Bio-Production of Poly-DOPA As a Functional Material and Electron Acceptor for Extracellular Electron Transport and Bioelectrochemical Systems

Biopolymers have attracted considerable interest as material coatings that could interface biologics and abiological materials for drug delivery, biosensing, and bioelectronic applications. One such bio-polymer, Poly-DOPA, has recently gained traction in the fields of energy storage and bioelectrochemical systems. However, despite its wide use, little work has been done on engineering L-DOPA production so that cells might create their own Redox-active coatings. We have now developed genetically modified strains of Escherichia coli and Shewanella oneidensis that produce extremely high concentrations of the monomer L-DOPA. When grown under aerobic condition, the L-DOPA undergoes self-oxidation, polymerizing into PolyDOPA. Liquid media turns black, resulting in a broad UV-Vis absorbance spectra from the supernatant, and on solid media the PolyDOPA permeates through the hydrogel. L-DOPA production and polymerization can be controlled temporally and spatially to create gradients of PolyDOPA, resulting in different compositions and colors within hydrogels. Upon electrodeposition and polymerization of L-DOPA to PolyDOPA on a graphite electrode, we found an increased ability of the bacterial cells to bind to the electrode, which in turn resulted in more rapid establishment of a bioelectrochemical cell, and an overall higher current output. Furthermore, L-DOPA is capable of acting as a soluble, and PolyDOPA, as an insoluble electron acceptor. Taken together, these results suggest a path to a green, self-producing, readily controlled, and (most importantly) scalable material coating that could create more efficient energy production systems.