Dielectrophoretic Focusing of Microparticles in Curved Microchannels

Focusing particles into a tight stream is usually a necessary step prior to counting, detecting and sorting them in microfluidic devices such as flow cytometers [1] and continuous-flow separators [2]. The diverse approaches to particle focusing may be classified as active or passive ones in nature. Active focusing utilizes external force field(s) to manipulate particles other than the force to pump the particle solution. This category covers the conventional sheath flow focusing method and the various sheathless focusing methods where a transverse acoustic, AC dielectrophoretic, or magnetic force must be externally imposed. Passive focusing exploits the geometric topology-induced internal force(s) to alter the particle motion. So far dielectrophoretic, hydrodynamic and inertial forces have been demonstrated to focus particles [3]. Here, we introduce a novel passive particle focusing technique in electrokinetic flow through curved microchannels. This focusing stems from the cross-stream dielectrophoretic motion induced by channel curvatures [4], and is demonstrated in a serpentine and a spiral microchannel.Copyright © 2009 by ASME