AC Frequency Tuned Transverse Migration of Particles and Cells in a Rectangular Microchannel

Recent studies reported a wall-repulsion of dielectric particles during alternating current (AC) electrophoresis in a Poiseuille flow. This center-directed particle migration decreases with increasing AC frequency because of the suppressed concentration polarization electroosmosis (CPEO) around charged particles. We observe, in the absence of hydrodynamic flow, an unprecedented transition of particle migration from center-directed at low frequencies to wall-directed at high frequencies in a rectangular microchannel. This AC frequency-tuned transverse migration of particles is speculated to arise from the reversed CPEO because of the phase lag of the concentration polarization relative to the applied AC electric field. We also perform a systematic experimental study of the effects of electric field, fluid, and particle-related parameters on the reversal of such transverse migration. Moreover, we extend the parametric study to yeast cells and demonstrate that adding a small direct current (DC) bias to the AC electric field can completely suppress the wall-directed particle migration enforcing a center-focusing state across the entire frequency range tested.