Application Of Molecularly Imprinted Materials In Marine Pollutants And Food Contaminants Detection

This dissertation takes typical marine pollutions and food contaminants as the research objects. Molecularly imprinted polymers (MIPs) of typical marine pollutants and food contaminants were prepared by molecular imprinting technology (MIT), and then combined to several analytical techniques for the detection of typical marine pollutants and food contaminants. This dissertation consists of six chapters as follow:Chapter one consists of two parts. In the first part, a brief introduction of molecular imprinting technology is given, and the topics discussed include the history, principle and classification of MIT, the synthesis methods, applications of MIPs and some new hot topics in the area of MIT. In the second part, a brief introduction of typical marine pollutants and food contaminants is summarized. The research objective and experimental plan of this dissertation are also presented.In chapter two, the synthesis of the surface imprinted core-shell nanoparticles and their application in 2,4-dichlorophenoxyacetic acid (2,4-D) detection are discussed. At first, monodisperse silica nanoparticles were synthesized by Stober method. Then the trichloro (4-chloromethyl-phenyl) silane was immobilized on the surface of silica nanoparticles, forming benzyl chloride functionalized silica (silica-Cl). With the coaction of Grignard reagent and carbon disulfide, benzyl chloride was transformed into chain transfer agent (dithiobenzoate) for the reversible addition-fragmentation chain transfer (RAFT) polymerization. The grafting copolymerization of 4-vinlpyridine and ethylene glycol dimethacrylate using surface RAFT polymerization in the presence of 2,4-D as the template led to the formation of surface imprinted core-shell nanoparticles. The resulting surface imprinted core-shell nanoparticles bind the original template 2,4-D with an appreciable selectivity over structurally related compounds. At last, the synthesized surface imprinted core-shell nanoparticles are used as the recognition element in competitive fluorescent binding assay for 2,4-D detection.In chapter three, the synthesis of the surface imprinted core-shell superparamagnetic nanoparticles and their application in bisphenol A detection are discussed. At first, monodisperse paramagnetic Fe3O4 nanoparticles were synthesized by solvothermal method. Then the Fe3O4 nanoparticles were coated with a thin silica layer through a sol-gel approach to obtain silica-Fe3O4 composites (Fe3O4@SiO2). After that, the silane agent (3-aminopropyltrimethoxysilane) was immobilized on the surface of silica-Fe3O4 composites, forming amino group functionalized silica-Fe3O4 nanoparticles (Fe3O4@SiO2@NH2). After reaction with 2-bromoisobutyrylbromide, amino group was transformed into chain transfer agent for the atom transfer radical polymerization (ATRP). The grafting copolymerization of 4-vinlpyridine and ethylene glycol dimethacrylate using surface ATRP polymerization and in the presence of bisphenol A as the template led to the formation of surface imprinted core-shell superparamagnetic nanoparticles. The resulting surface imprinted core-shell superparamagnetic nanoparticles bind the original template bisphenol A with an appreciable selectivity over structurally related compounds. And they could be used for magnetic separation of bisphenol A in solutions. Combined with the high performance liquid chromatography (HPLC), the surface imprinted core-shell superparamagnetic nanoparticles could be used for detection of bisphenol A in marine environment.In chapter four, the synthesis of domoic acid-selective MIPs and their application in domoic acid detection in sea food and sea water are discussed. Domoic acid, an amnesic shellfish poison, was used as the target compound while 1,3,5-pentanetricarboxylic acid was used as template molecules. The molecularly imprinted polymers were prepared used 4-vinyl pyridine as the functional monomer and ethylene glycol dimethacrylate as the cross-linking agent. The molecularly imprinted polymer was investigated with the aid of equilibrium binding experiments to evaluate the molecular recognition and binding characteristics of the imprinted polymer. The results show that the imprinted polymer exhibits a much higher affinity for domoic acid compared with non-imprinted polymer. In addition, the domoic acid imprinted polymer can be used as the sorbent in solid-phase extraction (SPE) to determine domoic acid in Mytilus edulis and seawater with satisfactory recovery. The mean recoveries of domoic acid from Mytilus edulis and artificial seawater spiked with 2 mg/L domoic acid were 93.4±4.9% and 89.7±5.3%(n=3), respectively. It was demonstrated that this MIP-SPE-HPLC method could be applied to direct preconcentration and determination of domoic acid in sea food and sea water.In chapter five, the piezoelectric sensor based on molecularly imprinted polymers and its application in domoic acid detection are discussed. Polymerization of dopamine in the presence of template molecule 1,3,5-pentanetricarboxylic acid could produce an adherent polydopamine molecularly imprinted film coating on quartz crystal microbalance (QCM) crystals, which could rebind domoic acid from complex matrices. Selective rebinding of domoic acid on polydopamine molecularly imprinted polymer coated crystal was observed as a frequency shift quantified by the QCM system. The decreasing frequency shows a good linear relationship with the concentration of domoic acid. The QCM sensor had high selectivity and was able to distinguish domoic acid from its analogous p-phthalic acid and o-phthalic acid owing to the molecular imprinting effect. In addition, the practical analytical performance of the sensor was examined by evaluating the detection of domoic acid in mussel extracts with satisfactory results. It is envisaged that polydopamine molecularly imprinted polymer could be suitable as recognition element for sensors and the proposed MIP-QCM sensor could be employed to detect domoic acid in complex matrices.In the final part of the dissertation, Chapter six, the synthesis of the melamine molecularly imprinted polymer and its application in melamine detection from milk products are discussed. A molecularly imprinted polymer was prepared by virtue of the molecular imprinting technique, with melamine as the template molecular, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the cross-linking agent. The molecularly imprinted polymer was investigated with the aid of equilibrium binding experiments to evaluate the molecular recognition and binding characteristics of the melamine imprinted polymer. The results show that compared with non-imprinted polymer, the imprinted polymer exhibits a much higher affinity for melamine. In addition, this chapter also proved that the melamine imprinted polymer can be used as the sorbents in solid-phase extraction to isolate the melamine in milk powder and pure milk extracts with satisfactory recovery. The recoveries were range of 91.2%-102.8%(RSD=7.9%, n=3) and 92.9%-98.0%(RSD=1.1%, n=3), respectively. Furthermore, the melamine imprinted polymer can also be applied in other milk products analysis.