  Plasmon-enhanced chemical transformations at the solid-liquid interface can
be imaged with high sensitivity, chemical selectivity, and nanoscale precision
through tip-enhanced Raman scattering (TERS). We demonstrate the latter for the
first time through measurements aimed at (i) locating plasmonic hotspots at the
solid-liquid interface at which chemical transformations take place, (ii)
monitoring the evolution from reactants to products through their distinct
Raman spectra, and (iii) 2D correlation analysis of Raman time trajectories to
unambiguously extract the spectral components that mark chemical transformation
and to understand the correlations between the product and parent signatures.
For our proof-of-principle study, we select a model plasmon-enhanced chemical
process, namely, the dimerization of p-nitrothiophenol to dimercaptoazobenzene,
but now, at the solid-liquid interface. Our plasmonic construct otherwise
consists of chemically functionalized gold microplates in aqueous solution,
which we image using a gold-coated TERS probe irradiated at 633-nm. Overall, we
demonstrate chemical reaction imaging in aqueous solution via TERS for the
first time, herein, at a pixel-limited lateral spatial resolution of 10 nm.
