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Jun 2008

Volume 2, Issue 2, Articles (02xxxx)

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Investigation of microflow reversal by ac electrokinetics in orthogonal electrodes for micropump design

Kai Yang and Jie Wu

Biomicrofluidics 2, 024101 (2008); http://dx.doi.org/10.1063/1.2908026 (8 pages) | Cited 4 times

Online Publication Date: 4 April 2008

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Orthogonal electrodes have been reported to produce high velocity microflows when excited by ac signals, showing potential for micropumping applications. This paper investigates the microflow reversal phenomena in such orthogonal electrode micropumps. Three types of microflow fields were observed by changing the applied electric signals. Three ac electrokinetic processes, capacitive electrode polarization, Faradaic polarization, and the ac electrothermal effect, are proposed to explain the different flow patterns, respectively. The hypotheses were corroborated by impedance analysis, numerical simulations, and velocity measurements. The investigation of microflow reversal can improve the understanding of ac electrokinetics and hence effectively manipulate fluids.
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47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.85.Np Fluidics
47.11.-j Computational methods in fluid dynamics
47.80.Cb Velocity measurements

Size-dependent trajectories of DNA macromolecules due to insulative dielectrophoresis in submicrometer-deep fluidic channels

Gea O. F. Parikesit, Anton P. Markesteijn, Oana M. Piciu, Andre Bossche, Jerry Westerweel, Ian T. Young, and Yuval Garini

Biomicrofluidics 2, 024103 (2008); http://dx.doi.org/10.1063/1.2930817 (14 pages) | Cited 20 times

Online Publication Date: 6 May 2008

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In this paper, we demonstrate for the first time that insulative dielectrophoresis can induce size-dependent trajectories of DNA macromolecules. We experimentally use λ (48.5 kbp) and T4GT7 (165.6 kbp) DNA molecules flowing continuously around a sharp corner inside fluidic channels with a depth of 0.4 μm. Numerical simulation of the electrokinetic force distribution inside the channels is in qualitative agreement with our experimentally observed trajectories. We discuss a possible physical mechanism for the DNA polarization and dielectrophoresis inside confining channels, based on the observed dielectrophoresis responses due to different DNA sizes and various electric fields applied between the inlet and the outlet. The proposed physical mechanism indicates that further extensive investigations, both theoretically and experimentally, would be very useful to better elucidate the forces involved at DNA dielectrophoresis. When applied for size-based sorting of DNA molecules, our sorting method offers two major advantages compared to earlier attempts with insulative dielectrophoresis: Its continuous operation allows for high-throughput analysis, and it only requires electric field strengths as low as ∼ 10 V/cm.
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87.15.Tt Electrophoresis
87.14.gk DNA
87.80.-y Biophysical techniques (research methods)
47.85.Np Fluidics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.60.Dx Flows in ducts and channels

A microfluidic cell for studying the formation of regenerated silk by synchrotron radiation small- and wide-angle X-ray scattering

Anne Martel, Manfred Burghammer, Richard Davies, Emanuela DiCola, Pierre Panine, Jean-Baptiste Salmon, and Christian Riekel

Biomicrofluidics 2, 024104 (2008); http://dx.doi.org/10.1063/1.2943732 (7 pages) | Cited 7 times

Online Publication Date: 6 June 2008

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A tube-in-square-pipe microfluidic glass cell has been developed for studying the aggregation and fiber formation from regenerated silk solution by in-situ small-angle X-ray scattering using synchrotron radiation. Acidification-induced aggregation has been observed close to the mixing point of the fibroin and buffer solution. The fibrous, amorphous material is collected in a water bath. Micro-wide-angle X-ray scattering of the dried material confirms its β-sheet nature.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.85.Np Fluidics
78.70.Ck X-ray scattering

A transparent cell-culture microchamber with a variably controlled concentration gradient generator and flow field rectifier

Ji-Yen Cheng, Meng-Hua Yen, Ching-Te Kuo, and Tai-Horng Young

Biomicrofluidics 2, 024105 (2008); http://dx.doi.org/10.1063/1.2952290 (12 pages) | Cited 10 times

Online Publication Date: 17 June 2008

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Real-time observation of cell growth provides essential information for studies such as cell migration and chemotaxis. A conventional cell incubation device is usually too clumsy for these applications. Here we report a transparent microfluidic device that has an integrated heater and a concentration gradient generator. A piece of indium tin oxide (ITO) coated glass was ablated by our newly developed visible laser-induced backside wet etching (LIBWE) so that transparent heater strips were prepared on the glass substrate. A polymethylmethacrylate (PMMA) microfluidic chamber with flow field rectifiers and a reagent effusion hole was fabricated by a CO2 laser and then assembled with the ITO heater so that the chamber temperature can be controlled for cell culturing. A variable chemical gradient was generated inside the chamber by combining the lateral medium flow and the flow from the effusion hole. Successful culturing was performed inside the device. Continuous long-term (>10 days) observation on cell growth was achieved. In this work the flow field, medium replacement, and chemical gradient in the microchamber are elaborated.
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87.80.Ek Mechanical and micromechanical techniques
07.10.Cm Micromechanical devices and systems
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