Fig. 1.

Schematic diagrams of the SECM experiments with single cells (A–D) and an optical micrograph of a typical nanotip used in such experiments (E). (A) The tip is positioned in the solution close to the cell surface. Positive feedback is due to bimolecular electron transfer between hydrophobic redox mediator (O/R) and cell-bound redox moieties (O2/R2). (B) The lipid cell membrane is impermeable for a hydrophilic redox mediator. Negative feedback is due to the hindered diffusion of redox species to the tip electrode. (C) Nanoelectrode voltammetry inside the cell. (D) Positive feedback is produced by mediator regeneration by way of electron transfer at the underlying Au surface.