Preparation And Application Of Highly Sensitive Flexible SERS Substrate Based On Silver Nanowires

In recent years,with the development of science and technology,various industries have gradually become large-scaled,and production efficiency has been continuously improved.At the same time,many environmental problems have arisen under large-scale production.Various gas-liquid inherently toxic wastes are produced in industrial production,various pesticides are abused in agricultural production,and water resources are increasingly scarce.The environment which mankind depends on for survival is gradually being destroyed,then it affects the survival and development of mankind.Among them,water and soil pollution and agricultural products in agricultural production are closely related to our lives.Although the relevant departments attach great importance to such environmental issues,the expensive and time-consuming inspection process is still beyond the reach of ordinary people.Therefore,the development of a technology that can quickly detect pollutants in water and agricultural products on site is a key problem to be solved urgently.Commonly used detection methods are chromatography and spectroscopy.Chromatography is known for its accuracy and it mainly include gas chromatograph and liquid chromatograph.Chromatographs have always dominated the laboratory and are the best method for quantitative testing.Combining them with detectors such as mass spectrometers can obtain extremely high-precision quantitative capabilities.Spectroscopy has always been loved by scientists because of its rapidity and convenience.The commonly used types of spectrometers mainly include infrared absorption spectrometers,ultraviolet-visible absorption spectrometers,fluorescence spectrometers,and Raman spectrometers.The surface-enhanced Raman spectroscopy method based on Raman spectroscopy is convenient,fast,simple,cheap,stable,efficient,and non-destructive,making it the most promising instrument for on-site inspection.The core problem of surface-enhanced Raman spectroscopy application is to construct a suitable SERS substrate.Among them,the flexible SERS substrate is particularly suitable for on-site rapid analysis,because the flexible SERS substrate is prone to deformation to better fit the target surface,and can effectively collect some harmful molecules to be tested by wrapping or wiping during the on-site detection.Moreover,these flexible substrates can be easily cut into samples of different sizes and shapes as needed,and can be easily integrated with other equipment.Common flexible SERS substrates mainly include polymer membranes,carbon nanotubes,graphene,cellulose and filter paper.As a flexible substrate with better enhanced performance,silver nanowire membranes have attracted more and more attention,because silver nanowires with a certain aspect ratio can be easily loaded on the filter membrane through filtration to make a flexible SERS substrate.Without a complicated manufacturing process.The assembled silver nanowire film has a three-dimensional multilayer structure,and a strong electromagnetic field enhancement effect(SERS hot spot)is generated at the intersection of the silver nanowire.Although silver nanowire films have been used in chemical analysis in many fields,SERS hot spots only exist in a few areas of silver nanowire films and the low density of SERS hot spots still hinders their wide application.There have been many studies to increase the density of SERS hotspots on silver nanowires,including the fabrication of gold nanoparticle/silver nanowire heterostructures and the conversion of disordered silver nano wires to ordered at the oil-water-air interface.However,these processes are cumbersome and time-consuming,which hinders the further application of silver nanowire films.In response to the above problems,this thesis uses silver nanowires as the basis,and prepares two high-performance flexible SERS substrates based on cyclic voltammetry nanostructure reconstruction and 1,4-benzenendithiol-guided self-assembly methods,and the mechanism of the preparation process,SERS performance,environmental analysis application and other aspects have been studied and discussed,specifically including the following four parts:In the first chapter,the basic principles of Raman spectroscopy and surface-enhanced Raman are reviewed,and their applications in virus science,environmental monitoring,and medical diagnosis are introduced.Finally,the concept and research content of this article are put forward.In the second chapter,cyclic voltammetry based reconstruction of silver nanowire film for preparing a highly sensitive and flexible SERS substrate.The surface reconstruction process of silver nanowire film treated by cyclic voltammetry was studied.The morphological changes of the silver nanowire film before and after the cyclic voltammetry treatment were characterized by SEM and TEM.The latter produced an aggregated structure of nanoparticles and nanorods,which greatly enhanced the hot spot density of the substrate.The changes in the physical and chemical properties of the silver nanowire film before and after the treatment were characterized by XRD,XPS,and diffuse reflectance absorption spectroscopy.It was found that the treated silver nanowire film had stronger surface plasmon resonance absorption than before.Then,the Raman performance of the silver nano-film was characterized by using p-aminothiophenol as the probe molecule.It is found that the Raman enhancement effect of this film is 14.4 times higher than that of the untreated conventional silver nanowire film.This flexible substrate has good reproducibility,uniformity and stability.Afterwards,DDA theoretical simulation calculations were performed on the silver nanowire film before and after the treatment,and it was found that the treated silver nanowire film has a stronger electromagnetic enhancement effect than that of the untreated silver nanowire film.This flexible substrate will play an important role in future on-site inspections.The third chapter is the application of cyclic voltammetry to reconstruct the silver nanowire film to prepare the highly sensitive flexible SERS substrate in the field analysis.Using the cyclic voltammetry-treated silver nanowire film flexible substrate prepared in the second part,the water samples containing crystal violet,tetramethylthiuram disulfide,and sodium perchlorate residues were detected,and then calculated The detection limits were 5.1×10-11 M,5.4×10-11 M,and 6.3×10-9 M.Then the solid residues containing malachite green,fluoranthene and potassium nitrate on the surface of the simulated solid were subjected to wiping extraction detection,and then the detection limits were calculated to be 0.00693 ng,0.0810 ng and 0.0273 ng,respectively.In the fourth chapter,the orderly silver nanowire film was prepared by agitation method,and the highly sensitive SERS substrate was wiped and extracted to test thiram.The self-assembly process of silver nanowires under the stirring method was studied.The morphological changes of the silver nanowire film before and after the self-assembly process were characterized by SEM and TEM.The latter silver nanowires formed a parallel arrangement structure,which greatly enhanced the hot spot density of the substrate.The changes in the physical and chemical properties of the silver nanowire film before and after the treatment were characterized by XRD,XPS,and diffuse reflectance absorption spectroscopy.It was found that the treated silver nanowire film had stronger surface plasmon resonance absorption than before.Then,the Raman performance of the silver nano-film was characterized by using 1,4-benzenendithiol as the probe molecule.It is found that the Raman enhancement effect of this film is 3.1 times higher than that of the untreated conventional silver nano wire film.This flexible substrate has good uniformity and stability.Then it was applied to the wipe extraction experiment of thiram,and its detection limit was 0.24 ng.This parallel flexible substrate will have more applications in field testing.