| Surface Enhanced Raman Spectroscopy（SERS）has been widely used in the fields of biological sample analysis,chemical analysis,food testing and environmental monitoring since its discovery,with its high sensitivity,high accuracy and trace substance detection in complex systems.The current research on SERS only focused on the enhancement mechanism,the construction of substrates with different sizes and morphologies,and the application of SERS.In this thesis,a microemulsion method is used to construct a SERS substrate with controllable surface properties.Based on the hydrophobicity and surface charge properties of the SERS substrate,the selective detection of different charged probe molecules in a complex environment is achieved.At the same time,the loading method is innovated,and the loading of probe molecules on the metal substrate can be realized without sulfhydryl group,which expands the application range of SERS.This thesis has carried out the following two aspects of work:（1）For the construction of SERS substrates,we constructed gold and silver SERS substrates with hydrophobic and hydrophilic properties respectively.First,by the inverse microemulsion method,the hydrophobic substrates CTAB-Au NPs and CTAB-Ag NPs were synthesized in a water/cetyltrimethylammonium bromide（CTAB）/chloroform microemulsion system.Then the morphology and structure of the materials were characterized by TEM,FT-IR,DLS,UV-Vis and other characterization methods.The results of the study show that CTAB molecules are oriented and modified on the surface of gold and silver nanoparticles,and are arranged with the hydrophobic end facing outward and the hydrophilic end facing inward,making the nanoparticles hydrophobic.Phase transfer reaction was performed on CTAB-Au NPs and CTAB-Ag NPs,and a layer of CTAB molecular layer was inserted on the CTAB molecular layer modified on the surface of nanoparticles to prepare a hydrophilic SERS substrates（CTAB）2-Au NPs and（CTAB）2-Ag NPs.Corresponding characterization of its morphology and surface properties showed that CTAB molecules formed a cross-layer structure on the surface of gold and silver nanoparticles through the hydrophobic-hydrophobic interaction of their hydrophobic ends,which changed the surface properties of hydrophobic gold and silver nanoparticles into hydrophilic.At the same time,the hydrophilic end of the CTAB molecule has a positive charge,which also makes the surface of（CTAB）2-Au NPs and（CTAB）2-Ag NPs positive.（2）The performance of hydrophobic and hydrophilic substrates in SERS analysis and detection was investigated.Firstly,the detection performance of the hydrophobic substrate CTAB-Au NPs and CTAB-Ag NPs were investigated,and the hydrophobic probe molecule 4-ethynyl benzoic acid（EBA）and the hydrophilic probe molecule methyl orange（MO）were selected for SERS detection.It is found that due to the interface compatibility between the substrate and the probe molecule,the hydrophobic substrate can only detect the SERS signal of the hydrophobic probe.For hydrophilic substrates（CTAB）2-Au NPs and（CTAB）2-Ag NPs,the anionic probe molecule methyl orange（MO）and cationic probe molecule rhodamine（R6G）were selected for SERS detection,and it was found that（CTAB）2-Au NPs and（CTAB）2-Ag NPs could only detect the SERS signal of anionic probes,this is because the positive charges on the surface of（CTAB）2-Au NPs and（CTAB）2-Ag NPs,and the interaction between the charges makes the cationic probe molecules unable to be loaded on（CTAB）2-Au NPs and（CTAB）2-Ag NPs,this substrate has charge selectivity in SERS detection.And（CTAB）2-Au NPs and（CTAB）2-Ag NPs were used to detect the anionic probe methyl blue（MB）,which proved the universality of this substrate for the detection of anionic probe molecules.The selection of（CTAB）2-Ag NPs for SERS detection of benzoic acid proved that this substrate can realize the immobilization of probe molecules on the metal substrate without sulfhydryl group,breaking the traditional sulfhydryl bonding method for SERS analysis and detection,has accelerated the development of SERS technology in analysis and detection. |
