Observation of reactions in single molecules/nanoparticles using light microscopy

Recent techniques for direct observation of single molecules or nanoparticles provide methodologies for imaging the activation sites of heterogeneous catalysts (spatially resolved) and observing intermediates that are not visible in the ensemble average (temporally resolved). Accordingly, the primary challenge for related experiments is obtaining sufficient spatial and temporal resolutions for microscopic observation of the chemical reaction of interest. This review discusses recent advances in fluorescence—for example, total internal reflection fluorescence (TIRF)—and dark-field microscopy—for example, imaging plasmonic probes—used for observing organic, inorganic, and biological reactions. The following key factors for microscopic observation of chemical reactions are discussed: (1) design of the chemical reaction and probe, (2) selection of microscope based on reaction's temporal information, and (3) use of machine learning algorithms to analyze the sequence imaging data. This review summarizes experimental techniques and detailed examples of reactions at the single molecule and nanoparticle level. Furthermore, it discusses avenues of development. These observations can guide the development of new and systematic methodological approaches for investigating important unsolved problems in chemistry.