Nanoscale Visualization of Microdroplet-Regulated Interfacial Reaction Pathways by Tip-Enhanced Raman Spectroscopy.

Microdroplets provide highly dynamic interfacial environments capable of regulating chemical reactivity through the generation of localized electric fields (EFs) and reactive oxygen species, such as hydroxyl radicals (·OH), at their interfaces. However, direct nanoscale visualization of microdroplet-regulated interfacial reaction pathways remains a fundamental challenge. Herein, we report a tip-enhanced Raman spectroscopy (TERS) approach to probe and visualize competing surface reactions induced by microdroplets at the nanometer scale using a model system consisting of 4-mercaptophenylboronic acid (4-MPBA) on Au(111). By coupling TERS with controlled microdroplet treatments, we identify and spatially resolve two competing surface reaction pathways: EF-mediated covalent condensation and ·OH-mediated oxidation. Density functional theory (DFT) calculations and radical scavenging experiments provide additional support for the proposed reaction mechanism. Systematic modulation of the interfacial EF strength and ·OH abundance enables precise control over the product distribution, as revealed by high-resolution TERS imaging. Our results demonstrate that TERS provides an exceptional platform for mapping microdroplet-regulated interfacial reaction pathways, opening new avenues for mechanistic studies and reaction control in confined interfacial environments.