Preparation Of Fluorescent Sensors And Its Application In Visual Detection

Fluorescence analysis method has the advantage of less sample injecting, high sensitivity and easy to operate, which has been widely used in various fields of inorganic, organic, pharmaceutical, biochemical and clinical testing. In addition to the traditional organic fluorescent dyes-based probe used in the fluorescence analysis, a variety of novel nanomaterials have been developed and used for new analysis technique in recent years. The booming of fluorescent materials contributes to the development of fluorescence analysis method and makes it the most widely used technique of numerous of detection and analysis techniques. In this paper, quantum dots fluorescent probe and simple organic molecule were used to quantitative detect trace nitric oxide and zinc ions, respectively. The strategy we proposed in this paper was proved to be useful in environmental analysis.In chapter1, we mainly introduce the photoluminescence theories and methods of fluorescence, newly developed nanomaterials and most used method for detection of free radical species.In chapter2, a novel quantum dots (QDs) grafted with ferric dithiocarbamate complex layers (QDs-Fe(Ⅲ)(DTC)3) were fabricated and demonstrated to be selectively reactive to nitric oxide. The as-prepared probe shows good water solubility and photostability. In this part, first, we synthesized amino-coated polymer, then the amino-coated polymer was introduced to the surface of CdSe/ZnS, forming the water soluble quantum dots. The dithiocarbamate (DTC) was covalently conjugated to the amine-coated QDs by condensation reaction of the carboxyl in DTC and the amino polymer in surface of QDs. The weak fluorescence QDs-Fe(Ⅲ)(DTC)3was attributed to the energy transfer between CdSe/ZnS and Fe(Ⅲ)(DTC)3complex at surface of the functionalized quantum dots. Nitric oxide could greatly turn on the fluorescence of QDs-Fe(III)(DTC)3by displacing the DTC in the Fe(III)(DTC)3accompanied with reducing Fe(III) to Fe(II), thus cutting off the energy transfer way. The detection limit for nitric oxide was estimated to be3.3μM and the specific detection was not interfered by other similar reactive oxygen species. Moreover, the probe was demonstrated for the sensing of gaseous nitric oxide and the visual detection limit was as low as10ppm, showing the potential for sensing nitric oxide by the naked eye.In chapter3, we report that the simple Schiff base molecule, 2-(((pyridin-2-ylmethyl)imino)methyl)phenol, can efficiently chelate zinc (II) to produce highly fluorescent complex, ML2, which could be useful in the development of turn-on fluorescence detection of zinc (II). The compound initially shows very weak fluorescence, however, the coordination with zinc ion inhibits the C=N bond isomerization and subsequently enhances the fluorescence efficiency. Based on the turn-on fluorescence, the limit of detection for zinc (II) was measured to be62nM, which is lower than the allowable level of zinc (～70μM) in drinking water set by U.S. Environmental Protection Agency. With the aim of visual detection, we tried to make fluorescence test strips by dropping the probe solution in silica gel plates and demonstrated the application for visualization of zinc screening in water and aerosol samples. The visual limit of test strips detection was estimated as low as9μM.