Single Molecule Detection Using Surface-Enhanced Raman Scattering (SERS)

By exploiting the extremely large effective cross sections (10^-17--10^-16cm^2/molecule) available from surface-enhanced Raman scattering (SERS), we achieved the first observation of single molecule Raman scattering. Measured spectra of a single crystal violet molecule in aqueous colloidal silver solution using one second collection time and about 210^5W/cm^2 nonresonant near-infrared excitation show a clear ``fingerprint'' of its Raman features between 700 and 1700cm^-1. Spectra observed in a time sequence for an average of 0. 6 dye molecule in the probed volume exhibited the expected Poisson distribution for actually measuring 0, 1, 2, or 3 molecules.