Interrogation of Single Droplet Behavior via Scanning Electrochemical Microscopy and Its Application to Precursor-Free Nanoparticle Synthesis

Single-entity electrochemistry is a powerful tool for studying electrochemical processes in nanoscale environments and elucidating the intrinsic physicochemical properties of individual entities such as liquid droplets. Although the adsorption and deformation of droplets on electrodes upon collisional contact have been extensively investigated, their behavior after detachment remains poorly understood. In this study, scanning electrochemical microscopy (SECM) with a dual ultramicroelectrode (UME) configuration was employed to monitor the behavior of a few hundred attoliter aqueous droplets that detached from an electrode and traveled through an immiscible organic phase. Analysis of discrete current spikes arising from droplet collisions at both electrodes provided insight into the properties of the detached droplets, including their redox composition and transport dynamics. Furthermore, the results demonstrate that attoliter-scale droplets can function as mobile electrochemical reactors that selectively generate metal ions at one electrode and subsequently drive secondary synthetic reactions at a spatially separated electrode, thereby enabling precursor-free nanoparticle synthesis.