Novel coupling mechanism-based imaging approach to scanning electrochemical microscopy for probing the electric field distribution at the microchannel end

A novel coupling mechanism-based imaging approach to scanning electrochemical microscopy (SECM) was used to image the distribution of electric field at the end channel of a poly(dimethylsiloxane) (PDMS) capillary electrophoresis (CE) microchip in the absence of redox species. The coupling imaging mechanism was systematically investigated and qualitatively illustrated. It was proved that the distribution of solution potentials within the scanning plane caused a different reduction rate of water at the tip electrode, which led to the variation in tip current. Within the scanning plane, the solution potentials measured in the central area of the microchannel were usually higher than those measured outside. The SECM images showed a strong dependence on tip potential, tip-to-channel distance, and separation potential. According to the Tafel equation, SECM images were converted to parameters that directly showed the distribution of solution potential. Change in the solution potential along the central axial line of the microchannel was also continuously sensed by allowing the tip to approach the microchannel in the presence of high voltage. Using dopamine as a model compound, the effect of solution potential on electrochemical detection was estimated by detecting separation parameters.