Controlled Synthesis of Ag2 Te@Ag2 S 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 Ag₂ Te quantum dots (QDs) surface with sulfur source is successfully engineered to prepare a larger bandgap of Ag₂ S shell to passivate the Ag₂ Te core via a facile colloidal route, which greatly enhances the PLQY of Ag₂ Te QDs and significantly improves the stability of Ag₂ Te QDs. This strategy works well with different sized core Ag₂ Te QDs so that the NIR-II PL can be tuned in a wide range. In vivo imaging using the as-prepared Ag₂ Te@Ag₂ S QDs presents much higher spatial resolution images of organs and vascular structures as compared with the same dose of Ag₂ Te nanoprobes administrated, suggesting the success of the core-shell synthetic strategy and the potential biomedical applications of core-shell NIR-II nanoprobes.