Plasmonic Sensing and Control of Single-Nanoparticle Electrochemistry

Plasmonic nanoparticles offer promise in photoelectrochemistry by enhancing the rate and selectivity of reactions and in sensing by responding optically to local reactions. Optical electrochemical measurements at the single-particle level are necessary for understanding and eventually controlling the role of plasmons in such complex environments. Recently, researchers have developed techniques to optically measure electrochemical reactions at the surface of single nanoparticles and individual aggregates, allowing for the high-throughput screening necessary to resolve subpopulations of active nanoparticle catalysts and identify active sites on aggregate structures. This review highlights single-nanoparticle and nanoparticle aggregate electrochemical techniques and how they can be used to isolate and elucidate the role of surface plasmons in enhancing catalyst activity and sensing electrochemical processes at the nanoscale. Metals such as gold and silver are largely inert on the bulk scale, but nanoparticles of these metals exhibit more active catalytic properties. In addition to increased surface areas and diverse crystal structures, metal nanoparticles can both sense and control electrochemical reactions through surface plasmon excitation by visible light. The collective oscillation of conduction-band electrons at a nanoparticle surface—the localized surface plasmon resonance—creates local electric-field enhancements, generates energetic charge carriers, and increases local temperature. We must understand the electrocatalytic and photocatalytic contributions of plasmonic nanoparticles before we can incorporate them within renewable energy and sensing technologies. This challenge requires an interdisciplinary approach combining plasmonic spectroscopy and electrochemistry for the investigation of heterogeneous nanoparticle samples at the single-particle level. Combing electrochemistry with plasmonics has recently led to advances in dynamic optical tuning, sensing, and photocatalysis. This review highlights the use of single-particle optical microscopy techniques for the study of plasmon resonances in sensing and driving electrochemical processes.