Magnetic Pumping Of Continuous Magnetic Fluid In A Spin-Valve Sensor

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 mu V output signal was achieved when the magnetic fluid including a 10(6) 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 mu V 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. (C) 2011 American Institute of Physics. [doi:10.1063/1.3562870]