| Among more than twenty amino acids which make up proteins, cysteine is the only one with a thiol. It plays a crucial role both in biological process and the control of human body disease, thus its detection and application arouse people's widespread concern. The interaction of cysteine and heavy metal ions is primarily based on the different combining ability between thiol and heavy metal ions, and it has been reported that the thiol of cysteine can be selectively oxidated by copper ions. The present thesis intends to apply the interactions between cysteine and heavy metal ions to their analyses and detections. In this way, it not only expands the application field of cysteine, but also sets up a new method to detect cysteine. The following three parts are included in the thesis:(1) The interaction between cysteine and copper ions can be utilized to analyze and detect copper ions(Cu2+). The study has found that through the combination of Au-S covalent band, cysteine is able to induce the aggregation of CTAB-coated gold nanoparticles (AuNPs) in the acidic conditions, resulting in plasma resonance absorption changes of AuNPs. However, due to its selective oxidation of cysteine's thiol, Cu2+ are capable of preventing the formation of Au-S covalent bond to restrain the aggregation of AuNPs. Therefore, with AuNPs acting as the visualization indicator of oxidating cysteine by Cu2+, a colorimetric method is established for the determination of Cu2+ in aqueous solution. In optimal experimental conditions, a good linear relation can be observed between the ratio of absorbance value at 525 nm and the concentration of Cu2+ in the range of 8.0×10-8～2.0×10-6 mol/L:the correlation coefficient (r) is 0.9962, while the detection limit (3σ/k) is 1.5×10-9 mol/L. The proposed method has been successfully applied for the analysis of synthetic mixtures and water samples.(2) Fluorescence detection of silver ions and cysteine based on unlabeled DNA. Sybr Green I is usually used as the fluorescent indicator of PCR expanding reaction since it can alternatively distinguish between single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). The paper designs a C-base riched ssDNA,and form a similar structure of dual-DNA by the C-Ag-C complex constructed of the combination between silver and C-base. In the presence of cysteine, it will compete with C-base to restrain the formation of C-Ag-C complex. Consequently, with Sybr Green I being the fluorescent indicator, a unlabelled DNA method is established for simultaneously detecting cysteine and silver ions (Ag+) with high selectivity and sensitivity. The following results have been got:the linear range of silver is 12.5-450 nmol/L, its correlation coefficient (r) 0.9962 and its detection limit 1.25 nmol/L; the linear range of cysteine is 1.25-425 nmol/L, its correlation coefficient (r) 0.9962 and its detection limit 0.125 nmol/L(3) Detection of cysteine based on the Recovered Fluorescence of the gold clusters-Hg(II) System. Mercury ion is a kind of good fluorescence quencher which can extinct the fluorescence of small fluorescent molecules, organic dyes, quantum dot, etc. Acting as fluorescence nanomaterials with their excellent optical properties, gold clusters have attracted people's great interest. Owing to the interactions of Hg2+-Au+ between Hg2+ and gold clusters which are synthesized by biological macromolecules of Bovine Serum Albumin (BSA), the fluorescence of gold clusters will be quenched by mercury ions. After that, if we make use of the strong combination between thiol and mercury ions, it is confine the interactions between gold clusters and Hg2+. So the fluorescence of gold clusters can be recovered. Therefore, based on this theory, a new method of detecting cysteine with high selectivity is constructed.
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