Enzymatic synthesis and electrochemical characterization of sodium 1,2-naphthoquinone-4-sulfonate-doped PEDOT/MWCNT composite.

The development of novel materials with improved functional characteristics for supercapacitor electrodes is of current concern and calls for elaboration of innovative approaches. We report on an eco-friendly enzymatic synthesis of a composite based on poly(3,4-ethylenedioxythiophene) (PEDOT) and multi-walled carbon nanotubes (MWCNTs). The redox active compound, sodium 1,2-naphthoquinone-4-sulfonate (NQS), was used as a dopant for the backbone of the polymer. Oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) was catalyzed by a high redox potential laccase from the fungus Trametes hirsuta. Atmospheric oxygen served as an oxidant. A uniform thin layer of NQS-doped PEDOT formed on the surface of MWCNTs as a result of the enzymatic polymerization. The PEDOT-NQS/MWCNT composite showed a high specific capacitance of ca. 575 F g-1 at a potential scan rate of 5 mV s-1 and an excellent cycling stability within a potential window between -0.5 and 1.0 V, which makes it a promising electrode material for high-performance supercapacitors.

Intact and permeabilized cells of the yeast Hansenula polymorpha as bioselective elements for amperometric assay of formaldehyde.

Intact and permeabilized yeast cells were tested as the biorecognition elements for amperometric assay of formaldehyde (FA). For this aim, the mutant C-105 (gcr1 catX) of the methylotrophic yeast Hansenula polymorpha with a high activity of AOX was chosen. Different approaches were used for monitoring FA-dependent cell response including analysis of their oxygen consumption rate by the use of a Clark electrode, as well as assay of oxidation of redox mediator at a screen-printed platinum electrode covered by cells entrapped in Ca-alginate gel. It was shown that oxygen consumption rate of permeabilized cells reached its saturation at 4mM of FA (23 degrees C). The detection limit was found to be 0.27mM. In the presence of redox mediator 2,6-dichlorophenolindophenol (DCIP), the screen-printed platinum band electrode covered by permeabilized cells did not show any current output to FA. In contrast, well-pronounced amperometric response to FA was observed in the case of intact yeast cells in the presence of DCIP. It was shown that current output reached its maximum at 7mM concentration of FA. The detection limit was found to be 0.74mM. Obviously, it is necessary to perform a directed genetic engineering of the yeast cells to improve their bioanalytical characteristics in the corresponding biosensors.