Focusing and Sorting Polystyrene Particles and Liposomes via Diffusiophoresis in Straight Flat Microchannels

We report a novel phenomenon that enables the pre-concentration and sorting of charged polystyrene particles and liposomes dispersed in a continuous flow within a straight flat microchannel. A 3-inlet junction microfluidic device is used to generate a steady-state salt concentration gradient in the direction perpendicular to the flow. As a result, particles dispersed in the electrolyte solution accumulate into two symmetric regions of the channel by forming two distinct focusing spots. Despite a similar colloid behaviour being reported in previous studies with a similar flow configuration, our numerical and experimental analysis show that the observed particle dynamics is driven by a novel unreported physical mechanism, that combines diffusiophoresis, diffusioosmosis and hydrodynamic effects.

In addition, we developed a proof-of-concept microfluidic device that exploits this new mechanism to enable the focusing and filtration of colloidal particles based on their zeta potential under continuous and steady-state flow settings. The proposed method offers great potential for microfluidic bio-analytical testing applications, including bioparticle pre-concentration and filtration.