Controlled Synthesis of Fe3O4 Single Crystalline Spheres in One Solvothermal System and Their Application in MRI

Spherical Fe3O4 particles with tunable diameters and structures have been successfully synthesized using a modified one-pot solvothermal method in an ethylene glycol/diethylene glycol (EG/DEG) binary system, with the assistance of dodecylamine (DDA) as the template agent. The obtained Fe3O4 particles varied from solid nanospheres about 10 nm to hollow microspheres about 480 nm via careful adjustment of the VEG/VDEG ratio. All the individual particles demonstrated a significant feature of single crystal, regardless of the varied sizes and structures. The as-prepared Fe3O4 spheres exhibited superparamagnetic properties with relatively high saturation magnetization (similar to 93 emu/g) at room temperature and strong magnetocaloric effect (up to 68.5 degrees C in 3 min), which is indicative of their potential biomedical applications. Based on serials of experiments, a reasonable formation mechanism of the Fe3O4 spheres were proposed, attributing to the cooperation of oriented aggregation, gas-bubble-assisted Ostwald ripening process and regulation of viscosity. The application of these nanospheres in MRI in vitro showed a high T-2 relaxivity, and in vivo MRI analysis demonstrated significant enhancement on the image contrast and concentrated aggregation of Fe3O4 nanospheres in tumor rather than other organs, which inferred that these nanospheres could be served as ideal candidates for MRI contrast agents.