The Construction Of New Methods For Colorimetric Detection Of Heavy Metal Ions Based On Au/Ag Nanoparticles And Their Applications In Food Detection

The unreasonable discharge of industrial wastes such as smelting and mining has caused heavy metals to pollute soil,water sources and crops,seriously affecting food safety,and threaten human health and safety through food chain enrichment and biological amplification effects.Excessive levels of heavy metals in the human body can cause multiple organ failure,and in severe cases can cause cancer and life-threatening.At present,the common methods for heavy metal detection mainly rely on traditional large instruments such as Inductively coupled plasma mass spectrometry(ICP-MS).These methods have high detection costs,require professional operations and complex sample pre-processing,and cannot achieve real-time,on-site detection.Therefore,the establishment and development of simple,convenient and efficient heavy metal ion detection methods is particularly important for food safety and human health.Nano colorimetric detection technology provides a convenient,effective and visually impressive method for the detection of heavy metal ions.The Au/Ag nanomaterial-based etching colorimetric method can be used for the detection of heavy metal ions due to its advantages of simple preparation,fast response,and intuitive effect.In this thesis,based on the etching effect of H₂O₂ on Ag nano-cubes(Ag NCs),HBr on Au nano-double cone@Ag nano-rods(Au NDC@Ag NRS)and Na₂S₂O₃ on Ag nano-triangle@Au nano-hexagons(Ag NT@Au NHs),three kinds of nano colorimetric probe were constructed.The morphological characterization and optical performance of the synthesized nanoparticles and the constructed nanometer colorimetric probe were investigated by Transmission electron microscopy(TEM)and Ultraviolet-visible spectrophotometer.The response and performance of the nano colorimetric probe to the detection of Cu²⁺,Cr⁶⁺and Pb²⁺three different heavy metal ions were explored.And the constructed nano colorimetric probe has been successfully used for the rapid and real-time detection of Cu²⁺,Cr⁶⁺and Pb²⁺in environmental water and food samples.The main research contents are as follows:(1)A sulfide-mediated polyol synthesis process was used to prepare regular hexahedral Ag NCs.Based on the weakening effect of Cu²⁺on H₂O₂ etched Ag NCs,which caused the changes in absorbance at about 417.5 nm in the UV absorption spectrum and color intensity of Ag NCs solution,the Ag NCs nano colorimetric probe was successfully constructed to realize the visual and quantitative detection of Cu²⁺in solution.The results show that under the best experimental conditions,the linear detection range of the probe for Cu²⁺is 0.01?40?M(R²=0.9917),and the detection can be as low as 0.01?M by naked eyes.The Euclidean distance(ED)of the RGB value of color change images of Ag NCs nano colorimetric probe solution under different Cu²⁺concentration(2.5?40?M)shows a good linear relationship with Cu²⁺concentration,and the probe has good selectivity to Cu²⁺.In addition,satisfactory recovery rates have also been achieved in the recovery of river water,rice and onion samples,which are 90.60?96.10%,91.80?96.45%and 94.60?96.40%,respectively.The detection result is close to the ICP-MS measurement result.The above results indicate that the Ag NCs nano colorimetric probe has practical application value.(2)The Au NDC@Ag NRs with core-shell structure were synthesized by seed growth method.Based on the catalysis of Cr⁶⁺on HBr etching Au NDC@Ag NRs,which caused the red shift of the LSPR absorption peak of Au NDC@Ag NRs solution and the change of solution color,Au NDC@Ag NRs nano colorimetric probe was successfully constructed to realize the visual and quantitative detection of Cr⁶⁺in solution.Under the optimal experimental conditions,the linear detection range of this probe for Cr⁶⁺is 2.5?40?M(R²=0.9920),and the limit of detection(LOD)is 0.02?M(S/N=3).The ED of the RGB value of color change images of Au NDC@Ag NRs nano colorimetric probe solution at different concentrations of Cr⁶⁺(2.5?50?M)showed a good linear correlation with the concentration of Cr⁶⁺,and the probe showed good selectivity in the process of Cr⁶⁺detection.In addition,satisfactory recovery rates have also been achieved in the recovery of river water,rice and onion samples,which are 90.50?97.10%,90.80?98.00%and 94.40?95.77%,respectively.The detection result is close to that of ICP-MS.The above results indicate that the Au NDC@Ag NRs nano colorimetric probe has practical application value.(3)The Ag NT@Au NHs with core-shell structure were synthesized by epitaxial growth method.Based on the catalytic action of Pb²⁺and Cu²⁺on Na₂S₂O₃ etching Ag NT@Au NHs,the decrease in absorbance at about 585 nm in UV absorption spectra and the red shift of LSPR absorption peak of Ag NT@Au NHs solution and the different color changes of the solution were respectively induced by Pb²⁺and Cu²⁺,the Ag NT@Au NHs nano colorimetric probe was successfully constructed to realize the visual and quantitative detection of Pb²⁺and Cu²⁺in solution.Under the optimal experimental conditions,the linear ranges of the probe for detecting Pb²⁺are 10?200?M,200?300?M and 300?550?M(R² are 0.9714,0.9908 and 0.9824,respectively),and the LOD is0.41?M(S/N=3).The linear detection ranges of Cu²⁺are 1?50?M and 50?250?M(R² are 0.9918 and 0.9804,respectively),and the LOD is 0.11?M(S/N=3).Under different Pb²⁺or Cu²⁺concentrations,the ED of the RGB value of color change images of the Ag NT@Au NHs nano colorimetric probe solution shows a good linear relationship with the Pb²⁺or Cu²⁺concentration respectively.And the probe shows good selectivity in the detection process of Pb²⁺or Cu²⁺,and can distinguish Pb²⁺and Cu²⁺well.Satisfactory recovery rates have been achieved in the recovery of Pb²⁺and Cu²⁺in river water,rice and onion samples(Pb²⁺:93.60?97.63%,95.87?98.00%and 94.80?96.56%;Cu²⁺:90.80?97.80%,97.75?98.00%and 92.28?98.56%).The detection result is close to that of ICP-MS.The above results all show that the constructed Ag NT@Au NHs nano colorimetric probe has practical application value.