Light-Driven CO₂ Reduction with a Surface-Displayed Enzyme Cascade-C₃N₄ Hybrid

Efficient and cost-effective conversion of CO₂ to biomass holds the potential to address the climate crisis. Light-driven CO₂ conversion can be realized by combining inorganic semiconductors with enzymes or cells. However, designing enzyme cascades for converting CO₂ to multicarbon compounds is challenging, and inorganic semiconductors often possess cytotoxicity. Therefore, there is a critical need for a straightforward semiconductor biohybrid system for CO₂ conversion. Here, we used a visible-light-responsive and biocompatible C₃N₄ porous nanosheet, decorated with formate dehydrogenase, formaldehyde dehydrogenase, and alcohol dehydrogenase to establish an enzyme-photocoupled catalytic system, which showed a remarkable CO₂-to-methanol conversion efficiency with an apparent quantum efficiency of 2.48% in the absence of externally added electron mediator. To further enable the in situ transformation of methanol into biomass, the enzymes were displayed on the surface of Komagataella phaffii, which was further coupled with C₃N₄ to create an organic semiconductor-enzyme-cell hybrid system. Methanol was produced through enzyme-photocoupled CO₂ reduction, achieving a rate of 4.07 mg/(L·h), comparable with reported rates from photocatalytic systems employing mediators or photoelectrochemical cells. The produced methanol can subsequently be transported into the cell and converted into biomass. This work presents a sustainable, environmentally friendly, and cost-effective enzyme-photocoupled biocatalytic system for efficient solar-driven conversion of CO₂ within a microbial cell.