Fabricating High-Performance T2-Weighted Contrast Agents via Adjusting Composition and Size of Nanomagnetic Iron Oxide

Magnetic relaxation switch demonstrated that the aggregated nanomagnetic iron oxide (NMIO) nanocrystal possessed a lower T2 value and better relaxivity compared with monodispersed NMIO nanocrystal. However, we found that NMIO nanoclusters (NMIONCs) showed a different magnetic resonance (MR) imaging property in comparison with NMIO nanocrystals. Herein, three types of NMIONCs were used to explore the effects of size and compositions on the variations of magnetism and MR contrast ability. It was found that the transverse relaxation rate (r2) of NMIONCs depended on the contact area between particles and water molecules. The smaller size and higher solubility could carry out higher contact area between NMIONCs and water molecules. Therefore, the monodispersed NMIONC showed a better T2 contrast ability in comparison with the aggregated NMIONC. In addition, for NMIONCs with the same composition, the magnetism and contrast ability gradually increased with the particle size decreasing. In vivo, NMIONCs that posse...