Magneto-microfluidic three-dimensional focusing of magnetic particles

We present a method for magneto-microfluidic three-dimensional focusing of magnetic microparticles from a dense plug into a single streamline with longitudinal inter-particle spacing. Plug formation on-chip is induced by a high-gradient magnetic field generated at the sidewall of a microchannel by an integrated micromachined magnetic tip that is connected to an external electromagnet. Controlled release of the microparticles is achieved using an exponential damping protocol of the magnetic retention force in the presence of an applied flow.