One of the key advances in enzymatic biofuel cells has been the development of electrodes that allow direct electron transfer (DET) instead of meditated electron transfer (MET). Although DET has been demonstrated with just a handful of enzymes, it still represents a significant achievement in ensuring that problems associated with the use of mediators are overcome. Nonetheless, issues such as proper orientation of enzymes on electrodes and limited lifetime of enzymes continue to be a challenge for researchers. While efforts are underway to overcoming these limitations, our lab is interested in exploring alternative solutions that used different biomolecules, such as DNA aptamers, instead of protein enzymes. Aptamers are single-stranded DNA or RNA sequences that bind to a target with affinity and specificity. In some instances, aptamers have displayed catalytic activity. Oxidoreductase enzymes used in enzymatic biofuel cells are only active when bound to a redox cofactor, which acts as mediator to shuttle electrons between the enzymes’ active sites and electrode surfaces. Flavin adenine dinucleotide (FAD), nicotinamide adenine dinucleotide (NAD<sup>+</sup>) and pyrroloquinoline quinone (PQQ) are the three redox cofactors commonly found in these enzymes. We reason that developing DNA-oxidoreductase mimics will require identifying DNA sequences that bind to these cofactors. Aptamers for FAD and NAD<sup>+</sup> have previously been reported and we recently reported two DNA aptamers that bind to PQQ with micromolar affinities. We observed that the redox ability of PQQ is not affected when bound to the aptamers. To establish whether such aptamer-cofactor complexes could be useful as possible catalysts in biofuel cells, we are challenging the complexes to oxidize various substrates. We have observed via UV-Vis spectroscopy and amperometry studies that the PQQ-aptamer complexes are able to oxidize NADH. Other substrates are currently under investigation and these studies are being extended to include FAD and NADH-aptamer complexes. The results and our current progress will be discussed.

Redox cofactor-aptamer complexes as possible catalysts for biofuel cells

249th National Meeting (2015)

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