Translated Abstract
Fe3O4 nanomaterials have received great attention in applications of tumor diagnosis and tumor heat therapy based on their good biocompatibility, magnetic targeting ability and local heating ability in alternating magnetic fields (AMF). An idea magnetic heat treatment agent should possess high heating efficiency and at the same time, should have superparamagnetic properties to avoid magnetic reunion in the process of magnetic targeting. Most superparamagnetic nanoparticles obtained by traditional methods exhibit low heating efficiency, because of their small particle sizes and lower saturation magnetization (Ms). Enlarging the particle size is favorable to increase the Ms of magnetic particles, so that increase the heating efficiency. However, the superparamagnetism of the particle could be lost with the increase of particle size. This is not favorable to the targeting delivery of magnetic particles. For this purpose, in this paper, a novel controlled hydrothermal method has been proposed to prepare superparamagnetic hollow Fe3O4 nanoparticles with hierarchical structure and high Ms. The structure, magnetic properties and magnetothermal effect have been studied. The main achievements are as bellow:
(1) In the process of hydrothermal reaction, it was found that spherical Fe3O4 particles with mesoporous hollow structure can be obtained when the FeCl3?6H2O is 0.27g, Sodium Citrate is 0.88g, Urea is 0.36g, polyacrylamide (PAM) is 0.35g, the reaction temperature is 200℃ and reaction time is 12 h. The hollow Fe3O4 particles possess hierarchical structure, in which large particles (120nm) are assembled by 20nm and smaller primary Fe3O4 crystals. The formation of hierarchical hollow structure is believed to be due to the Ostwald ripening process.
(2) As-obtained hollow Fe3O4 particles exhibit typical superparamagnetic properties. The Ms is 73.3emu/g, which is significantly greater than that of traditional small superparamagnetic nanoparticles. It is believed that the superparamagnetism of as-obtained hollow Fe3O4 particles is originated from the superparamagnetic properties of primary crystals whose particle size is in the range of superparamagnetic region.
(3) The in vitro inductive heating experiment shows that at the same conditions the hollow Fe3O4 particles exhibit higher heating efficiency than that of solid Fe3O4 particles. When the concentration of magnetic fluid is 10mg/ml, the frequency of external AC magnetic field is 55 kHz and the input power is 4.5kW, the highest heating temperature of hollow Fe3O4 fluid can reach 60.8 ℃. The everage heating rate is 4.8℃/min. The specific absorbtion rate (SAR) reaches 116.53 w/g . The magnetothermal effect is believed to be due to the Neel Relaxation
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