Studies On The Surface Modification And Properties Of Iron Oxide Nanoclusters

Magnetic iron oxide nanomaterials become a hot topic because of its excellent magnetic properties, good biocompatibility and broad application in magnetic resonance imaging?MRI?, hyperthermia, targeted drug delivery and other areas. Individual superparamagnetic particles have the disadvantages of smaller size and low magnetic response in a magnetic field, have limited its application in biomedicine fields. With the increase of diameter, Fe₃O₄ nanoparticles will change from superparamagnetic to ferromagnetic. Nanoclusters assembled by small aggregates of iron oxide nanocrystals, not only have the appropriate particle size, higher response in a magnetic field, but also maintain the superparamagnetic of primary nanoparticles, which attracted a lot of research interest.In this work, superparamagnetic iron oxide nanoclusters were prepared by microwaveassisted solvothermal method using poly-acrylic acid as surfactant and ammonia as precipitating agent. The Fe₃O₄@SiO₂ core-shell nanoparticles were prepared by modified St?ber method. The influence of the iron oxide nanoclusters concentration, the amount of TEOS and ammonia, ultrasonic time were studied. The biological toxicity, magnetic induction heating performance and magnetic resonance imaging performance of iron oxide nanoclusters and Fe₃O₄@SiO₂ nanoparticles were studied. The composition, structure and morphology of the products were characterized by X-ray powder diffraction?XRD?, Transmission Electron Microscope?TEM? and Scanning Electron Microscope?SEM?. The hydrodynamic size distribution and Zeta potential of the products were characterized by Nano Particle Sizer. The magnetic properties of the sample were characterized by Vibrating Sample Magnetometer?VSM?.The results indicate:?1? Iron oxide nanoclusters with an average size of 60 nm were prepared by microwaveassisted solvothermal method, which have regular morphology, good water dispersibility and colloidal stability. It exhibits superparamagnetism at room temperature.?2? By changing the TEOS adding times and ultrasonic duration, can reduce the adhesion and agglomeration between Fe₃O₄@SiO₂ particles. The concentration of Fe₃O₄ nanoclusters, the amount of ammonia and TEOS have an important influence on the thickness of the coated SiO₂ layer.?3? The Fe₃O₄ clusters and Fe₃O₄@SiO₂ core-shell particles have low cytotoxicity. Therefore they can be used in biomedical fields.?4? The Fe₃O₄ clusters and Fe₃O₄@SiO₂ core-shell particles have a good magnetic induction heating effect in an alternating magnetic field. The results indicate that the samples can be applied in magnetic hyperthermia. By varying the concentration of the samples and the intensity of alternating magnetic field, we can control the heating rate of the samples.?5? With the increase of Fe concentration, the Fe₃O₄ clusters and Fe₃O₄@SiO₂ coreshell particles generate MR contrast enhancement on T2-weighted MR imaging. Therefore they can be used for T2-weighted MRI contrast agents.