Electrochemical analysis in micrometer and nanometer-sized droplets on a surface: From static toward dynamic

This mini-review discusses about the recent progress in electrochemical analysis of micrometer and nanometer-sized droplets. The static droplet on a support is only briefly mentioned, and the focus is on dynamic droplets that hit, land and evolve on electrodes. The analysis of hitting droplets generally follow the norm of single-entity electrochemistry, which tracks collision events between the droplet and the electrodes. The landing droplet approach confines the electrochemical measurements in the area of droplet/sample contact. In general, we emphasize that the droplet is not a solid object. It may dynamically deform before, during, and after hitting or landing on the electrode surface, as governed by interfacial tensions. The latter can be affected by the chemical reactions occurring at the droplet/electrode or droplet/environment interface, which is often underestimated. Thus, unifying the treatment of shape and composition changes considering conjugated physical and chemical effect would be highly desired in future.