The Preparation And Plasma Optical Response Of Chiral Silver Nanoparticles

Chiral silver nanoparticles have attracted great interest in recent years because of their widely applications in chiral discrimination,chiral catalysis and the field of chiral optical.In this paper chiral silver nanoparticles were prepared by photochemical reduction and liquid-phase chemical reduction with different chiral small molecules as chiral inducers and modifiers.The prepared silver nanoparticles are characterized by UV-vis Spectrometer,circular dichroism spectrometer（CD）and Transission Electron Microscopy（TEM）.The mechanism of the chirality of silver nanoparticles was discussed.NaDC-capped silver nanoparticles were prepared with AgNO₃ as precursor in the presence of deoxycholate sodium as chiral inducer and stabilizer by photochemical reduction method.Silver nitrate in the mixed solution of AgNO₃ and deoxycholate was reduced by the UV light irradiation at pH=10.When the molar ratio of sodium deoxycholate to Ag+ was 6:1,the chiral signals of silver nanoparticles are the strongest.The rate of reduction reaction is relatively slow when molar ratio of sodium deoxycholate to Ag+ is low.The SPR absorption band of the generated silver nanoparticles locates at around 455 nm with wide half band width.The size of the particles is larger and the size distribution is wide.With the increase of the molar ratio,the rate of reduction reaction is relatively fast.The size of the silver nanoparticles produced in the solution is uniform,and the size of the particles is small with narrow half band width.The yellow-green silver nanoparticles were prepared with AgNO₃ as precursor by reduction of AgNO₃ with fresh prepared solution of NaBH4 by liquid-phase chemical reduction method.The NaDC-modified silver nanoparticles were prepared by ligand exchange reaction.With the increase of the concentration of sodium deoxycholate,the intensity of SPR absorption peak of silver nanoparticles gradually increased,and the half band width was gradually decreased.The position of the maximum absorption peak of SPR of silver nanoparticles exhibited a blue shift.With the increase of sodium chloride,the absorption peak of silver nanoparticles at 400 nm gradually decreased,and the position of the maximum absorption peak of SPR had a red shift.The half width of the absorption band of the silver nanoparticles gradually narrowed,and a new SPR absorption peak appeared at about 600 nm.The addition of an appropriate amount of HCl solution to the silver nanocolloid solution can promote the aggregation of the nanoparticles and enhance the chiral signal of the silver nanoparticles.By reduction of AgNO₃ with fresh prepared solution of NaBH4,yellow-green silver nanoparticles were prepared with AgNO₃ as precursor by liquid-phase chemical reduction method.The L-His-modified silver nanoparticles were prepared by ligand exchange reaction.L-His is an amino acid that exists in the form of zwitterion.Electrostatic interactions between the protonated amino group and the carboxyl group exist,which can induce the aggregation of histidine-modified silver nanoparticles.When the concentration of L-His is relatively low,the aggregation degree of silver nanoparticles is low,the particles aggregated orderly,causing the local electromagnetic field to enhance,so that the CD signal enhanced.When the concentration of L-His continues to increase,it will cause the degree of particle aggregation to increase,resulting in disorder aggregation of the particles,so that the CD signal of the particles weakened.Adding the appropriate amount of NaCl to the silver nanocolloid solution can promote the aggregation of the nanoparticles and enhance the CD signal of the silver nanoparticles.