Real time observation of chemical reactions of individual metal nanoparticles with high-throughput single molecule spectral microscopy.

Real time observation of chemical reactions of individual noble metal nanoparticles (MNPs) is fundamentally important to their controlled synthesis, chemical sensing and catalysis applications. Here, with a simple and high-throughput single-molecule darkfield spectral imaging technique, we demonstrate that the reaction-induced plasmonic resonance variations of multiple MNPs could be monitored in parallel. Oxidation kinetics of individual gold nanorods (AuNRs), either immobilized on a glass substrate or moving freely in homogeneous solution, was recorded successfully. Heterogeneous reaction pathways and intermediate states unobservable in ensemble UV-visible measurements were revealed. Interestingly, the oxidation rate of individual immobilized AuNRs was much slower than that of the bulk AuNR solution, which implies the existence of a novel self-catalysis mechanism. This high-throughput darkfield spectral imaging technique could be applied to chemical reaction kinetics and heterogeneous catalysis studies of other MNPs at single particle level.