Europium-engineered iron oxide nanocubes with high T-1 and T-2 contrast abilities for MRI in living subjects

Magnetic resonance imaging (MRI) contrast agents with both positive (T-1) and negative (T-2) contrast abilities are needed in clinical diagnosis for fault-free accurate detection of lesions. We report a facile synthesis of europium-engineered iron oxide (EuIO) nanocubes as T-1 and T-2 contrast agents for MRI in living subjects. The Eu(III) oxide-embedded iron oxide nanoparticles significantly increase the T-1 relaxivity with an enhanced positive contrast effect. EuIO nanocubes with 14 nm in diameter showed a high r(1) value of 36.8 mM(-1) s(-1) with respect to total metal ions (Fe + Eu), which is about 3 times higher than that of Fe3O4 nanoparticles with similar size. Moreover, both r(1) and r(2) values of EuIO nanocubes can be tuned by varying their sizes and Eu doping ratios. After citrate coating, EuIO nanocubes can provide enhanced T-1 and T-2 contrast effects in small animals, particularly in the cardiac and liver regions. This work may provide an insightful strategy to design MRI contrast agents with both positive and negative contrast abilities for biomedical applications.