Lanthanidae doped CaF2 nanoparticles : biocompatible multifunctional materials for biomedical imaging

Water dispersible Gd3+,Yb3+,Er3+ and Gd3+,Yb3+,Tm3+ doped CaF2 nanoparticles (NPs) were prepared byone-pot hydrothermal synthesis using citrate ions as capping agents without the need for any postsynthesisreaction. UC emissions are easily observed in the visible and infrared regions upon NIR diodelaser excitation at 980 nm. EPR spectroscopy confirms the substitutional nature of the rare-earth doping,while magnetometric studies reveal that the NPs have a useful magnetization. MRI experiments conductedin vivo show that after 40 min from the injection, the NPs localize in the liver and spleen. Electronmicroscopy images of liver tissue reveal that the NPs are located in the Kupffer cells, although a smallamount is also found in the hepatocytes. An excitation with a 980 nm emission on the excised liver andepithelial tissue induces clearly visible UC emission. The local temperature upon 980 nm irradiation wasmonitored in situ and it was found to increase slowly with the exposure time, maintaining under 1–2 °Cfor less than 60 second exposure. The NPs show a low toxicity towards cultured HeLa cells and humanprimary dendritic cells (DCs), and did not induce pro-inflammatory cytokine secretion by cultured humanDCs, indicating that the NPs do not cause relevant adverse reactions in immune cells. Therefore, thepresent NPs are suitable candidates to be efficiently used in surgery applications, where spatial resolutionand lack of harmful effects on human health are important issues.