Continuous separation of magnetic beads using a Y-shaped microfluidic system integrated with hard-magnetic elements

A Y-shaped microfluidic separator with an array of hard-magnetic elements integrated in a non-magnetic substrate is designed to realize continuous separation of magnetic beads under an external bias field. By fixing the magnetization directions of the hard-magnetic elements parallel to the wall of microchannel, the spatial distribution of the magnetic field can be adjusted by the geometrical size of elements, the gap between two neighboring elements, and the direction of the external bias field. In this work, magnetic beads comprising of multiple magnetic/superparamagnetic nanoparticles (10 nm Fe₅Si₃, Fe₃Si or Fe₃O₄) in polymer matrixes are used. Herein, Kelvin force on the magnetic bead is described by treating each magnetized superparamagnetic nanoparticle as an equivalent magnetic dipole. With the closed-form Kelvin force, a two-way model that takes bead-fluid interaction into account is adopted to investigate the trajectories of magnetic beads in our Y-shaped microfluidic system. Using the two-way model, the influence of the beads' size, the direction of the external bias field, the magnetic bead concentration and the bead-fluid interaction on the trajectories of magnetic beads is also investigated. 100% collection or separation efficiency can be realized just by adjusting inlet velocities. In addition, it is theoretically demonstrated that two kinds of magnetic beads with small size difference (down to 100 nm) can be successfully separated by using our Y-shaped microfluidic separator.