Magnetic pumping of continuous magnetic fluid in a spin-valve sensor

Abstract

To investigate the manipulation of magnetic particles diluted in magnetic fluid, we fabricated a spin valve sensor consisting of sensing and reference sensors and a current-carrying wire near the sensing sensor as well as a microfluidic channel. We designed the microfluidic channel to operate only on the top surface of the sensing sensor. Although a 40 μV output signal was achieved when the magnetic fluid including a 106 bead/ml concentration passed through the channel, the signal disappeared when we switched on the line current. Such a result indicated that the magnetic force, induced by the gradient near the current-carrying wire, caused magnetic particles to exit from the top surface of the sensing sensor. In particular, the output signal recovered to a value of 40 μV when the current was switched off. In addition, the output signal was proportional to the concentration of magnetic fluid. The results in this study indicated that magnetic pumping employing a current-carrying wire near sensors can be effectively used to manipulate magnetic particles on sensor surfaces, allowing use of spin-valve sensors after a detection of magnetic particle.