Electrochemically Generated Interfacial pH Change: Application to Signal‐Triggered Molecule Release

Abstract

AbstractElectron transfer processes during redox reactions are frequently accompanied with protonation/deprotonation processes, thus changing H+/OH− concentrations. When the redox reactions proceed at electrode surfaces, being electrochemically processed, changes in local interfacial pH are possible, particularly when the electrolyte solution is not strongly buffered. The pH gradient can be produced in the diffusion layer and its thickness depends on the rate of electrochemical process, which is measured as the current density, diffusion rates, and buffer capacity. While conventional techniques for measuring pH values are not applicable to a very thin diffusional layer, special methods have been developed for the interfacial pH measurements, including scanning electrochemical microscopy (SECM), rotating ring‐disk electrode (RRDE) measurements, various optical methods, particularly using confocal fluorescent microscopy, and others. Dramatic pH changes proceeding in a near‐electrode layer have been reported for H2O reduction/oxidation, O2 reduction, and some other electrochemical electron/proton transfer processes. These pH changes can be used to trigger some other physical processes, particularly (bio)molecule release processes from modified electrodes, which can be destabilized upon the electrochemically generated pH changes, thus releasing entrapped/loaded target molecules. This review‐type article overviews the formation and analysis of locally produced interfacial pH changes and their use for electrochemically triggered (bio)molecule release. The paper briefly reviews the research area, then concentrating on the systems designed recently by the authors.