Gd- and Eu-Loaded Iron Oxide@Silica Core-Shell Nanocomposites as Trimodal Contrast Agents for Magnetic Resonance Imaging and Optical Imaging.

Superparamagnetic maghemite core-porous silica shell nanoparticles, γ-Fe2O3@SiO2 (FS), with 50 nm diameter and a 10 nm core, impregnated with paramagnetic complexes b-Ln ([Ln(btfa)3(H2O)2]) (where btfa = 4,4,4-trifluoro-l-phenyl-1,3-butanedione and Ln = Gd, Eu, and Gd/Eu), performing as promising trimodal T1-T2 MRI and optical imaging contrast agents, are reported. These nanosystems exhibit a high dispersion stability in water and no observable cytotoxic effects, witnessed by intracellular ATP levels. The structure and superparamagnetic properties of the maghemite core nanocrystals are preserved upon imbedding the b-Ln complexes in the shell. Hela cells efficiently and swiftly internalize the NPs into the cytosol, with no observable cytotoxicity below a concentration of 62.5 μg mL-1. These nanosystems perform better than the free b-Gd complex as T1 (positive) contrast agents in cellular pellets, while their performance as T2 (negative) contrast agents is similar to the FS. Embedding of the b-Eu complex in the silica pores endows the nanoparticles with strong luminescence properties. The impregnation of gadolinium and europium complexes in a 1:1 ratio afforded a trimodal nanoplatform performing as a luminescent probe and a double T1 and T2 MRI contrast agent even more efficient than b-Gd used on its own, as observed in cell-labeled imaging experiments and MRI cell pellets.