Quinone-Grafted Chitosan Polymers Enhance Microbial Extracellular Electron Transfer for Living Bioelectronic Devices

Microbial bioelectronics using electroactive bacteria provide robust and sustainable solutions for sensing, power generation, and chemical production. While most rely on a limited group of Gram-negative bacteria, Gram-positive species offer devices with additional functionality and broader environmental ranges. However, their thick, nonconductive cell walls hinder efficient extracellular electron transfer (EET). Here, a living bioelectronic device using a redox-active polymer to encapsulate Gram-positive bacteria near an electrode while simultaneously enhancing EET is reported. The redox-active polymer NQ-Chit contains naphthoquinone redox groups grafted onto a chitosan backbone and can be ionically cross-linked to produce redox- active hydrogels. To fabricate living bioelectronic devices, NQ-Chit is blended with the Gram-positive bacterium Lactiplantibacillus plantarum, deposited on an electrode, and ionically cross-linked in situ. The NQ-Chit hydrogel enhances EET current compared to both pure Chit-encapsulated bacteria and planktonic bacteria with NQ-Chit-coated electrodes, and Michaelis-Menten kinetics can describe the dependence of EET current on the concentration of quinone units. The devices remain functional after multiple medium exchanges. Additionally, the redox polymer enhances EET across diverse electroactive bacteria and enables a proof-of-concept for detecting environmental chemicals. This work demonstrates that encapsulating electroactive bacteria with redox-active hydrogels enhances EET and can be implemented in practical bioelectronic devices.