Cubic sub-20 nm NaLuF4-based upconversion nanophosphors for high-contrast bioimaging in different animal species

A new upconversion luminescence (UCL) nanophosphors based on host matrix of cubic NaLuF4 with bright luminescence have been synthesized by a solvothermal method, facilitate the nanocrystals potential candidates for imaging in vivo, especially large-animals. The sub-20 nm NaLuF4 co-doped Yb3+ and Er3+ (Tm3+) showed about 10-fold stronger UCL emission than that of corresponding hexagonal NaYF4-based nanocrystals with a 20 nm diameter. Near-infrared to near-infrared (NIR-to-NIR) UCL emission of PAA-coated NaLuF4:20%Yb,1%Tm (PAA-LuTm) can penetrate >1.5 cm tissue of pork with high contrast. Based on super-strong UCL emission and deep penetration, PAA-LuTm as optical bioprobe has been demonstrated by in vivo UCL imaging of a normal black mouse, even rabbit with excellent signal-to-noise ratio. Furthermore, such cubic NaLuF4-based nanophosphor was applied in lymph node imaging of live Kunming mouse with rich white fur.