(208b) Size-Selective Magnetophoretic Trapping of Submicrometer, Nonmagnetic Particles Immersed in a Magnetic Nanofluid

Hatton, T. A., Massachusetts Institute of Technology
Smith, K. A., Massachusetts Institute of Technology
Park, E. S., Georgia Institute of Technology

Magnetic particles have been widely used for biological separations. Most of these applications, particularly in cell separations, involve attachment of the magnetic particles to the species of interest. In this work, we were able to selectively trap submicron, nonmagnetic species based on size using magnetic fluids, but without attaching the magnetic particles to the species of interest. Instead, separation was achieved by a balance between magnetic-buoyancy effects and hydrodynamic drag on the nonmagnetic species. Separations were conducted in microdevices (chips) designed to generate sawtooth-like magnetic-field profiles and allow for real-time species-concentration measurements. Experiments demonstrated size-based trapping, where 840 nm polystyrene beads were trapped near the beginning of the channel, while 510 nm beads were trapped further downstream. The magnetophoretic trapping demonstrated in this work could form the basis of high-resolution, size-based separation methods for DNA, cellular organelles, viruses, and other like-sized biological and non-biological species.