Ever since its discovery in 1988 by two research groups in France and Germany, Giant Magnetoresistance (GMR) has revolutionized the application of magnetic sensors in hard disk drives and magnetic memories.1,2 It also offers an inspiration for their use in magnetic biodetections, a growing field with great promises. One of them is the spin valve (SV) sensor, a magnetic field sensor sensing the magnetic fringing field of captured magnetic nanoparticles.3 Compared to other structures, SV sensors are easier to fabricate and in an advance stage of development. Biosensors of microarrays or biochips are widely used to assay nucleic acids or proteins in a solution, which play important toles in gene expression and proteomic studies. Most commercial microarrays utilize fluorescent labeling to quantify biomolecules analytes. But they have limited sensitivity as well as signal crosstalk and bleaching due to the optical detection systems.4 Comparatively, GMR based SV biosensors can give higher selectivity, increased sensitivity, lower cost and better portability since biomolecule analytes are essentially nonmagnetic so that interference effects and background signals are much reduced.5
. A. Fert, Phys. Rev. Lett., vol. 61, p. 2472, 1988.
. P.Grünberg, Phys. Rev. B, vol. 39, p. 4828, 1989.
. G. Li, J. Appl. Phys., vol. 93, pp. 7557–7559, 2003.
. M. Schena, Microarray Biochip Technology. borough, MA: Eaton, 2000, pp. 1–18.
. S.X. Wang, IEEE Transactions on Magnetics, Vol. 44, No. 7, July 2008.