The Development Of Core/Shell Nanoparticles And Their Application In Colorimetric Detection

Colorimetric assay is a powerful tool for sensing targets due to its rapid feedback,easy operation,visual inspection,without complex equipment.It has been widely used in the field of biological analysis,food safety,environmental monitoring and forensic science.Recently,metal nano-materials?MNPs?have been widely used as optical sensing nano-materials due to their high extinction coefficients and distance-dependent optical properties in the visible-region.As a result,a series of MNPs based colorimetric assays are developed.In this study,citrate stabilized Au NPs?13-nm diameter?were prepared based on Frens' method,and the Au@Ag core/shell NPs were synthesized using citrate-stabilized Au NPs as templates in the presence of Tollens reagents?the key component is [Ag?NH₃?₂]⁺?and HCHO.The silver shells generated by the classic Tollens reaction proved to coat on the Au NPs to form core/shell structures.The structures,physical and chemical properties of core/shell nanoparticles were studied in detail.Finally,we analyzed the concentration of CN^-and I^-in the environment combined with ultraviolet spectrophotometer.In the first chapter,the basic mechanism of colorimetry,the properties,classification and colorimetric application of core/shell nanoparticles were systematically introduced,and then the research plan was proposed.In the second chapter,citrate stabilized Au NPs?11¹4-nm diameter?were prepared based on Frens' method with little modification.The Au@Ag core/shell NPs were synthesized using citrate-stabilized Au NPs as templates in the presence of Tollens reagents?the key component is [Ag?NH₃?₂]OH?and HCHO.The silver shells generated by the classic Tollensreaction proved to coat on the Au NPs to form core-shell structures.Transmission Electron Microscopy?TEM?study revealed that the majority of the as-synthesized NPs belonged to sphere shapes,which displayed inhomogenous electronic density with a dark core deposited by a lighter shell.Au@Ag core/shell nanoparticles were used for the colorimetric sensing of cyanide ions.The results showed that the cyanide is able to modify the dimensional shell-to-core ratio by sequentially dissolving silver shells and gold cores,which enables a visual detection of cyanide bare eyes.The corresponding apparent color changes are also in direct relation to the cyanide concentration.This assay has a high selectivity and an obvious color change.The lowest concentration of cyanide that can be visually distinguished was 1.2?M,which is one of the most sensitive colorimetric assays.In the third chapter,Au@Ag core/shell NPs-Cu²⁺ was immobilized into agarose gels as portable "test strips" for the colorimetric sensing of I^-.In this chapter,we developed a simple,sensitive and selective colorimetric assay for sensing I^-by coupling Au@Ag core/shell NPs with Cu²⁺.When I^-was exposed to the mixture solution of Au@Ag core/shell NPs-Cu²⁺,Cu²⁺can oxidize I^-into I₂,(2Cu²⁺+4I^-=2CuI+I₂),which can sequentially oxidize silver shells to be AgI?I₂+2Ag=2AgI?.With the addition of incremental concentration of I^-,the color changes from red to purple,which could be used for the semi-quantitative detection of I^-.A new absorption band emerged at 422 nm,which corresponds to the formation of AgI as mentioned in the literature.Coupled with ultraviolet spectrophotometer,the core/shell NPs was used to analyze I^-and conditions that might affect the experiment were optimized.A method was established for the analysis of I^-in dried kelp.It is worth mentioning that the Au@Ag core/shell NPs-Cu²⁺detection systems were immobilization into agarose gels,which have realized their application in the semi-quantitative determination of I^-in dried kelps.