Formation Mechanism Of Cysteine Molecular Network On The Surface Of Gold Nanorods And Its Application In The Detection Of Copper Ions

Chirality exists widely in nature.Among them,many biomolecules and some drug molecules have this chirality because of their structural asymmetry.Chiral molecules have a pair of enantiomers with opposite chirality.Although the two enantiomers of the same molecule have similar chemical and physical properties,their biochemical properties are obviously different.One enantiomer may have drug effect,while the other enantiomer may be toxic.In general,the analysis of these enantiomers depends on their small differential absorption between right-handed and left-handed circularly polarized light,namely circular dichroism(CD).However,because the size of these molecules is very small and their differential absorption is small,the CD signal is very weak,so a large molecular concentration is needed to meet the requirements of analysis,which is not conducive to the analysis and detection of trace molecules.Chiral nanostructures can be used to improve the circular dichroism signal of chiral molecules and improve the sensitivity of CD measurement.Cysteine is a common chiral amino acid.At present,cysteine molecules have been widely used in chiral research.When chiral cysteine interacts with anisotropic gold nanorods,chiral cysteine molecules bind to the surface of gold nanorods by gold-sulfur covalent bonds,and interconnect by intermolecular hydrogen bonds to form a unique helical molecular network structure.The formation of chiral cysteine molecular network on the surface of gold nanorods means that there may be other states compared to the discrete chiral cysteine found in previous studies.In recent years,the development of nanomaterials has further promoted the precise construction and functional adjustment of chiral nanostructures.Among them,gold nanorods are anisotropic nanoparticles,which show different optical properties in transverse and longitudinal direction.It has a wide range of applications in fluorescence analysis,dark field imaging,Raman spectroscopy and so on.In addition,gold nanorods have also been used in the construction of chiral structures and chiral molecular recognition,including controllable gold nanorods assembly or growth based on chiral molecules or DNA origami techniques,and chiral molecular signal recognition and discrimination based on hot spots of polaritons on the surface of gold nanorods.At present,it is widely believed that the chirality of precious metal nanostructures mainly comes from the excitation of special chiral geometric structures or the induction of chiral molecules,which means that the geometric structure and composition of precious metal nanostructures are of great significance to their chirality.On the other hand,the resonance enhancement effect of plasmon on the surface of precious metal nanoparticles also limits the further development of the discrete distribution of molecules,and the special binding mode of molecular network shows great potential in chiral nanomaterials and analytical applications.In view of this,the main research contents of this work are as follows:Part I: Study on the molecular network structure of chiral cysteine on the surface of gold nanorods.The chiral signal change of the molecular network can reveal the adhesion density of cysteine molecules on the surface of gold nanorods.To explore the changing rules and principles of molecular networks when changing different conditions,so as to lay a theoretical foundation for the expansion and application of subsequent molecular networks.First of all,this work explored the distribution and density of molecular networks on the surface of gold nanorods by changing the concentration of cysteine,and obtained the range of cysteine concentration needed to form molecular networks on the surface of gold nanorods.Then,by changing the reaction temperature of cysteine molecules with gold nanorods,the appropriate temperature for forming molecular networks on the surface of gold nanorods was explored.Secondly,by changing the p H conditions of the solution environment,the formation and signal intensity of molecular networks under different conditions were observed to examine the effect of acidity on molecular networks.Finally,cysteine can bind with gold nanorods by gold sulfur bond and further form a molecular network by hydrogen bond,but the formation of this molecular network on the surface of gold nanorods will also be affected by other molecules containing similar functional groups.therefore,it is necessary to examine the influence of other molecules on the molecular network.Part II: The study of chiral transfer mechanism between molecular network and threaded gold nanorods.In this part,we study the relationship between the state of molecular network and the growth of threaded gold nanorods by regulating the state of molecular network.In this work,according to the proved law of concentration and temperature of molecular network,the state of molecular network in solution was changed,and the change of chiral signal of molecular network and the chiral signal of final threaded gold nanorods were studied.it is proved that the molecular network is used as a chiral source in the synthesis of threaded gold nanorods.In the study of the mechanism of chiral transfer,p-aminothiophenol was added in the process of synthesis as a breakthrough.The addition of p-aminophenylthiophenol to the solution which has formed the molecular network can lead to the obvious decrease or disappearance of the molecular network signal.Due to the binding of paminophenylthiophenol molecules to the surface of gold nanorods,the intramolecular binding of amino groups and cysteine molecules makes the gold and silver ions in the growth agent selectively deposited near the p-aminophenylthiophenol and cysteine molecules during deposition,resulting in the formation of a unique threaded gold and silver shell around the molecular network,which induces chirality.Part III: The hot spot enhancement of cysteine molecular network and its application in the detection of copper ions.The above studies show that cysteine forms a chiral analysis network on the surface of gold nanorods.However,cysteine is oxidized to cystine under the catalysis of copper ions,and cystine can not form a molecular network structure on the surface of gold nanorods,resulting in the disappearance of molecular network chiral signals.Based on this,a simple method for the detection of copper ions in solution can be established and applied to the detection of copper ions in serum,expanding the application of molecular networks.In a word,based on the unique chiral signal of molecular network,this paper studies the response ability of molecular network to different influencing factors;secondly,the chiral transfer mechanism between molecular network and chiral nanomaterials is explored by using the signal change of molecular network;finally,based on the special chiral signal of molecular network,a copper ion detection method is established,which expands the application of molecular network in analysis and detection.