This review focuses on the development of microbial biofuel cells to demonstrate how similar principles apply to the development of bioelectronic devices. The low specificity of microorganism-based amperometric biosensors can be exploited in designing microbial biofuel cells, enabling them to consume a broader range of chemical fuels. Charge transfer efficiency is among the most challenging and critical issues while developing biofuel cells. Nanomaterials and particular redox mediators are exploited to facilitate charge transfer between biomaterials and biofuel cell electrodes. The application of conductive polymers (CPs) can improve the efficiency of biofuel cells while CPs are well-suitable for the immobilization of enzymes, and in some specific circumstances, CPs can facilitate charge transfer. Moreover, biocompatibility is an important issue during the development of implantable biofuel cells. Therefore, biocompatibility-related aspects of conducting polymers with microorganisms are discussed in this review. Ways to modify cell-wall/membrane and to improve charge transfer efficiency and suitability for biofuel cell design are outlined.

This research aimed to evaluate the toxic effect of multi-walled carbon nanotubes (MW-CNTs) on yeast cells in order to apply MW-CNTs for possible improvement of the efficiency of microbial biofuel cells. The SEM and XRD analysis suggested that here used MW-CNTs are in the range of 10–25 nm in diameter and their structure was confirmed by Raman spectroscopy. In this study, we evaluated the viability of the yeast Saccharomyces cerevisiae cells, affected by MW-CNTs, by cell count, culture optical density and atomic force microscopy. The yeast cells were exposed towards MW-CNTs (of 2, 50, 100 μg/mL concentrations in water-based solution) for 24 h. A mathematical model was applied for the evaluation of relative growth and relative death rates of yeast cells. We calculated that both of the rates are two times higher in the case if yeasts were treated by 50, 100 μg/mL of MW-CNTs containing solution, comparing to that treated by 0 and 2 μg/mL c of MW-CNTs containing solution. It was determined that the MW-CNTs have some observable effect upon the incubation of the yeast cells. The viability of yeast has decreased together with MW-CNTs concentration only after 5 h of the treatment. Therefore, we predict that the MW-CNTs can be applied for the modification of yeast cells in order to improve electrical charge transfer through the yeast cell membrane and/or the cell wall.

Electrically conductive polymers are promising materials for charge transfer from living cells to the anodes of electrochemical biosensors and biofuel cells. The modification of living cells by polypyrrole (PPy) causes shortened cell lifespan, burdens the replication process, and diminishes renewability in the long term. In this paper, the viability and morphology non-modified, inactivated, and PPy-modified yeasts were evaluated. The results displayed a reduction in cell size, an incremental increase in roughness parameters, and the formation of small structural clusters of polymers on the yeast cells with the increase in the pyrrole concentration used for modification. Yeast modified with the lowest pyrrole concentration showed minimal change; thus, a microbial fuel cell (MFC) was designed using yeast modified by a solution containing 0.05 M pyrrole and compared with the characteristics of an MFC based on non-modified yeast. The maximal generated power of the modified system was 47.12 mW/m², which is 8.32 mW/m² higher than that of the system based on non-modified yeast. The open-circuit potentials of the non-modified and PPy-modified yeast-based cells were 335 mV and 390 mV, respectively. Even though applying a PPy layer to yeast increases the charge-transfer efficiency towards the electrode, the damage done to the cells due to modification with a higher concentration of PPy diminishes the amount of charge transferred, as the current density drops by 846 μA/cm². This decrease suggests that modification by PPy may have a cytotoxic effect that greatly hinders the metabolic activity of yeast.

Microbial fuel cell (MFC) efficiency depends on charge transfer capability from microbe to anode, and the application of suitable redox mediators is important in this area. In this study, yeast viability experiments were performed to determine the 2-methyl-1,4-naphthoquinone (menadione (MD)) influence on different yeast cell species (baker’s yeast and Saccharomyces cerevisiae yeast cells). In addition, electrochemical measurements to investigate MFC performance and efficiency were carried out. This research revealed that baker’s yeast cells were more resistant to dissolved MD, but the current density decreased when yeast solution concentration was incrementally increased in the same cell. The maximal calculated power of a designed baker’s yeast-based MFC cell anode was 0.408 mW/m² and this power output was registered at 24 mV. Simultaneously, the cell generated a 62-mV open circuit potential in the presence of 23 mM potassium ferricyanide and the absence of glucose and immobilized MD. The results only confirm that MD has strong potential to be applied to microbial fuel cells and that a two-redox-mediator-based system is suitable for application in microbial fuel cells.

The most common neurological disorders, i.e., Parkinson’s disease (PD) and Alzheimer’s disease (AD), are characterized by degeneration of cognitive functions due to the loss of neurons in the central nervous system. The aggregation of amyloid proteins is an important pathological feature of neurological disorders.The aggregation process involves a series of complex structural transitions from monomeric to the formation of fibrils. Despite its potential importance in understanding the pathobiology of PD and AD diseases, the details of the aggregation process are still unclear. Nanoparticles (NPs) absorbed by the human circulatory system can interact with amyloid proteins in the human brain and cause PD. In this work, we report the study of the interaction between TiO₂ nanoparticles (TiO₂-NPs) and ZnO nanoparticles (ZnO-NPs) on the aggregation kinetics of β-amyloid fragment 1-40 (βA) and α-synuclein protein using surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS). The characterizations of ZnO-NPs and TiO₂-NPs were evaluated by X-ray diffraction (XRD) spectrum, atomic force microscopy (AFM), and UV-Vis spectroscopy. The interaction of nanoparticles with amyloid proteins was investigated by SERS. Our study showed that exposure of amyloid protein molecules to TiO₂-NPs and ZnO-NPs after incubation at 37 °C caused morphological changes and stimulated aggregation and fibrillation. In addition, significant differences in the intensity and location of active Raman frequencies in the amide I domain were found. The principal component analysis (PCA) results show that the effect of NPs after incubation at 4 °C does not cause changes in βA structure.