(a-NaYbF_4:Tm~(3+))/CaF_2 Core/Shell Nanoparticles with Efficient Near-Infrared to Near-Infrared Upconversion for High-Contrast Deep Tissue Bioimaging

摘要

We describe the development of novel and biocompatible core/shell (a-NaYbF4:Tm~3+)/CaF_2 nanoparticles that exhibit highly efficient NIR_in-NIR_out. upconversion (UC) for high contrast and deep bioimaging. When excited at -980 nm, these nanoparticles emit photolumines-cence (PL) peaked at ~800 nm. The quantum yield of this UC PL under low power density excitation (-0.3 W/cm~2) is 0.6 0.1%. This high UC PL efficiency is realized by suppressing surface quenching effects via heteroepitaxial growth of a biocompatible CaF_2 shell, which results in a 35-fold increase in the intensity of UC PL from the core. Small-animal whole-body UC PL imaging with exceptional contrast (signal-to-background ratio of 310) is shown using BALB/c mice intravenously injected with aqueously dispersed nanoparticles (700 pmol/kg). High-contrast UC PL imaging of deep tissues is also demonstrated, using a nanoparticle-loaded synthetic fibrous mesh wrapped around rat femoral bone and a cuvette with nanoparticle aqueous dispersion covered with a 3.2 cm thick animal tissue (pork).