Polydopamine-coated photoautotrophic bacteria for improving extracellular electron transfer in living photovoltaics

Living photovoltaics are microbial electrochemical devices that use whole cell–electrode interactions to convert solar energy to electricity.The bottleneck in these technologies is the limited electron transfer between the microbe and the electrode surface.This study focuses on enhancing this transfer by engineering a polydopamine(PDA)coating on the outer membrane of the photosynthetic microbe Synechocystis sp.PCC6803.This coating provides a conductive nanoparticle shell to increase electrode adhesion and improve microbial charge extraction.A combination of scanning electron microscopy(SEM),transmission electron microscopy(TEM),UV–Vis absorption,and Raman spectroscopy measurements were used to characterize the nanoparticle shell under various synthesis conditions.The cell viability and activity were further assessed through oxygen evolution,growth curve,and confocal fluorescence microscopy measurements.The results show sustained cell growth and detectable PDA surface coverage under slightly alkaline conditions(pH 7.5)and at low initial dopamine(DA)concentrations(1 mM).The exoelectrogenicity of the cells prepared under these conditions was also characterized through cyclic voltammetry(CV)and chronoamperometry(CA).The measurements show a three-fold enhancement in the photocurrent at an applied bias of 0.3 V(vs.Ag/AgCl[3 M KCl])compared to non-coated cells.This study thus lays the framework for engineering the next generation of living photovoltaics with improved performances using biosynthetic electrodes.

In vivo polydopamine coating of Rhodobacter sphaeroides for enhanced electron transfer

Recent advances in coupling light-harvesting microorganisms with electronic components have 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.This study focuses on overcoming this bottleneck through the metabolically-driven encapsulation of photosynthetic cells with a bio-inspired conductive polymer.Cells of the purple non sulfur bacterium Rhodobacter sphaeroides were coated with a polydopamine(PDA)nanoparticle layer via the self-polymerization of dopamine under anaerobic conditions.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 were 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.