Study On The Preparation And Applications In Spectral Analysis Of Gold Nanoparticles

Owing to the special optical and electrical properties, good catalytic activity and favorable biocompatibility, gold nanoparticle and its thin films have extensive application prospects in fabricating nonlinear optical and microelectronic devices, catalyzing, analytical science and etc. The new preparation method and applications in spectral analysis of gold nanoparticles were studied in this dissertation.The dissertation includes six parts:Chapter 1: The preparation, assembly, and analytical applications of gold nanoparticles were reviewed in detail.Chapter 2: A facile method for the preparation of gold nanoparticles in aqueous solution was developed by using glycosaminoglycan-heparin as reducing agent and HAuCl₄ as precursor. The properties of gold nanoparticles were characterized by UV-vis spectroscopy, resonance light scattering spectroscopy (RLS), transmission electron microscopy (TEM) and electrophoresis technology. The effects of reactant concentration ratio for the preparation of gold nanoparticles were investigated. The results showed that the gold nanoparticles carried negative charges in the aqueous solution and the size and shape of the gold nanoparticles could be controlled by changing the concentration ratio of the heparin and the HAuCl₄. Preparing gold nanoparticles in this way had environment-friendly characteristics, and it was a green preparation method.Chapter 3: The monolayer and multilayers of gold nanoparticles were constructed on the glass by electrostatic self-assembly method. The morphology and optical properties of thin films were characterized by AFM, UV-Vis spectroscopy and Raman spectroscopy. Plasmon absorbance peak of gold nanoparticles thin films were broad and red-shift compared with the gold nanoparticles in aqueous solution. As the layer increased, this feature strengthened and the peak shifted to longer wavelength. AFM images showed a close-packed array of gold nanoparticles in monolayer with small region defects. The 2-layers showed that the interparticle distance was very small to form a compact, continuous film on the glass slide. The roughness of gold nanoparticles monolayer was bigger than the 2-layers's. The measurements of the Raman spectrum of crystal violet indicated that the gold nanoparticles self-assembly thin film has the high SERS activity. Therefore, it can be used for the study of SERS and fabricating chemical sensors.Chapter 4: The Spectroscopic characteristic of interaction between fluorescein sodium and gold nanoparticles with different sizes was investigated via UV-vis and fluorescence spectrophotometry. It was found that gold nanoparticles quench the fluorescence of fluorescein sodium in water. The quenching mechanism and size-dependence quenching effect were discussed. The results showed that the degree of quenching was concerned with the size of gold nanoparticles. The smaller gold nanoparticles were efficient quenchers than the larger ones due to larger surface areas. It showed that the gold nanoparticles quenching of fluorescein sodium follows Stern-Volmer relation for plots of F₀/F against gold nanoparticles concentration. In additation, the results showed that the quenching of fluorescein sodium by gold nanoparticles was a dynamic quenching, and the quenching constants respectively were 1.5×10⁴ L/mol (25℃) , 1.7×10⁴ L/mol (35℃) and 1.9×10⁴ L/mol (45℃) .Chapter 5: It was found that the gold nanoparticles have strong catalysis for the redox reaction between methylene blue and NaBH₄. The catalytic reaction kinetics was studied and the catalytic reaction mechanism was investigated. The effects of reaction temperature, solution acidity and different kinds of surfactants were discussed. It was indicated the gold nanoparticles provided a substrate via which electron transfer can easily occur between the reactants. The rate of catalytic reaction increased linearly with the concentration of catalyst for the reaction system catalyzed by the gold nanoparticles in the range of 1.47×10^-7—2.36×10^-6 mol/L. A change of the initial rates was observed in cationic and nonionic surfactants above and below the critical micelle concentration. Anionic surfactants restrained the catalytic reaction due to the association reaction of surfactants with methylene blue.Chapter 6: A sensitive method for detecting Vitamin B₄ was proposed by resonance light scattering (RLS) spectroscopy with gold nanoparticles as probe. In a weak acid medium (pH4.2), the resonance light scattering spectrum of gold nanoparticles had a maximum peak at 635 nm and the RLS intensity was enhanced by trace amount of Vitamin B₄ due to forming aggregate with bigger diameters between gold nanoparticles and Vitamin B₄. The RLS spectral characteristics of gold nanoparticles-Vitamin B₄ system and the optimum conditions of the reaction were investigated. The mechanism for the enhancement of RLS was also discussed. The results showed that the enhancement of the RLS signal (â–³I) was proportional to the concentration of Vitamin B₄ in the range of 0.1—5.0μg/mL. The corresponding detection limit (3σ) was 12ng/mL, and the RSD was 2.2 %. The method was applied to the determination of Vitamin B₄ in tablets with satisfactory results.