Gold Nanoparticles Synthezied By Microwave-assisted Heating Method And Hydrothermal Method And Its Applications In Spectral Analysis

Gold nanomaterials have the advantages of good stability, simple preparation,uniform particle size, strong affinity, good biocompatibility and easy to biolabeling,which could be widely used in nano-biosensors and the diagnosis and treatment of thedisease. Gold nanomaterials with different shapes and sizes of can be synthesized bycontrolling the conditions and methods during the synthesizing process. Goldnanomaterials can be used in various fields in analytical chemistry. It is of mostimportance to synthesize gold nanomaterials with better properties, better stability, andmore uniform. In this thesis, we started from the establishment of new synthesismethods to synthesize gold nanoparticles.Microwave-assisted heating methods andhydrothermal methods were used. The conditions of the synthetic process wereoptimized and the characters of the as-prepared gold nanomaterials were measured. Theapplications of the as-prepared gold nanomaterials in different fields were determinedby spectrophotometry method.The main contents and conclusions are as follows:1. Gold nanoparticles （GNPs） were synthesized by microwave-assisted heatingunder reflux, using trisodium citrate as the reducing agent. GNPs had a maximumabsorption peak at520nm, with an average diameter of13.3nm in spherical shape.GNPs were then successfully used in the fluorescence quenching of lysozyme. Thefluorescence intensities of lysozyme were declined gradually with the increase of theconcentration of the GNPs. The fluorescence quenching mechanism was studied by theStern-Volmer quenching constant and the bimolecular quenching constant through theStern-Volmer equation. It was proved that the reactions of GNPs and lysozyme werestatic quenching processes. Binding constant and the number of the binding site of thereaction systems were also calculated. There is only one single binding site in lysozymewas existed for GNPs, while the binding constant increased with the increase of thetemperature, which suggesting that the interaction was endothermic. As can be inferredfrom the thermodynamic parameters, the binding processes between GNPs andlysozyme were spontaneous, while accompany with a strong contribution of thehydrophobic effect.2. GNPs synthesized by microwave-assisted heating method were successfullyused as catalyst in the borohydride reduction of nitrophenols without any further modification. The reaction could be monitored by time-dependent UV spectra. Theconcentration of NaBH4in the reactive system was so much excess to that of p-NP, sothat the rates of the reduction are assumed to be independent of the concentration ofNaBH4, and thus the kinetics of the reduction could be treated as pseudo-first-order inp-NP concentration. The apparent rate constant of the reaction system raised almostlinearly with the increase of the GNPs concentrations. Under the same reactionconditions, the apparent rate constant of different isomeric nitrophenols followed theorder m-nitrophenol> p-nitrophenol> o-nitrophenol. The reason why these phenomenahappened was analyzed.3. Gold nanoparticles with a13nm diameter were synthesized by using trisodiumcitrate as the reducing agent and modified by2-thiobarbituric acid （TBA）. Aftermodification, the maximum absorbance wavelength shifted from520to524nm. Themodified TBA-GNPs were pH-sensitive, and were hopefully applied in the research ofpH sensors. Compared with GNPs with no modification, TBA-GNPs existed morestability, and contained more negative charges, which causing the GNPs more stable inNaCl solutions and more sensitive by adding metal ions. The catalytic activity ofTBA-GNPs was determined, and was compared with unmodified GNPs. It was provedthat the catalytic activity of TBA-GNPs was reduced obviously either in theborohydride reduction of nitrophenols or redox reaction between potassium ferricyanideand sodium thiosulfate. The reason why this happened was analysed.4. BSA-gold nanoclusters with red fluorescence were synthesized by hydrothermalmethod at90oC for40min were reported, using BSA as the reducing regent. Themaximum excitation and emission wavelength was550and650nm, respectively. ALissamine rhodamine-B sulphonyl chloride （LRSC） dye solution was used as areference, and the quantum yield of the BSA-gold nanoclusters synthesized byhydrothermal method was1.11%. The fluorescence intensity of BSA-gold nanoclusterscould be switched on and off by controlling the pH value of the solution. SuchBSA-gold nanoclusters could be precipitate in acidic conditions or re-disperse inalkaline conditions. The BSA-gold nanoclusters could be used as fluorescence probe forHg²⁺sensing with high sensitivity and selectivity. The fluorescence intensity ofBSA-gold nanoclusters toward Hg²⁺decreased linearly over the Hg²⁺concentrationrange of2×10^-7to1×10^-5M. The limit of detection （LOD） for Hg²⁺was0.6×10^-7M.Under similar conditions, HSA-gold nanoclusters with red fluorescence were alsosynthesized by hydrothermal method.5. Ovalbumin-gold nanoclusters were synthesized by water bath heating method at 37oC and hydrothermal method at90oC, using ovalbumin as the reducing regent. Whenthe concentration of HAuCl4was constant at2.33mM, the optimum reaction conditionswere discussed and the best reaction concentration of ovalbumin and NaOH were10.71mg mL^-1and0.095M, respectively. The fluorescence intensity of OVA-goldnanoclusters reached to its maximum values when reacting at37oC,6h for water bathheating and at90oC,30min for hydrothermal heating. The maximum fluorescenceemission were636and637nm for gold nanoclusters synthesized by water bath heatingor hydrothermal heating, respectively, with bright red color. FT-IR spectra of theOVA-gold nanoclusters synthesized by different ways suggested that OVA weremodified on the surface of the gold nanoclsters successfully. While keeping theconcentration of all the reactants constant, the FL intensities of OVA-gold nanoclusterssynthesized by different ways were observed. The results suggested that OVA-goldnanoclusters synthesized by hydrothermal method have the highest FL intensity.