Comparative study of polydopamine and polypyrrole modified yeast cells applied in biofuel cell design

Abstract

Due to high global energy requirements, the research for green-renewable energy has skyrocketed in the past few years. Yeast-based microbial fuel cell (MFC) is one of the biofuel cell designs that could serve as a potential alternative energy source. The main advantage of yeast-based MFC is that it can be coupled with wastewater purification in food processing. One of the major challenges associated with the utilization of yeast-based MFCs is the poor charge transfer from the yeast cells yielding low power output, which could be enhanced by redox mediators. Nevertheless, mediators themselves showed multiple bottlenecks, including high production costs and cytotoxicity. Redox-active polymers are currently featured as a promising new class of electron mediators with lower cytotoxicity compared to other conventional electron mediators. In this study, we tested two electroconductive polymers, polypyrrole (Ppy) and polydopamine (PDA), which possess good electrical properties and are biocompatible with microorganisms. Yeast cells were modified by PDA in a controlled fashion: cells were soaked in a buffer at pH 5 mixed with dopamine, and then dopamine polymerization was triggered via changing the buffer pH to 7.5. Dopamine polymerization conditions were optimized and optically evaluated using UV/VIS and FTIR spectroscopy. Electrochemical properties were assessed by constructing a controlled flow-through system, which imitates a simplified version of the commercially available MFCs, where chronoamperometry was used to evaluate the modified free flowing yeast cells. The power density of classical MFC was evaluated using a two-electrode microbial biofuel cell. Both PDA and Ppy modifications are deemed successful, which is indicated by an increase in the charge transfer from the yeast cells to the electrodes. Overall, our modifications applied shorter incubation times in the polymerization bulk solution and generated a greater electric current of approximately 5-fold power increase compared to the regular yeast MFCs.