Chemistry Synthesis And Enzymatic Study Of Peptide-Protected Fluorescent Au Nanoclusters

Noble metal nanoclusters have been widely used in biological imaging and detection due to their unique properties of light,electricity,catalysis and ultra-small structures.However,metal nanoclusters usually introduce a reducing agent during the preparation process.Most chemical reducing agents,such as citric acid,sodium borohydride may destroy the structure of the biologically active ligand,affecting subsequent coupling and modification,making the synthesis process more difficult to control.In this paper we reference and summarize the previous studies,using the biocompatibility and regulatable reducing ability of the polypeptide without the introduction of a chemical reducing agent,and using the polypeptide as protecting and reducing agent to prepare Au nanoclusters.In this paper,we designed and synthesized a bifunctional polypeptide CCY-GG-Dmt-DArg-F-K-Dmt-DArg-F-K-amide,referred to as CK-9.Domain 1CCY provides the reductive power for the synthesis of Au clusters and also play the role of binding to Au.Domain 2 Dmt-DArg-F-K-Dmt-DArg-F-K has the function of targeting mitochondria.By investigating the synthesis conditions and changing the molar ratio of chloroauric acid to CK-9,we synthesized two kinds of red and green fluorescent Au nanoclusters with different emission wavelengths.These two Au nanoclusters have good dispersibility in an alkaline solution,but they can be Aggregated under neutral conditions which is disadvantageous for cell experiments.Then we studied the fluorescence properties,fluorescence lifetime,particle size morphology,and valence state of the two Au clusters.We found that the two Au clusters of two different fluorescence emission synthesized by the same ligand in different proportions have great differences in fluorescence lifetime,molecular,and composition valence,but there is not so much difference in gold core particle size.Since the different valence states of surface Au,the fluorescence emission mechanism of red and green Au clusters is different.According to X-ray photoelectron spectroscopy?XPS?results and previous research experience,we suspect that the surface of the red Au cluster is Au?0?-S shell,and its fluorescence comes from the electron transfer between Au?0?and S;green Au clusters'surface contains a large amount of Au?I?,and its fluorescence comes from the electronic transition of the sp band to the d band in the Au metal.In addition,we have also confirmed that the synthesized red and green Au clusters have peroxidase activity and are resistant to acid and alkali,and their enzymatic activities are not affected by pH.The optimum catalytic temperature is 50°C,which is slightly higher than the natural enzyme.In the choice of substrate,the red and green Au clusters have higher affinity for TMB than H₂O₂,and the green Au cluster has higher affinity for the substrate TMB than the red Au cluster.