Research On The Synthesis, Modication And Cell Transfection Of Magnetite (fe3O4) Nanoparticles

Magnetic nanoparticles, which display superparamagnetic property and biocompatibil-ity, have been found wide potential applications in biomedical fields. For example, theycan be used as magnetic resonance image (MRI) agents, drug delivery carrier, and used inhyperthermia, DNA and protein bioseparation, etc. Along with the development in thesebiomedical fields, the requirements for the synthesis and modification of magnetic nanopar-ticles are improving. Therefore, the Fe3O4 nanoparticles (MNPs), which were researchedmost intensively, were chosen in this thesis.A novel interfacial coprecipitation method was proposed to prepare MNPs. In thisapproach, ferrous and ferric precursors were solved in water, while di-n-propylamine wasdiluted by cyclohexane to be used as precipitation agent. Therefore, the coprecipitationreaction was confined to the interface between water and oil because dipropylamine can notbe solved in water. MNPs were nucleated on the interface and move toward water phase,after they immersed in water completely, they would stop growing because of the absence ofalkali. As a result, about 10±5nm-sized MNPs can be prepared, and they possess relativelygood hydrophicility and stability in water. It is confirmed that the resultant MNPs possessnot only relatively narrow size distribution but also a hydrophilic amine-decorated surface,which provides them with the capability of being further modified.Consequently, we studied the interfacial coprecipitation mechanism by evaluating theeffects of the concentration of precursors and the temperature in preparation. If the concen-tration of Fe2+ is lower than about 7.5 mmol/L, no matter what concentration of the amine is,Fe3O4 would not be synthesized. The interfacial coprecipitation follows the mechanism ofseparated two steps, which is similar to the coprecipitation happens in homogeneous aque-ous medium. When the concentration of iron salt is higher than the critical limit, the sizeof the resultant nanoparticles would not change significantly. The effect of preparation tem-perature is totally different from the coprecipitation in aqueous medium, especially on thesize. In the interfacial coprecipitation, the size would not increase and dispersibility would be modified with the temperature increasing, which is caused by the mechanism of the for-mation of MNPs and their surface chemistry. Our efforts further confirmed the mechanismof formation of the nanoparticles in interfacial coprecipitation method, and the reaction pro-cedures of the coprecipitation, which maybe helpful for the phase control in the preparationof MNPs.Dextran, which is a kind of biocompatible macromolecule was chosen to modify MNPs.Both classical and interfacial coprecipitation were utilized to prepared dextran/MNPs hybridnanoparticles. The in?uences of the mass and molecular weight of dextran on the interfacialcoprecipitation were evaluated, and the comparison of two methods were carried out. Basedon the classical theory of nucleation, it is believed that the macromolecular chains can playthe role as a substrate for the nucleation of magnetite, thus to make the nanoparticles grow ona dextran chain just like pearls on a necklace. Furthermore, these"necklaces"can aggregateas clusters. The classical nucleation theory also shows that the shape and size of nanoparticlecould be affected by the shape of macromolecular chains and the interface tension betweenmacromolecule and MNPs. It was found that the content of dextran of resultant sampleprepared by interfacial coprecipitation is less than that prepared by the classical coprecipi-tation. Meanwhile, the saturation magnetization of nanoparticles prepared by the interfacialcoprecipitation is much higher than those prepared by the classical coprecipitation, which ismainly caused by their difference in dextran percentage.However, some drawbacks were found in the coprecipitation strategy, such as the dis-persibility, crystallinity, etc. Therefore a novel method were put forward for overcomingthese drawbacks, in which diethylene glycol was used as solvent to partly reduce ferrousion. Because of the relative high reaction temperature (about 220℃), the crystallinity of as-prepared nanoparticles was improved. Meanwhile, the dispersibility was also improved orig-inated from diethylene glycol absorbing on nanoparticles surface. In addition, this method isgeneral for many kinds of water-soluble macromolecules to modify the magnetite nanopar-ticles.Microemulsion method was utilized to coat a large mount of MNPs by silica layer.The thickness of coating layer can be easily tuned by the amount of Fe3O4 and silica, andthe resultant particles possess a relative high supersaturation magnetization. However, thecontrol of the size and shape of nanoparticles is difficult, which needs further studies.The transfection of magnetite nanoparticles to cell was evaluated and the results showsthat dextran/magnetite hybrid nanoparticles can be successfully transfected to bone marrowstem cells. When the concentration of magnetite is below 3232μg/ml, they almost have no in?uence on the differentiation of cells. This experiment identify the possibility of furtherresearch on the molecule and cell image and tracking.