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Mar 2009

Volume 3, Issue 1, Articles (01xxxx)

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Announcement: Chinese, Japanese, and Korean characters available for author names

Mark M. Cassar

Biomicrofluidics 3, 010701 (2009); http://dx.doi.org/10.1063/1.3078245 (1 page)

Online Publication Date: 20 January 2009

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01.60.+q Biographies, tributes, personal notes, and obituaries
01.10.Cr Announcements, news, and awards
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Editorial: Biomicrofluidics—Growing with the micro/nanofluidics community

Hsueh-Chia Chang

Biomicrofluidics 3, 010901 (2009); http://dx.doi.org/10.1063/1.3068295 (1 page) | Cited 2 times

Online Publication Date: 2 January 2009

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01.10.Cr Announcements, news, and awards
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Preface to Special Topic: Invited Papers from the 2009 Conference on Advances in Microfluidics and Nanofluidics, The Hong Kong University of Science & Technology, Hong Kong, 2009

Leslie Y. Yeo, Weija Wen, and Hsueh-Chia Chang

Biomicrofluidics 3, 011901 (2009); http://dx.doi.org/10.1063/1.3119803 (4 pages) | Cited 1 time

Online Publication Date: 31 March 2009

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01.10.Cr Announcements, news, and awards
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Understanding electrokinetics at the nanoscale: A perspective

Hsueh-Chia Chang and Gilad Yossifon

Biomicrofluidics 3, 012001 (2009); http://dx.doi.org/10.1063/1.3056045 (15 pages) | Cited 24 times

Online Publication Date: 2 January 2009

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Electrokinetics promises to be the microfluidic technique of choice for portable diagnostic chips and for nanofluidic molecular detectors. However, despite two centuries of research, our understanding of ion transport and electro-osmotic flow in and near nanoporous membranes, whose pores are natural nanochannels, remains woefully inadequate. This short exposition reviews the various ion-flux and hydrodynamic anomalies and speculates on their potential applications, particularly in the area of molecular sensing. In the process, we revisit several old disciplines, with some unsolved open questions, and we hope to create a new one.
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87.85.Rs Nanotechnologies-applications
81.07.Nb Molecular nanostructures
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)

Ultrafast microfluidics using surface acoustic waves

Leslie Y. Yeo and James R. Friend

Biomicrofluidics 3, 012002 (2009); http://dx.doi.org/10.1063/1.3056040 (23 pages) | Cited 57 times

Online Publication Date: 2 January 2009

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We demonstrate that surface acoustic waves (SAWs), nanometer amplitude Rayleigh waves driven at megahertz order frequencies propagating on the surface of a piezoelectric substrate, offer a powerful method for driving a host of extremely fast microfluidic actuation and micro/bioparticle manipulation schemes. We show that sessile drops can be translated rapidly on planar substrates or fluid can be pumped through microchannels at 1–10 cm/s velocities, which are typically one to two orders quicker than that afforded by current microfluidic technologies. Through symmetry-breaking, azimuthal recirculation can be induced within the drop to drive strong inertial microcentrifugation for micromixing and particle concentration or separation. Similar micromixing strategies can be induced in the same microchannel in which fluid is pumped with the SAW by merely changing the SAW frequency to rapidly switch the uniform through-flow into a chaotic oscillatory flow by exploiting superpositioning of the irradiated sound waves from the sidewalls of the microchannel. If the flow is sufficiently quiescent, the nodes of the transverse standing wave that arises across the microchannel also allow for particle aggregation, and hence, sorting on nodal lines. In addition, the SAW also facilitates other microfluidic capabilities. For example, capillary waves excited at the free surface of a sessile drop by the SAW underneath it can be exploited for micro/nanoparticle collection and sorting at nodal points or lines at low powers. At higher powers, the large accelerations off the substrate surface as the SAW propagates across drives rapid destabilization of the drop free surface giving rise to inertial liquid jets that persist over 1–2 cm in length or atomization of the entire drop to produce 1–10 μm monodispersed aerosol droplets, which can be exploited for ink-jet printing, mass spectrometry interfacing, or pulmonary drug delivery. The atomization of polymer/protein solutions can also be used for the rapid synthesis of 150–200 nm polymer/protein particles or biodegradable polymeric shells in which proteins, peptides, and other therapeutic molecules are encapsulated within for controlled release drug delivery. The atomization of thin films behind a translating drop containing polymer solutions also gives rise to long-range spatial ordering of regular polymer spots whose size and spacing are dependent on the SAW frequency, thus offering a simple and powerful method for polymer patterning without requiring surface treatment or physical/chemical templating.
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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

Direct measurements of the frequency-dependent dielectrophoresis force

Ming-Tzo Wei, Joseph Junio, and H. Daniel Ou-Yang

Biomicrofluidics 3, 012003 (2009); http://dx.doi.org/10.1063/1.3058569 (8 pages) | Cited 11 times

Online Publication Date: 2 January 2009

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Dielectrophoresis (DEP), the phenomenon of directed motion of electrically polarizable particles in a nonuniform electric field, is promising for applications in biochemical separation and filtration. For colloidal particles in suspension, the relaxation of the ionic species in the shear layer gives rise to a frequency-dependent, bidirectional DEP force in the radio frequency range. However, quantification methods of the DEP force on individual particles with the pico-Newton resolution required for the development of theories and design of device applications are lacking. We report the use of optical tweezers as a force sensor and a lock-in phase-sensitive technique for analysis of the particle motion in an amplitude modulated DEP force. The coherent detection and sensing scheme yielded not only unprecedented sensitivity for DEP force measurements, but also provided a selectivity that clearly distinguishes the pure DEP force from all the other forces in the system, including electrophoresis, electro-osmosis, heat-induced convection, and Brownian forces, all of which can hamper accurate measurements through other existing methods. Using optical tweezers-based force transducers already developed in our laboratory, we have results that quantify the frequency-dependent DEP force and the crossover frequency of individual particles with this new experimental method.
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87.80.Qk Biochemical separation processes
87.80.Cc Optical trapping
87.15.Tt Electrophoresis

Single nanopore transport of synthetic and biological polyelectrolytes in three-dimensional hybrid microfluidic/nanofluidic devices

Travis L. King, Enid N. Gatimu, and Paul W. Bohn

Biomicrofluidics 3, 012004 (2009); http://dx.doi.org/10.1063/1.3059546 (11 pages) | Cited 5 times

Online Publication Date: 2 January 2009

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This paper presents a study of electrokinetic transport in single nanopores integrated into vertically stacked three-dimensional hybrid microfluidic/nanofluidic structures. In these devices, single nanopores, created by focused ion beam (FIB) milling in thin polymer films, provide fluidic connection between two vertically separated, perpendicular microfluidic channels. Experiments address both systems in which the nanoporous membrane is composed of the same (homojunction) or different (heterojunction) polymer as the microfluidic channels. These devices are then used to study the electrokinetic transport properties of synthetic (i.e., polystyrene sulfonate and polyallylamine) and biological (i.e., DNA) polyelectrolytes across these nanopores using both electrical current measurements and confocal microscopy. Both optical and electrical measurements indicate that electro-osmotic transport is predominant over electrophoresis in single nanopores with d>180 nm, consistent with results obtained under similar conditions for nanocapillary array membranes.
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82.39.Wj Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes
82.45.Wx Polymers and organic materials in electrochemistry
82.80.Fk Electrochemical methods
87.15.Tt Electrophoresis
87.85.M- Biotechnology
47.85.Np Fluidics

Polydimethylsiloxane microfluidic chip with integrated microheater and thermal sensor

Jinbo Wu, Wenbin Cao, Weijia Wen, Donald Choy Chang, and Ping Sheng

Biomicrofluidics 3, 012005 (2009); http://dx.doi.org/10.1063/1.3058587 (7 pages) | Cited 11 times

Online Publication Date: 2 January 2009

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A microheater and a thermal sensor were fabricated inside elastomeric polydimethylsiloxane microchannels by injecting silver paint (or other conductive materials) into the channels. With a high-precision control scheme, microheaters can be used for rapid heating, with precise temperature control and uniform thermal distribution. Using such a microheater and feedback system, a polymerase chain reaction experiment was carried out whereas the DNA was successfully amplified in 25 cycles, with 1 min per cycle.
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87.80.Ek Mechanical and micromechanical techniques
07.10.Cm Micromechanical devices and systems
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
87.14.gk DNA
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.15.R- Reactions and kinetics

Microfluidics as a functional tool for cell mechanics

Siva A. Vanapalli, Michel H. G. Duits, and Frieder Mugele

Biomicrofluidics 3, 012006 (2009); http://dx.doi.org/10.1063/1.3067820 (15 pages) | Cited 13 times

Online Publication Date: 5 January 2009

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Living cells are a fascinating demonstration of nature’s most intricate and well-coordinated micromechanical objects. They crawl, spread, contract, and relax—thus performing a multitude of complex mechanical functions. Alternatively, they also respond to physical and chemical cues that lead to remodeling of the cytoskeleton. To understand this intricate coupling between mechanical properties, mechanical function and force-induced biochemical signaling requires tools that are capable of both controlling and manipulating the cell microenvironment and measuring the resulting mechanical response. In this review, the power of microfluidics as a functional tool for research in cell mechanics is highlighted. In particular, current literature is discussed to show that microfluidics powered by soft lithographic techniques offers the following capabilities that are of significance for understanding the mechanical behavior of cells: (i) Microfluidics enables the creation of in vitro models of physiological environments in which cell mechanics can be probed. (ii) Microfluidics is an excellent means to deliver physical cues that affect cell mechanics, such as cell shape, fluid flow, substrate topography, and stiffness. (iii) Microfluidics can also expose cells to chemical cues, such as growth factors and drugs, which alter their mechanical behavior. Moreover, these chemical cues can be delivered either at the whole cell or subcellular level. (iv) Microfluidic devices offer the possibility of measuring the intrinsic mechanical properties of cells in a high throughput fashion. (v) Finally, microfluidic methods provide exquisite control over drop size, generation, and manipulation. As a result, droplets are being increasingly used to control the physicochemical environment of cells and as biomimetic analogs of living cells. These powerful attributes of microfluidics should further stimulate novel means of investigating the link between physicochemical cues and the biomechanical response of cells. Insights from such studies will have implications in areas such as drug delivery, medicine, tissue engineering, and biomedical diagnostics.
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87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.18.-h Biological complexity
87.17.Rt Cell adhesion and cell mechanics
87.15.R- Reactions and kinetics
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Polydimethylsiloxane-based conducting composites and their applications in microfluidic chip fabrication

Xiuqing Gong and Weijia Wen

Biomicrofluidics 3, 012007 (2009); http://dx.doi.org/10.1063/1.3098963 (14 pages) | Cited 14 times

Online Publication Date: 23 March 2009

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This paper reviews the design and fabrication of polydimethylsiloxane (PDMS)-based conducting composites and their applications in microfluidic chip fabrication. Owing to their good electrical conductivity and rubberlike elastic characteristics, these composites can be used variously in soft-touch electronic packaging, planar and three-dimensional electronic circuits, and in-chip electrodes. Several microfluidic components fabricated with PDMS-based composites have been introduced, including a microfluidic mixer, a microheater, a micropump, a microdroplet controller, as well as an all-in-one microfluidic chip.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
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Preface to Special Topic: Papers from the 82nd American Chemical Society Colloid and Surface Science Symposium, Raleigh, North Carolina, 2008

Dimiter N. Petsev and Patrick S. Doyle

Biomicrofluidics 3, 012701 (2009); http://dx.doi.org/10.1063/1.3109652 (2 pages) | Cited 1 time

Online Publication Date: 30 March 2009

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This Special Topic section of Biomicrofluidics contains original contributions that were presented at the 82nd Colloid and Surface Science Symposium, which took place on 15–18 June 2008 at North Carolina State University. The Symposium covered a wide range of topics that are relevant to the fundamentals of fluidics and their application to biological systems.
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01.30.-y Physics literature and publications
47.57.J- Colloidal systems
47.85.Np Fluidics
47.60.Dx Flows in ducts and channels
87.15.Tt Electrophoresis
47.10.A- Mathematical formulations

Microfluidic electrospinning of biphasic nanofibers with Janus morphology

Yasmin Srivastava, Manuel Marquez, and Todd Thorsen

Biomicrofluidics 3, 012801 (2009); http://dx.doi.org/10.1063/1.3009288 (6 pages) | Cited 8 times

Online Publication Date: 7 January 2009

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In this paper a method of electrospinning conducting and nonconducting biphasic Janus nanofibers using microfluidic polydimethylsiloxane (PDMS)-based manifolds is described. Key benefits of using microfluidic devices for nanofiber synthesis include rapid prototyping, ease of fabrication, and the ability to spin multiple Janus fibers in parallel through arrays of individual microchannels. Biphasic Janus nanofibers of polyvinylpyrrolidone (PVP)+polypyrrole (PPy)/PVP nanofibers with an average diameter of 250 nm were successfully fabricated using elastomeric microfluidic devices. Fiber characterization and confirmation of the Janus morphology was subsequently carried out using a combination of scanning electron microscopy, energy dispersion spectroscopy, and transmission electron microscopy.
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87.80.Ek Mechanical and micromechanical techniques
87.85.Lf Tissue engineering
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Transient electro-osmotic flow in cylindrical microcapillaries containing salt-free medium

Shih-Hsiang Chang

Biomicrofluidics 3, 012802 (2009); http://dx.doi.org/10.1063/1.3064113 (9 pages) | Cited 3 times

Online Publication Date: 7 January 2009

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A theoretical study on the transient electro-osmotic flow through a cylindrical microcapillary containing a salt-free medium is presented for both constant surface charge density and constant surface potential. The exact analytical solutions for the electric potential distribution and the transient electro-osmotic flow velocity are derived by solving the nonlinear Poisson-Boltzmann equation and the Navier-Stokes equation. Based on these results, a systematic parametric study on the characteristics of the transient electro-osmotic flow is detailed. The general behavior of transient electro-osmotic flow in a cylindrical tube is similar to that observed in a microchannel containing an electrolyte solution. However, the steady-state electro-osmotic flow significantly deviates from the typical plug flow at higher surface charge and the rate of increase in the electro-osmotic mobility is strongly suppressed due to the effect of counterion condensation. In addition, the applicability limit of these solutions is also discussed.
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82.45.Hk Electrolysis
73.40.Cg Contact resistance, contact potential
47.60.Dx Flows in ducts and channels
47.10.ad Navier-Stokes equations
02.50.Ey Stochastic processes
82.39.Wj Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes

Simulation of electrophoretic stretching of DNA in a microcontraction using an obstacle array for conformational preconditioning

Daniel W. Trahan and Patrick S. Doyle

Biomicrofluidics 3, 012803 (2009); http://dx.doi.org/10.1063/1.3055275 (14 pages) | Cited 9 times

Online Publication Date: 7 January 2009

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Recently our group has reported experiments using an obstacle array to precondition the conformations of DNA molecules to facilitate their stretch in a microcontraction. Based upon previous successes simulating electrophoretic stretching in microcontractions without obstacles, we use our simulation model to study the deformation of DNA chains in a microcontraction preceded by an array of cylindrical obstacles. We compare our data to the experimental results and find good qualitative, and even quantitative, agreement concerning the behavior of the chains in the array; however, the simulations overpredict the mean stretch of the chains as they leave the contraction. We examine the amount of stretch gained between leaving the array and reaching the end of the contraction and speculate that the differences seen are caused by nonlinear electrokinetic effects that become important in the contraction due to a combination of field gradients and high field strengths.
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82.37.Rs Single molecule manipulation of proteins and other biological molecules
87.14.gk DNA
87.15.La Mechanical properties
87.15.Tt Electrophoresis
87.80.Ek Mechanical and micromechanical techniques

Extracting the hydrodynamic resistance of droplets from their behavior in microchannel networks

Vincent Labrot, Michael Schindler, Pierre Guillot, Annie Colin, and Mathieu Joanicot

Biomicrofluidics 3, 012804 (2009); http://dx.doi.org/10.1063/1.3109686 (16 pages) | Cited 12 times

Online Publication Date: 30 March 2009

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The overall traffic of droplets in a network of microfluidic channels is strongly influenced by the liquid properties of the moving droplets. In particular, the effective hydrodynamic resistance of individual droplets plays a key role in their global behavior. Here we propose two simple and low-cost experimental methods for measuring this parameter by analyzing the dynamics of a regular sequence of droplets injected into an “asymmetric loop” network. The choice of a droplet taking either route through the loop is influenced by the presence of previous droplets that modulate the hydrodynamic resistance of the branches they are sitting in. We propose to extract the effective resistance of a droplet from easily observable time series, namely, from the choices the droplets make at junctions and from the interdroplet distances. This becomes possible when utilizing a recently proposed theoretical model based on a number of simplifying assumptions. Here we present several sets of measurements of the hydrodynamic resistance of droplets, expressed in terms of a “resistance length.” The aim is twofold: (1) to reveal its dependence on a number of parameters, such as the viscosity, the volume of droplets, their velocity as well as the spacing between them. At the same time (2), by using a standard measurement technique, we compare the limitations of the proposed methods. As an important result of this comparison, we obtain the range of validity of the simplifying assumptions made in the theoretical model.
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47.60.Dx Flows in ducts and channels
66.20.-d Viscosity of liquids; diffusive momentum transport
47.80.Fg Pressure and temperature measurements
47.85.Dh Hydrodynamics, hydraulics, hydrostatics
47.55.D- Drops and bubbles
47.85.Np Fluidics
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Vertical hydrodynamic focusing in glass microchannels

Tony A. Lin, A. E. Hosoi, and Daniel J. Ehrlich

Biomicrofluidics 3, 014101 (2009); http://dx.doi.org/10.1063/1.3055278 (11 pages) | Cited 3 times

Online Publication Date: 8 January 2009

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Vertical hydrodynamic focusing in microfluidic devices is investigated through simulation and through direct experimental verification using a confocal microscope and a novel form of stroboscopic imaging. Optimization for microfluidic cytometry of biological cells is examined. By combining multiple crossing junctions, it is possible to confine cells to a single analytic layer of interest. Subtractive flows are investigated as a means to move the analysis layer vertically in the channel and to correct the flatness of this layer. The simulation software (ADINA and Coventor) is shown to accurately capture the complex dependencies of the layer interfaces, which vary strongly with channel geometry and relative flow rates.
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87.80.Ek Mechanical and micromechanical techniques
87.17.Aa Modeling, computer simulation of cell processes
87.64.mk Confocal
47.85.Dh Hydrodynamics, hydraulics, hydrostatics

Rapid production of protein-loaded biodegradable microparticles using surface acoustic waves

Mar Alvarez, Leslie Y. Yeo, James R. Friend, and Milan Jamriska

Biomicrofluidics 3, 014102 (2009); http://dx.doi.org/10.1063/1.3055282 (12 pages) | Cited 10 times

Online Publication Date: 21 January 2009

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We present a straightforward and rapid surface acoustic wave (SAW) atomization-based technique for encapsulating proteins into 10 μm order particles composed of a biodegradable polymeric excipient, using bovine serum albumin (BSA) as an exemplar. Scans obtained from confocal microscopy provide qualitative proof of encapsulation and show the fluorescent conjugated protein to be distributed in a relatively uniform manner within the polymer shell. An ELISA assay of the collected particles demonstrates that the BSA survives the atomization, particle formation, and collection process with a yield of approximately 55%. The SAW atomization universally gave particles with a textured morphology, and increasing the frequency and polymer concentration generally gave smaller particles (to 3 μm average) with reduced porosity.
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87.85.J- Biomaterials
87.14.E- Proteins
87.15.rs Dissociation

Enhanced discrimination of normal oocytes using optically induced pulling-up dielectrophoretic force

Hyundoo Hwang, Do-Hyun Lee, Wonjae Choi, and Je-Kyun Park

Biomicrofluidics 3, 014103 (2009); http://dx.doi.org/10.1063/1.3086600 (10 pages) | Cited 14 times

Online Publication Date: 17 February 2009

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We present a method to discriminate normal oocytes in an optoelectrofluidic platform based on the optically induced positive dielectrophoresis (DEP) for in vitro fertilization. By combining the gravity with a pulling-up DEP force that is induced by dynamic image projected from a liquid crystal display, the discrimination performance could be enhanced due to the reduction in friction force acting on the oocytes that are relatively large and heavy cells being affected by the gravity field. The voltage condition of 10 V bias at 1 MHz was applied for moving normal oocytes. The increased difference of moving velocity between normal and starved abnormal oocytes allows us to discriminate the normal ones spontaneously under the moving image pattern. This approach can be useful to develop an automatic and interactive selection tool of fertilizable oocytes.
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87.50.ch Electrophoresis/dielectrophoresis and other mechanical effects
87.80.Cc Optical trapping
85.60.-q Optoelectronic devices

On-chip microfluidic systems for determination of L-glutamate based on enzymatic recycling of substrate

W. Laiwattanapaisal, J. Yakovleva, M. Bengtsson, T. Laurell, S. Wiyakrutta, V. Meevootisom, O. Chailapakul, and J. Emnéus

Biomicrofluidics 3, 014104 (2009); http://dx.doi.org/10.1063/1.3098319 (12 pages) | Cited 5 times

Online Publication Date: 16 March 2009

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Two microfluidic systems have been developed for specific analysis of L-glutamate in food based on substrate recycling fluorescence detection. L-glutamate dehydrogenase and a novel enzyme, D-phenylglycine aminotransferase, were covalently immobilized on (i) the surface of silicon microchips containing 32 porous flow channels of 235 μm depth and 25 μm width and (ii) polystyrene Poros™ beads with a particle size of 20 μm. The immobilized enzymes recycle L-glutamate by oxidation to 2-oxoglutarate followed by the transfer of an amino group from D-4-hydroxyphenylglycine to 2-oxoglutarate. The reaction was accompanied by reduction of nicotinamide adenine dinucleotide (NAD+) to NADH, which was monitored by fluorescence detection (εex = 340 nm, εem = 460 nm). First, the microchip-based system, L-glutamate was detected within a range of 3.1–50.0 mM. Second, to be automatically determined, sequential injection analysis (SIA) with the bead-based system was investigated. The bead-based system was evaluated by both flow injection analysis and SIA modes, where good reproducibility for L-glutamate calibrations was obtained (relative standard deviation of 3.3% and 6.6%, respectively). In the case of SIA, the beads were introduced and removed from the microchip automatically. The immobilized beads could be stored in a 20% glycerol and 0.5 mM ethylenediaminetetraacetic acid solution maintained at a pH of 7.0 using a phosphate buffer for at least 15 days with 72% of the activity remaining. The bead-based system demonstrated high selectivity, where L-glutamate recoveries were between 91% and 108% in the presence of six other L-amino acids tested.
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87.80.Ek Mechanical and micromechanical techniques
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.14.ej Enzymes

Three-dimensional two-component velocity measurement of the flow field induced by the Vorticella picta microorganism using a confocal microparticle image velocimetry technique

Moeto Nagai, Masamichi Oishi, Marie Oshima, Hiroshi Asai, and Hiroyuki Fujita

Biomicrofluidics 3, 014105 (2009); http://dx.doi.org/10.1063/1.3105106 (13 pages) | Cited 5 times

Online Publication Date: 26 March 2009

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Understanding the biological feeding strategy and characteristics of a microorganism as an actuator requires the detailed and quantitative measurement of flow velocity and flow rate induced by the microorganism. Although some velocimetry methods have been applied to examine the flow, the measured dimensions were limited to at most two-dimensional two-component measurements. Here we have developed a method to measure three-dimensional two-component flow velocity fields generated by the microorganism Vorticella picta using a piezoscanner and a confocal microscope. We obtained the two-component velocities of the flow field in a two-dimensional plane denoted as the XY plane, with an observation area of 455×341 μm2 and the resolution of 9.09 μm per each velocity vector by a confocal microparticle image velocimetry technique. The measurement of the flow field at each height took 37.5 ms, and it was repeated in 16 planes with a 2.50 μm separation in the Z direction. We reconstructed the three-dimensional two-component flow velocity field. From the reconstructed data, the flow velocity field [u(x,y,z),v(x,y,z)] in an arbitrary plane can be visualized. The flow rates through YZ and ZX planes were also calculated. During feeding, we examined a suction flow to the mouth of the Vorticella picta and measured it to be to 300 pl/s.
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47.63.-b Biological fluid dynamics
87.85.gf Fluid mechanics and rheology

Micromixer based on viscoelastic flow instability at low Reynolds number

Y. C. Lam, H. Y. Gan, N. T. Nguyen, and H. Lie

Biomicrofluidics 3, 014106 (2009); http://dx.doi.org/10.1063/1.3108462 (13 pages) | Cited 7 times

Online Publication Date: 30 March 2009

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We exploited the viscoelasticity of biocompatible dilute polymeric solutions, namely, dilute poly(ethylene oxide) solutions, to significantly enhance mixing in microfluidic devices at a very small Reynolds number, i.e., Re ≈ 0.023, but large Peclet and elasticity numbers. With an abrupt contraction microgeometry (8:1 contraction ratio), two different dilute poly(ethylene oxide) solutions were successfully mixed with a short flow length at a relatively fast mixing time of <10 μs. Microparticle image velocimetry was employed in our investigations to characterize the flow fields. The increase in velocity fluctuation with an increase in flow rate and Deborah number indicates the increase in viscoelastic flow instability. Mixing efficiency was characterized by fluorescent concentration measurements. Our results showed that enhanced mixing can be achieved through viscoelastic flow instability under situations where molecular-diffusion and inertia effects are negligible. This approach bypasses the laminar flow limitation, usually associated with a low Reynolds number, which is not conducive to mixing.
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47.50.Gj Instabilities
47.51.+a Mixing
47.57.Ng Polymers and polymer solutions
47.61.Ne Micromixing
47.80.Jk Flow visualization and imaging
47.85.-g Applied fluid mechanics
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