The Green Synthesis Of Gold Nanoparticles And The Applications In Optics And Electrochemistry

Gold nanoparticles have been widely used in catalysis,molecular detection,bioimaging and other fields due to its unique physical and chemical properties.The gold nanoparticles with the size of 2-100 nm show the surface plasmon resonance effect,which can be used for surface enhanced Raman scattering(SERS)detection.The gold nanoclusters with the size less than 2 nm show the fluorescent properties,which can be used for bioimaging field.Gold nanoparticles can also be used for electrochemistry detection.However,it’s easy to introduce impurities in the gold nanoparticles which are synthesized through the current widely used chemical method,thus cause some interference to electrochemistry detection.To solve this problem,we utilize the method of gamma ray irradiation to prepare the gold nanoparticles and use it for electrochemistry detection.Gamma ray irradiation is a green and clean experimental method,gamma ray can react with chloroauric acid solution directly at room temperature,no additives and by-products,the process is simple and the product purity is high.Besides,the size and shape of the prepared gold nanoparticles can be changed by changing the gamma irradiation dose and the chloroauric acid solution concentrationThis paper utilized the simple method of "one pot",using sodium citrate as the reductant and stabilizer to synthesize gold nanoparticles and then the obtained gold nanoparticles were further used to prepare Au/Ge active substrate.And the Au/Ge active substrate was used for SERS detection.Utilizing the method of gamma ray irradiation to prepare gold nanoparticles and used it in the electrochemistry detection of dopamine.Utilizing the method of "one pot" to synthesize fluorescent gold nanoclusters BSA-Au NCs with bovine serum albumin as the stabilizer and reductant,and the effects of gamma ray irradiation on the fluorescence properties of BSA-Au NCs was studied firstly.In addition,the application of the prepared BSA-Au NCs in bioimaging was slao studied by us.The main contents were as follows:(1)A noble metal/semiconductor Au/Ge SERS substrate was prepared and its SERS performance was studied.The gold seeds in diameter of about 20 nm were synthesized with the method of "one pot",using sodium citrate as reducing agent and stabilizer.After that,the uniform dense gold membrane was obtained through gas-liquid interface self-assembly.Then the gold film placed on Ge wafer was put into muffle furnace with burning to get Au/Ge substrate.Rhodamine 6G,4-mercaptobenzoic acid and Sudan Red I were detected as probe molecules by this Au/Ge substrate respectively.Results showed that the three molecules at the concentration of 1×10-10 M could be clearly and persistently detected by this obtained Au/Ge substrate.Showing the excellent SERS effect of high sensitivity,high stability and good repeatability for this Au/Ge substrates.Electric field distribution of the substrate was also simulated by the three-dimensional finite-difference time-domain(3D-FDTD)method at the same time.The simulation exhibited that the "hot spot" was formed between two gold nanoparticles on Au/Ge substrate,which led to the excellent SERS performance.(2)Uniform and stable gold nanoparticles were synthesized by a green gamma ray irradiation method and then were used for electrochemistry study.Chloroauric acid solution was directly irradiated by an optimal 80 kGy doses of gamma rays to generate gold nanoparticles with the diameter of about 50 nm.The obtained gold nanoparticles were used for electrochemistry detection with dopamine as the probe molecule,and the electrochemical behavior of it was also studied.The result suggested that the gold nanoparticles modified glassy carbon electrode showed favourable electrochemical performance for dopamine detection with high sensitivity,good repeatability and excellent stability,and the limit of detection is 0.1μM.(3)A red fluorescent gold nanoclusters stabilized by bovine serum albumin BSA-Au NCs(Ex=470 nm,Em≈660 nm)was synthesized with the "one pot" method.The effects of gamma ray irradiation on the fluorescence properties of BSA-Au NCs suspension were also studied firstly.There are mainly three kinds of free radicals emerged in y-ray irradiated aqueous solution,known as the oxidizing hydroxyl radicals(·OH),the reducing hydrogen radical(·H)and the hydrated electron radicals(eaq-).The corresponding free radical capture agents were added to the BSA-Au NCs suspension respectively,then exposured to gamma irradiation.The effect of radicals on fluorescence changes of the BSA-Au NCs suspension after irradiation was observed.Oxygen was employed as the reductive free radical scavenger and ethanol as the oxidizing free radical scavenger.The results showed that the reductive radicals could enhance the fluorescence degree while the oxidizing radicals reduced the fluorescence degree.It’s instructive to further expound the light-emitting mechanism of fluorescent gold nanoclusters.In addition,cell toxicity and biological imaging experiments were performed and proved that the BSA-Au NCs suspension had very weak cell toxicity and a better biological imaging effect after 40 kGy y-ray irradiated with ethanol.In conclusion,the prepared gold nanoparticles have good SERS performance and electrochemistry catalytic properties.The experiment of gamma ray irradiation on BSA-Au NCs suspension proved that the reductive radicals produced by irradiation could enhance the fluorescence degree of BSA-Au NCs while the oxidizing radicals reduced the fluorescence degree.Moreover,the fluorescent BSA-Au NCs have a good application prospect in the field of bioimaging.Besides,gamma ray irradiation method can be widely used in the material preparation and has broad evolutive space as a green and environment friendly preparation means.