Spin valve biosensors: Signal dependence on nanoparticle position

Experimental and theoretical studies have been carried out on the spin valve sensor signal dependence on the spatial locations of magnetic nanoparticles as potential biomolecular labels in the magnetic biodetection technology. Superparamagnetic 16 nm magnetite (Fe3O4) nanoparticles were site specifically deposited at different positions relative to a submicron-wide spin valve sensor. The spin valve sensor signal showed both polarity and magnitude differences with the particles at different positions. A theoretical model including magnetic sensor-particle interaction confirms the experimental results and provides a design guide to the sensing area. Moreover, the theoretical calculations reveal a nonmonotonic signal dependence on the vertical particle-to-sensor distance due to the sensor-particle interaction, and show that an optimum distance exists for signal strength and quantification.