Polydopamine encapsulation of Rhodobacter sphaeroides for energy transduction

In Bio-electrochemical systems, living and metabolically active microorganisms can be used for the sustainable production of energy. The direct electron transfer couples the microbial metabolism with external charge transport and requires the intimate contact between the bacterial cell membrane and the electron acceptor surface. The membrane of the caroteinodless mutant strain of the photosynthetic purple non sulfur bacterium Rhodobacter (R.) sphaeroides R26 was coated with a melaninlike material to improve the interface between electrodes and photosynthetic microorganisms. Polydopamine (PDA), a bioinspired polymer produced by the self-polymerization of dopamine in mild condition was selected for its biocompatibility and its adhesive properties. The coating, obtained by introducing dopamine monomers into the growth medium of R. sphaeroides [1, 2] does not interfere with the proper cell growth and allows the satisfactory electronic communication with the glassy carbon electrodes. Electrochemical characterization was performed to investigate the electronic behavior of these biohybrids, unveiling that the polymer layer on the bacterial cells does not hinder the diffusion of the mediator and its capability to react at the electrode surface. The effects of dopamine concentration on the light-induced photoresponse of the biohybrid systems will be discussed and compared to bare bacteria.