Assembly and Synthesis Mechanism of CdSe Quantum Dots in Recombinant Escherichia coli Expressing Metallothionein

Quantum dots (QDs) are widely used in sensors, photovoltaic cells, and other fields due to their unique structural and optical properties. Physical and chemical methods that are commonly used for the synthesis of QDs require high-temperature and high-pressure environments, as well as toxic reagents. Biosynthesis overcomes these limitations and offers a novel method for producing QDs that is both cost-effective and environmentally friendly. Mercaptan substances in organisms play a key role in the synthesis of QDs, such as glutathione (GSH) and plant chelating peptides. However, the preparation of QDs using metallothionein (MT) has rarely been reported, and the synthesis mechanism is lacking. In this paper, we describe the in vivo biosynthesis of CdSe QDs by recombinant Escherichia coli expressing metallothionein, which has a synthetic advantage compared to the original strain. The fluorescence emission spectrum of the synthesized QDs was located at 550 nm with a Stokes shift of 140 nm, and the yield of the biological QDs was calculated to be 2.91%. Furthermore, the role of metallothionein in the synthesis of QDs was tentatively validated. The initial nucleus of the QDs is proposed to be originating from the Cys-Cd, followed by the subsequent introduction of the HSe- group, and its coordination with Cd2+ promotes layer-bylayer growth. Here, we established a green, mild, and efficient in vivo synthesis pathway for QDs, providing more possibilities for the synthesis of biological QDs in the future.