Research On The Fluorescence Sensors Based On Quantum Dots And Porphyrin For Fluazinam And Amitrole Detection And Its Mechanism

China is a traditional agricultural country,increasing pesticide residues pollutions draws more and more concerns as increase of agricultural products.Among them,fluazinam is a new widely used broad-spectrum fungicide,and amitrole is a non-selective chemical herbicide with strong toxicity.Presently,their detection methods are mainly based on chromatography,chromatography-mass spectrometry and other conventional instrumental.Although these methods show the advantages of high sensitivity and reliability,they suffered from some drawbacks,including time-consuming,high cost,and professional personnel,which hindered their fast,real-time and on-site detection.Therefore,development of rapid,simple,low cost,high reliability and sensitive detection methods for fluazinam and amitrole analysis is of great importance.As an ideal fluorescent probe,quantum dots have many advantages,such as high luminous efficiency,tunable optics,wide excitation range and good light stability.So they have been widely used in the fields of trace substances analysis.In addition,because of the unique structures and properties,porphyrins play an important role in analytical chemistry.In recent years,fluorescence chemical sensors have become one of the most active frontier research fields.In this thesis,sensitive materials of fluorescent sensors,quantum dots and porphyrin compounds are firstly prepared and synthesis,and four fluorescent sensors based on FRET and IFE were built to detect fluazinam and amitrole in real samples.Researches were carried out as follows:?1?Firstly,eight porphyrin molecules were synthesized and characterized by NMR,IR,UV-Vis spectra and fluorescence spectra.Then,the structures of eight porphyrin molecules are optimized by Gauss calculation.And the energy of HOMO and LUMO orbitals of their frontier orbital energy levels are analyzed and discussed theoretically,which provided the theoretical basis for the experimental analysis.Finally,the interactions of eight porphyrin molecules and fluazinam were studied.And the results show that the binding constants was 2.75×10⁷ L/mol,the number of binding sites of 1.83,were obtained for the interaction between TMaPP and fluazinam.So,TMaPP was selected for further fluazinam detection studies,which provided preliminary guidance for the subsequent design of fluorescent sensors.?2?High quality luminescent QDs is one of the most important parameters of fluorescent sensors.In this work,CdS QDs,ZnS:Mn QDs,CdTe QDs and N,S-CDs were synthesized by hydrothermal methods and characterized using XRD,XPS,SEM,TEM,IR and UV-Vis respectively.The fluorescence quenching of fluazinam on QDs as-synthesized were studied and the quenching constants were calculated.Accordingly,CdTe QDs and N,S-CDs were selected as the fluorescent probes for the subsequent design of fluorescent sensors.?3?The ratiometric fluorescence sensor based on FRET was designed and constructed with N,S-CDs as the fluorophore and TMaPP as recognition groups for detection of fluazinam in vegetables.Firstly,the effects of solvent,TMaPP concentration and interaction time on N,S-CDs@TMaPP system were investigated.Under the optimal conditions,the linear range of the sensor for the detection of fluazinam ranged from 0.01?M to 5?M,with low detection limit of 6.8nM were acquired.The recovery rate ranged from 95.4%to 112%with the relative standard deviation below 3.3%was obtained.These all demonstrated the practicability of the sensor.?4?Three FRET system for the detection of fluazinam,including to CdTe QDs_537nm@TMaPP,CdTe QDs_617nm@TMaPP and CdTe QDs_637nm@TMaPP,were developed based on CdTe QDs and TMaPP.Their linear ranges and lowest detection limits were also determined.Then the ratiometric fluorescence sensor based on CdTe QDs_537nm-TMaPP was fabricated with the linear range of 0.01?M to 5?M,and the detection limit of 2.3nM.And the detection system was used to detect fluazinam in vegetable samples and the recoveries ranged from95.4%to 107%was obtained,which meets the requirements of real application.?5?The ratiometric fluorescence sensor based on IFE was designed and constructed with N,S-CDs as the fluorophore and aptamers as recognition groups for detection of fluazinam in vegetables and soil.Firstly,the experimental conditions for combination of N,S-CDs and aptamers were investigated,including the dosage of aptamers,incubation time.And then,effects of GO dosage,pH value and time on the fluorescence detection system of N,S-CDs@Aptamers@GO for fluazinam analysis were studied.Under the optimal conditions,the linear range of the sensor for the fluazinam detection was 5 to500nM,and the detection limit was 0.023nM.The fluazinam content detected in vegetable and soil samples were lower than 0.01ppm,no more than the fluazinam limited requirements set by the European Union and the United States Environmental Protection Agency and our country of fluazinam.Therefore,the biological fluorescence sensor displayed the apotential real application.?6?A simple yet sensitive fuorescent sensor was reported for amitrole analysis based on integration of gold nanoparticles?AuNPs?and CdTe quantum dots?CdTe QDs?via IFE.The fuorescence of GSH-coated CdTe QDs can be signicantly quenched by AuNPs,and gradually restored in the presence of amitrole.Addition of amitrole induced AuNPs aggregation and decreased their characteristic surface plasmon absorption,which diminished the IFE between them.The sensor platform realized high sensitivity and good reproducibility in low concentration amitrole ranging from 9.5nM to 1000nM with a detection limit down to 4.75nM under the optimized conditions.It also resisted a wide range of interfering counterparts and showed analytical performance comparable to the majority of analytical methods reported in prior studies.We envisioned the first fluorescent amitrole sensor would be potentially useful for low cost on-site amitrole monitoring in real application.As a control experiment,the results of HPLC were compared and analyzed with those of the four fluorescent sensors.The results showed that there was no significant difference between HPLC and the fluorescent sensors.That is,there is no significant difference between the standard methods and the methods established in this paper,which illustrated that the fluorescent sensors were of high precision and accuracy,and have the application prospect of rapid,real-time and on-site detection.