Single Ag Nanoparticle Spectroelectrochemistry via Dark-Field Scattering and Fluorescence Microscopies

The spectroelectrochemical properties of individual luminescent, plasmonic silver nanoparticles (Ag NPs) are investigated using the combined methods of dark-field scattering (DFS) and photoluminescence (PL) spectroelectrochemistry. Individual NP light scattering and PL intensities are measured while the substrate’s electrochemical potential is controlled to produce and oxidize the NPs. The spectroelectrochemical responses of individual NPs are used to study heterogeneities in their redox properties not visible in bulk voltammetric measurements. Our studies show that the Ag NPs exhibit a range of redox potentials, and their statistical distribution is dependent on the electrolyte system used. No variations in the spectral profile of bulk NP samples are observed, implying no correlation between the redox potentials of individual NPs and the energy of emitted photons from fluorescent sites on Ag NPs. This is due to a negligible difference in the redox potentials for individual emissive sites on a given Ag NP and/or the shrinking of the polarizable bulk of the Ag NP.