On-chip manipulation of nonmagnetic particles in paramagnetic solutions using embedded permanent magnets

This study develops a method for embedding permanent magnets into poly(dimethylsiloxane) (PDMS)-based microfluidic chips. Magnets can be brought very close to the planar microchannels for enhanced magnetic field and field gradients, which enables on-chip continuous-flow manipulation of nonmagnetic particles in typical paramagnetic solutions. We performed a systematic study of the transport of polystyrene particles suspended in manganese (II) chloride (MnCl2) solutions through a rectangular microchannel. Owing to their smaller magnetization than the suspending fluid, particles experience negative magnetophoresis and are deflected away from the magnet. The effects of particle position (relative to the magnet), particle size, MnCl2 salt concentration, and fluid flow velocity on the horizontal magnetophoretic deflection are examined using a combined experimental and theoretical approach. The experimental results agree quantitatively with the predictions of an analytical model. The demonstrated nonmagnetic particle deflection may be used with the potential to focus and sort cells in lab-on-a-chip for bio-applications.