Fixation and Permeabilization Approaches for Scanning Electrochemical Microscopy of Living Cells

Scanning electrochemical microscopy (SECM) has been widely used for the electrochemical imaging of dynamic topographical and metabolic changes in alive adherent mammalian cells. However, extracting intracellular information by SECM is challenging, since it requires redox species to travel in and out the lipid cell membrane. Herein, we present cell fixation and permeabilization approaches as an alternative tool for visualizing cell properties by SECM. With this aim, adherent cells were analyzed in the SECM feedback mode in three different conditions: (i) alive; (ii) fixed, and (iii) fixed and permeabilized. The fixation was carried out with formaldehyde and does not damage lipid membranes. Therefore, this strategy can be used for the SECM investigation of cell topography or the passive transport of the redox mediator into the cells. Additional permeabilization of the cell membrane after fixation enables the analysis of the intracellular content through the coupling of SECM with immunoassay strategies for the detection of specific biomarkers. The latter was successfully applied as an easy and fast screening approach to detect the expression of the melanoma-associated marker tyrosinase in adherent melanoma cell lines corresponding to different cancer progression stages using the SECM substrate generation-tip collection mode. The present approach is simple, fast, and reliable and can open new ways to analyze cell cultures with electrochemically based scanning probe techniques.