Influence of Photostability on Single-Molecule Surface Enhanced Raman Scattering Enhancement Factors

Experimental determinations of enhancement factors in Surface Enhanced Raman Scattering (SERS) are intimately intertwined with the photostability of the probes. We study the effect of the limited photostability in single-molecule SERS (SM-SERS) events and show explicitly how this may result in a large under-estimation of the SERS enhancement factors (EFs) obtained experimentally. To this end, we use the bianalyte technique with isotopically edited probes to provide the best-case scenario for the isolation of single molecule events, and study the statistics of EFs at different incident laser powers. When photobleaching stops playing an important role within the integration time used to capture the spectra, SM-SERS EFs approach an upper bound, which is in agreement with estimations of the EFs within the electromagnetic theory of SERS enhancements. Our results reinforce, in addition, the fact that the highest SM-SERS EFs observed experimentally are typically of the order of ∼1010.