On-chip manipulation and magnetization assessment of magnetic bead ensembles by integrated spin-valve sensors

Manipulation and detection of magnetic beads on a semiconductor chip opens up new perspectives for analysis of magnetically labeled specimens in biomechanical micro-electromechanical systems for biological applications. Sensitive spin-valve sensors were integrated with magnetic field generating conductors to assess the behavior of ensembles of superparamagnetic nanoparticles 300 nm in diameter that contain 75%-80% magnetite. The spin-valve multilayer including a nanooxide layer achieves 8% magnetoresistance (MR) for an integrated device of 2x16 mum(2). Motion of the magnetic particles towards and across the sensor is achieved by two tapered magnetic field generating current conductors. The spin-valve sensor detects the stray magnetic field that emanates from the ensemble of magnetic particles. We study the transients in the magnetic signal on the order of 1% MR. These results lead to a model that describes magnetization configurations of the cluster of beads. (C) 2002 American Institute of Physics.