Adjustable near-infrared fluorescence lifetime emission of biocompatible rare-earth-doped nanoparticles for in vivo multiplexing

Rare-earth-doped inorganic nanocrystals are an important class of nanoparticles for bioimaging applications due to the facility of providing them with tailored emissions in the visible and near-infrared regions of the electromagnetic spectrum. Recently it has become of interest to engineer the dopant composition of these materials in order to enable multiplexed lifetime imaging for autofluorescence-free in vivo bioimaging. Herein we report a simple approach to obtain different fluorescence lifetimes for the Yb3+emission (2F5/2 → 2F7/2) in Nd3+, Yb3+, Tm3+ co-doped NaGdF4 nanoparticles by only changing their crystal size while keeping their hydrodynamic diameter constant. This allowed straightforward transformation of infrared images in the time domain into lifetime maps. The particles were then deployed as in vivo contrast agents for near-infrared imaging in a mouse demonstrating their multiplexing capability. © 2022