Scalable Ammonia Synthesis in Fermentors Using Quantum Dot-Azotobacter vinelandii Hybrids

This study introduces a scalable synthesis of ammonia through photochemical reactions, wherein nitrogen-fixing bacterial cells, Azotobacter vinelandii (A. vinelandii), form hybrids with colloidal quantum dots (QDs). Irradiation of the QD-A. vinelandii hybrids with visible light is found to significantly enhance ammonia production efficiency. The inherently low ammonia conversion rate of wild-type A. vinelandii is substantially increased upon incorporation of QDs. This increase is attributed to the electron transfer from QDs within the bacterial cells to intracellular bio-components. Transferring this chemistry to a large-scale reaction presents a tremendous challenge, as it requires precise control over the growth conditions. We explore the scalability of the QD-A. vinelandii hybrids by conducting the photochemical reaction in a 5-L fermentor under various parameters, such as dissolved oxygen, nutrient supply, and pH. Interestingly, ammonia was produced in media depleted of carbon sources. Consequently, a two-step fermentation process was designed, enabling effective ammonia production. Our findings demonstrate that the QD-A. vinelandii hybrid system in a bioreactor setup achieves an ammonia turnover frequency of 11.96 s⁻¹, marking a more than sixfold increase in efficiency over that of nitrogenase enzymes alone. This advancement highlights the potential of integrating biological and nanotechnological elements for scalable ammonia production processes.