Self-assembly Of Noble Metal Nanostructure At Liquid-liquid Interface For SERS Detection Study

Throughout the process of surface-enhanced Raman spectroscopy(SERS),the great-leap-forward development of SERS in recent decades has been inseparable from the booming of nanotechnology and nanomaterials.SERS detection based on nanomaterials and sensing is a non-invasive and highly sensitive vibrational spectroscopy technology,also a rapidly-developed analytical method.The SERS substrates,which are always prepared by various noble nanostructures,have a large number of potential applications in materials,analytical chemistry,surface science and life sciences.However,as to the SERS development of practical detection and analysis and the bottleneck problems in the stability,reproducibility and quantitative detection capabilities of the SERS detection method,it does not meet the needs of practical applications.Considering the operability and practicability,researchers were devoted to assembly as the obstacle of individual particle or monodisperse system is difficult to implement.One of effective ways to fabricate SERS substrate is assembly at liquid-liquid interface.In this thesis,the construction of high-density self-assembled structures of noble nanostructures at the liquid-liquid interface and their applications in SERS detection were carried out by the following several parts:(1)The method of self-assembly at liquid-liquid interface was developed based on surface ligand exchange and solvent-induced strategies.As a typical representative,AuNRs were selected to self-assemble at the liquid-liquid interface.First,the surfactant of hexadecyl trimethyl ammonium bromide(CTAB)was replaced by polyvinylpyrrolidone(PVP)via ligand exchange strategy to regulate the charge of the surface of AuNRs.Then,it was dispersed in ethanol and added to the cyclohexane/water interface.At this time,the interface energy of the AuNRs was rapidly reduced and thus driving the AuNRs to self-assemble.In addition,gold nanoparticles(AuNPs)synthesized with CTAB,as a dispersant,also successfully self-assembled at the cyclohexane-water interface using the same method,indicating that the strategy has a degree of universality.The complete assembled film was obtained by the in-situ cell technique.Through scanning electron microscopy and regional SERS mapping of the assembled film,it was found to be a large-area densely-ordered monolayer which exhibit high sensitivity and homogeneity as SERS substrates.(2)The practicability of the high-density hot spot SERS substrate was explored the SERS detection that structure of the self-assembly at liquid-liquid interface.Cyclohexane can be selected as extractant for the pretreatment of human body fluids containing drugs.Cyclohexane was selected as a drug extractant for pretreatment of drug-containing body fluids.As a result,the drug molecules were adsorbed on the surface of the nanofilm for microenvironmental disturbance and the extraction of cyclohexane with NPs formed a liquid-liquid interface self-assembled structure at the cyclohexane/water interface.The assembled film obtained by in-situ cell can be used as a 2D SERS detection platform,on the other hand,it can be enriched with analytes,so 100 ppb methamphetamine could be detected,and it is also suitable for high sensitive SERS detection of ecstasy,ketamine.In addition,when hydrophilic molecules are present in the aqueous phase and lipophilic molecules are dissolved in the oil phase,both phases can be directly detected after the interface assembly is completed.This method can also be used for bimolecular two-phase detection.(3)The strategy was proposed to solve the feasibility of SERS quantitative detection of the system at the liquid-liquid interface by constructing a self-assembly of liquid-liquid interface with internal standard molecular nanostructure.Firstly,the AuNPs were modified by internal standard molecules,then a silver shell with a certain thickness was grown on the surface of the AuNPs to regulate and control the assembly of liquid-liquid interface.The high-density nano-arrays assembled at the liquid-liquid interface of noble metal ensure high reproducibility as SERS substrates,while the internal signal molecules serve as internal standards.Relatively quantitative SERS detection can be performed for some systems under test.It was used for SERS detection of the antibiotic malachite green(MG)in aquaculture water.The results showed that nanostructure containing the internal standard molecule was dispersed in the water sample containing MG and then proceeded at the interface of cyclohexane-water.Self-assembling strategy allowed quantitative detection of MG molecules.In addition,further research shows that this method is also used for SERS quantitative detection of pesticide residues in the aqueous phase.