Towards Microorganism-Based Biofuel Cells: The Viability of Saccharomyces cerevisiae Modified by Multiwalled Carbon Nanotubes

Abstract

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.

Keywords: Saccharomyces cerevisiae; X-ray diffraction; biocompatibility; carbon nanotubes; cell viability.

Figure 1

SEM image of carbon nanotube-based nanostructure.

Figure 2

X-ray spectra of the MW-CNTs.

Figure 3

Raman spectra of MW-CNTs used in the experiment.

Figure 4

The images of the yeast Saccharomyces cerevisiae cells in an identical with field stained by: (a) methylene blue (bright cells, living; dark, dead) and (b) PI (bright, dead; dark, living).

Figure 5

Relative death of the yeast cells. Blue symbols correspond to cell staining with methylene blue and monitoring by optical microscopy, the red, to PI and the fluorescence microscope. The number of cells without MW-CNTs x or + and with MW-CNTs squares, triangles, and rhombs.

Figure 6

Dependence of optical density on time at different MW-CNTs concentration: (a) without MW-CNTs; (b) 2 µg/mL MW-CNTs; (c) 50 µg/mL MW-CNTs; (d) 100 µg/mL MW-CNTs.

Figure 7

Dependence of optical density on MW-CNTs concentration at a different time: (a) 1–3 h; (b) 5–16 h.

Figure 8

AFM image of yeast cells: (a) AFM image of yeast cells and Raman spectra of MW-CNTs at the point of MW-CNTs at the point A (insert), (b) AFM image of yeast cells without MW-CNTs.

Figure 9

Cyclic voltammograms of PQ and PQ/MW-CNT modified biofuel cell anode (graphite electrode), immersed in a phosphate buffer solution with 10 mM K₃[Fe(CN)₆], 70 mM glucose, and 3 mg/mL yeast cells.

Figure 10

Electrochemical impedance spectroscopy based measurements: (a) Nyquist plot, (b) Bode plot. Measurements conditions are the same as in Figure 9.

Figure 11

Generated potential dependence on applied load, using (a) PQ- and (b) PQ/MW-CNT-modified graphite electrode as an anode.

Figure 12

Generated power dependence on potential, (a) PQ- and (b) PQ/MW-CNT-modified graphite electrode as an anode.