Focusing microparticles in a microfluidic channel with ferrofluids

We report a novel on-chip microparticles focusing technique 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 field. The design, modeling, fabrication, and characterization of the focusing scheme are presented. Focusing of 4.8, 5.8, and 7.3 mu m microparticles at various flow rates are demonstrated in a microfluidic channel. Our scheme is simple, low-cost, and label-free compared to other existing techniques.