Direct electron transfer-based bioanodes for ethanol biofuel cells using PQQ-dependent alcohol and aldehyde dehydrogenases

This paper compares the performance of a DET (direct electron transfer) bioanode containing both PQQ-ADH (pyrroloquinoline quinone-dependent alcohol dehydrogenase) and PQQ-AldDH (PQQ-dependent aldehyde dehydrogenase) immobilized onto different modified electrode surfaces employing either a tetrabutylammonium (TBAB)-modified Nafion® membrane polymer or polyamidoamine (PAMAM) dendrimers for the enzyme immobilization. The electrochemical characterization showed that the prepared bioelectrodes were able to undergo DET onto glassy carbon surface in the presence as well as the absence of multi-walled carbon nanotubes (MWCNTs); also, in the latter case a relevant shift in the oxidation peak of about 180 mV vs. saturated calomel electrode (SCE) was observed. A very similar redox potential was achieved with the self-assembled bioelectrode prepared onto modified-gold surfaces with dendrimers, indicating that both methodologies provide an environment that enables the PQQ-enzymes to undergo DET. The biofuel cell tests confirmed the ease of the DET process and the enhanced performance in the presence of the carbon nanotubes. Considering the bioanodes prepared with PAMAM dendrimers, the power density values vary from 19.4 μW cm−2 without MWCNTs to 25.7 μW cm−2 in the presence of MWCNTs. Similarly, with the bioanodes prepared with the TBAB-modified-Nafion® polymer, the results indicate power densities of 27.9 and 38.4 μW cm−2 respectively. These electrode modifications represent effective methods for immobilization and direct electrical connection of quinohemoproteins to electrode surfaces.