  We demonstrate fast (0.25 s/pixel) nanoscale chemical imaging in aqueous
solution via tip-enhanced Raman scattering (TERS), with sub-15 nm spatial
resolution. The substrate consists of 4-mercaptobenzonitrile-functionalized
monocrystalline gold triangular platelets immersed in H2O, which we map using a
gold-coated AFM probe illuminated using a 633 nm laser source. We find that the
recorded TERS images trace the enhanced local optical fields that are sustained
towards the edges and corners of the triangles. In effect, we directly map
local optical fields of a plasmonic substrate in aqueous solution through
molecular TERS. Overall, our described platform and approach may generally be
used for chemical and biological imaging, and potentially, to follow chemical
transformations at solid-liquid interfaces through TERS.
