New tools for investigating electromagnetic hot spots in single-molecule surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) is quickly growing as an analytical technique, because it offers both molecular specificity and excellent sensitivity. For select substrates, SERS can even be observed from single molecules, which is the ultimate limit of detection. This review describes recent developments in the field of single-molecule SERS (SM-SERS) with a focus on new tools for characterizing SM-SERS-active substrates and how they interact with single molecules on their surface. In particular, techniques that combine optical spectroscopy and microscopy with electron microscopy are described, including correlated optical and transmission electron microscopy, correlated super-resolution imaging and scanning electron microscopy, and correlated optical microscopy and electron energy loss spectroscopy.