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Originally published in Science Express on 5 July 2007
Science 10 August 2007:
Vol. 317. no. 5839, pp. 783 - 787
DOI: 10.1126/science.1145002
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Reports

Label-Free, Single-Molecule Detection with Optical Microcavities

Andrea M. Armani,1 Rajan P. Kulkarni,2 Scott E. Fraser,1,2* Richard C. Flagan,3* Kerry J. Vahala1

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.

1 Department of Applied Physics, MC 128-95, California Institute of Technology, Pasadena, CA 91125, USA.
2 Division of Biology, MC 139-74, California Institute of Technology, Pasadena, CA 91125, USA.
3 Division of Chemistry and Chemical Engineering, MC 210-41, California Institute of Technology, Pasadena, CA 91125, USA.

* To whom correspondence should be addressed. E-mail: sefraser{at}caltech.edu (S.E.F.); flagan{at}caltech.edu (R.C.F.)

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Single virus detection from the reactive shift of a whispering-gallery mode.
F. Vollmer, S. Arnold, and D. Keng (2008)
PNAS 105, 20701-20704
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