists of trapping one population to the bottom of the microfluidic channel using positive DEP, while the other population that exhibits negative DEP is levitated and flowed out. Viable and nonviable yeast cells were used for testing of the separation method.
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87.80.Ek Mechanical and micromechanical techniques
47.85.Np Fluidics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
82.45.-h Electrochemistry and electrophoresis
87.15.Tt Electrophoresis
87.17.-d Cell processes

A microfluidic DNA computing processor for gene expression analysis and gene drug synthesis

Yu Zhang, Hao Yu, Jianhua Qin, and Bingcheng Lin

Biomicrofluidics 3, 044105 (2009); http://dx.doi.org/10.1063/1.3259628 (8 pages) | Cited 4 times

Online Publication Date: 6 November 2009

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Boolean logic performs a logical operation on one or more logic input and produces a single logic output. Here, we describe a microfluidic DNA computing processor performing Boolean logic operations for gene expression analysis and gene drug synthesis. Multiple cancer-related genes were used as input molecules. Their expression levels were identified by interacting with the computing related DNA strands, which were designed according to the sequences of cancer-related genes and the suicide gene. When all the expressions of the cancer-related genes fit in with the diagnostic criteria, positive diagnosis would be confirmed and then a complete suicide gene (gene drug) could be synthesized as an output molecule. Microfluidic chip was employed as an effective platform to realize the computing process by integrating multistep biochemical reactions involving hybridization, displacement, denaturalization, and ligation. By combining the specific design of the computing related molecules and the integrated functions of the microfluidics, the microfluidic DNA computing processor is able to analyze the multiple gene expressions simultaneously and realize the corresponding gene drug synthesis with simplicity and fast speed, which demonstrates the potential of this platform for DNA computing in biomedical applications.
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82.39.Pj Nucleic acids, DNA and RNA bases
87.15.Qt Sequence analysis
87.80.St Genomic techniques
47.85.-g Applied fluid mechanics

Cascade optical chromatography for sample fractionation

Alex Terray, Joseph D. Taylor, and Sean J. Hart

Biomicrofluidics 3, 044106 (2009); http://dx.doi.org/10.1063/1.3262415 (6 pages) | Cited 6 times

Online Publication Date: 16 November 2009

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Optical chromatography involves the elegant combination of opposing optical and fluid drag forces on colloidal samples within microfluidic environments to both measure analytical differences and fractionate injected samples. Particles that encounter the focused laser beam are trapped axially along the beam and are pushed upstream from the laser focal point to rest at a point where the optical and fluid forces on the particle balance. In our recent devices particles are pushed into a region of lower microfluidic flow, where they can be retained and fractionated. Because optical and fluid forces on a particle are sensitive to differences in the physical and chemical properties of a sample, separations are possible. An optical chromatography beam focused to completely fill a fluid channel is operated as an optically tunable filter for the separation of inorganic, polymeric, and biological particle samples. We demonstrate this technique coupled with an advanced microfluidic platform and show how it can be used as an effective method to fractionate particles from an injected multicomponent sample. Our advanced three-stage microfluidic design accommodates three lasers simultaneously to effectively create a sequential cascade optical chromatographic separation system.
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87.80.Ek Mechanical and micromechanical techniques
87.50.wf Biophysical mechanisms of interaction
42.62.Be Biological and medical applications

Development and fertility studies on post-bio-electrosprayed Drosophila melanogaster embryos

Pascal Joly, Barbara H. Jennings, and Suwan N. Jayasinghe

Biomicrofluidics 3, 044107 (2009); http://dx.doi.org/10.1063/1.3267044 (8 pages) | Cited 10 times

Online Publication Date: 18 November 2009

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Bio-electrosprays (BESs) provide a means of precisely manipulating cells and thus have the potential for many clinical uses such as the generation of artificial tissues/organs. Previously we tested the biological safety of this technology with a variety of living cells and also embryos from the vertebrate model organisms Danio rerio (zebrafish) and Xenopus tropicalis (frog). However, the viability and fertility of the treated embryos could not be fully assessed due to animal licensing laws. Here we assay the viability and fertility of Drosophila melanogaster (fruit fly) embryos in conjunction with the bio-electrospray procedure. Bio-electrosprayed Drosophila embryos developed into fully fertile adult flies that were indistinguishable from wild-type. Thus, we demonstrate that the bio-electrospray procedure does not induce genetic or physical damage that significantly affects the development or fertility of a multicellular organism. This study along with our previous investigations demonstrates the potential of this approach to be developed for the precise manipulation of sensitive biological materials.
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87.80.Fe Micromanipulation of biological structures
87.85.jc Electrical, thermal, and mechanical properties of biological matter
87.18.-h Biological complexity

Glutaraldehyde enhanced dielectrophoretic yeast cell separation

Zachary Gagnon, Jill Mazur, and Hsueh-Chia Chang

Biomicrofluidics 3, 044108 (2009); http://dx.doi.org/10.1063/1.3257857 (11 pages) | Cited 11 times

Online Publication Date: 23 November 2009

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We introduce a method for improved dielectrophoretic (DEP) discrimination and separation of viable and nonviable yeast cells. Due to the higher cell wall permeability of nonviable yeast cells compared with their viable counterpart, the cross-linking agent glutaraldehyde (GLT) is shown to selectively cross-link nonviable cells to a much greater extent than viable yeast. The DEP crossover frequency (cof) of both viable and nonviable yeast cells was measured over a large range of buffer conductivities (22 μS/cm–400 μS/cm) in order to study this effect. The results indicate that due to selective nonviable cell cross-linking, GLT modifies the DEP cof of nonviable cells, while viable cell cof remains relatively unaffected. To investigate this in more detail, a dual-shelled oblate spheroid model was evoked and fitted to the cof data to study cell electrical properties. GLT treatment is shown to minimize ion leakage out of the nonviable yeast cells by minimizing changes in cytoplasm conductivity over a large range of ionic concentrations. This effect is only observable in nonviable cells where GLT treatment serves to stabilize the cell cytoplasm conductivity over a large range of buffer conductivity and allow for much greater differences between viable and nonviable cell cofs. As such, by taking advantage of differences in cell wall permeability GLT magnifies the effect DEP has on the field induced separation of viable and nonviable yeasts.
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87.80.-y Biophysical techniques (research methods)
87.50.ch Electrophoresis/dielectrophoresis and other mechanical effects
87.85.jc Electrical, thermal, and mechanical properties of biological matter
87.16.dp Transport, including channels, pores, and lateral diffusion

Electrokinetic focusing and filtration of cells in a serpentine microchannel

Christopher Church, Junjie Zhu, Gaoyan Wang, Tzuen-Rong J. Tzeng, and Xiangchun Xuan

Biomicrofluidics 3, 044109 (2009); http://dx.doi.org/10.1063/1.3267098 (10 pages) | Cited 25 times

Online Publication Date: 24 November 2009

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Focusing cells into a single stream is usually a necessary step prior to counting and separating them in microfluidic devices such as flow cytometers and cell sorters. This work presents a sheathless electrokinetic focusing of yeast cells in a planar serpentine microchannel using dc-biased ac electric fields. The concurrent pumping and focusing of yeast cells arise from the dc electrokinetic transport and the turn-induced ac/dc dielectrophoretic motion, respectively. The effects of electric field (including ac to dc field ratio and ac field frequency) and concentration (including buffer concentration and cell concentration) on the cell focusing performance were studied experimentally and numerically. A continuous electrokinetic filtration of E. coli cells from yeast cells was also demonstrated via their differential electrokinetic focusing in a serpentine microchannel.
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87.50.ch Electrophoresis/dielectrophoresis and other mechanical effects
87.16.-b Subcellular structure and processes
82.45.Tv Bioelectrochemistry
07.10.Cm Micromechanical devices and systems
87.15.Tt Electrophoresis

dc electrokinetic transport of cylindrical cells in straight microchannels

Ye Ai, Ali Beskok, David T. Gauthier, Sang W. Joo, and Shizhi Qian

Biomicrofluidics 3, 044110 (2009); http://dx.doi.org/10.1063/1.3267095 (16 pages) | Cited 12 times

Online Publication Date: 24 November 2009

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Electrokinetic transport of cylindrical cells under dc electric fields in a straight microfluidic channel is experimentally and numerically investigated with emphasis on the dielectrophoretic (DEP) effect on their orientation variations. A two-dimensional multiphysics model, composed of the Navier–Stokes equations for the fluid flow and the Laplace equation for the electric potential defined in an arbitrary Lagrangian–Eulerian framework, is employed to capture the transient electrokinetic motion of cylindrical cells. The numerical predictions of the particle transport are in quantitative agreement with the obtained experimental results, suggesting that the DEP effect should be taken into account to study the electrokinetic transport of cylindrical particles even in a straight microchannel with uniform cross-sectional area. A comprehensive parametric study indicates that cylindrical particles would experience an oscillatory motion under low electric fields. However, they are aligned with their longest axis parallel to the imposed electric field under high electric fields due to the induced DEP effect.
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87.17.Rt Cell adhesion and cell mechanics
47.85.Np Fluidics
47.60.Dx Flows in ducts and channels
47.10.ad Navier-Stokes equations
82.45.-h Electrochemistry and electrophoresis

Nanoparticle image velocimetry at topologically structured surfaces

Gea O. F. Parikesit, Jeffrey S. Guasto, Salvatore Girardo, Elisa Mele, Ripalta Stabile, Dario Pisignano, Ralph Lindken, and Jerry Westerweel

Biomicrofluidics 3, 044111 (2009); http://dx.doi.org/10.1063/1.3270523 (15 pages) | Cited 3 times

Online Publication Date: 1 December 2009

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Nanoparticle image velocimetry (nano-PIV), based on total internal reflection fluorescent microscopy, is very useful to investigate fluid flows within ∼ 100 nm from a surface; but so far it has only been applied to flow over smooth surfaces. Here we show that it can also be applied to flow over a topologically structured surface, provided that the surface structures can be carefully configured not to disrupt the evanescent-wave illumination. We apply nano-PIV to quantify the flow velocity distribution over a polydimethylsiloxane surface, with a periodic gratinglike structure (with 215 nm height and 2 μm period) fabricated using our customized multilevel lithography method. The measured tracer displacement data are in good agreement with the computed theoretical values. These results demonstrate new possibilities to study the interactions between fluid flow and topologically structured surfaces.
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47.85.Np Fluidics
47.80.Jk Flow visualization and imaging
81.16.Nd Micro- and nanolithography

The role of DNA diffusion in solid phase polymerase chain reaction with gel-immobilized primers in planar and capillary microarray format

Alexei L. Drobyshev, Tatiana V. Nasedkina, and Natalia V. Zakharova

Biomicrofluidics 3, 044112 (2009); http://dx.doi.org/10.1063/1.3271461 (12 pages)

Online Publication Date: 1 December 2009

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The solid phase polymerase chain reaction (PCR) on a gel-based microarray system was studied under various durations of individual stages of the PCR cycle and spatial restriction of the reaction volume. Combining the experimental study with numerical modeling, we demonstrated that the diffusion of the PCR product in and out of a microarray element during the annealing and melting stages, respectively, is the main factor responsible for distinctive features of the studied type of PCR. The restriction of reaction volume leads to faster PCR signal growth. Particularly, the capillary array, whereby gel-based microarray elements are located on a glass bar inserted into capillary chamber, was found to be a suitable format for the development of the platform.
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87.15.R- Reactions and kinetics
47.85.Np Fluidics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
82.35.Pq Biopolymers, biopolymerization
87.80.Ek Mechanical and micromechanical techniques

An electrohydrodynamic flow in ac electrowetting

Horim Lee, Sungchan Yun, Sung Hee Ko, and Kwan Hyoung Kang

Biomicrofluidics 3, 044113 (2009); http://dx.doi.org/10.1063/1.3274511 (12 pages) | Cited 9 times

Online Publication Date: 17 December 2009

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In ac electrowetting, hydrodynamic flows occur within a droplet. Two distinct flow patterns were observed, depending on the frequency of the applied electrical signal. The flow at low-frequency range was explained in terms of shape oscillation and a steady streaming process in conjunction with contact line oscillation. The origin of the flow at high-frequency range has not yet been explained. We suggest that the high-frequency flow originated mainly from the electrothermal effect, in which electrical charge is generated due to the gradient of electrical conductivity and permittivity, which is induced by the Joule heating of fluid medium. To support our argument, we analyzed the flow field numerically while considering the electrical body force generated by the electrothermal effect. We visualized the flow pattern and measured the flow velocity inside the droplet. The numerical results show qualitative agreement with experimental results with respect to electric field and frequency dependence of flow velocity. The effects of induced-charge electro-osmosis, natural convection, and the Marangoni flow are discussed.
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47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.55.-t Multiphase and stratified flows
87.19.R- Mechanical and electrical properties of tissues and organs
47.80.Jk Flow visualization and imaging
82.45.-h Electrochemistry and electrophoresis
47.80.-v Instrumentation and measurement methods in fluid dynamics

A programmable microvalve-based microfluidic array for characterization of neurotoxin-induced responses of individual C. elegans

Hui Ma, Lei Jiang, Weiwei Shi, Jianhua Qin, and Bingcheng Lin

Biomicrofluidics 3, 044114 (2009); http://dx.doi.org/10.1063/1.3274313 (8 pages) | Cited 12 times

Online Publication Date: 23 December 2009

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The soil dwelling nematode Caenorhabditis elegans (C. elegans) is an excellent model organism for the study of numerous disease including neurodegenerative disease. In this study, a programmable microvalve-based microfluidic array for real-time and long-term monitoring of the neurotoxin-induced responses of the individual C. elegans was developed. The device consisted of a flow layer and a control layer, which were used for worm manipulation. By activating the programmable microvalves in the control layer, mutiple worms could be individually captured and intermittently immobilized in parallel channels. Thus the mobility behavior, together with the corresponding dopaminergic neuron features of the worms in response to neurotoxin, could be investigated simultaneously. It was found that the neurotoxin MPP+ enabled to induce mobility defects and dopaminergic neurons loss in worms. The established system is easy and fast to operate, which offers not only the controllable microenvironment for analyzing the individual worms in parallel, monitoring the same worm over time, but also the capability to characterize the mobility behavior and neuron features in response to stimuli simultaneously. In addition, the device enabled to sustain the worm culture over most of their adult lifespan without any harm to worm, providing a potential platform for lifespan and aging research.
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87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
47.85.Np Fluidics
47.60.Dx Flows in ducts and channels
87.85.D- Applied neuroscience
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