| Pesticides play a very important role in the agricultural production process in our country. But along with increase of pesticide usage, pesticides brought benefits to agricultural production and economic development. However, they threatened to human health seriously. Nowadays, organophosphorus pesticide are the most used pesticide category. They are also known as one of the most toxic substances and widely used as pesticide and insecticide in modern agricultural production. According to report, five hundred thousand tons of organicphosphorus pesticide were released into the environment, food and water supplies all around the world every year, which do great harm to human health, ecosystems, and homeland security. They enter the human body through contacting and breath, etc and then recyle to the body organs and tissues. Organophosphorus pesticides toxicity in the central and peripheral nervous system have irreversible inhibition to acetylcholine enzyme activity, which result in the abundant accumulation of neurotransmitter acetylcholine in the body. As a result, they lead to organ failure and eventually and the death of the animal body.At present, lots of methods have developed for the quantitative detection of organophosphorus pesticides, including gas chromatography (GC), fluorescence and high performance liquid chromatography (HPLC). But some of them required expensive instruments or consume large amounts of samples. Based on the technical requirement of pesticide residue detection and the needs of economic development in our country, it is of great significance to research and develop a rapid, economic environmental, sensitive and reliable analysis methods for pesticide residue detection and establish a monitoring system for our country’s pesticide detection. Capillary electrophoresis (CE), with its low cost, small analyte consumption, low pollution, short analysis time, high efficiency and high sensitivity, meets the strict needs of pesticide detection and has become one of the most powerful analytical methods. CE with laser induced fluorescence (CE-LIF) shows huge potential application in the field of environment detection.Quantum dots emerged as a luminescent nanometer material. Compared to conventional organic fluorescent dyes, QDs have better optical properties, such as wide absorption spectrum, narrow emission spectrum. In addition, they are unstable and prone to photobleaching. By varying the size of QDs, the emission wavelength can be turned to different color, which make it easy to label, distinction and identification of different molecules. So QDs have been widely used in chemistry and environment analysis. It has far-reaching meaning to explore the application in capillary electrophoresis.Based on high performance fluorescent quantum dots, this dissertation has build several rapid, sensitive, reliable and effective methods for the dectection of organophosphorus pesticides in actual samples by capillary electrophoresis with laser induced fluorescence technique. The preliminary research is the feasibility of quantum dots instead of other organic fluorescent dyes and the application in the capillary electrophoresis analysis. A study on the feasibility of fluorescent quantum dots instead of organic fluorescent dyes for organophosphorus pesticides detection by CE-LIF is studied.The dissertation makes up of four parts:Chapter 1. IntroductionIn this chapter, the actualities, harm and detection methods of organophosphorus pesticide were introduced. The principle, separation mode and applications of capillary electrophoresis were outlined, and the optical properties, synthetic method and applications in environmental analysis of quantum dots were ighlighted.Chapter 2. Quantum dot-DNA aptamer conjugates coupled with capillary electrophoresis:A universal strategy for ratiometric detection of organophosphorus pesticidesBased on the highly sensitivity and stable-fluorescence of water-soluble CdTe/CdS core-shell quantum dots (QDs) with broad-specificity DNA aptamers, a novel ratiometric detection strategy was proposed for the sensitive detection of organophosphorus pesticides by capillary electrophoresis with laser-induced fluorescence (CE-LIF). The as-prepared QDs were first conjugated with the amino-modified oligonucleotide (AMO) by amidation reaction, which is partial complementary to the DNA aptamer of organophosphorus pesticides. Then QD-labeled AMO (QD-AMO) was incubated with the DNA aptamer to form QD-AMO-aptamer duplex. When the target organophosphorus pesticides were added, they could specifically bind the DNA aptamer, leading to the cleavage of QD-AMO-aptamer duplex, accompany with the release of QD-AMO. As a result, the ratio of peak height between QD-AMO and QD-AMO-aptamer duplex changed in the detection process of CE-LIF. This strategy was subsequently applied for the detection of phorate, profenofos, isocarbophos, and omethoate with the detection limits of 0.20,0.10,0.17, and 0.23 μM, respectively. This is the first report about using QDs as the signal indicators for organophosphorus pesticides detection based on broad-specificity DNA aptamers by CE-LIF, thus contributing to extend the scope of application of QDs in different fields. The proposed method has great potential to be a universal strategy for rapid detection of aptamer-specific small molecule targets by simply changing the types of aptamer sequences.Chapter 3. Ultrasensitive laser-induced fluorescence detection of organphosphorus pesticides in capillary electrophoresis based on their coordinated with quantum dotsBased on the coordination between water-soluble CdTe quantum dots (QD) and organophosphorus pesticide (OPs), a an efficient, time-saving and convenient method was developed to determine OPs in real samples by using capillary electrophoresis coupled with laser-induced fluorescence technique (CE-LIF). Our proposed method was readily used to for the separation and detection of three OPs, including isocarbophos, parathion and ethyl-p-nitrophenyl phenylphosphonothioate (EPN). Under the optimum conditions (i.e., running buffer:pH= 8.7,25% v/v, acetonitrile/40 mM borate solution with 30 mM SDS), the detection limits were 2.00,1.67, and 1.00 nM; the linear dynamic ranges were 6.00-30.0,5.00-30.0, and 3.00-30.0 nM; and the average recoveries of spiked samples were 99.4-106.2,91.2-102.3, and 91.5-104.5% for isocarbophos, parathion and EPN, respectively. Moreover, our presented method was successfully applied to the monitoring of the above analytes in real samples. The method thus satisfies the need for a simple, quick and selective method to detect residual OPs in complex vegetable matrix as required by the increasingly strict regulations for health protection introduced in recent years. The novel and facile strategy reported herein is expected to allow for the assay of OPs in agricultural products but also for the detection of a wide range of organic and biological molecules. The method also provides a new method for the development of organophosphorus pesticide, thus expanding the use of high performance quantum dots in capillary.Chapter 4. Ultrasensitive ratiometric laser-induced fluorescence detection of organphosphorus pesticides in capillary electrophoresis Quantum Dot-Peptide ConjugatesBased on the highly sensitivity and stable-fluorescence of water-soluble CdSe/ZnS core-shell quantum dots (QDs) with peptide, a novel ratiometric detection strategy was proposed for the sensitive detection of organophosphorus pesticides by capillary electrophoresis with laser-induced fluorescence (CE-LIF). Firstly, the His6-peptide was designed to self-assemble with QDs by strong coordination between the cadmium ion and histidine. Then the QD-peptide probe was obtained. When the target organophosphorus pesticides were added, they could affinity bind the QD-peptide probe, forming the QD-peptide-ddvp adduct. As a result, with the change of the concentration of organophosphorus pesticides, the ratio of peak height between QD-peptide and QD-peptide-ddvp adduct changed in the detection process of CE-LIF. This strategy was subsequently applied for the detection of dichlorvos with the detection limits of 13.0 nM. This is the first report about using peptide molecules for organophosphorus pesticides detection by CE-LIF. The proposed method provides a new pathway for organophosphorus pesticide determination, making peptide as a highly selective biological molecules for rapid detection of small molecule targets in other areas. |
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