| As a new type of luminescent nanomaterial, metal nanoclusters consisting of a small number of atoms possess interesting catalytic and optical properties:small sizes, water solubility, good stability, high emission rates, and low toxity. Metal nanoclusters have recently attracted widespread interest in bioimaging, biosensors, and new catalytic materials. The fluorescence analytical method has many remarkable characteristics, such as high sensitivity, simple operation, and quick response. In this thesis, polyethyleneimine-capped silver nanoclusters are utilized as a fluorescence probe for Sudan dyes, hemin, hemoglobin and pyrophosphate sensing. The specific contents of the study are as follows:Part1Utilizing polyethyleneimine-capped silver nanoclusters as a new fluorescence probe for Sudan I-IV detection in ethanol. In this work, fluorescence resonance energy transfer (FRET) between Sudan I-IV and polyethyleneimine-capped silver nanoclusters (PEI-AgNCs), which are smaller than the critical size for electronic energy quantization (-2nm), is investigated and subsequently utilized for Sudan I-IV sensing in ethanol. The PEI-AgNCs exhibit strong blue fluorescence when excited at375nm, and the fluorescence would be greatly enhanced when the nanoclusters are dissolved in given organic solvents, especially in n-propanol and ethanol. The characteristic emission peak of Ag nanoclusters is centered at450nm in ethanol. Upon addition of Sudan dyes, the fluorescence of PEI-AgNCs can be efficiently quenched. The fluorescence quenching efficiency was proportional to the concentration of Sudan dyes. Thus, precise quantification of Sudan I-IV can be made. Under optimum conditions, this fluorescence method shows a wide linear range of0.4-25μM Sudan I,0.4-30uM Sudan II,0.2-20μM Sudan III, and0.2-25μM Sudan IV, with the corresponding detection limits (3s/slope) of11.0,12.2,8.0, and7.6nM, respectively. Using commercial chilli powder as a model sample, detection of Sudan I-IV could be made with satisfactory results. Furthermore, the sensing mechanism for detection of Sudan dyes is discussed.Part2Using fluorescent polyethyleneimine-capped silver nanoclusters to detect hemin and hemoglobin. Hemoglobin(Hb) and hemin, which is the prothetic group of Hemoglobin, are found to quench the fluorescence of PEI capped silver nanoclusters with good sensitivity. The calibration equations are (1-I/I0)hemin=0.000429Chemin+0.00816, and (1-I/I0)Hb=0.00114CHb+0.01516over the corresponding linear range of0.02-1and0.03-0.3μM, respectively. The detection limits (3s/slope) are calculated to be3.22and5.25nM, respectively. UV-vis absorption spectroscopy, fluorescence spectroscopy, infrared spectroscopy, and cyclic voltammetry were utilized to study the quenching mechanism, which was supposed to be based on electron transfer from excited PEI-AgNCs to FeⅢ/FeⅡ redox couple.Part3Selective signal-on fluorescent sensing for pyrophosphate based on the polyethylemeimine-capped silver nanoclusters-copper ions system. A simple and selective fluorescence method was proposed for selective pyrophosphate sensing. The fluorescence of the silver nanoclusters was quenched by copper ions, and the fluorescence was recoverd in the presence of pyrophosphate. Cupric amine can be formed between copper ions and amine groups at the surface of PEI capped AgNCs and subsequent energy transfer from the AgNCs to the cupric amine coordinates occurs, leading to fluorescence quenching of AgNCs, while the fluorescence of the PEI capped AgNCs restored in the prescence of pyrophosphate ion (P2O74-, PPi). PPi chelated with Cu2+, resulting in Cu2+being removed from the surface of PEI capped AgNCs and fluorescence being restored. The linear equation was calculated as (I/I0-1)PPi=0.0264C PPi+0.1079, with the corresponding detection limit (3s/slope) of50nM. |
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