Water-Soluble High-Quality Ag₂Te Quantum Dots Prepared by Mutual Adaptation of Synthesis and Surface Modification for In Vivo Imaging

Near-infrared (NIR) in vivo fluorescence imaging has exhibited the distinct advantage of high optical resolution at deeper penetration into biological tissues. Ag₂Te quantum dots (QDs), with a relatively narrow band gap, show great promise for fluorescence emission at long wavelengths in the second near-infrared (NIR-II) window for bioimaging. However, existing Ag₂Te QDs have severely hindered the application of in vivo bioimaging due to their poor fluorescence brightness and stability, so it is important to prepare Ag₂Te QDs with high quantum yield and stability as well as high biocompatibility in the NIR-II window. Herein, we designed an integrated method for the preparation of water-soluble Ag₂Te QDs by mutual adaptation of QD synthesis and surface modification. We first synthesized high-quality Ag₂Te QDs with different NIR-II emission wavelengths and the photoluminescence quantum yields (PLQYs) up to 6.51% by rapidly injecting the TBP-Te precursor into a hot solvent to form a highly fluorescent Ag₂Te core. Then water-dispersible Ag₂Te QDs were obtained by direct exchange of the hydrophobic Ag₂Te QD surface ligands with thiol ligands. The PLQY of the water-soluble Ag₂Te QDs obtained by this method can still be maintained at 4.94%. With these highly bright and stable Ag₂Te QDs, the abdominal vessels, hindlimb arterial vessels, venous vessels, sacral lymph nodes, and tumor vessels were visualized non-invasively in vivo in the NIR-II window in mice. The results demonstrate that the integrated strategy of QD synthesis and modification provides valuable technical support for further in-depth applications of Ag₂Te QDs.