| In this thesis, gold nanoparticles (Au-NPs), which have unique optical properties, have been investigated. Thus, new analytical methods based on the LSPR absorption and scattering properties of Au-NPs have been established. The mainly points are as follows:1. An ethylenediamine terminated (3-cyclodextrin derivate was synthesized according to the literature. Because of the affinity of Au-N atom, the amino group can capture the dissociative gold ions. By using additional reductant, we can obtain the gold nanoclusters whose size was relative to the size of the cavity ofβ-cyclodextrin. Different reducing capability of the reductant would make the fluorescence emission of the acquisition solution be different. For example, the gold nanocluster was dominated in Au7 by employing sodium borohydride which has a strong reducing ability, the obtained solution which was reduced by ascorbic acid, a mild reducing agent, contained three kinds of emission wavelength, and the emission intensity of 470 nm is the strongest. The quantum yield of the obtained gold nanocluster solution is 5.2%. The influence of reaction time, the concentration of template and various reductant were investigated. This research will enhance the potential application of gold nanoclusters in biochemical analysis and fluorescence resonance energy transfer.2. According to the energy transfer between fluorescent dye and gold nanoparticle surface, sensitive detections of amino acid and aqueous lead were developed. The research shows, when the fluorescent dye, such as Rhodamine B, which was absorbed on the surface of citrate stabilized gold nanoparticles through the electrostatic interaction was excitated by the light, the fluorescence of the Rhodamine B gets quenched because of the occurrence of surface energy transfer from the fluorophore of Rhodamine B to the gold nanoparticles. However, with the addition of cysteine, the strong covalent combination between the mercapto group of cysteine and gold nanoparticles drives Rhodamine B molecular apart from the gold nanoparticles surface, which reduce the energy transfer efficiency and result in a significantly increase of fluorescence of the solution. It was found that the fluorescence gets increased linearly with the concentration of cysteine ranging from 0.025μmol/L to 4.5μmol/L. This phenomenon allows sensitive detection of cysteine with a limit of detection of 8.0 nmol/L (3σ). Other 19 kinds of natural amino acids have a weak influence on the surface energy transfer. According to the same principle, the efficiency of surface energy transfer can be controlled through the conformation transition of thrombin-binding aptamer (TBA) induced by lead ion, which changed the distance between gold nanoparticles and the dye molecule. This make the lead ion-dependent conformation transition process can be monitored based on the change of the fluorescent intensity. The sensitive detection of lead ion with a limit of detection of 10 nmol/L (3σ) and linear range from 12.5 nmol/L to 100nmol/L was provided.3. Both localized surface plasmon resonance light scattering (LSPR-LS) and dynamic light scattering (DLS) techniques are powerful tool to monitor the aggregation of particles. With the development of nanosciences, both of them have been widely used for quantitative purposes with high sensitivity. In this contribution, we make a comparison of the two light scattering techniques by employing gold nanoparticles (AuNPs) aggregation induced by mercuric ions. It was found that citrate-stabilized AuNPs get aggregated in aqueous medium in the presence of mercuric ions through a chelation process, resulting in greatly enhanced LSPR-LS signals and increased hydrodynamic diameter. The enhanced LSPR-LS intensity (ΔI) is proportional to the concentration of mercuric ions in the range of 0.4-2.5μmol/L following the linear regression equation ofΔI=125.7+569.5c with the correlation coefficient of 0.992 (n=6) and the limit of determination (3σ) about 94.3 nmol/L However, the increased hydrodynamic diameter can be identified by the DLS signals only with a concentration of Hg2+ beyond 1.0μmol/L, and a linear relationship between the average hydrodynamic diameters of the resulted aggregates and the concentration of Hg2+ can be expressed as d=-6.16+45.9c with correlation coefficient of 0.994. In such case, LSPR-LS signals were further applied to the selective determination of mercuric ions in lake water samples with high sensitivity and simple operation.4. We synthesized gallic acid-capped gold nanoparticles (GA-AuNPs) by reducing chloroauric acid trihydrate using gallic acid in the alkalescent condition. The average diameter of the synthesized GA-AuNPs is about 15 nm and size distribution is narrow. Because of the rigid structure of gallic acid molecule, it can selectively bind lead ions. The enhanced LSPR-LS intensity (ΔI) caused by the increase of aggregation is proportional to the concentration of lead ions in the range of 0.2-1.0μmol/L. A LSPR light scattering method for detecting aqueous lead ions based on gold nanoparticles was developed. This research promoted the application of LSPR light scattering to common biochemical analysis.In conclusion, a series novel analytical methods based on localized surface plasmon resonance properties of gold nanoparticles were established in this thesis. A few-atoms gold nanoparticle was synthesized and its fluorescene property was also investigated. This will improve the the application of AuNPs in optical analytical chemistry.
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