Single-cell detection by cavity ring-down spectroscopy

The implementation of cavity ring-down spectroscopy in an optical fiber resonator extends the viability of this highly sensitive technique for label-free detection of biological species. By chemically treating the surface of discrete tapered sensing regions along the length of a physically extended optical fiber resonator, we show single-cell sensitivity arising from optical scattering of the evanescent field surrounding the fiber. The observed detection limits, based on a minimum detectable scattering cross section on the order of 10μm2, suggest a broad range of new applications in a simple, inexpensive device for real-time cavity ring-down biosensing.