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

Microbial bioelectronic devices using electroactive bacteria provide robust, low-cost, 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 naphthoquinone-grafted chitosan (NQ-Chit) is produced by grafting naphthoquinones onto chitosan. To fabricate living bioelectronic devices, NQ-Chit is blended with the Generally-recognized-as-safe (GRAS) Gram-positive bacterium Lactiplantibacillus plantarum, deposited on an electrode, and ionically crosslinked. 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 hybrid devices remain functional even after multiple medium exchanges. The effectiveness of the NQ-Chit to enhance EET across diverse electroactive bacteria and a proof-of-concept biosensor integrating engineered L. plantarum within NQ-Chit hydrogel for detecting environmental chemicals are demonstrated. It is anticipated that the NQ-Chit hydrogel will propel microbial bioelectronics from lab to field.