# Scanning Electrochemical Microscopy of Nystatin-Treated Yeast Used for Biofuel Cells

## TL;DR

This paper explores how treating yeast with nystatin improves electron transfer in biofuel cells, boosting their electrical output.

## Contribution

The study introduces a sub-lethal nystatin treatment combined with a dual-mediator system to enhance yeast-based biofuel cell performance.

## Key findings

- Nystatin-treated yeast showed higher electrochemical activity than untreated yeast.
- A dual-mediator system increased local current responses fivefold compared to a single mediator.
- Nystatin treatment increased maximum power density in microbial fuel cells.

## Abstract

Biofuel cells (BFCs) generate electricity by converting chemical energy into electrical energy using biological systems. Saccharomyces cerevisiae (yeast) is an attractive biocatalyst for BFCs due to its robustness, low cost, and metabolic versatility; however, electron transfer from the intracellular reactions to the electrode is limited by the cell membrane. Nystatin is an antifungal antibiotic that increases the permeability of fungal membranes. We hypothesized that sub-lethal nystatin treatment could enhance mediator-assisted electron transfer without compromising cell viability. In this work, yeast was treated with nystatin during cultivation at concentrations of up to 6 µg/mL and combined with a dual-mediator system consisting of a lipophilic mediator (9,10-phenanthrenequinone, PQ) and a hydrophilic mediator (potassium ferricyanide). Scanning electrochemical microscopy revealed that the dual-mediator system increased local current responses by approximately fivefold compared to a single mediator (from ~11 pA to ~59 pA), and that nystatin-treated yeast exhibited higher local electrochemical activity than untreated yeast (maximum currents of ~0.476 nA versus ~0.303 nA). Microbial fuel cell measurements showed that nystatin treatment increased the maximum power density from approximately 0.58 mW/m2 to approximately 0.62 mW/m2 under identical conditions. Nystatin concentrations between 4 and 5 µg/mL maintain yeast viability at near-control levels, while higher concentrations cause a decrease in viability. These results demonstrate that controlled, sub-lethal membrane permeabilization combined with a dual-mediator strategy can enhance electron transfer in yeast-based biofuel cells.