Synthesis Of Hollow And Doped Quantum Dots Nanomaterials And Its Application In Food Detection

Nowadays, nanomaterials have attracted many researchers’attentions due to their special properties. Quantum dots (QDs) nanoparticles, because of their unique optical properties such as broader excitation spectrum, narrower emission spectrum and longer lifetime, become one of the hottest researches in nanomaterials field. Lots of researchers do their best to explore simple and effective methods to synthesize QDs nanomaterials with appropriate size, uniform morphology and good biological compatibility for desired applications. The hollow structured QDs materials integrates photoluminescence property of QDs and tailored structure of hollow nanomaterials. The quantum confinement and photocatalytic effect of hollow structured QDs materials are more superior, so they have broad application prospects in nanomaterials field. Doped quantum dots nanomaterials, as a kind of new materials, can reducing the self quenching phenomenon of QDs materials and improving the thermal and photochemical stability of nanomaterials. As a result, doped quantum dots nanomaterials have been widely applied in solving practical problems.Sudan dyes (Sudan Ⅰ, Ⅱ, Ⅲ, and IV) are phenyl-azoic derivatives with an orange-red appearance and extensively using as color waxes, oils, petroleum, solvents, and polishes. The aniline and naphthol, which will be produced during the Sudan dyes metabolic processes, can attack the hepatocytes and lead to toxic hepatic disease. European Union and our country have prohibited Sudan dyes using in various processed foods. However, A variety of foodstuffs contaminated with Sudan dyes (particularly Sudan I) have been detected. So, the accurate and reliable methods for the determination of Sudan dyes in foodstuff are required and helpful for the assurance of consumer healthiness.In view of this, a straightforward one-step route is developed to synthesize hollow CdSe nanospheres with adjustable inner and outer diameters. Meanwhile, a novel luminescence sensing system is also designed for Sudan dyes detection base on the quenching fluorescence of oleic acid-functionalized Mn-ZnS quantum dots. This dissertation consists of three chapters:Chapter1The properties, preparation and application potential of nanomaterials, especially quantum dots, are briefly summarized. The preparation and application of hollow quantum dots nanomaterial are described, in detail. And, the application of luminescence quantum dot in biology and chemistry is also discussed.Chapter2In this study, the desired hollow and grain-like CdSe nanospheres are synthesized by expediently regulating the reaction conditions. Especially, this chapter focuses on studying the influence of solution pH on the morphology and optical characteristics of the hollow CdSe nanospheres, and discussing the formation mechanism in detail. The results suggest that synchronous formation rate of initial CdSe nanocrystals and H2bubbles is the key to prepare hollow nanospheres. The salient advantages of the present work are as follows:(1) Na2SeO3is used as Se source, which avoiding an extra process to synthesize the unstable Se precursor;(2) all experiments are perform under open air condition instead of inert atmosphere protection;(3) citrate is used as stabilizing reagent, which is low cost, nontoxic and widely existing in nature;(4) the experiments proceeding in aqueous medium, so reducing the pollution to the environment;(5) the morphology, microstructure and size of as-prepared hollow CdSe nanospheres can be easily controlled by only changing the solution pH or other experimental conditions, and the auxiliary post-treatment is not needed.Chapter3A novel luminescence sensing system is designed for Sudan dyes detection based on the quenched fluorescence of oleic acid-functionalized Mn-ZnS quantum dots. The Sudan dyes can quench the fluorescence signal of Mn-ZnS QDs due to the so-called inner filter effect. It is demonstrated that this facile methodology can offer a rapid, reliable and selective detection of Sudan dyes, and the detection limits of Sudan I, II, III, and IV are24.6,32.7,2.1, and3.2ng/mL, respectively. Sudan dyes are mainly detected in hot chili sauce, sausage, egg and tomato sauce, and Sudan I is chosen as spiked substance owing to the widely use as a coloring matter among Sudan dyes in many industrial and daily used products. Furthermore, the average recoveries of Sudan I from the standard fortified blank samples are in a range of93.0-107.0%, and the relative standard deviations (RSD) are lower than2.8%(n=3). The salient advantages of the present work are as follows. Firstly, it is the first time to apply Mn-ZnS QDs luminescence sensing system to detect Sudan dyes. Secondly, no complex process and expensive instruments except fluorescence spectrophotometer are needed. What’s more, the interferences from some hydrophilic chemicals such as salts are avoided due to the detection progress conveying in cyclohexane system.