Microchip electromagnetophoresis with staggered magnetic field for continuous separation of micro-particles

Abstract

We report a novel separation method of microparticles using microchip electromagnetophoresis, which is obserbed when electric and magnetic fields are applied to particles in a conductive solution, with the staggered being magnetic field generated by two external magnets. In this method, because particles experience two local ized electromagnetophoresis (EMP) in a microchannel, they are focused and separated to different outlets based on their EMP migration velocities, which depend on their sizes or properties. We used a commercially available Y-shape microchip that had a inlet and two outlets. The particles mixture injected from the inlet by the flow of an aqueous medium were once focused on the channel wall by an EMP force of which direction was orthogonal to the flow. Then, the particles experienced an EMP force whose direction was opposite to the focusing process. Particles with low EMP migration velocity traveled toward the parallel outlet, while those with a large EMP migration velocity eluted off from the diagonal outlet. This elution behavior should result in the separation of the particles based on their sizes or properties. We designed the staggered magnetic field using two external magnets for the focusing and separation processes. Using this method, we demonstrated the size-based separation of polystyrene (PS) particles (3 and 6 μm in diameter) using localized EMP migration by designing the magnetic field. Consequently, both 3 and 6 μm PS particles could be separately recovered at the different outlets with 100 purity and recovery, respectively. Moreover, yeast cells and 6 μm PS particles could be separated with a high separation efficiency by this technique.