Preparation And Sers Effect Of Graphene/Ag Flexible Hybrid Films

Aiming at the requirement of in-situ detection of harmful molecules in food and exploring a new way to develop flexible surface-enhanced Raman scattering(SERS)films with high sensitivity and superior quality.This paper develops flexible films with the structure composed mainly of graphene/Ag nanoparticles(G/Ag NPs).Three flexible transparent SERS films with graphene as an isolation layer were prepared based on electron beam vacuum physical deposition process and wet transfer method.Raman,SEM and AFM were used to characterize the microstructures and basic properties of the prepared films.Combining with FDTD simulation,the Raman enhancement mechanism of the composite films were studied,and the in-situ detection of pesticide residues on three SERS films was verified.In order to meet the requirements of high enhancement factor,good spectral quality and durability of flexible SERS films,the overall scheme of G/Ag NPs as the main structure,preparing Ag NPs by electron beam vacuum physical deposition method,and then transfering graphene using wet transfer technology to obtain hybrid structure was determined.Through repeated experimental studies,a process route was finally formed,in which Si O2/Si wafer was used as a substrate,graphene was transferred first,then silver film was deposited,and the substrate was exfoliated by HF etching method.In order to ensure the preparation of a complete and clean flexible film,the method utilizes the protective effect of graphene to solve the problem of impurity residues and easy oxidation of Ag nanoparticles in the process.FDTD simulation analysis shows that electromagnetic field enhancement is the main Raman enhancement mechanism of G/Ag NPs hybrid structure.The enhancement effect depends on the size,gap and distribution of Ag nanoparticles.Among the prepared substrates,when the thickness of Ag particles is 12 nm,the enhancement effect is the best.The results show that the RSD values of SERS intensities of G/Ag NPs/PMMA and G/Ag/G/Ag/PMMA films are less than 20%,which show good signal repeatability and excellent flexural deformation resistance.Using R6 G as probe molecule,the enhancement factors are 2.2×104 and 6.4×104,and the limit detection concentration was 5×10-8 M and 1×10-8 M,respectively.On the basis of the above research,polystyrene(PS)with shape memory function was used as flexible substrate material,and the shrinkage deformation of multi-layer hybrid structure was carried out by heating method.The 3D-G/Ag NPs/PS hybrid structure with three-dimensional wrinkle morphology was obtained for the first time.Theoretical calculations and experiments show that the increased molecular adsorption area and the decrease of gaps of Ag nanoparticles in Raman laser effectively improve the adsorption efficiency of the films to probe molecules and the resonance intensity of hot spot.Therefore,the wrinkled hybrid structure has higher detection sensitivity,and opens up a new way for the preparation of highly sensitive and flexible SERS substrates.Three kinds of flexible films including G/Ag/PMMA?G/Ag/G/Ag/PMMA and 3D-G/Ag/PS were used to detect pesticide residues in fruits,vegetables and drinking water,such as thiram,malachite green and triphenylphosphine.The results show that the G/Ag NPs hybrid flexible substrates have high detection sensitivity,and the Raman spectra are of good quality.Moreover,they can be used in a wide range of applications and can be reused.The detection sensitivity of the three substrates increases orderly.3D-G/Ag NPs/PS has more advantages in the in-situ detection of pesticide trace...