Application Research Of Fluorescent Probe Based On Gold Nanoclusters

Fluorescence method is very promising due to its advantages over other methods,including simplicity,selectivity,sensitivity,low instrument cost and convenience,and is widely used for quantitative analysis in the field of environment and biochemistry.Various fluorescent probes was synthesized,such as semiconductor quantum dots,organic compounds,carbon nanomaterials and metal nanoclusters.However,it is complicated to synthesize organic compounds,and quantum dots are environmental toxicity.In addition,carbon nanomaterials are usually synthesized at high temperatures.Herein,gold nanoclusters were selected as fluorescent probe for analytical applications.Gold nanoclusters as novel fluorescent probe may open a new window of interest in the field of fluorescence analysis due to their non-toxic and unique optical properties,good biocompatibility,simple synthesis process.While there are problems need to be solved urgently,such as the fluorescence quantum yields of gold nanocluster,the sensitivity and selectivity of the fluorescent probe.To our knowledge,the study of aggregation induced emission properties?AIE?is limited to thiol compound capped gold nanoclusters,whether non-thiolate ligands capped gold nanoclusters exhibit AIE behavior is worth studying.Accordingly,three kinds of fluorescent probes based on gold nanoclusters were designed and applied to quantitatively analyze the targets in environmental and biological samples.The detailed content are divided into the following three parts:Part 1:Contrary to organic solvent-induced aggregation of gold nanoclusters,herein,we reported aggregation induced emission enhancement?AIEE?of gold nanoclusters in an aqueous media through confinement of gold nanoclusters by in situ formed Zn-MOF for detecting Zn²⁺.Glutathione capped AuNCs?GSH-AuNCs?was synthesized through reduction of Au³⁺by glutathione.Zn²⁺could significantly enhance the fluorescence of GSH-AuNCs upon addition of 2-methylimidazole?2-MIM?,which was attributed to the formation of Zn-MOF.XRD and TEM were used to characterize the in situ formed Zn-MOF,TEM demonstrated the aggregation behavior of GSH-AuNCs.The quantum yields?QYs?of GSH-AuNCs after aggregation induced by in situ formed Zn-MOF attained to 36.6%,which was nearly 9 times that of the sole GSH-AuNCs.On this basis,a fluorogenic sensor was reported for Zn²⁺detection with a linear range from 12.3 nM to 24.6?M and a detection limit of 6 nM?S/N=3?.This method was applied to Zn²⁺in actual samples and the results are satisfactory.Part 2:In this work,the novel AIE-type AuNCs were synthesized through the capping ability of kojic acid?KA?,a non-thiolate green ligand.The KA-AuNCs exhibited excellent optical properties,such as bright green fluorescence at 500 nm upon excitation at 375 nm and a nanosecond level fluorescent lifetime?0.37 ns?.The QYs of the KA-AuNCs was as high as 22%in aqueous solution,which was higher than most of the previously reported AuNCs.Surprisingly,the QYs increased dramatically to 58%due to the aggregation induced behavior of KA-AuNCs in ethanol solution with the prolonged lifetime of 1.30 ns.Interestingly,the large agglomerates appeared after addition of Eu³⁺and the fluorescence of KA-AuNCs was quenched significantly,for there existed charge transfer between KA-AuNCs donor and Eu³⁺acceptor which competes with and overcomes the radiative pathway to reduce the fluorescence intensity.While the formed agglomerates get dispersed upon addition of PO₄^3-because of stronger affinity between PO₄^3-and Eu³⁺than that between KA-AuNCs and Eu³⁺.Based on these findings,a sensitive and simple PO₄^3-fluorescence sensor was developed,the linear range is 40 nM-20?M and the LOD is as low as 23 nM?S/N=3?.The proposedsensor was successfully applied to assay the activity of ALP and to screen its inhibitor.In aword,Unconventional AIE-type KA-AuNCs modified by non-thiol compounds with high quantum yield and excellent stability were prepared,which may open a newperspective for the investigation of the AIE property.Part 3:In this study,by using L-histidine caped gold-nanoclusters?His-AuNCs?as both fluorescence indicator and enhancer,we report a simple and label-free ratiometric fluorescent platform for sensitively and selectively sensing of tetracycline?TC?.The His-AuNCs were facilely prepared by chemical reduction of Au?III?by L-histidine as both the reducer and the protecting agent.The synthesized His-AuNCs exhibited good stability?such as outstanding stability toward high ionic strength conditions,and storage stability?and good optical properties,such as bluish green fluorescence at 475 nm when excited at 375 nm.Impressively,when co-existing with Eu³⁺ions,the His-AuNCs/Eu³⁺system displays strong fluorescent emission of His-AuNCs at 475 nm and the weak characteristic emission of Eu³⁺at 620 nm.Interestingly,upon further introduction of TC into the His-AuNCs/Eu³⁺system,fluorescent emission of His-AuNCs is quenched,while the characteristic emission of Eu³⁺at 620 nm is greatly enhanced,which is attributed to the formation of the His-AuNCs–Eu³⁺–TC system.Thus,a ratiometric fluorescent signal can be acquired and used for the detection of TC by simply mixing His-AuNCs and Eu³⁺.Under the optimized conditions,the linear range from 10 nM to60?M and a detection limit of 4 nM?S/N=3?for TC were obtained.The application of the assay platform for the detection of TC in environmental and biological samples was demonstrated.The sensing platform promises advantages of easy preparation,rapid response,high sensitivity and good selectivity,showing great potential in chemo/biosensing.