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

By exploiting the extremely large effective cross sections ( ${10}^{-17\mathrm{}}–{10}^{-16\mathrm{}}{\mathrm{cm}}^2/\mathrm{molecule}$) 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 $2\times {10}^5\mathrm{W}/{\mathrm{cm}}^2$ nonresonant near-infrared excitation show a clear “fingerprint” of its Raman features between 700 and $1700{\mathrm{cm}}^{-1\mathrm{}}$. 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.