Cation Exchange of Anisotropic-Shaped Magnetite Nanoparticles Generates High-Relaxivity Contrast Agents for Liver Tumor Imaging

Cation exchange is a powerful means to adjust the properties of nanocrystals through composition change with morphology retention. Herein, we demonstrate that cation exchange can engineer the composition of iron oxide nanocrystals to dramatically improve their contrast ability in magnetic resonance imaging (MRI). We successfully construct manganese and zinc engineered iron oxide nanoparticles with diverse shapes (sphere, cube, and octapod) by facile cation exchange reactions. Extended X-ray absorption fine structure (EXAFS) study indicates that Mn 2+ and Zn 2+ ions are doped into the crystal lattice of ferrite, and more importantly, most of them are distributed in T d sites of ferrite. These engineered shaped-anisotropic iron oxide nanoparticles exhibit both high saturated magnetization and large effective boundary radii, which leads to remarkable transverse relaxivity ( r 2 ), for example, 754.2 mM –1 s –1 for zinc engineered octapod iron oxide nanoparticles. These engineered iron oxide nanoparticles, as high-performance T 2 contrast agents for in vivo MR imaging, enable sensitive imaging of early hepatic tumors and metastatic hepatic tumors (as small as 0.4 mm), holding great promise for prompt and accurate diagnosis of cancers and metastases.