Flashy silver nanoparticles

Temporal fluctuations in the Raman spectrum from molecules adsorbed to noble metal colloids (i.e., "blinking") has been viewed as a single molecule signature. It is demonstrated here that silver colloids exhibit blinking that is independent of the nature of the adsorbate. Blinking was observed on silver colloids in the presence and absence of a SERS probe (e.g., R6G, BPE), sodium chloride, POIY-L-lysine, an alkanethiol layer, and a liquid overlayer (e.g., water, methanol). These observations suggest that the mechanism that gives rise to blinking is insensitive to the nature of the adsorbate and is likely to be a property of the nanoparticle. Consistent with this idea, blinking was observed from vapor-deposited silver films and silver powders with no added molecular probe. In addition, two distinct broad luminescence-like (continuum) features also exhibited blinking and spectral diffusion, with no apparent adsorbate dependence. Evidence that SERS and the underlying continuum are associated is provided by an observed correlation of "on" and "off" states for both processes.