Carbon Dot–Mediated Bidirectional Electron Transport for Synergistic Bioenergy Enhancement in Microbial Biohybrids

Electron transport dynamics govern microbial energy conversion through spatiotemporal regulation of electron flux and redox cascades, yet conventional paradigms predominantly emphasize unidirectional energy transfers (e.g., hydrogen or current). This study unlocks the inherent multifunctionality of electron flow through precisely engineered syringaldehyde-derived carbon dots (CDs), which orchestrate bidirectional electron transport networks in Lactobacillus plantarum (L. plantarum). Our innovative microbial electrolysis platform reveals two synergistically amplified energy conversion pathways: Intracellular proton-coupled electron transfer, achieving recorded hydrogen biosynthesis (1.43 ± 0.07 mmol L^-1 vs. 0.48 ± 0.04 mmol L^-1, a 2.98-fold enhancement over abiotic control), and extracellular direct electron transfer, driving anodic current amplification (885.67 ± 273.54 μA vs. 38.84 ± 9.06 μA, 22.80 × baseline performance). Concomitant metabolic rewiring elevated lactic acid production to 0.26 ± 0.01 mmol L^-1 (200% of control yield) via CDs-enabled NAD⁺/NADH redox cycling acceleration. Mechanistic studies attribute these enhancements to the hierarchical electron configuration of CDs-pyridinic-N-dominated active sites synergizing with extended π-conjugation systems to modulate interfacial charge transfer thermodynamics. Our work establishes a new paradigm for strengthening microbial electrochemistry by engineering an CDs mediated integrated biohybrid system that simultaneously enhances energy harvesting and directs metabolic pathways, providing a scalable blueprint for future biorefineries.