Sub-10 nm Sr2LuF7:Yb/Er@Sr2GdF7@SrF2 Up-Conversion Nanocrystals for Up-Conversion Luminescence–Magnetic Resonance–Computed Tomography Trimodal Bioimaging

Herein, sub-10 nm core-shell nanocrystals (NCs), which select Sr₂LuF₇:Yb/Er as core, Sr₂GdF₇ as middle shell, and SrF₂ as an outermost shell, were synthesized by a seed-mediated growth process. The NCs possess good crystallinity, morphology, and up-conversion luminescent properties. After modification by polyethylenimine branched (PEI), in vitro cell up-conversion imaging with low autofluorescence was realized. Due to the presence of Gd³⁺ ions, in vivo magnetic resonance (MR) imaging was also achieved with these designed NCs. More significantly, these special core-shell NCs exhibited high contrast in in vivo X-ray computed tomography (CT) imaging because of their good X-ray absorption ability. These results indicate that the core-shell up-conversion NCs can serve as promising contrast agents for up-conversion luminescence-MR-CT trimodal bioimaging.