The Construction Of Fluorescence Sensing Systems Based On Copper Nanoclusters And Quantum Dots For The Detection Of Pesticides

Pesticides are widely applied in agriculture to control weeds and pests,so as to increase food production.However,the overused pesticides would cause non-target environment pollution and seriously threaten our human health.As a traditional detection method of pesticides residues,the large-scale instruments detection such as High performance liquid chromatography（HPLC）and gas chromatography（GC）have a high sensitivity though,some defects still exist,such as large expensive equipment and complicated pretreatment process,etc,which limit their practical application in detection.In recent years,fluorescence spectroscopy method has been widely used in pesticide detection due to its advantages of simple operation,quick response,high sensitivity,low cost,accuracy and reliability.In this study,copper clusters,carbon quantum dots and silicon quantum dots were mainly used as fluorescent nanomaterials.The three fluorescent sensing systems were constructed based on the principles of IFE and FRET,which successfully achieved to detecte pesticides of fluazinam,cartap and glyphosate.In order to prove the successful synthesis of nanomaterials in the systems,TEM,XPS,XRD,FT-IR,UV-Vis and other methods were used to characterize the synthesized nanomaterials.Meanwhile,fluorescence spectrophotometer,fluorescence lifetime tester,Zeta potentiometer and other instruments were used to systematically analyze the detection mechanism of the constructed fluorescence sensing systems.Thus,the main contents of this study are as follows:（1）Copper nanoclusters（L-cys-Cu NCs）with L-cysteine stable were synthesized in one step by stirring under room temperature with anhydrous copper sulfate,L-cysteine and sodium hydroxide as raw materials,whose optimal fluorescence excitation wavelength and emission wavelength are respectively 365 nm and 497 nm,respectively.In the presence of fluazinam,the fluorescence of L-cys-Cu NCs was quenched.Based on the principle of IFE,the fluorescence sensing system of L-cys-Cu NCs was constructed to realize the detection of fluazinam and to optimized experiment conditions.Under the best experimental conditions,when the concentration of fluazinam is in the range of 0.05μM～25.00μM,fluorescence intensity change value（ΔF）has a great linear relationship with L-cys-Cu NCs（R²=0.9953）and the theoretical detection limit was 1.4 n M（S/N=3）.This study had a lower detection limit for fluazinam comparing with other studies.In addition,the detection performance of the fluorescent sensing system has been discussed in this study.It was shown that the fluorescent sensing system performed a good stability and reproducibility in the detection of fluazinam,with good anti-interference ability from other common pesticides and ions.What’s more,it had a satisfactory recovery rate（98.92%～104.63%）for the detection of actual samples（apples and pears）.The result indicated that the constructed L-cys-Cu NCs fluorescence sensing system had certain practical applications prospects.（2）Regarding phenol and ethylenediamine as raw materials,hydrothermal synthesis was applied to synthesize carbon dots（CQDs）with a quantum yield of up to29.00%,which showed a strong green light under an ultraviolet lamp with an average particle size of 3.37 nm.When the excitation wavelength was 410 nm,CQDs had a maximum emission peak at 513 nm.The green fluorescence of CQDs was quenched by burgundy gold nanoparticles（Au NPs）due to the IFE.With the addition of cartap,the Au-N interaction between Au NPs and cartap would cause the aggregation of Au NPs,and form the purple aggregations which did not overlap with the emission spectrum of CQDs as well as the fluorescence of CQDs was restored.The detection conditions of the constructed CQDs/Au NPs fluorescence sensing system were optimized.Under the optimal conditions,the concentration difference ofΔF would keep a good linear relationship with the concentration of cartap（R²=0.9910）when its concentration was at a range of 5 n M～120 n M.The detection limit was 3.84 n M（S/N=3）.The constructed CQDs/Au NPs fluorescence sensing system had excellent anti-interference ability and good stability and repeatability,and the actual sample recovery rate was between99.17%～101.70%.Thus the fluorescence sensing system provided a more potential method for the analysis of cartap in the environment.（3）By using ATPMS and trisodium citrate as raw materials,a simple one-step hydrothermal reaction was applied to synthesize silicon nanoparticles（Si NPs）with an average size of 2.03 nm.The optical characteristics exhibited that the emission is at 446nm under the excitation of 355 nm,with a strong blue light.At the same time,Cu²⁺can catalyze the oxidation of o-phenylenediamine（OPD）to 2,3-diaminobenazine（ox OPD）.Based on the principle of Fluorescence Resonance Energy Transfer（FRET）,a Si NPs/OPD/Cu²⁺ratio fluorescence sensing system was constructed,and sensitivity detection of glyphosate could be achieved under the optimal experimental conditions.The reaction conditions of the Si NPs/OPD/Cu²⁺sensing system were optimized.Under the optimal conditions,the fluorescent sensing system was used to quantitatively analyze glyphosate.When the concentration of glyphosate was between 0.15μg/m L to1.5μg/m L,F_556/F446obtained a good linear correlation（R²=0.9930）,and the detection limit of glyphosate was calculated to be 0.45 ng/m L（S/N=3）.The constructed fluorescence sensor system has achieved a satisfactory recovery rate（91.25%～103.71%）in the detection of actual samples.The anti-interference,stability and reproducibility have all proved the Si NPs/OPD/Cu²⁺ratio fluorescence sensing system has excellent detection performance,which has provided a new idea for the detection of glyphosate in the environment.