Size-controlled synthesis of water-dispersible superparamagnetic Fe3O4 nanoclusters and their magnetic responsiveness

Abstract

Highly water dispersible and size-controllable superparamagnetic Fe₃O₄ nanoclusters were synthesized by a simple solvothermal route with sodium citrate as a surface modifier in a mixed-solvent system with diethylene glycol (DEG) and ethylene glycol (EG). The Fe₃O₄ nanoclusters are small-molecule grafted and the size of the Fe₃O₄ nanoclusters can be effectively controlled by varying the volume ratio of DEG/EG from tens to hundreds of nanometers. Sodium citrate did not only act as a functional ligand anchor on the particle surface to enhance the dispersibility of the magnetite nanoclusters but also controlled the size of the clusters in the reaction. Magnetic measurements revealed the superparamagnetic nature of the magnetic nanoclusters with no coercivity and remanence but with a magnetization saturation of up to 68.0 emu g⁻¹ at room temperature. These monodisperse Fe₃O₄ nanoclusters can be used for color display and hyperthermia in biomedical applications because of strong magnetic responsiveness. The diffraction color in the visible light can be modulated under the induction of varied external magnetic fields. Furthermore, the temperature of 20 mg mL⁻¹ Fe₃O₄ (168 nm) water dispersions can be increased by 46.7 °C within 242 s under an alternating current magnetic field.