Electron transfer/ion transfer mode of scanning electrochemical microscopy (SECM): a new tool for imaging and kinetic studies

A new mode of the scanning electrochemical microscope (SECM) operation was developed that combines reagent delivery from the nanopipette with electron transfer at the conductive substrate and ion transfer across the liquid/liquid interface supported at the nanopipette tip. This approach offers potential advantages for measurements of heterogeneous electron transfer kinetics and reaction rate imaging by enabling straightforward separation of the contributions of surface topography and reactivity features to the tip current. It addresses some other long-standing technical issues, including sensitive probing of low signal sources (e.g., immobilized enzymes or catalyst particles) without diffusional broadening and the elimination of the elevated background signal in generation/collection-type experiments. The high spatial resolution attainable in electron transfer/ion transfer mode experiments and the absence of redox mediator species in the bulk solution are advantageous for studies of biological cells.