Resolving nanoparticle collision reactivity via simultaneous current and fluorescence detection

Operando analysis enables real-time monitoring of chemical processes, with spectroelectrochemical methods offering direct mechanistic insight. Here, we present an electrochemical-fluorescence approach that couples time-resolved fluorescence detection with nanoparticle collision electrochemistry. Fluorescein-functionalized silver nanoparticles (AgNPs) serve as dual probes, providing simultaneous picoampere-level current and fluorescence readouts. At low electrode potentials, weak electrostatic attraction limits oxidation, yielding few correlated current-fluorescence events. Increasing the potential enhances both collision frequency and electron transfer, producing more coincident spikes. In contrast, fluorescence spikes without current signals were suggested to be associated with 11-Mercapto-1-undecanol (MUD) functionalization that may reduce electron transfer. By correlating electrochemical and optical outputs, this strategy distinguishes reactive from nonreactive collisions. More broadly, it establishes a versatile platform for resolving single-nanoparticle reactivity beyond electrochemistry alone, with implications for catalysis, biosensing, and nanoparticle tracking in complex media.