Nanoparticle-free single molecule anti-stokes Raman spectroscopy

In the absence of large, plasmon-supporting nanoparticles, biocompatible dendrimer- and peptide-encapsulated few-atom Ag nanoclusters produce scaffold-specific single molecule (SM) Stokes and anti-Stokes Raman scattering. The strong SM vibrational signatures are enhanced by the Ag_n transitions in nanoparticle-free samples and cannot arise from plasmon enhancement. Characteristic SM-Raman intermittency is observed, with antibunching of the underlying Ag_n emission directly confirming the SM nature of the emissive species.