Facile one-pot synthesis of monodispersed NIR-II emissive silver sulfide quantum dots

Fluorescent imaging in the second near-infrared region (NIR-II, 1000–1700 nm) is optimal for in vivo imaging due to their low autofluorescence and weak tissue scattering. Recently, many efforts have been paid in search of NIR-II emitting agents. Herein, we report a facile one-pot approach for the synthesis of NIR-II emissive Ag₂S quantum dots (QDs). The effect of ligand was carefully investigated to improve the quality of QDs. It is found that the QDs tend to form clusters when 1-dodecanethiol was used as the only ligand. The addition of oleic acid can greatly improve the dispersity of the nanocrystals but lead to a significantly decrease of the emission intensity. Meanwhile, the present of small amount of oleylamine can prevent the formation of undesired silver nanoparticles and improve the fluorescent intensity at high temperature. Whole-body blood vessel imaging and tumor imaging were performed with these biocompatible Ag₂S QDs after PEGylation to demonstrate their potentials in vivo.