Synthesis And Applications Of Fluorescent Gold Nanoclusters

Fluorescent nanomaterials have become the focus of current nanoscience research due to their unique physical properties,ease of preparation,and light stability.To date,scientific researchers have developed several different types of fluorescent nanomaterials,including semiconductor quantum dots,carbon quantum dots,and metal nanoclusters.Among them,metal nanoclusters consist of several to several hundred atoms and have become a new type of luminescent nanomaterials.Their size is in the Fermi wavelength range and shows better electrical,optical and biomedical properties than other larger nanocrystals.In this dissertation,gold nanoclusters were synthesized by simple methods and different applications were studied.The specific method is as follows:?1?One-step hydrothermal method was developed for the preparation of water-soluble gold nanoclusters?Au NCs?with strong fluorescence by using11-mercaptoundecanoic acid?11-MUA?as reducing agent and protective agent.A turn-on fluorescent probe based on Cu²⁺modified Au NCs@11-MUA was developed for detection of DA with high sensitivity and selectivity.After Cu²⁺ions were added in Au NCs@11-MUA solution,the fluorescence of Au NCs@11-MUA was quenched,and the fluorescence signal of the system was in the?off?state.In the presence of DA,a more stable complex than the Au NCs@11-MUA-Cu²⁺complex was formed due to DA and Cu²⁺have a stronger binding force,which result in the departure of Cu²⁺from the surface of the Au NCs@11-MUA,and the fluorescence signal of the system was?open?.The fluorescence recovery degree of the Au NCs@11-MUA probe showed a good linear relationship with the concentration of DA from 0.02⁵.0?M.The limit of detection was estimated to be 8.0 nM?S/N=3?.The present method was successfully applied for the detection of DA in human serum and urine.Recoveries were found to be in the range of 93.2%-97.3%,and the result of statistical calculation shows that relative standard deviations?RSDs?were lower than 4.08%.The results indicate that present method can be applied for the detection of DA in the human body;?2?A fluorescent nanosensor for detecting hemoglobin was designed.The gold nanoclusters were modified with 11-MUA and methionine?Met?.The experimental results show that under the condition of hydrogen peroxide and hemoglobin respectively,the fluorescence of the gold nanoclusters can undergo weak annihilation.However,when both of them were added to the gold nanocluster solution,the fluorescence intensity of the nanoclusters was greatly reduced.After analysis,it was proved that it is based on the hemoglobin catalyzed generation of hydroxyl radicals.Under optimized conditions,the hemoglobin concentration and fluorescence intensity showed a good linear relationship in the range of 0.08⁸.0?M,and the detection limit was as low as 0.047?M?S/N=3?.This provides a fast,sensitive method for quantitative analysis of hemoglobin.And this method is successfully used for actual sample analysis;?3?We prepared gold nanoclusters quickly and simply by using green synthesis method with tryptophan as protective and reducing agent.The optical properties and the size of the gold nanoclusters were characterized by UV-vis absorption spectroscopy,fluorescence spectroscopy and transmission electron microscopy.The Trp-Au NCs have a maximum emission wavelength of 457 nm.We have developed a new method for the detection of nitrite ions,and this method has good selectivity and high sensitivity.Nitrite ions can cause aggregation of Trp-Au NCs and significantly reduce the fluorescence intensity of Trp-Au NCs.Since the level of fluorescence intensity is negatively correlated with the concentration of nitrite ions,we use this method for the detection of nitrite ions.The fluorescence intensity decreased proportionally with the increase of nitrite ion concentration,and the nitrite ion detection limit calculated by this method was as low as 0.042?M?S/N=3?.In addition,the detection method has a high selectivity for nitrite ion and has been successfully used for the detection of nitrite ions in pickles.