Sorting microparticles into lateral streams using a two-phase rectangular electrokinetic array

Abstract

In this paper, we study microparticles in liquid suspension streaming around a closed rectangular track and present lateral sorting of the particles into focused streams. The track consists of a two-phase interdigitated electrode array with symmetric electrodes but asymmetric electrode spacing. We demonstrate the ability to consistently focus an initially scattered suspension of mono-size polystyrene particles into a single narrow stream traveling around the circuit. We also demonstrate the ability of the device to separate suspensions of multiple sphere sizes into distinct streams according to size. We report that focusing positions are generally consistent for a given particle size, regardless of the presence of other particles in the suspension, and that particles sort by decreasing size from the center to the edge of the track. These results are compared with finite element analysis of the steady-state electric field and analytical approximations of the electrokinetic forces. We hypothesize that the sorting is due to a balance between phase-based and gradient-based dielectrophoretic forces.