Fluorescent Nanomaterial Sensor For Detection Of As(Ⅲ)and Thiram

Heavy metal pollution and pesticide residues in the environment have seriously affected the food chain and water bodies and will eventually endanger life and health.Sensors based on fluorescent nanomaterials have been widely used in the detection of environmental pollutants because of their advantages such as low cost,better sensitivity and selectivity.Fluorescent nanomaterials such as carbon dots（CDs）,sulfur dots（SQDs）and gold clusters（Au NCs）have attracted extensive attention due to their high water solubility,excellent biocompatibility,good optical properties,and low toxicity.In this paper,nitrogen and sulfur co-doped carbon dots（N,S-CDs）,Au NCs and SQDs were synthesized,and a method for the detection of heavy metal ion As（Ⅲ）based on N,S-CDs was constructed,as well as a method for the detection of pesticide thiram based on Au NCs and SQDs method.The specific research contents are as follows:1.Using citric acid,methionine and urea as raw materials,N,S-CDs were synthesized by one-step hydrothermal method.The average particle size of N,S-CDs is about 1.7 nm,and they have good stability.The optimal excitation wavelength of N,S-CDs is 340 nm,and the emission wavelength is at 446 nm.The surface of the N,S-CDs has carboxyl（-COOH）and sulfhydryl（-SH）functional groups,they can selectively combine with As（Ⅲ）to quench the fluorescence of N,S-CDs to achieve the purpose of quantitative detection of As（Ⅲ）.The quenching mechanism is static quenching.The linear range between fluorescence quenching degree and concentration of As（Ⅲ）was10-100 nmol/L,and the detection limit was 2.9 nmol/L.In the spike recovery experiment,the detection of As（Ⅲ）in the actual samples of lake water and tap water was realized.The results of recovery rate and RSD values indicated that this method is expected to be used in the detection of As（Ⅲ）pollutants in water.2.GSH-modified AuNCs were synthesized with chloroauric acid（HAu Cl₄）and glutathione（GSH）as raw materials,and PEG-modified SQDs were synthesized with sulfur powder,polyethylene glycol-400（PEG-400）,H₂O₂ and Na OH as raw materials.Au NCs can quench the fluorescence of SQDs,and there is a linear relationship between the degree of fluorescence quenching of SQDs and the concentration of Au NCs.The interaction between SQDs and Au NCs was explored,and the quenching mechanism was dynamic quenching.SQDs and Au NCs were doped to construct ratiometric fluorescent probes.Under excitation at 360 nm,SQDs emitted blue fluorescence at 446nm,and Au NCs emitted orange-red fluorescence at 638 nm.After thiram was added,the blue fluorescence of SQDs did not change,but the red fluorescence of Au NCs was quenched.After experimental investigation,the quenching mechanism was static quenching.The constructed SQDs/Au NCs ratiometric fluorescent probe realized the quantitative and visual detection of thiram.The change of SQDs/Au NCs fluorescence intensity ratio I₆₃₈/I₄₄₆ has two linear relationships with the concentration of thiram,and the linear ranges were 0.04-0.40μmol/L and 0.40-2.50μmol/L,the detection limit is18.5 nmol/L.RGB analysis was performed on the fluorescent photos.The linear ranges of R/B and thiram concentrations were 0.06-0.40μmol/L and 0.40-3.00μmol/L,and the visual detection limit was 29.4 nmol/L.In the spike recovery experiment,the detection of thiram in the actual samples of lake water,soil and peaches was realized.The results of recovery rate and RSD value showed that the method is promising for the detection of thiram residues in environment and foods.