Evidence of Natural Isotopic Distribution from Single-Molecule SERS

We report on the observation of the natural isotopic spread of carbon from single-molecule surface-enhanced Raman spectroscopy (SM-SERS). By choosing a dye molecule with a very localized Raman-active vibration in a cyano bond (C N triple bond), we observe (in a SERS colloidal liquid) a small fraction of SM-SERS events where the frequency of the cyano mode is softened and in agreement with the effect of substituting C-12 by the next most abundant isotope, C-13. This example adds another demonstration of single-molecule sensitivity in SERS through isotopic editing, which in this case is done not by artificial isotopic editing but rather by nature itself. It also highlights SERS as a unique spectroscopic tool that is capable of detecting an isotopic change in one atom of a single molecule.