Continuous dielectrophoretic separation of particles in a spiral microchannel

Particle separation is a fundamental operation in the areas of biology and physical chemistry. A variety of force fields have been used to separate particles in microfluidic devices, among which electric field may be the most popular one due to its general applicability and adaptability. So far, however, electrophoresis-based separations have been limited primarily to batchwise processes. Dielectrophoresis (DEP)-based separations require in-channel micro-electrodes or micro-insulators to produce electric field gradients. This article introduces a novel particle separation technique in DC electrokinetic flow through a planar double-spiral microchannel. The continuous separation arises from the cross-stream dielectrophoretic motion of particles induced by the non-uniform electric field inherent to curved channels. Specifically, particles are focused by DEP to one sidewall of the first spiral, and then dielectrophoretically deflected toward the other sidewall of the second spiral at a particle-dependent rate, leading to focused particle streams along different flow paths. This DEP-based particle separation technique is demonstrated in an asymmetric double-spiral microchannel by continuously separating a mixture of 5/10 mu m particles and 3/5 mu m particles.