Index of content:
Volume 2, Issue 2, June 2008
- REGULAR ARTICLES
Investigation of microflow reversal by ac electrokinetics in orthogonal electrodes for micropump design2(2008); http://dx.doi.org/10.1063/1.2908026View Description Hide Description
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 acelectrokinetic processes, capacitive electrodepolarization, 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 acelectrokinetics and hence effectively manipulate fluids.
Structural optimization for heat detection of DNA thermosequencing platform using finite element analysis2(2008); http://dx.doi.org/10.1063/1.2901138View Description Hide Description
For the past three decades, Sanger’s method has been the primary DNAsequencingtechnology; however, inherent limitations in cost and complexity have limited its usage in personalized medicine and ecological studies. A new technology called “thermosequencing” can potentially reduce both the cost and complexity of DNAsequencing by using a microfluidic platform [Esfandyarpour, Pease, and Davis, J. Vac. Sci. Technol. B26, 661 (2008)]. To optimize the efficiency of the technology,finite element analysis was used to model the thermosequencing system by simulating the DNA incorporation reaction series and the resulting product concentration and heat production. Different models of the thermosequencing platform were created to simulate the effects of the materials surrounding the system, to optimize the geometry of the system, and to concentrate reaction heat into specific regions for detection in the real system. The resulting concentrations of reaction products were used to calibrate the reaction speed and to design the heat sensors in the thermosequencing technology. We recommend a modified gated structure for the microfluidic detection platform by using control valves and show how this new platform could dramatically improve the detection efficiency.
Size-dependent trajectories of DNA macromolecules due to insulative dielectrophoresis in submicrometer-deep fluidic channels2(2008); http://dx.doi.org/10.1063/1.2930817View Description Hide Description
In this paper, we demonstrate for the first time that insulative dielectrophoresis can induce size-dependent trajectories of DNA macromolecules. We experimentally use (48.5 kbp) and T4GT7 (165.6 kbp) DNA molecules flowing continuously around a sharp corner inside fluidic channels with a depth of . 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 DNAdielectrophoresis. 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 .
A microfluidic cell for studying the formation of regenerated silk by synchrotron radiation small- and wide-angle X-ray scattering2(2008); http://dx.doi.org/10.1063/1.2943732View Description Hide Description
A tube-in-square-pipe microfluidic glass cell has been developed for studying the aggregation and fiber formation from regenerated silksolution 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 -sheet nature.
A transparent cell-culture microchamber with a variably controlled concentration gradient generator and flow field rectifier2(2008); http://dx.doi.org/10.1063/1.2952290View Description Hide Description
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 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 observation on cell growth was achieved. In this work the flow field, medium replacement, and chemical gradient in the microchamber are elaborated.