Renewable dehydrogenase-based interfaces for bioelectronic applications

Bioelectronic interfaces that establish electrical communication between redox enzymes and electrodes have potential applications as biosensors, biocatalytic reactors, and biological fuel cells. However, these interfaces contain labile components, including enzymes and cofactors, which have limited lifetimes and must be replaced periodically to allow long-term operation. Current methods to fabricate bioelectronic interfaces do not allow facile replacement of these components, thus limiting the useful lifetime of the interfaces. In this paper we describe a versatile new fabrication approach that binds the enzymes and cofactors using reversible ionic interactions. This approach allows the interface to be removed via a simple pH change and then replaced to fully regenerate the biocatalytic activity. The positively charged polyelectrolyte poly(ethylenimine) was used to ionically bond a dehydrogenase enzyme and its cofactor to a gold electrode that was functionalized with 3-mercaptopropionic acid and the electron mediator toluidine blue O. By reducing the pH, the surface-bound 3-mercaptopropionic acid was protonated, disrupting the ionic bonds and releasing the enzyme-modified polyelectrolyte. After neutralization, fresh enzyme and cofactor were bound, regenerating the bioelectronic interface. Cyclic voltammetry, chronoamperometry, constant potential amperometry, electrochemical impedance spectroscopy, and Fourier transform infrared spectroscopy analyses were used to characterize the bioelectronic interfaces. For the two enzymes tested (secondary alcohol dehydrogenase and sorbitol dehydrogenase) and their respective cofactors (beta-nicotinamide adenine dinucleotide phosphate and beta-nicotinamide adenine dinucleotide), the reconstituted interface exhibited a surface coverage, an electron-transfer coefficient, and a turnover rate similar to those of the original interface.