Preparation And Application Of Chiral Molecularly Modified Precious Metal Nanoparticles

Noble metal nanomaterials have very important applications in many frontier fields because of their unique optical and catalytic properties.In this paper,Au nanoparticles,Au@Ag-NPs and Au@Ag@mSiO₂ were successfully prepared by photochemical reduction,liquid-phase chemical reduction and sol-gel method.The chiral Au nanoparticles,Au@Ag-NPs and Au@Ag@mSiO₂ were prepared by using sodium cholate?NaC?and cysteine?Cys?as chiral inducers.The formation mechanism of the chiral nanoparticles was studied.And the effects of nanoparticles on their optical properties and ultraviolet-visible absorption were investigated by changing the experimental conditions.Au nanoparticles with chiral signal,good dispersion and stability were prepared by photochemical reduction with ultraviolet light as light source and chiral sodium cholate?NaC?as reductant.Because NaC molecule contains carboxyl group and hydroxyl group,hydroxyl group is oxidized under the excitation of ultraviolet light.At the same time,the original HAuCl4 forms gold nanoparticles.The addition of sodium hydroxide in the system helps to accelerate the photochemical reduction reaction rate.NaC molecule can be chemically adsorbed on the surface of gold nanoparticles by carboxyl group.When NaC concentration is not very high,the hydrophobic interaction between NaC molecule which grafted into gold nanoparticles leads to the easy aggregation of gold nanoparticles.The aggregated particles cause the coupling between chiral small molecules and gold nanoparticles due to the"hot spot"effect.The polar-dipole interaction is enhanced,and the chirality of small chiral molecules is transmitted to gold nanoparticles,so that chiral signals appear in the plasma resonance region of gold nanoparticles.Decreasing NaC concentration is helpful to enhance the CD signal of gold nanoparticles.Au@Ag-NPs core-shell nanoparticles were prepared by liquid-phase chemical reduction method.Au@Ag-NPs were modified with chiral small molecule L-Cys to have chiral signals in the 200-350 nm range.In weak acidic solution,the carboxyl group of cysteine molecule exists in the form of-COO^-and the amino group exists in the form of-NH₃⁺.The surface of cysteine molecule and Au@Ag-NPs can be chemically adsorbed by S-Ag bonding.Cysteine adsorbed on the surface of nanoparticles interacts electrostatically and hydrogen bonds between-COO^-and-NH₃⁺molecules to form a supramolecular chiral structure,which is the source of chiral signals in the 200-350 nm range.The concentration of cysteine has a great influence on the CD signal.With the increase of cysteine concentration,the CD signal increases gradually.It was found that the adsorption of cysteine on Au@Ag surface conformed to the first-order kinetics.Au@Ag@mSiO₂ was prepared by coating gold and silver core shell with mesoporous silica,and oxidative etching of Au@Ag was carried out to facilitate the adsorption of cysteine molecules.A method using etched mesoporous silica coated Au@Ag@mSiO₂ as probe was constructed to detect copper ions in solution by using copper ions as catalysts for oxidation of cysteine.In order to improve the efficiency of copper ion catalyzing the oxidation of cysteine,hydrogen peroxide was introduced into the reaction system,and the oxygen released from the decomposition of hydrogen peroxide was used to catalyze the oxidation of cysteine,so that copper ion could be detected at a lower concentration.It is found that when the concentration of copper ion is in the range of 20 nM¹0?M,the negative logarithm of the concentration of copper ion is linearly related to the CD signal at 200³50 nm.The detection platform can be used to quantitatively detect the concentration of copper ions in solution.