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Published Online July 5, 2007
Science DOI: 10.1126/science.1145002

Reports

Submitted on May 11, 2007
Accepted on June 14, 2007

Label-Free, Single-Molecule Detection with Optical Microcavities

Andrea M. Armani 1, Rajan P. Kulkarni 2, Scott E. Fraser 3, Richard C. Flagan 4, Kerry J. Vahala 1*

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

* To whom correspondence should be addressed.
Kerry J. Vahala , E-mail: vahala{at}caltech.edu

Current single-molecule detection techniques require labeling the target molecule. We report a highly specific and sensitive optical sensor based on an ultrahigh Q (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.


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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Science. ISSN 0036-8075 (print), 1095-9203 (online)