Tandem Photocatalytic CO 2 -to-C 2 H 4 Conversion through an Intracellularly Interfaced Quantum Dot-Molecular Catalyst-Bacteria Biohybrid

Semiartificial photosynthetic system (SAPS) combines the strengths of microbial enzyme machinery and semiconductor light harvesters, offering a promising platform to achieve solar-driven CO₂ conversion. However, existing CO₂-fixing SAPSs are constrained by the limited choices of CO₂-assimilating microorganisms, while the use of non-CO₂-assimilating microbes in SAPS for solar-driven CO₂ conversion has rarely been demonstrated. In this work, we developed an integrated nanobiohybrid by co-introducing quantum dots (QDs) and molecular catalysts (MCs) into a non-CO₂-assimilating bacterium, Azotobacter vinelandii (A. vinelandii), enabling a cascade photocatalytic reduction of CO₂ to C₂H₄ via CO intermediates. The intracellular microanaerobic environment protects the QD-MC assembly from O₂ and promotes the photocatalytic CO₂-to-CO conversion, while the intracellularly generated CO accelerates subsequent light-driven enzymatic synthesis of C₂H₄. The synergistic interactions among QD, MC, and bacteria were confirmed by fluorescent CO probing, time-resolved photoluminescence (TRPL), and in vitro control experiments. An optimized system achieved an accumulation of 7.9 μmol L^-1 C₂H₄ over 7 days without loss of activity, showing a yield of 2.1 × 10⁷ C₂H₄ per cell, surpassing the natural production by 162%. Our work introduced a novel integrated tandem biohybrid system that broadens the category of microbial organisms applied in CO₂-fixing SAPS. We envision that this tandem biohybrid strategy can be extended to broader non-CO₂-assimilating microbes for the production of other value-added chemicals beyond C₂H₄ from CO₂.