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

Abstract

On-chip spin-valve sensors $\text{(2×6\hspace{0.17em}μ}{\mathrm{m}}^2)$ 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 μm Micromer^®-M and 250 nm Nanomag^®-D labels, with signals ranging from ∼300 μV to ∼2 mV (8 mA sense current; ∼15 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 ${\text{2×10}}^{\text{−12}}\hspace{0.17em}\mathrm{emu}$ (2 μm labels), corresponding to signals of 100–400 μV. Although, theoretical calculations suggest that the minimum measurable moment is in the order of ${\text{6×10}}^{\text{−15}}\hspace{0.17em}\mathrm{emu},$ due to noise limitations of the present setup, this limit is in the order of ${\text{2×10}}^{\text{−13}}\hspace{0.17em}\mathrm{emu},$ corresponding to a single 250 nm label. On-chip tapered aluminum current line structures were used for placement of magnetic labels at sensor sites.