Visualizing Gas Generating Catalysis at the Single Nanoparticle Level via Multimodal Dark Field Microscopy

Understanding the dynamic and heterogeneous behavior of gas-generating catalysts at 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 to single nanocatalysts. Here we developed a multimodal dark-field microscopy (DFM) platform to observe gas-generating catalysis at the single-nanoparticle level, focusing on the decomposition of H ₂ O ₂ by MnO ₂ nanoparticles. By tracking scattering intensity fluctuations, nanobubble localization, and nanoparticle motion, we uncover the dynamic and heterogeneous behavior of individual catalysts. Our results reveal that catalytic activity is characterized by intermittent ON/OFF fluctuations following power-law kinetics, providing insight into the stochastic nature of catalysis. Active sites are shown to be spatially heterogeneous, with higher activity localized at nanoparticle edges and corners. Furthermore, we demonstrate that catalytic activity drives nanoparticle motion through asymmetric O ₂ release, offering a mechanical readout of reactivity. Systematic variation in H ₂ O ₂ concentration and surfactant environment allows us to correlate optical and mechanical signatures with changes in interfacial chemistry. This comprehensive approach not only improves our understanding of single-nanoparticle catalysis but also sets a framework for studying diverse gas-evolving reactions, with potential applications in energy, environmental science, and nanomotor technology.