Time-dependent study of single-molecule SERS signal from yeast cytochrome c

A study of cytochrome c from Saccharomyces cerevisiae adsorbed on silver colloids at very low concentration is carried out by surface-enhanced Raman scattering. Spectra acquired at different times exhibit dramatic fluctuations in both line frequency and intensity indicating that single molecule detection is approached. The intensity fluctuations are investigated by means of a second order time correlation analysis. Such an approach has allowed us to put into evidence the presence of two distinct dynamical phenomena. The results are discussed in connection with diffusion processes to which the protein undergoes with respect to the surface of the Ag nanoclusters and with a modulation of the enhancement of the Raman signal.