The Preparation Of Metal Nanomateirals And Their Application In Analytical Chemistry

Due to a series of special physical and chemical properties, the research on metal nano-materials have turned to be the hotspot in recent years. Colorimetric assays based on metalnanoparticles have the advantages of simpleness, speediness and observation with naked eye,which made them receiving more and more attention. Silver nanoparticles (AgNPs) are easyto be obtained and have remarkable properties known as localized surface plasmon resonance(LSPR), surface enhanced Raman scattering, resonance scattering, electrochemical activityand so on. Due to the strong surface plasmon resonance, AgNPs can be used as sensitiveprobes for colorimetric sensors. It is worth mentioning, extinction coefficient of AgNPs ishigher than that of AuNPs. So, for colorimetric assays, AgNPs have some advantages overAuNPs since they possess higher extinction coefficients relative to AuNPs of the same size.However, compared with AuNPs, little attention has been paid to AgNP-based colorimetricassays. The deeper study into the properties of AgNPs will be helpful to the development andapplication of new technology and new means. In this sense, AgNPs were chosen as researchobject to develop new colorimetric sensors. The concrete research content is as follows:(1) Ultrasensitive and dual functional colorimetric assay for mercury (II) ions andhydrogen peroxide were developed based on catalytic reduction property of silvernanoparticles. When Hg2+and H2O2were sequentially added to AgNPs, AgNPs aggregatedquickly. This was because the reaction of AgNPs and H2O2produced reducing species, whichcould reduce Hg2+to Hg. Due to the strong affinity between Hg and AgNPs, Hg could beeasily adsorbed on the surface of AgNPs through detaching citrate molecules, which resultedin the aggregation of AgNPs. The lowest concentration of Hg2+induced color change ofAgNPs was as low as2nM and the linear range of Hg2+was from0.02nM to0.9μM. ForH2O2, the lowest concentration of H2O2induced color change of AgNPs was50nM and thelinear range was50nM-50μM. Moreover, this sensor was successfully applied to thedetection of real samples.(2) The coexistence of nucleophilic reagents and electron acceptors would oxide and etchAgNPs and eventually AgNPs aggregated, based on which melamine and H2O2werecolorimetrically detected. The color of AgNPs could also change when the concentration ofmelamine in milk was as low as0.6nM or H2O2in rain water was as low as1nM. Therefore,this assay could be used to detect both melamine and H2O2and provided a new way fordetecting nucleophilic reagent and electron acceptor.(3) We have developed a novel sensing platform based on pH-dependent interaction ofAgNPs and H2O2for the selective determination of iodide with different mechanism. In acidicmedium, AgNPs reacted with H2O2to produce Ag+and powerful oxidizing species. Thepowerful oxidizing species could etch AgNPs seriously. While, iodide acted as an antioxidantcould protect AgNPs from oxidation-etching by the powerful oxidizing species. In neutral andalkaline medium, the reaction of AgNPs and H2O2mainly produced Ag+. The existence ofiodide could complex with Ag+, forming AgI, which paved the way for aggregation of AgNPs. Based on these, iodide could be detected. This sensor was applied to detect iodide anion inurine, with recoveries around95%.