Single-molecule recognition and mapping with chemical discrimination capability has been a long-standing goal in the fields of catalysis, molecular science, and biotechnology.

The research groups of DONG Zhenchao and HOU Jianguo of the University of Science and Technology of China and their collaborators demonstrated Raman spectral imaging with spatial resolution below one nanometre, resolving the inner structure and surface configuration of a single molecule. This is achieved by spectrally matching the resonance of the nanocavity plasmon to the molecular vibronic transitions, particularly the downward transition responsible for the emission of Raman photons. 

This matching is made possible by the extremely precise tuning capability provided by scanning tunnelling microscopy. Experimental evidence suggests that the highly confined and broadband nature of the nanocavity plasmon field in the tunnelling gap is essential for ultrahigh-resolution imaging through the generation of an efficient double-resonance enhancement for both Raman excitation and Raman emission.  

The technique not only allows for chemical imaging at the single-molecule level, but also offers a new way to study the optical processes and photochemistry of a single molecule.

Results of the study were published in Nature on June 6, 2013.