Preparation And Application Of Organic-inorganic Composites Based On Natural Polymers And Gold Nanoparticles

This thesis focuses on the preparation of organic-inorganic composites based on natural polymers, including hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), chitosan (CS) and gold nanoparticles (GNPs). There are three sections in this thesis, that is, reduction of chloroauric acid into GNPs by hydroxyethyl cellulose under UV irradiation, evolution of GNPs prepared in hydroxypropyl cellulose solutions under UV light irradiation and the construction of a new glucose biosensor based on chitosan, sodium alginate (SA), GNPs and glucose oxidase (GOD) through layer-by-layer assembly.In the first section, preparation of GNPs in HEC solutions was illustrated. The reduction process was characterized by UV–vis spectra, FTIR, pH tracing and TEM. Reduction of HAuCl4 to gold nanoparticles almost completed within about 60 min. FTIR analysis confirmed the oxidation of HEC, which provided electrons for reduction of gold ions. Both particle size and the UV–visible absorption peak were dependent on the HEC concentration. The effects of HAuCl4 concentration were also studied. The particles with obtuse triangle, hexagon and round shapes were synthesized and in situ stabilized by the biopolymer.In the second section, preparation of GNPs in another natural polymer, HPC solutions under UV irradiation was investigated. An apparent evolution of GNPs was observed. FTIR analysis indicated that HPC was easy to be oxidized under UV light irradiation. Results obtained from intrinsic viscosity measurement showed that molecular mass of HPC dropped quickly under UV irradiation. Oxidation of HPC not only provided free electrons to reduce gold ions, but also lead to the breakage of HPC molecular chains. It was supposed that the stability of HPC to gold nanoparticles was weakened due to the breakage of HPC chains, which further resulted in the evolution, that is, continuous aggregation of gold nanoparticles.In the last section, a new glucose biosensor based on CS, GNPs and SA modified glass carbon electrode was fabricated, and the properties of the biosensor were characterized. CS was chosen as the matrix material and was deposited on the surface of the electrode to form a nanofilm. Then, GNPs were immobilized on the film through an electrochemical process. Lastly, a mixture solution of SA and GOD was dropped onto the electrode to construct the glucose biosensor. Thanks to the strong electrostatic interaction between positively charged CS and negatively charged SA, GOD was steadily immobilized on the surface of the electrode. At the same time, the presence of GNPs enhanced the electronical conductivity and sensitivity of the biosensor as well as biocompatibility to the enzyme. The response time of the biosensor was less than 10s.