Sensing Technology Based On Catalysis And Fluorescence Characteristics Of Silver Nanomaterials

Silver nanomaterials, typically as silver nanoclusters(Ag NCs), possess excellent size effect, fluorescence properties, peroxidase-like catalysis activity. They have become the hot research topics in the fields of modern material science, chemistry, biology and nanomedicine. For example, these nanomaterials are widely applied in biological marking, cell imaging, enzyme catalysis, heavy metal ions, and biological small molecules sensing. In the present thesis, some silver nanomaterials-based sensing studies are carried out in the following aspects:(1) A temperature-switchable gelatin matrix has been successfully employed for the one-pot synthesis of catalytic small Ag NPs without any reductants. The resulting gel-Ag NPs could display mercury-stimulated catalysis activity toward a simple, rapid, label-free, and high-throughput colorimetric protocol for probing mercury(II) in blood and wastewater using 96-cell plates. The catalysis-based detection mechanism involved was thought to result mainly from the mercury etching of Ag NPs in the gelatin matrix leading to smaller sizes of Ag NPs with greatly enhanced catalysis activity for TMB–H2O2 reactions. The unique property of sol–gel transition of the gelatin matrix could not only facilitate the temperature-switchable catalysis of gel-Ag NPs, but also allow for high catalysis stability of gel-Ag NPs. Remarkably, the catalysis based method could detect Hg2+ ions in complicated wastewater and blood with high sensitivity, selectivity, and throughput. It might also circumvent some disadvantages of traditional detection approaches like fluorescence assays in terms of the detection stability and abilities against interferences from the complicated media.(2) Ag NCs were successfully synthesized and further passivated by GSH ligands to modulate the specific ion recognition from Hg2+ ions to Cu2+ ions inducing the linking or aggregation of nanoclusters with fluorescence quenching. The obtained GSH-passivated Ag NCs could display high aqueous stability and powerful red fluorescence. Meantime, they could present a rational change of UV-vis yellow absorbance spectra depending on the Cu2+ levels. Moreover, the Cu2+-induced loss of fluorescence and UV-vis absorption of GSH-passivated Ag NCs could be well restored by using the Cu2+ chelating agent of EDTA through the ligand exchanging. A simultaneous and reversible fluorimetric and colorimetric analysis protocol using GSH-passivated Ag NCs has thereby been proposed for probing Cu2+ ions in blood with high detection sensitivity and selectivity. Also, the feasibility of fluorescencetrackable live tissue imaging was verified using the fluorescent probes of GSHpassivated Ag NCs. The results indicate that GSH-passivated Ag NCs with high aqueous stability and powerful red fluorescence could not only facilitate the analysis of the meaningful ions in complicated blood, but also allow for biological imaging in live tissue, where the background interferences from the endogenous fluorescent species could be efficiently minimized.(3) Gelatin-silver nanocomposites were synthesized by the gelatin reduction reactions, which were skillfully stopped at a suitable reaction time by quick freezing. The so prepared nanocomposites contained silver nanoparticles and silver ions. It was found that the gelatin-silver nanocomposites showed the specific recognition to the formaldehyde under the alkaline environment. Here, silver ions could be reduced by formaldehyde through the catalysis of silver nanoparticles coming from gelatin-silver nanocomposites. Subsequently, the metallic silver could adhere to the surface of silver nanoparticles, so that the nanoparticles were growing up with a color change. Moreover, gelatin-silver nanocomposites could be fastened to the surface of the capillary with high stability by use of the special property of temperature-induced solgel transition of gelatin. Making use of the capillarity effects, the developed colorimetric sensing system with versatile nanomaterials could be expected to rapidly and visually probe formaldehyde in aquatic products with high detection sensitivity.