Highly Water-Soluble Superparamagnetic Ferrite Colloidal Spheres with Tunable Composition and Size

摘要

Monodisperse inorganic functional nanoparticles with controllable size and shape have aroused extensive research interest owing to their fundamental scientific importance and technological applications.[1] In particular, spinel ferrites MFe2O4 (M=Zn, Mg, Mn, Co, Ni, Fe), a type of very important magnetic material, have attracted considerable attention because of their unique magnetic properties and potential applications in, for example, information storage, magnetic resonance imaging (MRI), and biomedical areas.[2–6] For biomedical applications such as drug delivery and bio- ACHTUNGTRENUNGsepACHTUNGTRENUNGaration, it is desirable to obtain ferrite particles with superparamagnetic properties because this property can prevent the particles from strong magnetic interactions in dispersion.[ 7] Recently, several methods have been developed to prepare superparamagnetic ferrite nanoparticles including thermal decomposition,[8] reverse micelle synthesis,[9] and solvothermal synthesis.[10] However, owing to their small size (less than 20 nm), the superparamagnetic ferrite nanoparticles usually show low saturation magnetization. To promote the possibility of ferrite particles being applied in biomedical areas, high magnetization is needed because this can enable easy separation or control of the particles by an external magnetic field.[11] An increase in the size can increase the magnetization, but this may also induce the superparamagnetic– ferromagnetic transition. Therefore, it is a great challenge to acquire superparamagnetic ferrite particles with relatively high saturation magnetization.