Directed transport of superparamagnetic microbeads using periodic magnetically textured substrates

Abstract

Superparamagnetic microbeads (SPBs) have been widely used to capture and manipulate biological entities in a fluid environment. Chip-based magnetic actuation provides a means to transport SPBs in lab-on-a-chip technologies. This is usually accomplished using the stray magnetic field from patterned magnetic micro structures or domain walls in magnetic nanowires. Recently, many studies have focused on sub-micron sized antidot array of magnetic materials because non-magnetic holes affect the micromagnetic properties of film. In this work, a method is presented for directed transport of SPBs on magnetic antidot patterned substrates by applying a rotating elliptical magnetic field. We find a critical frequency for transport beyond which the bead dynamics transition from stepwise locomotion to local oscillation. We also find that the out-of-plane (Hoop) and in-plane (Hip) field magnitudes play crucial roles in triggering bead movements. Namely, we find threshold values in Hoop and Hip that depend on bead size which can be used to independently and remotely to address specific bead populations in a multi-bead mixture. In addition, these behaviors are explained in terms of the dynamic potential energy landscapes computed from micromagnetic simulations of the substrate magnetization configuration. Furthermore, we show that large-area magnetic patterns suitable for particle transport and sorting can be fabricated through a self-assembly lithography technique, which provides a simple, cost-effective means to integrate magnetic actuation into microfluidic systems. Finally, we observed the transport of bead motion on antidot arrays of multilayered structures with perpendicular magnetic anisotropy (PMA), and found that the dynamics of SPBs on a PMA substrate are much faster than on a substrate with in-plane magnetic anisotropy (IMA). Our findings provide new insights into the enhanced transport of SPBs using PMA substrates and offer flexibility in device applications using the transportation or sorting of magnetic particles.