On the nature of the electrochemical response in mediated bioanodes with yeast cells

Herein, the electrochemical responses of Saccharomyces cerevisiae cultivated in YPD medium were tested in amperometric mode using microanalytical screen-printed electrodes modified with potassium ferricyanide and 1,10-phenanthroline-5,6-dione as mediators. The electrochemical signals obtained correlated well with the yeast growth curve. Electrochemical analysis of the cell-free supernatants (CFSs), obtained after removing S. cerevisiae cells, indicated that the mediator response, whether using potassium ferricyanide or phenanthroline-5,6-dione, depends more on the composition of the CFSs than on the intrinsic electroactivity of the cells. FT-IR and GC-MS investigations confirmed the formation of several electroactive compounds in the CFSs, such as hydroquinones and organohydrazines. Model electrochemical tests using ferricyanide as redox mediator indicated that quinones and organohydrazines are the most electroactive components formed during microbial activity. These results suggest that the electrochemical response in mediated bioanodes containing living cells is primarily driven by interactions between the mediator and electroactive metabolic products, rather than by direct interactions between the mediator and the cells.