Real-time visualization of sub-particle reaction anisotropy via rotary-encoded scattering microscopy

Understanding nanoscale chemical transformations within liquid environments is essential for advancing catalysis, material synthesis, and nanotechnology. However, existing optical imaging techniques face significant challenges in resolve sub-particle-level dynamics due to intrinsic limitations in spatial resolution and sensitivity. Here, we introduce an optical imaging technique, Rotary-Encoded Scattering Microscopy (RESM), that achieves real-time, label-free visualization of sub-particle chemical transformations with high sensitivity and resolution. By dynamically engineering the point spread function (PSF) to encode sub-particle structural changes into distinctive scattering patterns, RESM enables direct tracking of chemical reactions at the sub-particle level. Using RESM, we elucidate concentration-dependent oxidation mechanisms during the oxidation of silver nanospheres (Ag NSs) in aqueous environments. At high Cl^- concentrations, anisotropic oxidation via AgCl precipitation emerges as a distinct liquid-phase pathway, marking a clear transition from the isotropic oxidation observed at lower concentrations and indicating that Cl^- controls pathway selection while Fe³⁺ sets the overall rate. We further demonstrate the versatility of RESM by capturing anisotropic intercalation kinetics of Prussian blue nanoparticles, uncovering sub-particle heterogeneity even in highly symmetric materials. By enabling direct visualization of previously hidden sub-particle reaction pathways, RESM establishes a broadly applicable platform for high-sensitivity chemical imaging, bridging structural characterization and functional performance at the nanoscale.