Spectroscopic Detection Of Pesticide Residues Based On Plant-esterase

The widespread application of pesticide brings out great economic value in modernagricultural production. However, with the ever-increasing amount in food production,pesticide residues have brought great threat on ecological environment and humanhealth. Although current routine analysis techniques based on large equipment provideabundant detection methods for detecting pesticide residues due to high sensitivity andaccuracy, unavoidable drawbacks such as high cost and complex operation proceduresgreatly limit their wide application. Therefore, it is extremely urgent to develop a newmethod for pesticide residues detection with high sensitivity, rapidity and reliability.In the present thesis, we study the fluorescent characteristics of plant-esterase andthe possibility to use this enzyme to detect pesticide residues. The mechanism of theinteraction between plant-esterase and carbamate pesticide was analyzed so as todevelop an enzyme-based fluorescent sensor for those kind of pesticide residues.Besides, it also found that the complex of plant-esterase and porphyrin provide a dualoptical detection system for the detection of pesticide residues. The current studyalternate an easy, fast and sensitive biosensor for pesticide detection, which would be agood choice to analyze pesticide residues in environment and food. The main content ofthe thesis are as following:(1)A method based on inhibition of plant-esterase from pesticides for carbendazimdetection has been proposed and validated for the determination of carbendazimresidues in aqueous samples. After optimization in solvents,pH, temperature anddetection time, a lower detection limit of0.105μM was obtained in linear range from0.105μM to41.84μM, with mere interference upon tested interfering counterparts. Theproposed method was satisfactorily applied to the analysis of carbendazim residues indifferent aqueous samples, with the recovery percentage ranged from93.4to105.0%,R.S.D. values smaller than3%. On analysis of the detection mechanism, carbendazimwas found to be bind to plant-esterase via van der Waals force and hydrogen bond.(2) Based on the inhibition effect of plant-esterase to pesticides, a brand-new dualsignal detection method was developed using acetoxyindole as enzymatic substrate andchromogenic reagent. It showed the best detection result for dipterex, and theultraviolet-visible and fluorescent detection limit were as low as7ppb and1ppb,respectively. For methomyl, the ultraviolet-visible and fluorescent detection limit were down to40ppb and11ppb, and for aldicarb, they were10ppb and20ppb. The detectionlimit for those pesticides except for carbendazim are all below the maximum residuelimit banned by Chinese officials, and they are promising for real application in theanalysis of related pesticide residues.(3) With the selection of different plant-esterase\porphyrin complexes, detection ofpesticide including dipterex, carbendazim, methomyl and aldicarb were studiedapplying ultraviolet-visible method and fluorescent method. Different detection limitsand sensitivities of different complexes to different pesticides were calculated accordingto related ultraviolet-visible absorption curves, fluorescent absorption curves, andstandard calibrate curves. After optimization of solvent conditions, plant-esterase\HTPPS4complexes shows good ultraviolet-visible detection result towards dipterex.The detection limit is down to7ppb with a sensitivity of0.86. The fluorescent detectionresult was not as good as ultraviolet-visible detection one for dipterex yet it also showeddetection limit below the maximum residue limit banned by Chinese officials. Theplant-esterase\ZnTPP complexes show the best dual optical detection ablility towardscarbendazim. The detection limit are down to9ppb and6ppb, with sensitivity of1.438and816.49. The plant-esterase\CuTPP complexes show the lowest ultraviolet-visibledetection limit towards methomyl. The detection limit is down to8ppb with a sensitivityof1.2. Almost all the plant-esterase\porphyrin complexes shows acceptableultraviolet-visible detection ability to aldicarb with detection limit lower than themaximum residue limit banned by Chinese officials, the lowest detection limit wasdown to10ppb. yet the fluorescent detection results showed that their detection limitwere higher than the maximum residue limit banned by Chinese officials thus notsuitable for practical pesticide residue analysis.