Microfluidics is the combination of micro/nano fabrication techniques with fluid flow at microscale to pursue powerful techniques in controlling and manipulating chemical and biological processes. Sorting and separation of bio-particles are highly considered in diagnostics and biological analyses. Dielectrophoresis (DEP) has offered unique advantages for microfluidic devices. In DEP devices, asymmetric pair of planar electrodes could be employed to generate non-uniform electric fields. In DEP applications, facing 3D sidewall electrodes is considered to be one of the key solutions to increase device throughput due to the generated homogeneous electric fields along the height of microchannels. Despite the advantages, fabrication of 3D vertical electrodes requires a considerable challenge. In this study, two alternative fabrication techniques have been proposed for the fabrication of a microfluidic device with 3D sidewall electrodes. In the first method, both the mold and the electrodes are fabricated using high precision machining. In the second method, the mold with tilted sidewalls is fabricated using high precision machining and the electrodes are deposited on the sidewall using sputtering together with a shadow mask fabricated by electric discharge machining. Both fabrication processes are assessed as highly repeatable and robust. Moreover, the two methods are found to be complementary with respect to the channel height. Only the manipulation of particles with negative-DEP is demonstrated in the experiments, and the throughput values up to 105 particles / min is reached in a continuous flow. The experimental results are compared with the simulation results and the limitations on the fabrication techniques are also discussed.
Cataloged from PDF version of article.The classical Graetz problem, which is the problem of the hydrodynamically developed, thermally\ud developing laminar flow of an incompressible fluid inside a tube neglecting axial conduction and viscous dissipation,\ud is one of the fundamental problems of internal-flow studies. This study is an extension of the Graetz problem to\ud include the rarefaction effect, viscous dissipation term and axial conduction with a constant wall temperature thermal\ud boundary condition. The energy equation is solved to determine the temperature field analytically using general\ud eigenfunction expansion with a fully developed velocity profile. To analyze the low-Peclet-number nature of the\ud flow, the flow domain is extended from −∞ to +∞. To model the rarefaction effect, a second-order slip model\ud is implemented. The temperature distribution, local Nusselt number, and local entropy generation are determined\ud in terms of confluent hypergeometric functions. This kind of theoretical study is important for a fundamental\ud understanding of the convective heat transfer characteristics of flows at the microscale and for the optimum design\ud of thermal systems, which includes convective heat transfer at the microscale, especially operating at low Reynolds\ud number
Washing, separation and concentration of bioparticles are key operations for many biological and chemical analyses. In this study, the simulation of an integrated microfluidic device is studied. The proposed device has the capability to wash the bioparticles (transferring the bioparticles from one buffer solution to another), to separate the particles based on their dielectric properties and to concentrate the bioparticles. Washing and concentration of bioparticles are performed by acoustophoresis and the separation is performed by dielectrophoresis. For simulating the flow within the microchannel, a computational fluid dynamics model using COMSOL Multiphysics software is implemented. In order to simulate the particle trajectories under ultrasonic and electric field, point-particle assumption is chosen using MATLAB software. To account for the size variation of the bioparticles, particles with normal size distributions are used inside the microchannel. The effect of the key design parameters such as flow rate, applied voltage etc. on the performance of the device is discussed.
DefinitionMicrofluidic optical devices (MOD) are the emerging technology that combines today's microfluidics technology with the optics. However, MOD can be classified as the integration of these two technologies rather than combination of them. This integration provides a new approach for using microfluidics for control and manipulation of samples and optics for sensing. In this entry we propose a comprehensive review of emerging applications for microfluidic optical devices. OverviewIn many of the biological applications, microfluidics and optics technology have already been used in combination -microfluidics for control and manipulation of the samples and optics for sensing. Microelectromechanical systems (MEMS) and lab-on-a-chip communities try to embed optical devices into their microsystems to improve functionality of their devices. Presenting a comprehensive review of all the research in the field of microfluidic and optics integration is out the scope of this entry, but several numbers of representative examples of this integration are provided. Moreover, this integration results in handing:• Electric field induction by light exposure [1] • Integrated detection systems for microfluidic application (which increases the portability of the entire system) [3-5] • Sensitivity increase for the existing detection system [7,8] • Cell manipulation [9,11,12] • Small cell population sorting with high accuracy by tunable optical fibers [12] • Rapid detection of environmental contaminants [13] • A platform to study mammalian individual axonal injury [14] • Variable-focus liquid lens [15] Basic MethodologyLatest developments related to the combination of integrated optics and microfluidics have evolved towards device miniaturization with the ultimate goal of integrating many optical components onto a compact microchip, producing photonic integrated circuits with low cost and high degrees of
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