title: Magnetophoretic Conductors and Diodes in a 3D Magnetic Field.
abstract: We demonstrate magnetophoretic conductor tracks that can transport single magnetized beads and magnetically labeled single cells in a 3-dimensional 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, we found that successful magnetic conductor geometries defined in soft magnetic materials must be composed of alternating sections of positive and negative curvature. In addition to the previously studied magnetic tracks taken from the magnetic bubble literature, a drop-shape pattern was 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, we demonstrate biological applications in transporting single cells and in the size based separation of magnetic particles.
authors.affiliation: Department of Mechanical Engineering and Materials Science, Duke University, Box 90300 Hudson Hall, Durham, NC 27708, USA.
authors.forename: Roozbeh
authors.initials: R
authors.lastname: Abedini-Nassab
authors.affiliation: Department of Biomedical Engineering, Duke University, Durham, North Carolina 27708, USA.
authors.forename: Daniel Y
authors.initials: DY
authors.lastname: Joh
authors.affiliation: Department of Medicine, Duke University, Durham, North Carolina 27708, USA.
authors.forename: Melissa
authors.initials: M
authors.lastname: Van Heest
authors.affiliation: Department of Mechanical Engineering and Materials Science, Duke University, Box 90300 Hudson Hall, Durham, NC 27708, USA.
authors.forename: Cody
authors.initials: C
authors.lastname: Baker
authors.affiliation: Department of Mechanical Engineering and Materials Science, Duke University, Box 90300 Hudson Hall, Durham, NC 27708, USA; Department of Biomedical Engineering, Duke University, Durham, North Carolina 27708, USA.
authors.forename: Ashutosh
authors.initials: A
authors.lastname: Chilkoti
authors.affiliation: Department of Medicine, Duke University, Durham, North Carolina 27708, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Murdoch
authors.affiliation: Department of Mechanical Engineering and Materials Science, Duke University, Box 90300 Hudson Hall, Durham, NC 27708, USA; Department of Biomedical Engineering, Duke University, Durham, North Carolina 27708, USA.
authors.forename: Benjamin B
authors.initials: BB
authors.lastname: Yellen
keywords: 3-dimensional field; magnetism; microfabrication; microfluidics; particle separation; single cell