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.