Biophotoelectrochemistry

At the heart of photosynthesis lie pigment-proteins called reaction centers, which capture solar energy to generate separated charges with nearly 100% efficiency. These charges, specifically high-energy electrons, go on to power an array of biochemical electron transfer pathways that sustain not just the life of the organism, but most of rest of life on Earth. Harnessing these pathways for biotechnological applications is feasible through the ‘rewiring’ of the inherent photosynthetic electron transfer chain¹, by integrating photosynthetic materials with conductive electrodes to create ‘biohybrids’. These photoelectrodes can be used to create biophotovoltaics for electricity generation², biosensors for herbicide detection3, and biosynthesis cells that synthesize value added chemicals.

Biological materials starting with whole photosynthetic cells⁴ down to isolated reaction centers are currently being explored and engineered for biohybrid function. Highlights include the capacity to incorporate extracellular wiring agents into cyanobacteria for direct electron transfer², and extracting electrons directly from RCs within living organisms using mediated electron transfer⁵. The structure holding the photosynthetic material is the electrode, whose elemental composition, architecture, optical properties and surface chemistry can be tuned to optimize loading and electrochemical communication¹. Perhaps the most challenging aspect of any biohybrid is the interface between the biological and electrode material, which is where most electron transfer loss processes are incurred. Careful selection of the mediator’s midpoint potential, quenching and toxicity⁶, are just a few of the numerous choices that are paramount in efficient rewiring of the photosynthetic ETC.
For a closer look, numerous resources are available. The following book chapter provides an excellent introduction for newcomers to the field, and a recent and comprehensive review from Lawrence et al.1 illustrates the many ways the natural photosynthetic ETC can be ‘re-wired’. Reviews detailing progress in of biohybrids based on isolated Photosystem I⁷, isolated Photosystem II and bacterial whole cells can also be found below:

1. Lawrence, J. M.; Egan, R. M.; Hoefer, T.; Scarampi, A.; Shang, L.; Howe, C. J.; Zhang, J. Z. "Rewiring Photosynthetic Electron Transport Chains for Solar Energy Conversion." Nat. Rev. Bioeng. 2023, 1–19. https://doi.org/10.1038/s44222-023-00093-x.
2. Reggente, M.; Schurgers, N.; Mouhib, M.; Politi, S.; Antonucci, A.; Boghossian, A. A. "Living Photovoltaics Based on Recombinant Expression of MtrA Decaheme in Photosynthetic Bacteria." bioRxiv March 1, 2023, p 2023.02.28.530417. https://doi.org/10.1101/2023.02.28.530417.
3. Modak, N.; Friebe, V. M. "Amperometric Biosensors: Harnessing Photosynthetic Reaction Centers for Herbicide Detection." Curr. Opin. Electrochem. 2023, 101414. https://doi.org/10.1016/j.coelec.2023.101414.
4. Torquato, L. D. D. M.; Grattieri, M. "Photobioelectrochemistry of Intact Photosynthetic Bacteria: Advances and Future Outlook." Curr. Opin. Electrochem. 2022, 34, 101018. https://doi.org/10.1016/j.coelec.2022.101018.
5. Baikie, T. K.; Wey, L. T.; Lawrence, J. M.; Medipally, H.; Reisner, E.; Nowaczyk, M. M.; Friend, R. H.; Howe, C. J.; Schnedermann, C.; Rao, A.; Zhang, J. Z. "Photosynthesis Re-Wired on the Pico-Second Timescale." Nature 2023, 615 (7954), 836–840. https://doi.org/10.1038/s41586-023-05763-9.
6. Sayegh, A.; Perego, L. A.; Arderiu Romero, M.; Escudero, L.; Delacotte, J.; Guille-Collignon, M.; Grimaud, L.; Bailleul, B.; Lemaître, F. "Finding Adapted Quinones for Harvesting Electrons from Photosynthetic Algae Suspensions." ChemElectroChem 2021, 8 (15), 2968–2978. https://doi.org/10.1002/celc.202100757.
7. Teodor, A. H.; Bruce, B. D. "Putting Photosystem I to Work: Truly Green Energy." Trends Biotechnol. 2020, 38 (12), 1329–1342. https://doi.org/10.1016/j.tibtech.2020.04.004.