Publication date: 8th October 2020
The field of biophotoelectrochemistry and its application in biophotovoltaics and biosensors has gained increasing attention in recent years. Knowledge of the redox potentials of the catalytically active protein cofactors and electron transfer rates in biophotovoltaic devices is crucial for accurate modelling and in discerning the mechanisms of their operation. Here, for the first time, we used spectroelectrochemical methods to investigate thermodynamic and kinetic parameters of a biophotoelectrode in situ and of its elements mixed in solution. We determined redox potentials of two elements of the system: the primary electron donor in photosynthetic reaction centers (RCs) of the bacterium Rhodobacter sphaeroides and osmium-complex based redox mediators that are both bound to a hydrogel matrix as well as an electron transfer rate between the primary donor in RCs and redox centers in the polymer suspended in solvent in different polymer to protein ratios. We observe that the midpoint potential of the primary donor is shifted towards a more positive potential in comparison to literature data for RCs solubilized in buffered water solution, likely due to interaction with the polymer matrix. We also demonstrate that the osmium-complex modified redox polymer efficiently wires the RCs to the electrode, maintaining a high Internal Quantum Efficiency with approximately one electron per two photons generated (IQE = 50±12%). Moreover, we show that a primary electron donor in RCs is reduced by redox polymer within the microsecond time scale (with the fastest lifetime ~1µs). Overall, this approach may be attractive for gaining insights into kinetic limitations and thereby help in the rational design of bioelectronic devices.
RB acknowledges support from the Ministry of Science and Higher Education, Poland (project entitled: “Construction of solar cells based on purple bacteria reaction centers and polymer hydrogels” no. 0129/DIA/2016/45). KG acknowledges support from the National Science Center, Poland (project entitled “Bio-semiconductor hybrids for photovoltaic cells” no. 2012/07/B/NZ1/02639). WS and AR thank the Deutsche Forschungsgemeinschaft (DFG) under Germany’s Excellence Strategy EXC-2033 (project number 390677874) for financial support. MRJ acknowledges support from the BrisSynBio Synthetic Biology Research Centre at the University of Bristol (BB/L01386X/1).
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