The Construction Of Fluorescence Sensing Systems Based On Carbon Quantum Dots And Gold Nanoclusters For The Detection Of Glyphosate

Glyphosate is a non-selective and broad-spectrum herbicide,which widely used for weed control in agricultural,forestry and urban environments.With the large-scale applied of glyphosate,it is easy for glyphosate residues found in the environment and foods,and its toxicity has attracted much attention.Some studies showed that glyphosate could disrupt animal metabolism and affect human liver,immune system and reproductive system.It has been listed as Group 2A by the International Agency for Research on Cancer.Therefore,it is important to monitor glyphosate residues in the environment and foods.However,conventional detection methods for glyphosate,such as chromatography and mass spectrometry,generally require complex and cumbersome pretreatment and derivatization steps,which are time-consuming,costly and high requirements for operators.These methods can’t meet the needs of batch detection of samples.In recent years,carbon quantum dots and gold nanoclusters have been widely used in the construction of fluorescent sensors because of their excellent fluorescence,light stability and chemical stability.The constructed fluorescence sensors,which have the benefits of quick reaction time and low cost,offer simple,rapid and accurate methods for detecting pesticide residues.Thus,a single-emission and ratiometric fluorescence sensing systems were constructed to detect glyphosate in this paper.The specific research content were as follows:1.Construction of single-emission fluorescence sensing system and its application:Blue fluorescent nitrogen-doped carbon quantum dots（NCDs）with high quantum yield and good water solubility were synthesized by one-step hydrothermal method usingsodium citrate and adenine as materials.Cu²⁺could effectively quench the fluorescence of NCDs through the photoinduced electron transfer（PET）.With the addition of glyphosate,the fluorescence of NCDs was restored due to the stronger chelating ability between glyphosate and Cu²⁺.Based on the above principles,a NCDs/Cu²⁺single-emission fluorescence sensing system was constructed to detect glyphosate sensitively.And the detection conditions such as buffer solution types,p H,Cu²⁺concentrations,and reaction time were optimized.Under the optimal detection conditions,the sensing system was used for the detection of glyphosate in water and rice.The linear ranges of the method were 0.10-10μg/m L in water and 0.10-8.0μg/m L in rice.The corresponding detection limits（LODs）were 0.021μg/m L and 0.049μg/m L,respectively.In the detection process of glyphosate,the NCDs/Cu²⁺fluorescence sensing system displayed strong anti-interference ability,good stability and reproducibility.The sensing system was successfully applied to the detection of glyphosate in environmental water and rice samples.2.Construction of ratiometric fluorescence sensing system and its application:Red fluorescent gold nanoclusters（Au NCs）were synthesized by reduction method using glutathione as the template.The average particle size was 1.75 nm and the maximum emission wavelength was 682 nm.A ratiometric fluorescent sensing system(Au NCs/OPD/Cu²⁺)for the detection of glyphosate was constructed based on gold nanoclusters,o-phenylenediamine and Cu²⁺.OPD could be oxidized by Cu²⁺,which produced bright yellow fluorescent oxidation products2,3-diaminophenazine（DAP）with a maximum fluorescence emission peak at 570 nm.When glyphosate existed in the system,the chelation between glyphosate and Cu²⁺hindered the formation of DAP and reduced the fluorescence intensity of the system at the wavelength of 570nm,while the fluorescence intensity at the wavelength of 682 nm remained basically stable.The fluorescence intensity at 570 nm wavelength dropped steadily with the increase of glyphosate concentration.Glyphosate was detected according to the calculated fluorescencechange(F₅₇₀/F₆₈₂)ratio.In addition,the fluorescence color change from orange to red was also observed in the reaction solution under ultraviolet lamp irradiation.In order to obtain the best detection performance,the buffer solution types,p H,Cu²⁺concentrations and reaction time were optimized.Under the optimal detection conditions,the linear range of the method was 0.050-3.0μg/m L,and the LOD was 0.0028μg/m L.The method can be applied to the detection of glyphosate in environmental water samples,and the visual semi-quantitative determination of glyphosate was realized according to the color change of fluorescence.