Bimetallic Gold-Silver Nanocluster Fluorescent Probes For Ions And Micromolecule

The fluorescence detection method based on nanomaterials has the advantages of simple operation,less time consuming and high sensitivity,and has potential application in chemical analysis,environmental monitoring,biological sensing and imaging.Gold-silver nanoclusters(AuAgNCs)are new members of noble metal nanomaterials.In recent years,researchers have been devoted to the controllable synthesis of AuAgNCs,and to explore the atomic-level origin of fluorescence.Bimetallic AuAgNCs possess a series advantages like gold nanoclusters does,such as low toxicity,good water solubility,large Stokes shift,good biocompatibility and so on,they also have higher fluorescence quantum yield and stability,and we can accurately control the number of Ag atoms and doping position to improve their physical and chemical properties.Therefore,this study attempts to prepare AuAgNCs with excellent fluorescent properties,and employ them as the fluorescence signal to construct fluorescent probes for the detection of Cr(III),Cr(VI)and glutathione.The main contents of the study are as follows:Charpter 1:Detection of Cr(III)and Cr(VI)by fluorescent probes based on bimetallic AuAgNCsAuAgNCs were successfully synthesized by using 11-mercaptoundecanoic acid as the reducing agent and capping ligand,and characterized them by UV-vis absorption spectrum,fluorescence spectrum,transmission electron microscopy and X ray photoelectron spectroscopy.In nature,the stable states of chromium are Cr(Ⅲ)and Cr(VI),and they can be transformed into each other.The toxicity of chromium is closely related to its valence state,Cr(Ⅲ)is an essential trace element for biochemical processes,but Cr(VI)is easily absorbed and enriched in human body.The pollution source of chromium comes from various industries sewage.Therefore,the detection of chromium in water samples is of great significance.In this work,we have constructed a fluorescent quenching sensor based on AuAgNCs to detect Cr(Ⅲ)and Cr(VI).Cr(III)can effectively quench the fluorescence of AuAgNCs,utilizing EDTA as the masking agent can realize the highly selective detection of Cr(III).In addition,the effect of ascorbic acid on the fluorescence of AuAgNCs was negligible.Using the redox reaction between Cr(VI)and AA facilitates the detection of Cr(VI)indirectly.Under the optimal experimental conditions,the limit of detection for Cr(Ⅲ)and Cr(VI)were 0.05 μM and 0,3 μM,respectively.The detection results of chromium in real samples showed that the quantitative recoveries were between 96.8%and 100%,which suggests that the proposed method can serve as a reliable candidate for the chemical speciation of chromium.Charpter 2:Detection of glutathione by fluorescent "turn-on" probes based on bimetallic AuAgNCsGlutathione(GSH),a thiol-containing tripeptide,is a well-known endogenous antioxidant,and plays a vital role in defending cellular components against reactive oxygen species and toxins.If cells are under the oxidizd circumstances,it will break the balance between GSH and its oxidized form,glutathione disulfide(GSSG).Under the effect of GSH reductase,GSSH then is promptly transformed into GSH to relieve the oxidative stress of cells.GSH level is directly associated with diseases,such as Alzheimer’s disease,AIDS,cancer,cardiovascular disease,diabetes and so on.Therefore,the development of highly simple,rapid,sensitive and selective detection assays of GSH is in urgent demand for practical application in clinical diagnosis.In this work,we developed a fluorescent "turn-on" method for the detection of glutathione.The fluorescence of AuAgNCs is effectively quenched by Cu2+,the affinity of Cu2+ ions toward the GSH was greater than that toward the carboxyl groups on the surface of the AuAgNCs,Cu2+ was far away from AuAgNCs and the fluorescence is restored.Under the optimal experimental conditions,the concentration of GSH in the range of 2.5-40 μM was linearly correlated with the fluorescence intensity of AuAgNCs,the limit of detection for GSH was 2.5 μM.