Homogeneity, transport, and signal properties of single Ag particles studied by single-molecule surface-enhanced resonance Raman scattering

We extended the sensitivity of Raman correlation spectroscopy in solution t o the single-molecule level by applying surface- and resonance-enhanced Ram an scattering (SERRS) combined with time-gated, confocal signal detection. The brightness of the SERRS signal of single Rhodamine 6G molecules adsorbe d on a single silver nanoparticle is comparable to fluorescence. Rare event analysis reveals the existence of few particles with simultaneous SERRS an d fluorescence signal. The observation of a dynamic exchange between hetero geneous binding sites is supported by the existence of multiple SERRS brigh tnesses in the signal intensity distribution and by signal fluctuations in the 60 mus time range detected by autocorrelation analysis. Finally, polari zation-dependent SERRS autocorrelation curves and single-particle analysis allowed us to measure individual rotational diffusion times and to directly analyze the heterogeneity of the ensemble in solution.