Particle motions and segregation in dielectrophoretic microfluidics

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We studied, experimentally and theoretically the motion and segregation of positively polarized particles flowing through dielectrophoretic microfluidics. The batch fabrication technique which we present enables one to construct an apparatus featuring a large number of mechanically robust and chemically inert microdevices having a very low ratio of dielectrophoretic-to-fluid residence time. Several apparatuses of this type can easily be integrated into a higher-level system able to handle flow rates several orders of magnitude larger than those in a single microdevice. Experiments were conducted on microfluidics with electrodes of different sizes arranged parallel and perpendicular to the flow. The simulations of the particle motions and their segregation required no fitting parameters because the suspension properties were measured independently. We demonstrate that the presence of the interparticle dipolar interactions imposes a lower bound on the size of the electrodes below which the miniaturization of microelectrodes adversely affects the ability to position the particles with precision in preselected locations [briefly reported by Markarian et al., Appl. Phys. Lett. 82, 4839 (2003)]. When the device characteristics meet certain requirements, the theoretical predictions for the variation of the amount of the segregated particles along the channel were found to be quantitatively consistent with experimental data. Combined with the earlier test of the predictions for the particle accumulation with time in millimeter-scale channels [J. Appl. Phys. 88, 5463 (2000); 92, 2829 (2002)], this completes the experimental validation of a theory for the kinetics of dielectrophoretic phenomena in a flowing dilute suspension. The results of our studies provide the basic characteristics of the ac-field-driven particle motions and segregation in a microchannel and validate a simulation procedure needed for the design and operation of dielectrophoretic microfluidics.