Study On Fluorescence Detection Of Pesticide Residues Using Quantum Dots

With the development of modern agriculture,pesticide utilization drawsmore and more concerns.However,pesticide residues pose a great threat to human health and environment.Therefore,development of simple,accurate and highly sensitive detection methods for pesticide residues analysis is the key aspect of the control and treatment of pesticide residues contamination.Among many pesticide residues analysis and detection methods,the fluorescence sensor based on quantum dots stand out the advantages of short response time and low cost,providing a simple,rapid,accurate and effective method for pesticide residues detection.As the most important fluoerescent sensor materials,quantum dots employed here were successfully synthesized and characterized by TEM,FTIR,XPS,XRD,UV-vis,and fluorescence spectrophotometer.In this study,three fluorescence sensors were constructed to detect methyl parathion,glyphosate and fluazinam,respectively,based on inner filtration effect（IFE）and complexation.The main work can be summarized as follows:（1）Nitrogen-doped carbon dots（N-CDs）with high fluorescence intensity and good dispersity were synthesized by one-step hydrothermal process,and subsequently used to develop fluorescent sensor for methyl parathion detection.Fluorescent inner filter effect occured between p-nitrophenol（the hydrolysate of methyl parathion）and N-CDs,resulting in quantitative analysis of methyl parathion.The effects of pH,temperature and reaction time on the performance of the sensor were investigated by fluorescence spectrophotometry.Under the optimal conditions,a linear range between fluorescent responses（ΔF）and MP concerntrations varied from 0.075 to 15 ppm was obtained with the limit of detection of 1.87 ppb.In addition,N-CDs-based sensors had good selectivity and precision during MP detection（RSD<5%）,and presented favorable recoveries（97.6%-104.3%）in actual samples（apples and rivers）,which demonstrated that the method was feasible in practical testing.（2）Carbon dots（CDs）with low cost,low toxicity and high quantum yield were prepared by simple hydrothermal synthesis using leaves of Sophora japonica as carbon source.A CDs/Fe³⁺sensor was constructed based on the photoinduced electron transfer effect（PET）between Fe³⁺and CDs for the quantitative detection glyphosate.And the effects of Fe³⁺concentration,pH,reaction time of the sensor were investigated.Under the optimal conditions,a concentration-dependent fluorescent response（ΔF）to glyphosate ranging from 0.1 to 16 ppm was acquired with the limit of detection of 5.99ppb.During the testing process,the CDs/Fe³⁺sensor exhibited a good selectivity and precision（RSD<5%）.Satisfactory recoveries from 96.2%to 105.8%were obtained in the actual samples（potato and soil）,indicating that as-presented method has great practical value in analysis and detection of glyphosate.（3）Disulfide quantum dots（MoS₂ QDs）were successfully prepared by a one step hydrothermal method.The flluorescent sensor was constructed based-on fluorescence inner filter effect（IFE）,and consequenty quantitative detection of fluazinam was achieved.The influences of alcohol water ratio,pH and reaction time on the performance of sensor were investigated by fluorescence spectrophotometry.Under the optimal conditions,a low detection limit of 2.5 nM（S/N=3）was acquired with a wide linear relationship ranging from 0.05μM to 25μM.In addition,MoS₂ QDs were also employed to fabricate paper-based sensors,which presented a linear ranging from 10μM to 1000μM in aqueous solution.The low detection limit was calculated to be 6.5μM（S/N=3）with an eye-naked concentration of 10μM.MoS₂ QDs-based fluorescence sensors exhibited a strong anti-interference ability to 11 kind of common pesticides.The fluorescent sensor was successfully applied for detection of fluazinam in tomato,potato and cucumber with satisfactory recoveries（97.6%-102.9%）.This strategy provides a new method for the actual detection of fluazinam.