| At present,pesticides have made great contributions to the development of agriculture,forestry,and animal husbandry with their ability to efficiently kill insects,sterilize and weed.However,the pesticides that can really act on targeted organisms are less than 1% of the pesticides applied,the rest are infiltrated into the surrounding environment,and will eventually be enriched in the human body along with the material circulation,atmospheric circulation and water circulation,resulting in human physiological dysfunction and causing lesions.Traditional pesticide detection methods(such as high performance liquid chromatography,liquid chromatography-mass spectrometry,etc.)are highly accurate,but the sample preparation is complex,the instrument is expensive,the detection time is long,and professionals are required to perform the operation and cannot satisfy large sample screening and control of sudden events.Therefore,it is necessary to develop a detection method with a fast response speed and simple operation to ensure food safety and human health.In view of this,this dissertation focuses on the construction of a quantum dot-based fluorescence sensing system,deeply studies its mechanism of action with pesticides,and constructs two kinds of quantum dot-based fluorescence sensing systems for the detection of pesticides.The content is as follows:(1)Preparation and characterization of cadmium telluride quantum dots(CdTe QDs)using mercaptopropionic acid(MPA)as the stabilizing group by aqueous-phase synthesis method;The selenium cadmium/zinc sulfide quantum dots with MPA as the stable group(LR-CdSe/ZnS QDs)was obtained by the ligand replacement of the oil soluble selenium cadmium/zinc sulfide quantum dots(OA-CdSe/ZnS);Commercially available water-soluble MPA-CdSe/ZnS QDs with MPA as a stable group were characterized.The detection of 100 μg/mL ethion was performed using the above three quantum dots.It was found that the LR-CdSe/ZnS QDs had the best detection effect and could reduce the fluorescence by 60%.(2)A sensing system based on LR-CdSe/ZnS QDs was constructed by ligand replacement method,and the detection and analysis of phosphorothiolate pesticide residues could be performed.The method detects pesticides by reducing the fluorescence of the quantum dots caused by the coordination interaction between the alkaline hydrolysis product of the pesticide and the surface metal of the quantum dot.This method is simple and sensitive,under the optimal conditions,in the case of ethion,it showed a linear relationship with the fluorescence of quantum dots in the concentration range of 0.0001-160 μg/mL,and the detection limit was 0.0967 ng/mL(0.00012 mg/kg),well below the EU’s maximum residue limit(0.01 mg/kg).The method has been successfully applied to the detection of ethion in tomato samples,providing a simple method for the detection of phosphorothiolate pesticide residues.(3)A fluorescence sensing system based on quantum dots and gold nanoparticles was constructed to analyze and detect the residues of dithiocarbamate pesticides(DTCs).The dual effect of quenching of quantum dot fluorescence by metal ions released from pesticide that interates with gold nanoparticles and the inner filter effect(IFE)between gold nanoparticles and quantum dots are sensitive to the detection of DTCs.The method is simple in operation and has high sensitivity.Under optimum conditions,ziram,for example,it exhibits a piecewise linear relationship with the fluorescence of quantum dots in the concentration range of 0.0156-1.22 μg/mL,and the detection limit is 0.00276 μg/mL.(0.00276 mg/kg),well below the national standard maximum residue limit(5 mg/kg).Moreover,this method has been successfully applied to the detection of ziram in tomato and rice samples,providing a new method with high sensitivity,specificity,convenience,and environmental protection for DTCs residue detection. |
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