Time-resolved single-particle kinetics of light-directed electrophoretic deposition

Electrophoretic deposition (EPD) is widely used in research and industry to create thin, uniform films from colloidal suspensions on conductive surfaces. The operational simplicity of EPD has facilitated steady methodological and theoretical advances over the past century. However, our current mechanistic understanding of deposition remains indirect, rooted in theory and ex-situ bulk measurements. Here, we introduce an interferometric scattering (iSCAT) microscopy methodology that enables direct, real-time spatiotemporal monitoring of the electrode during EPD. Using this approach, we detect and localize polystyrene nanoparticles as small as 15 nm. Real-time video captures the evolving deposition landscape, offering a highly sensitive and versatile platform that reveals electrochemical double-layer formation and deposition kinetics under varying photoelectrochemical conditions.