Bioelectronic interface regulation of outer-membrane cytochrome-mediated extracellular electron transfer for rapid bioelectrochemical detection of biochemical oxygen demand.

Microbial fuel cells (MFCs) directly convert microbial metabolism into electrical signals, offering a self-powered platform for biochemical oxygen demand (BOD) detection. However, sluggish electron transfer across the microbe-electrode interface remains a major barrier to rapid response. Here, Shewanella putrefaciens was employed as a model electroactive bacterium, and a three-dimensional hierarchical conductive scaffold comprising iron-cobalt sulfide nanoflowers supported on nickel foam was constructed. Polydopamine (PDA) and chitosan (CS) functional layers were separately introduced to coordinately regulate substrate transport, microbial colonization, and interfacial electronic coupling. Molecular dynamics simulations indicated that dopamine exhibited a stronger binding propensity and greater dynamic stability toward the outer-membrane cytochrome MtrC, providing molecular-scale support for understanding how cytochrome-functionalized interface interactions contribute to extracellular electron-transfer kinetics and rapid BOD sensing. Electrochemical and sensing measurements showed that, over a BOD range of 25-500 mg/L, the PDA-functionalized bioanode established a stable response within 6 min, representing an approximately 33% reduction in response time relative to the CS-based system, while maintaining a strong correlation between output voltage and BOD concentration (R2 = 0.972). Collectively, the hierarchical conductive scaffold and functionalized interface improved overall interfacial electron-transfer behavior and enabled rapid signal establishment, while the molecular simulations supported the potential contribution of interactions between cytochrome and interface to the observed enhancement in EET. This work provides a molecular-scale insight into the relationships among interfacial functional-group regulation, microbe-electrode electronic coupling and response kinetics, and offers a theoretical basis for interface engineering and functional-material optimization of MFC bioanodes.