Carbon nanograss and osmium redox polymer enhance biophotovoltaic current generation from the cyanobacterium Synechocystis sp. PCC 6803 forty-fold

Pyrolytic carbon derived from thermosetting polymer precursors is a promising electrode material for bioelectrochemical applications due to its structural robustness, chemical stability, biocompatibility, and amenability to surface modification. Crucially, it allows the integration of diverse nano- and microstructures on the electrode surface. In this study, we introduce pyrolytic carbon nanograss (CNG) electrodes fabricated from SU-8 photoresist as a novel and scalable platform for biophotovoltaic (BPV) applications. Using the cyanobacterium Synechocystis sp. PCC 6803 as a photobiocatalyst, we evaluate biophotocurrent generation both in the absence and presence of an osmium redox polymer mediator. The CNG structures, with tunable lengths, significantly increase the electroactive surface area compared to planar carbon electrodes. This enhancement, combined with the redox polymer, leads to a remarkable 40-fold increase in biophotocurrent output for the longest nanograss structures. Additionally, the nanostructured surfaces improve bacterial cell retention and promote stable electron transfer. Importantly, the bioanodes exhibit excellent operational stability under prolonged high-intensity illumination, highlighting their robustness. The simple and scalable microfabrication of CNG electrodes positions pyrolytic carbon as a compelling candidate for next-generation microbial solar cells. • Fabrication of carbon nanograss (CNG) electrodes by plasma etching and pyrolysis. • Biophotocurrent generation with the cyanobacterium Synechocystis sp. PCC 6803. • Up to 40-fold enhancement of biophotocurrents with CNG and OsRP mediator. • Improved bacteria retention with nanostructures and excellent operational stability.