The Design Of Fluorescence Sensing Systems Based Coumarin And Quantum Dots For The Detection Of Glyphosate And Carbendazim

In modern agriculture,pesticides are widely used to control pests and diseases of crops,which greatly increase food production and bring huge economic benefits.However,the long-term use or abuse of pesticides may easily lead to high-level residues in agricultural products,which can create a potential threat to human health.In commonly used methods,the traditional large-scale instruments are mainly applied to detect pesticides.Although these methods can provide sensitive and reliable results,most of them have some intrinsic disadvantages,such as huge instruments,expensive equipment,complicated sample preparation process,time-consuming detection process,and professional technicians to operate.Such defects may limit their wider applications and are not suitable for real-time detection in the field.In recent years,fluorescence methods have been frequently used in pesticide detection due to their simple operation,fast response,high sensitivity,low cost,accuracy and reliability.In this study,three kinds of fluorescence sensing systems based on the fluorescent materials（coumarin,silicon quantum dots and carbon quantum dots）and quenching materials(Cu²⁺and Au NPs)were successfully constructed for the determination of glyphosate and carbendazim.TEM,XPS,XRD,FT-IR and UV-Vis were used to achieve the characterization of synthesized materials.Using fluorescence spectrophotometer and fluorescence lifetime tester systematically studied the mechanism of the fluorescence sensing system.The main research work was as follows:（1）Coumarin derivative（CND）was synthesized by a one-step condensation reaction.Based on the interaction between CND and Cu²⁺,a CND/Cu²⁺fluorescence sensing system was constructed to achieve quantitative analysis of glyphosate.The experimental conditions containing Cu²⁺concentration,pH,temperature and reaction time were explored.Under the optimized experiment conditions,a good linear relationship between CND and Cu²⁺of glyphosate concentration in the range of 0.02μg/mL to 1.50μg/mL was obtained and the correlation coefficient was 0.99.The detection limit was 18.30 ng/mL（S/N=3）.The detection performance of the fluorescence sensing system was discussed.Good stability and reproducibility were realized by the fluorescence sensing system.Interfering study exhibited excellent anti-interference ability.In addition,satisfactory recoveries ranging from 91.31%to105.28%were also achieved in the spiked experiment.These results indicated that the CND/Cu²⁺fluorescence sensing system had practical application prospects.（2）Silicon quantum dots（SiQDs）were synthesized by high temperature transient reaction.The SiQDs/Cu²⁺fluorescence sensing system was constructed based on the interaction between SiQDs and Cu²⁺to achieve high sensitivity detection of glyphosate.We optimized the experimental parameters such as pH,temperature,and reaction time.Under the optimal detection conditions,a wide glyphosate concentration range of 0.03μg/mL to 12.00μg/mL was achieved by the fluorescence sensing system.And the limit of detection for glyphosate was 7.80 ng/mL.The fabricated fluorescence sensing system between SiQDs and Cu²⁺showed strong anti-interference ability and good stability and reproducibility.And the spiking experiments also achieved good results.Compared with the CND/Cu²⁺fluorescence sensing system,the SiQDs/Cu²⁺fluorescence sensing system showed superior stability,wider detection range and higher sensitivity for the detection of glyphosate.（3）N,P-doped carbon quantum dots（N,P-CQDs）were synthesized by one-step hydrothermal method.Based on the fluorescence resonance energy transfer（FRET）between N,P-CQDs and gold nanoparticles（Au NPs）,the N,P-CQDs/Au NPs fluorescence sensing system was constructed for the detection of carbendazim.We optimized the experimental conditions including Au NPs concentration,pH and reaction time.Under the optimized conditions,The N,P-CQDs/Au NPs fluorescence sensing system had a fine linear range from 0.001μg/mL to 0.03μg/mL with the correlation coefficients was 0.99.And the detection limit for carbendazim was to be 0.45 ng/mL.The fluorescence sensing system had strong anti-interference ability to common metal ions,pesticides and amino acids.Additionally,the fluorescence sensing system fabricated here manifested excellent capability of stability and reproducibility.In the spiking assays,it achieved good recovery results for real samples.The proposed assay offered a new idea for carbendazim monitoring.