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 (NaGdF4: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 Nd3+ 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
NaGdF4:Nd at high Nd3+ 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.