Enhancing Extracellular Electron Transfer of Geobacter sulfurreducens in Bioelectrochemical Systems Using N-Doped Fe3O4@Carbon Dots

A nanomaterial–living cell biohybrid system is an efficient energy conversion method due to enhanced interactions between inorganic materials and bacteria. However, inefficient electron transfer at the interface of the biohybrid remains as a limiting factor. Herein, an inorganic–biologic hybrid was proposed by combining a typical electroactive bacterium, Geobacter sulfurreducens, and a highly conductive N-doped Fe3O4 with a carbon dot shell (Fe3O4@CD) to boost energy conversion in bioelectrochemical systems (including microbial electrolytic cells and electro-methanogenesis). One-pot-synthesized Fe3O4@CDs enhanced extracellular electron transfer in the biohybrid system by forming an interaction network with conductive proteins inside and outside G. sulfurreducens. In the microbial electrolytic cell, the maximum current of Fe3O4@CDs-fed cells was 6.37 times higher than that of the control group without nanoparticle addition. This enhanced performance was accompanied with higher bioactivity, higher cellular adhesion, and lower biofilm resistance. The G. sulfurreducens–Fe3O4@CDs biohybrids supplemented during electro-methanogenesis remained stable on anodes, which promoted microbial syntrophy. The metabolic methanogenesis pathways are strongly related to the electron transfer ability of G. sulfurreducens, which demonstrates a new strategy to promote extracellular electron transfer through the constructed biohybrid system.