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Science. 2007 Aug 10;317(5839):783-7. Epub 2007 Jul 5.

Label-free, single-molecule detection with optical microcavities.

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Department of Applied Physics, MC 128-95, California Institute of Technology, Pasadena, CA 91125, USA.

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  • Science. 2011 Dec 16;334(6062):1496.


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 > 10(8)) 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 10(12) in concentration, establishing the microcavity as a sensitive and versatile detector.

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