Focusing microparticles in a microfluidic channel with ferrofluids

We report a novel on-chip microparticles focusing scheme using stable magnetic nanoparticles suspension (i.e., ferrofluids). The principle of focusing is based on magnetic buoyancy forces exerted on non-magnetic particles within ferrofluids under non-uniform magnetic fields. The design, modeling, fabrication and characterization of the prototype focusing device are presented. Our scheme is simple, low-cost, fast, and applicable to virtually all particles.