Surface-enhanced resonance Raman scattering spectroscopy of single R6G molecules

Surface-enhanced resonance Raman scattering (SERRS) ofRhodamine 6G (R6G) adsorbed on colloidal silver clusters has been studied.Based on the great enhancement of the Raman signal and the quench of thefluorescence, the SERRS spectra of R6G were recorded for the samples of dyecolloidal solution with different concentrations. Spectral inhomogeneitybehaviours from single molecules in the dried sample films were observed withcomplementary evidences, such as spectral polarization, spectral diffusion,intensity fluctuation of vibrational lines and even ``breathing' of themolecules. Sequential spectra observed from a liquid sample with an average of0.3 dye molecules in the probed volume exhibited the expected Poissondistribution for actually measuring 0, 1 or 2 molecules. Difference betweenthe SERRS spectra of R6G excited by linearly and circularly polarized lightwere experimentally measured.