Hydrodynamic density-based particle focusing in digital microfluidic systems

A particle-separation technique for digital microfluidic system is introduced to focus and concentrate non-buoyant particles in micro-droplets. The proposed method utilizes the combined effects of the gravitational forces and the fluid flow inside the droplet. This technique does not require any additional electrical or magnetic modules. The desired hydrodynamic effect is created by spinning the droplet in a controlled fashion on a circular pattern of electrodes using electrowetting-on-dielectric technique. The fabricated device successfully focuses the non-buoyant silica beads of 5 μm in a region on the central electrode; whereas the focusing behavior is not observed for the neutrally polystyrene beads.