Development of Biofilm-Based Electrocatalytic Materials for Biosensing and Bioenergetics

Biofilms, are polymeric aggregates of microorganisms, in which cells adhere to each other on the electrode surfaces. Such systems are characterized by extracellular electron transfers involving c-type cytochromes (heme-containing proteins). Biofilms can be grown on inert carbon electrode substrates tend to exhibit electrocatalytic properties towards oxygen and hydrogen peroxide reductions in neutral media. The processes have been found to be further enhanced by introduction of multi-walled carbon nanotubes (MCNTs) that are modified with ultra-thin layers of organic (e.g. 4-(pyrrole-l-yl) benzoic acid. We expect here attractive electrostatic interactions between carboxyl-group containing anionic adsorbates and positively charged domains of the biofilm with c-type cytochrome enzymatic sites. Coexistence of the above components leads to synergistic effect that is evident from positive shift of the oxygen reduction voltammetric potentials and significant increase of voltammetric currents. Most likely, the reduction of oxygen has been initiated at the molecular (e.g. intentionally added cobalt porphyrin redox centers), whereas the undesirable hydrogen peroxide intermediate are further decomposed at the cytochrome sites.

            An additional subject of interest is the process of carbon dioxide (CO₂) reduction. There has been a growing interest in catalytic systems capable of efficient conversion of carbon dioxide into fuels. One of the promising electrocatalytic materials exhibiting high activity in this process is a macromolecular complex of palladium (II) with Schiff-base-ligands. Reduction of carbon dioxide may lead to carbon-based fuels and its derivatives.

                Fabrication of the biofilm based matrices for anodic reactions has also been considered.  To facilitate electron transfers between the electrode surface and the redox protein centers, the concept of codeposition of multi-walled carbon nanotubes within the bioelectrocatalytic film has also been pursued here. First, carbon nanotubes are modified with ultra-thin layers of tetrathiafulvalene (TTF) or poly(dimethyldiallylammonium chloride) (PDDA) mediators. Their presence is expected to facilitate flow of electrons from the enzyme (e.g. glucose oxidase) active sites through biofilm to the electrode surface. Combination of intentionally derivatized carbon nanotubes with biofilm matrtices and the appropriate enzymes seems to produce biocatalytic systems capable of effective oxidation and sensing of glucose or ethanol in the neutral buffered solution.

Collaboration with W. Lotowska, E. Szaniawska, E. Seta, M. Gierwatowska, B. Kowalewska and I.A. Rutkowska (from Faculty of Chemistry) as well as A. Raczkowska and K. Brzostek (from Faculty of Biology) is acknowledged.