Composite Magnetite Nanoparticles' Preparation And Preliminary Biosensing Application

At present, considerable effort has been devoted to tailor the surface properties of the nanoparticles in order to meet their application requirement, which is"Nanoengineering of particle surfaces". In addition, as one of the important nanomaterials, magnetite nanoparticle has lots of promising applications due to their properties. Considering the above reasons, our research focused on the preparation and application of magnetite-based nanocomposites, and the thesis consists of the following contents:Chapter 1 summarized magnetic nanoparticles'preparation; their surface functionalization and their latest advances for biosensing application.Chapter 2 and chapter 3 reported the magnetite nanopowders preparation and related surface modification, and corresponding properties and structure were investigated. Silane bridged surface tailoring was employed to obtain amino-coated and thiolated magnetite NPs, corresponding properties and structure were compared. And major results were detailed as follows:1. Magnetite nanopowders of ca. 25 nm were prepared by modified chemical coprecipitation, corresponding properties and structure were thoroughly studied when they were treated under different drying conditions. The results revealed that the nanopowders after vacuum drying tended to agglomerate more easily than others when the grain average diameter was decreased because of the evaporation of the surface and inter-particles adsorptive water, but the structure and morphology were maintained better than others after ambient air drying. Among all drying treatments samples, the magnetic property was maintained best when the vacuum drying temperature was kept at T=70℃. Thus the drying treatments and methods were closely related to morphology and magnetic property of the magnetite nanopowders.2. Silane bridged surface tailoring of magnetite was employed to obtain amino-coated and thiolated magnetite NPs via corresponding 3-aminopropyltriethyloxysilane (APTES) and mercaptopropyltriethoxysilane (MPTES) modification, respectively. The results prove that the surface functionalized magnetic particles have slight dimensional increase in average diameter, and the functionalized NPs retain almost original saturation magnetization. The APTES modification is prone to maintain the morphology of the parent Fe₃O₄ NPs as compared with the MPTES coating; the MPTES coating has a more outstanding hypochromic effect comparably though it caused a slight decrease on the saturation magnetization.Chapter 4 described a new approach to prepare two noble mental functionalized magnetic nanoparticles (Fe₃O₄/Au and Fe₃O₄/Pt) by sonochemical synthesis. Meanwhile, their optical and magnetic properties were investigated. Based on a specific reaction of sodium formate and silver acetate, the Fe₃O₄/Ag magnetic nanoparticles were successfully synthesized, and the corresponding structure and properties also were investigated. The diameter of three magnetite metallized nanocomposites was around ca. 30 nm. The three nanoparticles were characterized and proven some results follows:1. Magnetic nanoparticles of Fe₃O₄/Au presented better paramagnetic properties at room temperature, and possessed a very high saturation magnetization of about 63 emu·g^-1. In addition, Fe₃O₄/Au nanoparticles had a steady optical absorption. These properties can readily extend to biochemical applications.2. The Fe₃O₄/Ag magnetic nanoparticles were prepared by the specific reaction of sodium formate and silver acetate, and they presented obvious characteristics of core-shell structure, and possessed steady optical properties, thus their preparation is facile.3. It is hardly obtained Fe₃O₄/Pt magnetic nanoparticles via traditional methods, but the sonochemical method is a time-consuming and effective alternative. The sonication was beneficial to form new phase, and had a shear effect for agglomeration, which was prone to prepare the high monodispersive nanoparticles. As-prepared Fe₃O₄/Pt magnetic nanoparticles through sonolysis processed a good dispersion, and their morphology was uniform.Chapter 5 demonstrated a new approach to prepare gold-support heterogeneous magnetite nanoparticles deposition films by aqueous synthesis. The films demonstrated a porous morphology of high surface area-to-volume ratio because of close-packed functionalized magnetite NPs with the diameter of ca. 500 nm on the reduced gold substrate, and their saturation magnetization is determined about 12.3 emu·g^-1. They can be possibly used in many regions such as gas sensor, electrode, etc. Chapter 6 reported that the Fe₃O₄/Au magnetic nanoparticles were used as carrier, and then antibody were immobilized onto the Fe₃O₄/Au nanoparticles for preparing the Fe₃O₄/Au-IgG composites. An enzyme immunoassay principle for detecting the antibody was proposed. After antibody loading, the results shown that the Fe₃O₄/Au nanoparticles bio-composites processed a high immobilization capacity of antibody. In addition, they still retained a very high saturation magnetization; these advantages permit possibilities of biomolecules'separation and detection.