Single Cells Polydopamine Coating of Rhodobacter Sphaeroides for Enhanced Electron Transfer
Authors: Labarile Rossella , Vona Danilo , Varsalona Maria , Grattieri Matteo , Reggente Melania , Farinola Gianluca M , Fischer Fabian , Boghossian Ardemis Anoush , Trotta Massimo 
Published: August 2024

Photosynthetic bacteria are anoxygenic microorganisms with highly versatile metabolism, as they use sunlight to oxidize a broad variety of organic compounds in addition to heterotrophic and photoautotropic alternative metabolisms. Recent advances in coupling light-harvesting microorganisms with electronic components has led to a new generation of biohybrid devices based on microbial photocatalysts. These devices are limited by the poorly conductive interface between phototrophs and synthetic materials that inhibit charge transfer.
Polydopamine (PDA), produced by self-assembly of dopamine, is a very versatile and bioinspired polymer with widespread applications1 mostly due 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. Post-functionalization of PDA2 also enables fine tuning of properties. Furthermore, the ability of this monomer to self-assemble and polymerize in the bacterial growth medium was considered one of the requirements of the polymer to be used as coating material beside the tunable conductive properties and the flexible structure.
Biocompatibility of dopamine was tested by in vivo addition in the growth media of the photosynthetic purple non sulphur Rhodobacter (R.) sphaeroides
3 in anoxygenic conditions. This study focuses on overcoming the bottleneck of biohybrid devices through the metabolically-driven encapsulation of photosynthetic cells with a bio-inspired conductive polymer. The treated cells show preserved light absorption of the photosynthetic pigments in the presence of dopamine concentrations ranging between 0.05 – 3.5 mM. The thickness and nanoparticle formation of the membrane-associated PDA matrix was further shown to vary with the dopamine concentrations in this range. Compared to uncoated cells, the encapsulated cells show up to a 20-fold enhancement in transient photocurrent measurements under mediatorless conditions. The biologically synthesized PDA can thus act as a matrix for electronically coupling the light-harvesting metabolisms of cells with conductive surfaces.

1Liu, 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.

2Buscemi, 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.

3 Labarile, R.; Varsalona, M.; Vona, D.; Stufano, P.; Grattieri, M.; Farinola, G. M.; Trotta, M., A novel route for anoxygenic polymerization of dopamine via purple photosynthetic bacteria metabolism. MRS Advances
2023