Magnetophoretic Conductors and Diodes in a 3D Magnetic Field

Magnetophoretic conductor tracks are used to transport single magnetized beads and magnetically labeled single cells in a 3D time-varying magnetic field. The vertical field bias, in addition to the in-plane rotating field, has the advantage of reducing the attraction between particles, which inhibits the formation of particle clusters. However, the inclusion of a vertical field requires the re-design of magnetic track geometries, which can transport magnetized objects across the substrate. Following insights from magnetic bubble technology, it is found that successful magnetic conductor geometries defined in soft magnetic materials must be composed of alternating sections of positive (convex) and negative (concave) curvature. In addition to the previously studied magnetic tracks from the magnetic bubble literature, a drop-shape pattern is found to be even more adept at transporting small magnetic beads and single cells. Symmetric patterns are shown to achieve bi-directional conduction, whereas asymmetric patterns achieve unidirectional conduction. These designs represent the electrical circuit corollaries of the conductor and diode, respectively. Finally, biological applications are demonstrated in the transport of single cells and in the size-based separation of magnetic particles.