Evidence of natural isotopic distribution from single-molecule SERS

TL;DR

This study demonstrates that single-molecule SERS can detect natural isotopic variations, specifically $^{12}$C and $^{13}$C, in a dye molecule, showcasing its extreme sensitivity to atomic-level changes.

Contribution

The paper provides the first evidence of natural isotopic distribution detection at the single-molecule level using SERS, without artificial isotopic labeling.

Findings

Detection of $^{13}$C isotopic substitution effects in single-molecule SERS spectra.

Observation of frequency shifts in the cyano vibrational mode due to isotopic variation.

Validation of SERS as a tool for atomic-level isotopic analysis in individual molecules.

Abstract

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$\equiv$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 $^{12}$C by the next most abundant $^{13}$C isotope. This example adds another demonstration of single molecule sensitivity in SERS through isotopic editing which is done, in this case, not by artificial isotopic editing but rather by nature itself. It also highlights SERS as a unique spectroscopic tool, capable of detecting an isotopic change in one atom of a single molecule.