Preparation And Characterization Of Molecular Imprinting Fluorescent Probes Base On Quantum Dot For Determination Of Organophosphorus Pestiside Residues

Detection of pesticide residues in food is an important problem in the international community. Because the pesticide samples are of low concentration, complex component and instability, therefore the pretreatment, separation and enrichment of target pesticides always needed. Traditional analysis systems always suffer from some disadvantages, such as, cumbersome and complex separation, time-consuming, poor selectivity, and sometimes poisonous solvent required. Thus, the development of simple, rapid and cost-effective sensor system for the detection of cartap is urgently needed.Molecular imprinting technique(MIT), a method in preparation of polymer containing three-dimensional structure and binding site targeting specific substance, are broadly utilized in fields of solid phase extraction, sample processing and sensor owing to their capability of selectivity and widely applications. Compared with traditional dyes and pigments, duantum dots(QDs) are characteristic with regulable fluorescent emission spectrum, broad emission spectrum, narrow excitation spectrum and stable photochemistry properties which makes these widely employed as probe system for the pesticide sensing. Mechanism of determination of pesticide based on QDs relyes on the interaction between their specific groups, and is not only cannot detect all of organic phosphorous pesticide, but also lack of selectivity towards sPho specific pesticide. In spite of structure-activity and capability of specificity of MIT, it cannot meet the requirements of the actual determination application due to its time-consuming. In this work, we have studied on the preparation of molecular imprinting quantum dot fluorescent composite microspheres for the discrimination of real organophosphorus samples, which would combine the advantages of excellent fluorescence and specific recognize ability. Our work can be summarized as follows:(1). Molecular imprinted polymers(MIPs) are prepared on the surface of activated silicon using the surface imprinting method. Functional monomer can be confirmed using UV-vis spectrophotPhoter. As can be seen from Field Emission Scanning Electron Microscope images, MIP-Pho are in good monodispersion. Furthermore, it shows stronger adsorption capacity to phoxim(pho) compared with NIPs. MIP-Pho displayed stronger adsorption capacity towards phoxim than chlorpyrifos, malathion and methyl parathion. Recovery of vegetable samples phoxim ranged from 96.6% to 102.5%, with RSD of 2.6%.(2). Lipophilic CdSe QDs coated by oleic acid and oleyl amine are synthesized for rapid determination of phoxim due to their high light stability and fluorescence quenching resulted by phoxim. Under the optimal detection condition, decent linear relationship for phoxim determination are obtained in the range from 2.69×10-7 to 1.07×10-5 M, with detection limit of 7.7×10-8 M, correlation coefficient of 0.997, for the CdSe QDs as-prepared, respectively. The oil phase CdSe quantum dots are used as a high-sensitivity fluorescent probe for the direct detection of phoxim sample. The results show good detection performance and poor selectivity, because its fluorescence can be quenched by ranges of organophosphorus pesticides. Recovery of vegetable samples phoxim ranged from 95.3% to 98.8%, with RSD of 3.1%.(3). Lipophilic CdSe QDs coated by HPA and ODA and its silanization, CdSe QDs fluorescence labeled molecularly imprinted polymer microspheres are prepared successfully. Diameter of microspheres is about 150 nm with cavity on its surface, which is confirmed by scanning electron microscope. Fluorescence of microspheres show excellent selectivity among other similar structure organophosphorus pesticides when their specific binding with phoxim. Therefore, the sensor systems are fabricated based on this CdSe QDs fluorescence labeled molecularly imprinted polymer microspheres for phoxim analysis. A decent linear relationship for phoxim is obtained in the range from 2.69×10-6 to 1.07×10-3 M, with detection limit of 1.26×10-9 M. It also shows excellent results in the vegetables samples detection with the recovery ranged from 95.1% to 99.3% and the RSD of 2.8%. These results demonstrated that the developed sensor would be a great potential application for phoxim detection.