Core/Shell-Structured Ag₂Te/Ag₂Se Quantum Dots for High-Resolution In Vivo Fluorescence Imaging in the Near Infrared IIb Region

Fluorescence in the near infrared IIb window (NIR-IIb, 1500–1700 nm) shows higher signal-to-noise ratio, better space-time resolution, and deeper tissue penetration. However, materials with excellent fluorescence properties in the NIR-IIb region were rarely reported. Ag 2 Te quantum dots (QDs) could emit variable fluorescence in the NIR-II window due to their narrow band gap. Unfortunately, the fluorescence in the NIR-IIb region was not strong enough to image in vivo because the lattice defects on the surface of Ag 2 Te increased non-radiative transitions and decreased fluorescence performance. In this work, we coated a Ag 2 Te core with a Ag 2 Se shell to passivate the lattice defects and enhance its fluorescence efficiency. The fluorescence property of the as-prepared Ag 2 Te/Ag 2 Se core/shell QDs is more than 10 times stronger than that of Ag 2 Te. The brighter Ag 2 Te/Ag 2 Se QDs showed high-resolution in vivo imaging in the NIR-IIb region to distinguish thin blood vessels up to 66 μm. Overall, Ag 2 Te/Ag 2 Se QDs with excellent fluorescence in the NIR-IIb region were prepared and showed great potential for biomedical imaging.