Spatiotemporal Heterogeneity of Reactions in Solution Observed with High‐Speed Single‐Nanorod Rotational Sensing

Abstract A high‐speed darkfield microscope has been developed to monitor the rapid rotation of single gold nanorods (AuNRs) and used to study the spatiotemporal heterogeneity of chemical reactions in free solution. A wide range of viscosities from 237 cP to 0.8 cP could be detected conveniently. We studied H 2 O 2 decomposition reactions that were catalyzed by AuNRs coated with Pt nanodots (AuNR@PtNDs) and observed two different rotational states. The two states and their transitions are related to the production and the amalgamation of O 2 nanobubbles on the nanorod surface depending on H 2 O 2 concentration. In addition, the local fluidic environment of pure water was found to be non‐uniform in time and space. This technique could be applied to study other chemical and biochemical reactions in solution.