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Label-Free, Single-Molecule Detection with Optical Microcavities

Science  10 Aug 2007:
Vol. 317, Issue 5839, pp. 783-787
DOI: 10.1126/science.1145002

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Abstract

Current single-molecule detection techniques require labeling the target molecule. We report a highly specific and sensitive optical sensor based on an ultrahigh quality (Q) factor (Q > 108) whispering-gallery microcavity. The silica surface is functionalized to bind the target molecule; binding is detected by a resonant wavelength shift. Single-molecule detection is confirmed by observation of single-molecule binding events that shift the resonant frequency, as well as by the statistics for these shifts over many binding events. These shifts result from a thermo-optic mechanism. Additionally, label-free, single-molecule detection of interleukin-2 was demonstrated in serum. These experiments demonstrate a dynamic range of 1012 in concentration, establishing the microcavity as a sensitive and versatile detector.

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