2nd and 3rd generation electrodes for biosensors and biofuel cells

Abstract: The catalytic and electrochemical properties of tryptophan repressor-binding protein (WrbA), pyranose dehydrogenase (PDH), cellobiose dehydrogenase (CDH) and glucose dehydrogenase (GDH) on carbon electrodes were investigated using cyclic voltammetry and flow injection amperometry to construct biosensors and biofuel cell (BFC) anodes. WrbA has a catalytic FMN-containing domain whereas both PDH and GDH have a catalytic FAD-containing domains. Different osmium redox polymers (Os-polymers) covering a broad potential range from +15 mV to +490 mV vs. NHE were used to "wire" WrbA, PDH and GDH to study catalytic and electrochemical properties through mediated electron transfer (MET). Unlike WrbA, PDH and GDH, CDH owns both a catalytic FAD-containing domain as well as a haem domain interconnected through a built-in electron transfer pathway from FAD to haem, which in turn can also connect to the electrodes. CDH is therefore able to give direct electron transfer (DET) by communicating directly with the electrodes. Single walled carbon nanotubes (SWCNTs) of different lengths were cross-linked with WrbA and Os-polymer to increase the catalytic current density. WrbA was used to construct NADH biosensor and a prototype BFC anode. Length fractionated SWCNTs were also embedded together with CtCDH on spectrographic graphite electrodes to enhance DET properties and a 3rd generation glucose biosensor working at physiological conditions and with a linear range from 0.5 to 30 mM for glucose could be developed. To further improve the performance and properties of 3rd generation glucose biosensor, we used commercially available screen-printed electrodes (SPE) made of carbon (SPCE), carboxyl functionalized single- (SPCE-SWCNT) or multi-walled (SPCE-MWCNT). An improved sensitivity and improved linear range from 0.025 to 30 mM for glucose was obtained with SPCE-SWCNT/CtCDH modified electrode. I could foresee that in future such a 3rd generation biosensor could replace the commercially available biosensors, which are based on mediators and thus have higher fabrication prices and more complicated design. PDH was “wired” with different Os-polymers to improve the current density to develop an anode for BFC. In the same way, GDH was also “wired” with different Os-polymers to construct glucose biosensor and BFC anode. With this study we found the best Os-polymers with maximum current density for both PDH and GDH. GDH and CDH can oxidize glucose at C-1 whereas PDH can oxidize glucose at C-2 and C-3. The PDH was combined with either GDH or CDH and cross-linked with the optimized Os-polymers to develop a BFC anode with increased current density and coulombic efficiency.