Fabrication Of Colorimetric System And Its Application In The Detection Of Tea

Tea is one of the most popular beverage in the world and its rapid discrimination and appreciation are show great importance for consumers. Up to date, the determination of teas mainly based on large-scale equipment, including High Performance Liquid Chromatography(HPLC), Near Infrared Spectroscopy(NIR) and Gas Chromatograph-Mass Spectrometer(GC-MS). These conventional analytical technologies offer highly sensitive and accurate assays of teas, but also suffer fro m many disadvantages such as time-consuming procedures, the use of bulk and expensive instruments and requirement of skilled personnel. In view of those problems, colorimetric sensor arrays based on molecular recognition, which offer the in situ analysis, real-time detection, high sensitivity and easy operation to deal with the dilemma and therefore attracted growing attention, including field of teas differentiation. Nevertheless, they are poor in selectivity and capacity of disturbance, which limits their in-field applications. Herein,a cross-response colorimetric sensor array was successfully fabricated for the simple, rapid, sensitive discrimination of species and quality of teas based on their amino acids and polyphenols. Additionally, a paper-based colorimetric sensor was also established, which was successfully utilized in the quantitative determination of polyphenol, providing more accurate information on evaluation of plant-derived drinks( such as teas and red wine). All the features demonstrate that the developed colorimetric sensor array shows a great potential in real application in the field of food security and environmental monitoring. In this dissertation, the work can be summarized as follows:(1) Two specific and a broad recognition systems were chose by indicator displacement assays(IDA), 3 dyes and pigments with various concentrations and ratios were selected to construct a 3×3 sensor array for the discrimination of 7 amino acids abundantly existed in teas and 14 teas. These amino acids and teas, including species and geographical origin, were differentiated without any misclassification using the hierarchical cluster analysis(HCA) and principal component analysis(PCA).(2) Hydrothermal reaction was applied to synthesize cerium oxide(CeO2) nanoparticles and zinc silicate nanoparticles with properties of redox and absorption capability, respectively. A liquid sensor arraybased on the complexation among polyphenol, ferric iron and thiocyanide, and the strong reduction of polyphenolswas successfully fabricated in present work. The interference of test results resulted fro m thiocyanatoiron was removed by zinc silicate and the sensibility of the as-prepared sensor array was also improved. Then the experimental results showed that sensor array displayed excellent differentiate capacity for 5 polyphenol a nd 14 teas. Furthermore,no errors in classification can be observed even for 21 teas in 105 trials. And then, the filter paper-based sensor functionalized with zinc silicate nanoparticles/thiocyanatoiron was fabricated for tea polyphenol analysis. 4 teas was discriminated successfully with low detection limit of 2.1 ?M.(3) The colorimetric multilayer sensor was fabricated by alternative assembly of chitosan layer, Fe3+ complexes and alginate sodium layer on filter paper modified with Ti O2 membrane for sensitive detection of two typical polyphenols(gallic acid and tannic acid). The research results displayed that the surface of as-prepared sensor exhibits uniform color without any disturbance from background, with wide linear responses to gallic acid and tannic acid in the ranges of 2 ?M- 6.1 mM and 2.3 ?M- 5.2 mM, and the calculated detection limitswere 1.2 ?M and 0.2 ?M, respectively. Its further application for discrimination plant-derived drinks including 5 red wine samples and Chinese green tea samples was much easiler and faster than conventional folin-reagent method. Statistical analysis including HCA and PCA showed that it realized successful discrimination within five closely alike red wines and five Chinese green teas of different quality grades.