Preparation Of WS₂ Nanocomposite Structures And Study Of Their SERS Properties

The Raman spectroscopy is mainly generated by inelastic light scattering during the oscillation of matter,which can obtain molecular structure information through different vibrational models of matter,providing fingerprint information for the identification of biological molecules.However,due to the weak intensity of conventional Raman spectroscopy,it is hard to detect directly and perform qualitative and quantitative analysis,thus limiting its research scope.Like Raman spectroscopy,the surface-enhanced Raman scattering spectroscopy can also provide fingerprint information of the detected molecules,and the obtained molecular structure information is much richer,which is a very powerful tool for trace detection,and is widely used in food safety,medical diagnosis,environmental monitoring and chemical analysis.Precious metal materials are excellent choices for SERS substrates because of their advantages of controllable morphology and particle size,good optical properties,and good enhancement effect.However,the susceptibility of precious metal substrates to oxidation in air and lack of signal stability limit their development in SERS.Semiconductor materials,especially two-dimensional semiconductor materials,are often used as SERS substrates because of their uniform surface,large specific surface area,good adsorption ability to molecules,high light transmission and optical properties,etc.However,the sensitivity of simple semiconductor substrates is low,and in order to prepare SERS substrates with high sensitivity and stability at the same time,we propose a metal-semiconductor based composite SERS substrate,and perform quantitative calculations and theoretical simulations to design Two composite SERS active substrates with high sensitivity,high reproducibility,high stability and high homogeneity were designed as follows:（ⅰ）A multilayer structure of Graphene oxide（GO）/Silver nanoparticles（Ag NPs）/Tungsten disulfide（WS₂）composite SERS active substrate was designed.Large area continuous brain mesh WS₂ films were synthesized using a tube furnace thermal decomposition method to provide a large molecular adsorption area.The Ag NPs with uniform particle size are chemically synthesized to provide smaller particle gaps and richer"hot spots"for the substrate to improve SERS activity.Graphene oxide exhibits excellent molecular adsorption capacity due to the presence of reactive oxygen sites,as well as good chemical stability and biocompatibility,and can act as a support layer for absorbing probe molecules and as a protective metal layer to prevent the oxidation of silver nanoparticles in air.The electric field distribution of the composite-structure was analyzed by the finite element method,by using COMSOL software to get the effective"hot spot"region,and the simulation results were consistent with the experimental results.EF（enhancement factor）=6.60×10¹⁰,the relative standard deviation（RSD）is 8.24%,for the peak at 611cm^-1 at 10^-12M for rhodamine 6g（R6G）,the composite SERS substrate can also achieve the ultra-low concentration of crystalline violet（CV）and methylene blue（MB）The detection of high sensitivity,high repeatability and stable SERS signals were obtained,which will promote the application of SERS technology in the field of quantitative analysis and detection of toxic substances.（ⅱ）In this work,we prepared a graphene oxide（GO）/silver nanoparticles（Ag NPs）/tungsten disulfide（WS₂）-polymethyl methacrylate flexible composite SERS active substrate based on polymethyl methacrylate（PMMA）thin film.The PMMA flexible film is used as a substrate and also as a Raman active substrate,which has a detection limit of 10^-10M for CV molecules and an enhancement factor EF=1.43×10⁹,and can be used as an effective SERS substrate to achieve ultra-sensitive detection of toxic molecules.The system not only has the advantages of high sensitivity,high stability and high reproducibility,but also has mechanical stability.After 60 times of stretching and bending experiments,the SERS signal intensity of the substrate almost did not change,and the relative standard deviation of peak intensity at R6G-611cm^-1 after 60 times of bending RSD=4.63%.In addition,the GO/Ag NPs/WS₂-PMMA flexible composite substrate enables in situ sensing of MB residues on the surface of fish,with a detection limit of 10^-7M.The results indicate that the GO/Ag NPs/WS₂-PMMA flexible composite substrate has great potential for in situ ultrasensitive detection of analytes on irregular objects.