Invited Paper BI+NC-WeM9
Biophotonics: Resonant Detection of Single Molecules

Wednesday, October 22, 2008, 10:40 am, Room 202

For many biological and chemical experiments, a sensor must have high sensitivity, high specificity, and fast response time. There are many technologies which are able to achieve one or two of these three requirements, but many still face fundamental sensitivity or response limitations. Silica optical resonators are able to overcome these limitations because of the high quality factor (Q).¹,² In their application as a single molecule sensor, the sensitivity is derived from the long photon lifetime inside the microcavity, and the specificity is derived from functionalization of the silica surface. During the initial series of label-free detection experiments, pure Interleukin-2 (IL-2) solutions were injected into the volume surrounding the microtoroid. The microtoroid successfully detected step-like shifts in resonance wavelength from individual IL-2 molecules binding. Additional experiments have shown that even in the more complex environment of serum individual binding events of IL-2 are still resolved.³ Therefore, this single molecule sensor will enable research in new areas of biophysics and cell biology. Acknowledgements: The author would like to thank Prof. Richard Flagan, Prof. Scott Fraser, and Dr. Rajan Kulkarni at the California Institute of Technology. A.M. Armani is supported by the Provost’s Initiative for Biomedical Nanoscience and the WiSE Program at the University of Southern California.

¹ A. M. Armani, D. K. Armani, B. Min, K. J. Vahala, and S. M. Spillane, Applied Physics Letters, vol. 87, pp. 151118, 2005.
² Armani, D. K., Kippenberg, T. J., Spillane, S. M. & Vahala, K. J. Ultra-high-Q toroid microcavity on a chip. Nature 421, 925-928 (2003).
³ A. M. Armani, R. P. Kulkarni, S. E. Fraser, R. C. Flagan, and K. J. Vahala, Science, vol. 317, pp. 783 (2007).