Synthesis,Characterization And Application Of Fluorescent Carbon-Based Nanoribbons And Noble Metal Alloy Nanoclusters In Sensors

Fluorescent carbon-based nanomaterials and noble metal alloy nanoclusters, as two novel fluorescent nanomaterials, not only possess unique optical properties, but also have chemical stablity and good biocompatibility. Therefore, they are considered as potential substitutes for semiconductor quantum dots. However, there are some challenges in the preparation and application of the two fluorescent nanomaterials. Firstly, the fluorescence quantum yield of the as-prepared two fluorescent nanomaterials is usually too low, which is not beneficial to develop fluorescent sensor. Secondly, uncertainty of the surface groups and the lack of diversity of fluorescent carbon-based nanomaterials lead to the limitation of their application. Therefore, the development of new preparation of fluorescent carbon-based nanomaterials and noble metal alloy nanoclusters with unique optical properties and how to make it applicable in more and more fields are very important. In this thesis, firstly, we prepared the oxygen-doped carbon-based nanoribbons and noble metal alloy nanoclusters. Then, we investigated their unique physical and chemical, and optical properties. Finally, we used them in the application of environmental and biological analysis.The main contents of the thesis consist of the following four parts:1、We propose a simple label-free method for the detection of sulfide (S^2-) ions with high selectivity and sensitivity by using fluorescent core-shell Au@Ag NCs （prepared according to the literature） in aqueous solution. The surface of the NCs possesses a small amount of Ag+ cations or Ag atoms, which should have strong and specific interactions with the S^2- ions due to the very low solubility product （Ksp） value of Ag₂S. Therefore, the introduction of S^2- ions could generate Ag₂S layers on the Au@Ag NC’s surfaces through the interaction between S^2- ions and the Ag atoms/ions and effectively quenches the fluorescence of the Au@Ag NCs, which allowed the determination of S^2- ions in a very simple and rapid way. Under the optimal conditions, an excellent linear relationship was present due to quenching of the Au@Ag nanoclusters over S^2- ions concentrations between 0 and 700 μM. Meanwhile, based on fluorescent intensity of the Au@Ag NCs, we could also semi-quantitatively detect the concentration of S^2- ions.2、simple and label-free fluorescent assay for the sensitive determination of biological thiols was developed using Au@Ag nanoclusters. The sensing approach was based on the strong affinity of thiols to silver on the surface of the nanoclusters. In the presence of thiol-containing amino acids, the fluorescence of the Au@Ag nanoclusters was quenched due to the formation of a non-fluorescent coordination complex via the robust Ag-S bond, which allowed the determination of thiol-containing amino acids in a very simple and rapid way. Under the optimal conditions, an excellent linear relationship was present due to quenching of the Au@Ag nanoclusters over cysteine concentrations between 20.0 nM and 80.0 μM with a low detection limit of 5.87 nM. Glutathione was determined between 2.0 μM and 70.0 μM with a detection limit of 1.01 μM. In addition, the results reveal that the fluorescent assay has excellent selectivity toward thiol-containing amino acids compared to non-thiol containing amino acids. Moreover, the assay was successfully used to determine cysteine in human plasma, and thus Au@Ag nanoclusters are a suitable fluorescent probe for biological applications.3、A one-pot route has been developed for the preparation of bovine serumalbumin-templated nickel-doped bimetallic gold-nickel nanoclusters （Au-Ni NCs） at a 10:1 M ratio of the precursor salts in a BSA matrix under alkaline conditions. The metal ions are reduced to the metal alloys by BSA. The resulting NCs display strong fluorescence and dual emission with peaks at 405 and 640 nm, respectively, under excitation at 340 nm. Fluorescence is strongly enhanced on addition of Cd（Ⅱ） ions, but quenched on addition of Hg（Ⅱ） ions. The findings have been exploited to design a fluorometric method for the separate determination of Cd（Ⅱ） and Hg（Ⅱ）, respectively. The optimized analytical nanosystem displays relatively good dynamics between enhancement and quenching. Cd（Ⅱ） and Hg（Ⅱ） can be quantified in the 0 to 200.0 μM and 0 to 24.0 μM, respectively. The limits of detection are-1.8 nM in both cases, which indicates the highest sensitivity to Cd（Ⅱ） and Hg（Ⅱ） ions for a fluorescent probe. This new kind of nanocrystal probe is hardly interfered by a range of commonly encountered metal ions. Its advantages were demonstrated by determining Cd（Ⅱ） and Hg（Ⅱ） ions in spiked serum samples.4、This work reports on a facile, economical, and green preparative strategy toward water-soluble, fluorescent oxygen-doped, nitrogen-rich, photoluminescent polymer carbon nanoribbons （ONPCRs） with a quantum yield of approximately 25.61% by the hydrothermal process using uric acid as a carbon-nitrogen source for the first time. The asprepared fluorescent ONPCRs showed paddy leaf-like structure with 80-160 nm length and highly efficient fluorescent quenching ability in the presence of mercury（Ⅱ） (Hg²⁺) or silver （Ag+） ions due to the formed nonfluorescent metal complexes via robust Hg²⁺-O or Ag+-N interaction with the O and N of fluorescent ONPCRs, which allowed the analysis of Hg²⁺ and Ag+ ions in a very simple method. By employing this sensor, excellent linear relationships existed between the quenching degree of the ONPCRs and the concentrations of Hg²⁺ and Ag+ ions in the range of 2.0 nM to 60.0 μM and 5.0 nM to 80.0 μM, respectively. By using ethylenediaminetetraacetate and ammonia as the masking agent of Hg²⁺ and Ag+ ions, respectively, Hg²⁺ or Ag+ ions were exclusively detected in coexistence with Ag+ or Hg²⁺ ions with high sensitivity, and the detection limits as low as 0.68 and 1.73 nM （3σ） were achieved, respectively, which also provided a reusable detection method for Hg²⁺ and Ag+ ions. Therefore, the easily synthesized fluorescent ONPCRs may have great potential applications in the detection of Hg²⁺ and Ag+ ions for biological assay and environmental protection.In summary, we explored a novel method to synthesize fluorescent carbon-based oxygen-doped nanoribbons and noble metal alloy nanoclusters. And then, those fluorescent nanomaterials are applied to the detection of heavy metal ions in environmental analysis, and we also developed the application of core-shell Au@Ag NCs in environmental and biological analysis.