Soft Polymers and Microbial Photosynthesis

Purple photosynthetic bacteria are anoxygenic microorganisms with very versatile metabolisms being able to use sunlight to oxidize a broad variety of organic compounds in addition to heterotrophic and photoautotrophic alternative metabolisms. Conductive polymer layers on the surface of several bacterial species have been used to intercept the electron flow produced by microbial metabolism, funnel it outside the cells, and eventually transfer it toward the electronic circuit of a biohybrid device.<br/>Biocompatibility of several monomers, such as gallic acid¹, L-DOPA, EDOT and dopamine were tested by <i>in vivo</i> addition in the growth media of the photosynthetic purple non sulphur <i>Rhodobacter (R.) sphaeroides.</i><br/>Furthermore, the ability of these monomers to self-assemble and polymerize was considered. Among the tested monomers, polydopamine (PDA), produced by self-assembly of dopamine, is a very versatile and bioinspired polymer which has found widespread applications²due its ability to adhere and cover surfaces of different chemical composition. The oxidative conditions employed for the formation of this dark insoluble polymer are mild and biocompatible and have inspired scientists to develop novel nanomaterials for optoelectronics. Post-functionalization of PDA³ also enables fine-tuning of properties.<br/>We have used PDA conductive coatings as biotic-abiotic interfaces in biohybrid photoelectrochemical devicesthrough the encapsulation of entire bacterial cells or single components – <i>e.g.</i> photosynthetic reaction center (RC) - of <i>R. sphaeroides^4,5, </i>ensuring electronic communication of the biological component with the electrodes’ surfaces in photoelectrochemical cells.<br/>¹ Vona, D., Buscemi, G., Ragni, R., Cantore, M., Cicco, S., Farinola, G.M., Trotta, M. Synthesis of (poly)gallic acid in a bacterial growth medium. MRS Advances, 2020.5(18-19): p. 957-963<br/>² Liu, Y.; Ai, K.; Lu, L. Polydopamine and its derivative materials: Synthesis and promising applications in energy, environmental, and biomedical fields. Chem. Rev. 2014, 114, 5057–5115.<br/>^3a Buscemi, G., Vona, D., Labarile, R. et al. Ethylenediammine is not detrimental to the photoactivity of the bacterial photosynthetic reaction center. MRS Advances 6, 265–269 (2021). https://doi.org/10.1557/s43580-021-00003-6<br/>^3bBuscemi, G., Vona, D., Ragni, R., Comparelli, R., Trotta, M., Milano, F., Farinola, G.M., Polydopamine/Ethylenediamine Nanoparticles Embedding a Photosynthetic Bacterial Reaction Center for Efficient Photocurrent Generation. Adv. Sustainable Syst. 2021, 2000303.<br/>⁴Lo Presti, M., Giangregorio, M. M., Ragni, R., Giotta, L., Guascito, M. R., Comparelli, R., Fanizza, E., Tangorra, R. R., Agostiano, A., Losurdo, M., Farinola, G. M., Milano, F., Trotta, M., Photoelectrodes with Polydopamine Thin Films Incorporating a Bacterial Photoenzyme. Adv. Electron. Mater. 2020, 6, 2000140.<br/>5Milano, F., Lopresti, M., Vona, D., Buscemi, G., Cantore, M., Farinola, G.M., Trotta M. (2020). Activity of photosynthetic Reaction Centers coated with polydopamine. MRS Advances 5 (45), 2299-2307.