Magnetic manipulation on the unlabeled nonmagnetic particles

This paper reports two basic microfluidic strategies for the magnetic manipulation of unlabeled nonmagnetic particles/cells. One is the deflection induced by a single magnet, and the other is the confusing effect produced by two magnets of opposite polarity. They can be combined into more completed particle manipulations like continuous flow separation, counting and detection, which are essential steps in biomedical applications. We experimentally studied the dynamics of 10.4 and 20 mu m nonmagnetic polystyrene particles within a flow rate range of 30, 50, 70 and 90 mu L/min in a straight channel. We defined the cross-section length that the particles occupy as the particle bandwidth to characterize the extent of deflection and focusing. To predict the trajectories of the particles, we established a simple theoretical model by considering the magnetic force and viscous drag force. Compared with the experimental results, the maximum deviation of the simulation is 9.28%. The influences of magnetic nanoparticle concentration, magnetic field parameters, size of microparticles and flow rate are systematically investigated. We also demonstrated that the effective deflection and focusing could be realized at low Fe3O4 nanoparticle concentrations, which means that this method can reduce the damage on cells in the practical applications.