Tandem Photocatalytic CO2-to-C2H4 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.