A New Class of NIR-II Gold Nanocluster-Based Protein Biolabels for In Vivo Tumor-Targeted Imaging.

The design of bright NIR-II luminescent nanomaterials that enable efficient labelling of proteins without disturbing their physiological properties in vivo is challenging. We developed an efficient strategy to synthesize bright NIR-II gold nanoclusters (Au NCs) protected by biocompatible cyclodextrin (CD). Leveraging the ultrasmall size of Au NCs (<2 nm) and strong macrocycle-based host-guest chemistry, the as-synthesized CD-Au NCs can readily label proteins/antibodies. Moreover, the labelled proteins/antibodies enable highly efficient in vivo tracking during blood circulation, without disturbing their biodistribution and tumor targeting ability, thus leading to a sensitive tumor-targeted imaging. CD-Au NCs are stable in the harsh biological environment and show good biocompatibility and high renal clearance efficiency. Therefore, the NIR-II biolabels developed in this study provide a promising platform to monitor the physiological behavior of biomolecules in living organisms.