(252b) Controlled Synthesis of Fe3O4 Single Crystal Spheres for Biomedical Application

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). The obtained Fe₃O₄ particles varied from solid nanospheres about 15nm to hollow microspheres about 500nm via careful adjustment of the V_EG/V_DEG ratio. All the individual particles demonstrated a remarkable feature of single crystal no matter what the size and structure they were. The as-prepared Fe₃O₄ spheres exhibited superparamagnetic properties with relatively high saturation magnetization (~93emu/g) at room temperature, strong magnetocaloric effect (up to 68.5℃ in 3 min) and large BET surface area (~30m²/g). 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. Fe₃O₄ nanospheres around 50nm in diameter were tested to be nontoxic. The application of these nanospheres in MRI in vitro showed a high T2 relaxivity, their application in vivo 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.