A Study On The Novel Fluorescence Method For Environmental Analysis Based On Polyethyleneimine

The objects of environmental analysis and monitoring are often trace substances. It needs space and timeliness. Thus, the demand of analytical method is higher and higher in this field. The traditional detection methods for environmental analysis were reported, such as chromatography, atomic absorption spectroscopy, immunoassay and biological chip and so on. But some shortcomings exist in the pretreatment of the samples, such as reagent-consuming and time-consuming. They are unable to satisfy fast and accurate determination. It is difficult to achieve effective and efficient analysis of detection. Compared with them, the fluorescence analytical method has some remarkable characteristics:high sensitivity, simple operation process, few reagents, rapid analysis speed, simpleness and convenience, and demonstrates its unique superiority in the field of environmental analysis. On the other hand, in environmental analysis, the design of fluorescence molecular probes, and fluorescence analysis methods have very wide applications. Samples originate from water, soil, atmosphere, plants, animals, and so on. Therefore, the fluorescence analysis method in the application of environmental analytical chemistry is ascendant.Polyethylenimine (PEI), a cationic water-soluble polymer, which is composed of a large number of amine groups, exhibits outstanding adsorption ability for different substances and can act as an adsorbent for some heavy metal ions via chelation. Moreover, it is well known that PEI has been used for a wide variety of biological applications. At the same time, PEI contains a large number of adsorbing units, and results in the change of fluorescence signals by transferring energy. Hence, PEI can be used as the optical platform in highly sensitive chemical and biological sensors. Furthermore, PEI can be associated to oligonucleotides to promote their transfection both in vitro and in vivo. It is reported that the PEI is extensively used in a wide range of industrial, technological and biologic fields. The properties of PEI have been greatly studied and are relatively well understood. Therefore, PEI can be used for biological and environmental applications.In this thesis, fluorescence analysis method is used to set up several new fluorescent platforms based on PEI, which are applied to glucose, heavy metal ion Cu2+, hydrogen peroxide and sodium dodecyl sulfate (SDS) analysis. This thesis mainly contains the content of two following respects:1. The basic principle of fluorescence and fluorescence analysis were summed up. Types and applications of some fluorescence probes were reviewed in details, and the properties and applications of PEI were summarized. Meanwhile, some analytical methods of objects in our study were reviewed, too.2. Exploration of several new fluorescence methods for environmental analysis based on polyethyleneimine:(1) Polyethyleneimine-capped silver nanoclusters as a fluorescence probe for sensitive detection of hydrogen peroxide and glucose. In this work, we developed a new method for simple and direct synthesis of highly fluorescent and water-soluble Ag nanoclusters. The PEI-Ag nanoclusters have an average size of2nm and show a blue emission at375nm. The photostable properties of the PEI-Ag nanoclusters were examined. It is found that the fluorescence of PEI-Ag nanoclusters is quenched linearly by H2O2in a certain concentration range. Moreover, glucose can be oxidized by oxygen (02) in the presence of glucose oxidase (GOx) via the following reaction:glucose+O2+H2O�'GOx gluconic acid+H2O2. Then, the concentration of glucose can be obtained by detecting the amount of the enzymatically generated H2O2. The quenching mechanism might be attributed to oxidation of Ag nanoclusters in the presence of H2O2. Thus, a cost-effective and sensitive fluorescence sensor for the determination of H2O2and glucose was constructed.(2) Efficient fluorescence "turn-off" method for Cu2+detection based on fluorophore-labeled DNA and polyethyleneimine. In this study, the6-carboxyfluorescein (FAM)-labeled DNA showed weak fluorescence at530nm in a pH4.8acetic acid-sodium acetate buffer solution. When the polyethyleneimine was introduced to the FAM-labeled DNA solution, the fluorescence signal was greatly amplified. Hereafter, upon the addition of Cu2+, Cu2+can be captured by the amino groups of the polyethyleneimine to form a complex, resulting in a strong quenching of the fluorescence of FAM-labeled DNA/polyethyleneimine via a fluorescence resonance energy transfer effect. An appropriate selection of the experimental conditions ensured the sensitivity of the analytical method. Under optimized condition, the system displayed a detection limit as low as20nM toward Cu2+and a good selectivity over other metal ions. The method has been successfully applied to the detection of Cu2+in real samples with satisfied recovery and accuracy. Overall, these results demonstrate that this method is capable of being a simple, practical, and reliable method in the detection of Cu2+and has a great promise for environmental applications.(3) Efficient fluorescence "turn-on" method for sodium dodecyl sulfate based on eosin Y and polyethyleneimine. In this work, a novel sensing system has been designed for the sodium dodecyl sulfate (SDS) detection based on the recovered fluorescence signal of eosin Y and PEI complex. First, the eosin Y shows strong fluorescence in pH4.0HAc-NaAc buffer solution. Then, adding PEI into eosin Y solution, PEI could bind the eosin Y to form the eosin Y/PEI complex and then the following photoinduced electron transfer results in high-efficiency fluorescence quenching of eosin Y. When SDS with more powerful affinity (strong competitor) for PEI than that of eosin Y (weak competitor) was added in the eosin Y/PEI system, PEI will preferentially adsorb the SDS over eosin Y to form PEI/SDS complex, then eosin Y is gradually desorbed from the eosin Y/PEI complex, inducing the fluorescence recovery. Thus, a rapid, reliable, selective, and high sensitive detection methof for SDS has been develpoed. Furthermore, the method has been successfully applied to the detection of SDS in real samples with satisfied recovery and accuracy.