(233d) Dispersive Kinetics of Fluorescent Two-State Reactions At the Single Nanoparticle Level
Metal nanoparticles are key components in the advancement of future energy technologies since they are catalytically active for several organic-inorganic syntheses, electron-transfer, and energy conversion reactions. They directly promote the chemical conversion and facilitate chemical transport to active interfaces. A detailed understanding of the relation between structure and properties of nanoparticles will lead to tailored catalytic properties. The surface of nanoparticles is not static during catalytic turnover, but rather dynamic due to the rearrangement of surface atoms and the surrounding adsorbate layer. The rearrangement of the surrounding adsorbate-solvent layer may always be in play, but restructuring of the nanoparticle surface will display particle-size dependent behavior. This rearrangement occurs on timescales commensurate with catalytic turnover since catalysis induces dispersion (stochastic behavior) in the characteristic waiting times for surface reaction and product desorption (and therefore the reaction turnover rate). In order to understand the origin of kinetic dispersion, we make use of a single-molecule fluorescence approach to monitor the real-time catalysis of individual gold nanoparticles for the reduction of resazurin (non-fluorescent) to resorufin (fluorescent) in the presence of a reductant and small molecule adsorbates with single turnover resolution. Coupled with particle size considerations, adsorbate layer-induced restructuring effects, and temperature considerations, we aim to fundamentally understand how real-time structural variations influence the dispersive kinetics in nanoparticle catalysts. Force-field (ReaxFF) molecular dynamics (MD) simulations, ensemble level reactivity measurements and isothermal titration calorimetry (ITC) complement the body of single nanoparticle reactivity data.