Preparation and growth orientation modulation of Mn0.6Zn0.4Fe2O4 nanoparticles as MRI contrast agents

Ferrite nanoparticles are widely used in magnetic resonance imaging as T2 contrast agent particles. In this study, we propose to utilize Mn and Zn doping into ferrite to prepare Mn-Zn doped ferrite and use it as T2 contrast agent core particles. Also, we aim to clarify the relationship between the Mn-Zn doped ferrite nanoparticles orientation and ratio of surfactant oleic acid to oleylamine as well as different solvents. The results shows that through high temperature thermal decomposition method can successfully prepared uniformly doped Mn-Zn ferrite nanoparticles (Mn0.6Zn0.4Fe2O4). And the ratio of surfactant oleic acid to oleylamine has a significant impact on the orientation of Mn0.6Zn0.4Fe2O4 nanoparticle growth. As the ratio of oleic acid increases, the Mn0.6Zn0.4Fe2O4 nanoparticles gradually change from growing along the [110] crystal direction to growing randomly with irregular orientation, the nanoparticles morphology and size tend from rhombohedral (37nm) to spherical (9.84nm). In terms of solvent, benzyl ether, 1-octadecene and hexadecylamine have no influence on the action of surfactants. The Mn0.6Zn0.4Fe2O4 nanoparticles in these three solvents were grown randomly without any obvious orientation changes. All nanoparticles obtained were spherical nanoparticles, indicating that the choosing three solvents has almost no effect on the orientation of the nanoparticles. However, three different solvents affect the crystallinity of Mn0.6Zn0.4Fe2O4 nanoparticles. Nanoparticles prepared with diphenyl ether as solvent showed higher crystallinity compared to those synthesized with 1-octadecene and hexadecylamine as solvents. In contrast performance, under the optimal surfactant ratio (11:1) and solvent selection (dibenzyl ether), the transverse relaxation rate r2 value of Mn-Zn ferrite nanoparticles reach 266.24mM-1s-1, while the longitudinal relaxation rate r1 value is 10.45mM-1s-1. The r2/r1 ratio is significantly larger than 10, indicating that the nanoparticles with random growth orientation serve as excellent T2 weighted contrast agents.