Plasmonic nanoparticles can be individually analyzed through optoelectrochemical imaging (in which electrochemical processes are measured by optical means). When electrochemistry is performed on a nanoparticle, the refractive index of its environment will change resulting in a shift of the localized surface plasmon resonance. The spectral difference can be measured through characterization techniques such as darkfield microscopy to monitor electrochemical reactions at the surface of plasmonic nanoparticles.
Plasmonics-based electrochemical current microscopy (PECM) measures the contrast that appears from the interference of localized surface plasmon scattered light and reflected light that, like above, is sensitive to changes in the refractive index. This can be used to quantify the electrocatalytic reactions occurring at Pt nanoparticles. Since nanoparticles are inherently heterogenous (which affects catalytic activity), SEE methods can provide more information than traditional methods that measure the average of an ensemble of nanoparticles.