Preparation Of Gold-maghemite Nanocomposites

The magnetic carrier-based biosensor technique displays widely promising applications in many fields of biomedical engineering. Magnetic nanoparticles (MNPs) could respond simultaneously as the magnetic field is applied, besides, the MNPs can be modified with different bioactivators such as antibody, antigen, nucleic acid, oligonucleotide and so on. Therefore, the noble such as gold functionalized MNPs are used as carrier and then can be widely applied in immunoassay, purification and separation of nucleic acid, target delivery, enzyme immobilization, cell separation and so on.This thesis reported that the MNPs were used as carrier core, then biocompatibile noble mental gold were modified onto the MNPs for preparing gold-coated nanocomposites. As an important component part of MNPs, Maghemite (γ-Fe₂O₃) MNPs have widely promising applications. Considering the above reasons, our research focused on the preparation of maghemite-based nanocomposites. The thesis includes the following parts:Charpter 1 Magnetic Fe3O4 nanopowders were prepared by modified chemical coprecipitation and then were used as precursors, the maghemite nanopowders were prepared under high temperature oxidation. The properties and structure of maghemite were thoroughly studied under different oxidation temperature. The results revealed that the nanopowders were of average diameter ca.20 nm. Moreover, as the oxidation temperature increases, the precursor nanoparticles gradully changed into maghemite (γ-Fe₂O₃) under proper temperature, and finally becameα-Fe₂O₃ if temperature continues to increase.Charpter 2 Reported silane tailoring of maghemite nanoparticles to obtain amino-coated and thiolated MNPs via 3-aminopropyltriethy loxysilane (APTES) and mercaptopropyltriethoxysilane (MPTES) modification, respectively. Corresponding structure and magnetics properties of the functinalized maghemite were thoroughly studied. The results prove that the surface functionalized MNPs have a slight dimensional increase in average diameter, and retain almost original structures and saturation magnetization (Ms) of parent maghemite.Chapter 3 Described two gold mental functionalized MNPs (γ-Fe₂O₃/Au and Gold-Mag) by sonochemical synthesis and self-assembly methods, respectively. Meanwhile, the structure and magnetic properties of the nanocomposites were investigated. Some results were as follows:1)γ-Fe₂O₃/Au nanocomposites presented paramagnetism at room temperature, and possessed a very high Ms of about 80 emu·g-1. In addition,γ-Fe₂O₃/Au nanoparticles had a steady optical absorption. These combined-properties can readily extend the nanocomposites to further biochemical applications.2) Gold-Mag nanocomposites particles were prepared by self-assembly. The nanoparticles demonstrated well magnetic response and had the similar optical properties of colloidal gold.