Biosynthesis of biocompatibility Ag₂Se quantum dots in Saccharomyces cerevisiae and its application

As fluorescence in the second near-infrared window (NIR-II, 1000-1400 nm) could image deep tissue with high signal-to-noise ratios compared with that in NIR-I (750-900 nm), Ag₂Se quantum dots (QDs) with fluorescence in the NIR-II could be ideal fluorophores. Here, we described a biosynthesis method to prepare the Ag₂Se QDs by using temporally coupling the irrelated biochemical reactions, whose photoluminescence (PL) emission can reach NIR-II. The nanoparticles were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The results showed that the nanoparticles obtained by extracellular purification were Ag₂Se QDs with a uniform size of 3.9 ± 0.6 nm. In addition, the fluorescence intensity of Saccharomyces cerevisiae was improved successfully by nearly 4-fold by constructed engineering strain. In particular, the biosynthesis of Ag₂Se QDs had good biocompatibility because it was capped by protein. Furthermore, investigating the toxicity of Ag₂Se on cells and NIR images of nude mice showed that the Ag₂Se synthesized using S. cerevisiae had low toxicity and could be used for in vivo imaging. In this work, the synthesis pathway of biocompatible Ag₂Se was broadened and laid a foundation for the enlarged applicability of bioimaging in the biosynthesis of NIR-II QDs.