Polydopamine-modified boron-doped diamond interfaces enhance photocurrent generation in cyanobacteria-based biohybrid electrodes

Biohybrid electrodes combine photosynthetic microorganisms with conductive substrates to facilitate light-driven photocurrent generation and fuel-forming reactions. While effective charge transfer at the biological-synthetic interface remains a critical challenge, the use of polydopamine (PDA) at cyanobacteria-diamond interfaces has remained unexplored. In this work, we demonstrate PDA as a multifunctional interfacial layer on semiconducting boron-doped diamond (BDD) to immobilize Limnospira indica cyanobacteria and enhance extracellular electron transfer. PDA modification enabled robust cell immobilization and significantly increased photocurrent densities compared to bare BDD. Furthermore, we observed strain-dependent photoresponses: the straight-trichome strain (P2) achieved a peak photocurrent density of 1020 nA/cm2 at higher PDA deposition cycles, whereas the helical strain (P6) peaked at 560 nA/cm2 with fewer cycles. Mechanistic investigations, including control assays and membrane-restricted interfaces, confirmed that the enhanced photocurrent originates primarily from the photosynthetic activity of L. indica, with PDA facilitating a ~50% contribution from direct electron transfer pathways. These findings establish PDA as a versatile material for optimizing cyanobacteria-diamond biohybrid electrodes, providing fundamental mechanistic insights into extracellular electron transfer that will guide the future design of bioelectrochemical energy conversion systems.