Scanning Electrochemical Microscopy of Individual Living Cells

摘要

Reduction-oxidation reactions are among the processes essential for many cellular functions, Intracellular redox activity can be probed noninvasively by measuring the rate of transmembrane charge transfer (CT), ~1 Previous measurements of inter-facial redox activity typically employed large cell populations. ~1 Measurements with ultramicroelectrodes made at the level of a single cell are much faster and provide valuable information that is hard to extract from the averaged signal produced by a large number of cells. The present work suggests the possibilities of measuring the rate and investigating the pathway of transmembrane charge transfer with the scanning electrochemical microscope (SECM).In an SECM experiment, a micrometer-sized ultramicroelectrode (UME) is placed in solution containing the oxidized (or reduced) form of a redox mediator. A mediator species is then reduced (or oxidized) at the tip electrode. If the tip is positioned near an electrically conductive substrate, the product of the tip reaction diffuses to its surface, where it may be re-oxidized (or re-reduced). This process produces an enhancement in the faradaic current at the tip electrode depending on the tip/substrate separation distance (d). The overall rate of mediator regeneration at the substrate can be evaluated from the tip current-distance (i_T - d) curve. ~2 We used this approach to measure the rate of CT across the membrane of an individual cell.