Particle Separation Systems Based On Rotating Magnetic Field

Magnetic particles technology has enjoyed growing popularity in varying fields such as magnetic device fabrication, bio-separation, hyperthermia, magnetic resonance imaging and drug targeting. Magnetic separation has become a significant technology considering particles monodispersity required in those fields.Multiple techniques based on a stationary magnetic field have been proposed, including magnetophoresis, catch-and-release, and magnetic field-flow fractionation, however, none of them has yielded satisfactory resolution due to irreversible adsorption and aggregation of magnetic analytes caused by the magnetic field. To alleviate these problems, we proposed development of two approaches: rotating magnetic field/cyclical sedimentation field-flow fractionation (RMF/CySd FFF) and magnetic focusing field-flow fractionation (MFcFFF).RMF/CySd FFF is based on the use of a rotating magnet on top of the separation channel to provide periodically changed force field acting on the particles. When the rotating magnet passes over the particles of different sizes, they are all driven to the top wall. As the rotation of the magnet continues, the particles begin to settle into different flow streamlines under gravity. With recycling of this catch-and-release process, the particles elute at velocities corresponding to their sedimentation coefficients.RMF/CySd FFF is, however, not applicable to particle separations on the basis of their magnetization. To overcome this problem, a novel MFcFFF was developed by increasing hydrodynamic lift force. In this mode of separation, the magnetic particles reach their equilibrium position at an elevated distance from the accumulation wall where the hydrodynamic lift force is balanced by magnetic force. The magnetic analytes with different magnetic susceptibilities locate at different flow streamlines thus elute at different times.A distinct advantage of the magnetic separation techniques developed in this thesis is that magnetic adsorption and aggregation of particles can be eliminated by the intermittent magnetic field in RMF/CySd-FFF and by shear force and viscous drag force in MFcFFF, thus giving rise to high resolution separatioins. Although only particle separation is demonstrated in this thesis, the techniques would be potentially useful for bioseparations such as cell separations when magnetic labeling is employed.