Design of integrated microfluidic device for sorting magnetic beads in biological assays

On-chip manipulation of nanoscopic magnetic particles in microfluidic channels has been demonstrated. The particles, obtained from Bangs Labs, were 460 nm in diameter and contained 12% ferrite. They were moving in a 12 /spl mu/m wide by 4 /spl mu/m deep channel etched into a deposited layer of silicon nitride. An Al current strap was buried beneath the channel and shaped in such a way to generate an in-plane cross-channel field gradient when it was energized by an electrical current. An in-plane external field of 20 kA/m was applied in order to magnetize the particles. They were observed to move across the channel as either the current or field polarity was changed.