SINGLE-MOLECULE DETECTION USING SURFACE-ENHANCED RAMAN-SCATTERING (SERS)

By exploiting the extremely large effective cross sections (10(-17)-10 (-16) cm(2)/molecule) available from surface-enhanced Raman scattering (SERS), we achieved the first observation of single molecule Raman sc attering. Measured spectra of a single crystal violet molecule in aque ous colloidal silver solution using one second collection time and abo ut 2 x 10(5) W/cm(2) nonresonant near-infrared excitation show a clear ''fingerprint'' of its Raman features between 700 and 1700 cm(-1). Sp ectra observed in a time sequence for an average of 0.6 dye molecule i n the probed volume exhibited the expected Poisson distribution for ac tually measuring 0, 1, 2, or 3 molecules.