Activatable Lanthanide Nanoprobes with Dye-Sensitized Second Near-Infrared Luminescence for in Vivo Inflammation Imaging.

Lanthanide nanoparticles exhibit unique photophysical properties and thus emerge as promising second near-infrared (NIR-II) optical agents. However, the limited luminescence brightness hampers their construction of activatable NIR-II probes. Herein, we report the synthesis of dye-sensitized lanthanide nanoprobes (NaGdF 4 :Nd/ICG; indocyanine green (ICG)) and their further development for in vivo activatable imaging of hypochlorite (ClO - ). Dye sensitization using ICG not only shifts the optimal doping concentration of Nd 3+ from 5 to 20 mol % but also leads to a 5-fold NIR-II enhancement relative to the ICG-free counterpart. Mechanistic studies reveal that such a luminescence enhancement of NaGdF 4 :Nd at high Nd 3+ concentration is ascribed to an alleviated cross-relaxation effect due to the broad absorption of ICG and faster energy transfer process. Taking advantage of dye oxidation, the nanoprobes enable activatable NIR-II imaging of hypochlorous acid (ClO - ) in a drug-induced lymphatic inflammation mouse model. This work thus provides a simple, yet effective luminescence enhancement strategy for constructing lanthanide nanoprobes at higher activator doping concentration toward activatable NIR-II molecular imaging.