The Surface Modification Of Magnetic Nanoparticles To Functionalize

Fe₃O₄ magnetic nanoparticles with appropriate surface chemical properties have been widely used experimentally for numerous in vivo applications such as magnetic resonance imaging contrast enhancement, tissue repair, immunoassay, hyperthermia, drug delivery and in cell separation, etc. All these biomedical and bioengineering applications require that these nanoparticles were non-toxic and biocompatible, have high magnetization values, size smaller than 100 nm with overall narrow particle size distribution. So the surface of magnetic nanoparticles must be modified with special materials.In this paper, Fe₃O₄ magnetic nanoparticles were coated by dextran which was natural polymer firstly. We made the reaction conduct in the solution of sodium citrate (0.075 M) instead of reacting in alkaline circumstances. After analyzing the results of Fourier transform infrared (FTIR),X-ray photoelectron spectrograph (XPS) and Thermal Gravity Analysis (TG), we found out the mechanism of reaction and the effect of sodium citrate. In addition, dextran successfully bound to the surface of nanoparticles. And the hydrodynamic diameters decreased, the distribution of size narrowed down after modified with dextran macromolecular. The nanoparticles coated by dextran could disperse in physiological environment stably because that the electrostatic repulsive force between particles increased after modifying the surface. Vibration Sample Meter (VSM) results shew the higher saturation magnetization and better paramagnetic feature of Fe₃O₄/Dextran nanoparticles.Secondly, the surface of magnetic nanoparticles with citric acid (CA) were modified. The optimum condition and the way of post treatment were determined through measuring the size of samples prepared in different condition by dynamic light scattering (DLS). We made out the reaction mechanism that CA was bound on the surface of Fe₃O₄ nanoparticles through Fe-O-C covalent bond, and the modes of metal-carboxylate complexation is bidentate chelating. The study of all results indicated that Fe₃O₄/CA complex had many surface negative charges, smaller size and better dispersivity; the water-solubility of the coated nanoparticles had improved greatly thanks to the carboxylic on surface, which had prolonged the time of blood circulation in biological system; Fe₃O₄/CA complex still had high saturation magnetization and good paramagnetic feature. In addition, we detected the contents of Fe and impurity belonged to Fe₃O₄/CA complex by ICP-MS, the results of which were compared with the analysis of TG. We concluded that the outcome of ICP-MS was preciser, and could be basis when making the experiment of biology.In the end, the Fe₃O₄ magnetic nanoparticles were coated by 3-aminopropyl triethoxysilane (APTES) in order to introduce the -NH2 functional group. After discussing and analyzing the influences on product's performance through changing the experiment conditions, we sum up the optimal conditions. The results of characterization shew that APTES was combined on the surface of nanoparticles via Fe-O-Si covalent bond; the contents of APTES and Fe₃O₄ in Fe₃O₄/APTES complex respectively were 5% and 94%, on the basis of which we figure out that the surface APTES coverage ratio of Fe₃O₄ nanoparticles is about 65%. Probably, the incompleteness (a near monolayer) of the surface coating is owing to the incompleteness of surface hydroxylation and the existence of the spatial resistance for the surface coating reaction. The size of modified nanoparticles became larger, the dispersivity was improved distinctly, and the magnetic property still good.All in all, three magnetic complexs Fe₃O₄/Dextran,Fe₃O₄/CA and Fe₃O₄/APTES were prepared, which had different surface functional group and electric charge. So we can make the control experiment to research the performances of the three different complexs applied in a kind of biomedical field such as the separation and purification of protein.