Enhancing Transversal Relaxation for Magnetite Nanoparticles in MR Imaging Using Gd3+-Chelated Mesoporous Silica Shells

A new magnetic nanoparticle was synthesized in the form of Gd3+-chelated Fe3O4@SiO2. The Fe3O4 nanoparticle was octahedron-structured, was highly magnetic (similar to 94 emu/g), and was the core of an encapsulating mesoporous silica shell. DOTA-NHS molecules were anchored to the interior channels of the porous silica to chelate Gd3+ ions. Because there were Gd3+ ions within the silica shell, the transverse relaxivity increased 7-fold from 97 s(-1) mM(-1) of Fe3O4 to 681 s(-1) mM(-1) of Gd3+-chelated Fe3O4@SiO2 nanoparticles with r(2)/r(1) = 486. The large transversal relaxivity of the Gd3+-chelated Fe3O4@SiO2 nanoparticles had an effective magnetic resonance imaging effect and clearly imaged lymph nodes. Physiological studies of liver, spleen, kidney, and lung tissue in mice infused with these new nanoparticles showed no damage and no cytotoxicity in Kupffer cells, which indicated that Gd-3+-chelated Fe3O4@SiO2 nanoparticles are blocompatible.