Scanning electrochemical microscopy of living cells. 4. Mechanistic study of charge transfer reactions in human breast cells

Scanning electrochemical microscopy (SECM) has recently been employed for probing the redox properties of individual mammalian cells. It was shown that intracellular redox activity can be probed noninvasively by measuring the rate of mediator regeneration by the cell. Depending on the properties of the mediator species (e.g., formal potential, ionic charge, and hydrophobicity), different steps can limit the rate of the mediator regeneration reaction. This paper describes the evaluation of several factors that determine the rates of different steps of the process. These include intracellular concentration of redox centers, mixed redox potential inside the cell, and the rate of membrane permeation by mediator species. The kinetic analysis has been carried out to clarify the origins of different rates of the overall charge-transfer reaction in different cell types and with different redox mediators. The results can be used to facilitate differentiation between different types of cells, for example, normal and metastatic breast cells, on the basis of differences in redox responses.