Visualizing Gas-Generating Catalysis at the Single-Nanoparticle Level via Dark-Field Microscopy with Multimodal Analysis.

Understanding the dynamic and heterogeneous behavior of gas-generating catalysts at the single-nanoparticle level is important to address many chemical and biological challenges. Most current studies rely on ensemble analysis, which fails to capture the unique and critical catalytic kinetics inherent in single nanocatalysts. Herein, we developed an integrated dark-field microscopy (DFM) platform with multimodal analysis capabilities to investigate gas-generating catalysis at the single-nanoparticle level, using the decomposition of H2O2 by MnO2 nanoparticles as a model reaction. By tracking scattering intensity fluctuations, nanobubble localization, and nanoparticle motion, we uncover the dynamic and heterogeneous behavior of individual catalysts. The catalytic activity exhibits intermittent high/low fluctuations following power-law kinetics, revealing the stochastic nature of single-nanoparticle catalysis. Spatial analysis of nanobubble localization reveals heterogeneous catalytic activity with preferential O2 nanobubble formation at nanoparticle edges and corners. Furthermore, we demonstrate that catalytic gas release induces detectable lateral nanoparticle motion through asymmetric O2 release, offering a mechanical readout of the catalytic activity. Systematic variation in H2O2 concentration and surfactant environment allows us to correlate optical and mechanical signatures with changes in the interfacial chemistry. This comprehensive approach not only improves our understanding of single-nanoparticle catalysis but also provides a framework for studying diverse gas-evolving reactions with potential applications in energy, environmental science, and nanomotor technology.