Biodetection using magnetically labeled biomolecules and arrays of spin valve sensors (invited)

On-chip spin-valve sensors (2x6 mum(2)) were used to detect the binding of streptavidin-functionalized superparamagnetic labels to sensor surface-bound biotin. Both micron-sized and nanometer-sized labels were studied. The detection of biomolecular recognition was demonstrated using 2 mum Micromer(R)-M and 250 nm Nanomag(R)-D labels, with signals ranging from similar to300 muV to similar to2 mV (8 mA sense current; similar to15 Oe in-plane magnetizing fields). For smaller labels, detection of biomolecular recognition was not achieved. The capability of detecting single labels was demonstrated for label moments down to 2x10(-12) emu (2 mum labels), corresponding to signals of 100-400 muV. Although, theoretical calculations suggest that the minimum measurable moment is in the order of 6x10(-15) emu, due to noise limitations of the present setup, this limit is in the order of 2x10(-13) emu, corresponding to a single 250 nm label. On-chip tapered aluminum current line structures were used for placement of magnetic labels at sensor sites. (C) 2003 American Institute of Physics.