Label-Free Imaging of Catalytic H 2 O 2 Decomposition on Single Colloidal Pt Nanoparticles Using Nanofluidic Scattering Microscopy.

Single-particle catalysis aims at determining factors that dictate the nanoparticle activity and selectivity. Existing methods often use fluorescent model reactions at low reactant concentrations, operate at low pressures, or rely on plasmonic enhancement effects. Hence, methods to measure single-nanoparticle activity under technically relevant conditions and without fluorescence or other enhancement mechanisms are still lacking. Here, we introduce nanofluidic scattering microscopy of catalytic reactions on single colloidal nanoparticles trapped inside nanofluidic channels to fill this gap. By detecting minuscule refractive index changes in a liquid flushed trough a nanochannel, we demonstrate that local H 2 O 2 concentration changes in water can be accurately measured. Applying this principle, we analyze the H 2 O 2 concentration profiles adjacent to single colloidal Pt nanoparticles during catalytic H 2 O 2 decomposition into O 2 and H 2 O and derive the particles' individual turnover frequencies from the growth rate of the O 2 gas bubbles formed in their respective nanochannel during reaction.