Studies On End-to-end Assembly Of Gold Nanobipyramids And Chiral Spectral Analysis Of Its Core-shell Silver Nanostructure

Gold nanobipyramids(Au NBPs)are considered as very promising metal nanomaterials owing to their excellent surface plasmon resonance performance.At present,the research of Au NBPs mainly focuses on photothermal therapy,catalysis,and biochemical sensing,etc.while the development of directional assembly is still insufficient.The directional assembly of Au NBPs,especially the end-to-end assembly,is difficult owing to the difficulties resulting from the existence of complex nanoscale forces among plasmonic nanoparticles and their sharp tips.On the other hand,the strong electromagnetic field at the tip of Au NBPs is conducive to enhance the plasmonic chirality,but the study of plasmonic chiral spectroscopy based on Au NBPs has not yet been developed.Therefore,this thesis took Au NBPs as the research object and aimed at the oriented assembly and plasmonic chiral spectroscopy research of Au NBPs,and carried out the following research:1.Application of end-to-end assembly of gold nanobipyramids in analytical sensing.The study found the simple regulation of Cysteine(Cys)and hydrochloric acid made the end-to-end directional assembly of Au NBPs.The dipole coupling between the nanoparticles in the assembly led to a decrease in the intensity of the longitudinal plasmon resonance absorption peak,and a new absorption peak appeared at the long wavelength.Scanning electron microscopy further confirmed that the end-to-end orientation of the assembly.This is a universal and simple directional assembly method.When the concentration of Cys was 500 nmol/L,the change in the intensity of the longitudinal plasmon resonance absorption peak had a good linear relationship with the concentration of HCl in the range of 0.001–0.04 mol/L.On this basis,the determination of Cys was further realized with a linear range of 0.15–0.5 ?mol/L and a detection limit of 24 nmol/L.Compared with previous reports,our method is simple and can be carried out without any other complicated additives and cumbersome procedures.2.Study on chirality spectroscopy based on chiral molecule cysteine-mediated silver coating on gold nanobipyramids.Chiral nanoparticles with gold nanobipyramids as the core were obtained by using the chiral molecule Cys to mediate the growth of silver on the surface of Au NBPs.It systematically studied that the plasmon-induced chirality of this chiral nanoparticle transferred from the plasmon resonance region of Au NBPs to the plasmon resonance region of Ag.During the growth process,we confirmed that Cys in the Ag nanoshell was very important for the plasmonic chirality signal,and found that Cys had the accelerating effect for the deposition of Ag atoms on the surface of Au NBPs.Different concentrations of L-Cys accelerated the deposition rate in different degrees.Among them,the mediated progress at 5 ?mol/L and 10 ?mol/L L-Cys reacted fastest.As the concentration of L-Cys increased,the rate of Ag deposition decreased.This was because the inhibitory effect of the sulfhydryl group counteracted with the accelerating effect of amino or carboxyl groups of the Cys molecule.In addition to accelerating the deposition of Ag atoms on Au NBPs by Cys,the direction of Ag growth on the surface of Au NBPs has changed to be a lateral growth.In the end,the discrimination of Lhomocysteine,L-cysteine,and L-glutathione with low concentrations was realized by naked eye via the reaction.In summary,firstly,by taking Au NBPs as the research object,we achieved the endto-end directed assembly of Au NBPs through a simple method and applied it for the detection of Cys.Secondly,we discovered plasmon-induced chirality transfer and the important role of chiral molecules in generating plasmonic chirality was revealed by using chiral molecules to mediate the process of Ag deposition on the surface of Au NBPs.Besides,L-homocysteine,L-cysteine,and L-glutathione was distinguished by nake eyes via this reaction.The study expands the application range of Au NBPs and their core-shell nanostructures in the field of analysis and helps to understand chiral plasmonic nanomaterials more deeply.It opens new possibilities for chiral plasmonic systems.