Controlled Synthesis of Ag2Te@Ag2S Core–Shell Quantum Dots with Enhanced and Tunable Fluorescence in the Second Near-Infrared Window

Fluorescence in the second near-infrared window (NIR-II, 900–1700 nm) has drawn great interest for bioimaging, owing to its high tissue penetration depth and high spatiotemporal resolution. NIR-II fluorophores with high photoluminescence quantum yield (PLQY) and stability along with high biocompatibility are urgently pursued. In this work, a Ag-rich Ag 2 Te quantum dots (QDs) surface with sulfur source is successfully engineered to prepare a larger bandgap of Ag 2 S shell to passivate the Ag 2 Te core via a facile colloidal route, which greatly enhances the PLQY of Ag 2 Te QDs and significantly improves the stability of Ag 2 Te QDs. This strategy works well with different sized core Ag 2 Te QDs so that the NIR-II PL can be tuned in a wide range. In vivo imaging using the as-prepared Ag 2 Te@Ag 2 S QDs presents much higher spatial resolution images of organs and vascular structures as compared with the same dose of Ag 2 Te nanoprobes administrated, suggesting the success of the core–shell synthetic strategy and the potential biomedical applications of core–shell NIR-II nanoprobes.