Although extremely sensitive, electrical measurements are essentially unable to discriminate complex chemical events involving individual nanoparticles. The coupling of electrochemistry to dark field imaging and spectroscopy allows the triggering of the electrodissolution of an ensemble of Ag nanoparticles (by electrochemistry) and the inference of both oxidation and dissolution processes (by spectroscopy) at the level of a single nanoparticle. Besides the inspection of the dissolution process from optical scattering intensity, adding optical spectroscopy reveals chemical changes through drastic spectral changes. The behaviours of single NPs and NP agglomerates are differentiated: in the presence of thiocyanate ions, the transformation of Ag single nanoparticles to AgSCN is investigated in the context of plasmonic coupling with the electrode; tentative interpretations for optically unresolved groups of nanoparticles are proposed.