Direct Current Redox Imaging of Single Retinal Pigment Epithelial Cells Using Light-Addressable Electrochemistry at Semiconductor Electrodes

Light-addressable electrochemistry (LAE) enables the activation and detection of localized faradaic electrochemical processes on a flat, unconstructed semiconductor electrode through targeted light illumination, making it a promising approach for single-cell electrochemistry. Herein, we report a direct current (DC) redox imaging technique for single retinal pigment epithelial cells utilizing LAE with an α-Fe₂O₃ electrode activated by a constant, focused laser beam. The proposed DC-LAE method showed micron-scale resolution and was successfully used to image single cells under physiological conditions. We demonstrated that the visualization was primarily due to the hindrance of photoinduced OH^- oxidation by adherent cells, resulting in a reduction of local photocurrents. Inspired by this funding, electroactive substances with high redox activities, such as hydroquinone (HQ), l-ascorbic acid (AA), and potassium ferricyanide (K₄Fe(CN)₆) were introduced into the culture medium. These substances significantly enhanced the DC redox imaging performance under low-intensity laser conditions without compromising cell viability. We believe that integrating pure DC-LAE with cell imaging advances quantitative analyses of cellular electrochemical behavior, offering valuable insights into cellular functions and processes.