Preparation And Properties Of Flexible SERS Substrates

Surface-enhanced Raman scattering(SERS),with high sensitivity and selectivity,has been developed as a spectral analytical method for detecting interactions between interfacial properties and molecules.Raman scattering spectrum belongs to molecular vibrational spectrum,which can reflect the characteristic structures of molecules.Any change of molecular structure can be reflected in Raman spectrum,therefore it can be used for quantitative and qualitative analysis of measured substances.It is widely believed to be a potential molecular detection method.In recent years,real-time in-situ SERS detection technology has been developed rapidly,the detection of this method usually needs to attach the SERS substrates to the solid surfaces,or placed in the liquid and gas.The flexible substrate with good flexibility and mechanical resistance is a good means to carry out in-situ detection,which can be deformed according to the object surfaces,and even residues on complex surfaces can be detected.In this paper,several flexible SERS substrates with high sensitivity,high reproducibility and high stability have been designed,and their performance has been studied in detail,and the main research contents are as listed follows:1.A three-dimensional hybrid structure based on graphene oxide(GO)/silver nanoparticle(AgNPs)/polymethyl methacrylate(PMMA)flexible SERS substrate was designed.The pyramid silicon(PSi)was utilized as the template to fabricate this three-dimension flexible structure.The structure with large specific surface area and good structural periodicity was propitious to capture probe molecules and establish high-density active hot spots.The SERS substrate enabled the lowest detectable concentration(LDC)of10~-1313 M for rhodamine 6G(R6G)and 10~-99 M for crystal violet(CV),and the enhancement factor reached up to 10~9 using R6G as probe molecules.At the same time,the in situ detection of the MG on the shrimp surface was carried out to achieve detect surface analytes.This provides a new method for in-situ detection and analysis of the surface residues,which can efficiently collect the residual pollutants on different surfaces,thus avoiding the use of the toxic and harmful organic solvent.2.A composite structrue based on silver nanoparticle(AgNPs)/silver nanoparticles(AgNPs)-polydimethylsiloxane(PDMS)flexible substrate was constructed.This SERS substrate was no longer based on pure polymer,which can be used not only as a tool for preparing flexible SERS substrates,but also directly as a Raman active substrates for trace detection of R6G molecules with the lowest detectable concentration of 10~-1313 M.The SERS substrate had good flexibility and mechanical stability.After undergoing the cyclic mechanical deformation,the SERS substrate still maintained high mechanical stability and stable SERS signals.However,upon stretching the flexible substrate,there was an amusing phenomenon that SERS signals can be highly increased.The result displayed that when the tensile strain was as high as 80%,the SERS signal intensity of the flexible substrate was 2.4times higher than that of the original state.We used the finite-difference time-domain(FDTD)software to simulate the electric field distribution and verify this point.It is suggested that mechanical strain can be used to control the electromagnetic field at the nanometer scale.3.A novel flexible SERS substrate based on Ag nanoravines(AgNRs)/ZnO nanosheets(ZnO NSs)/polydimethylsiloxane(PDMS)was prepared.We have constructed the composite structure of AgNRs/ZnO NSs on PDMS thin films.The design of this 3D nanostructure integrated advantageous aspects of the high-efficiency light utilization by multiple reflections within the adjacent ZnO NSs and the formation of abundant localized surface plasmon resonance(LSPR)hotspots between AgNRs,which enabled the lowest detectable concentration of 10~-1212 M for R6G and 10~-99 M for CV,and in situ detection in the MG aqueous solution to successfully implement.The FDTD software was used to simulate the local electric field distribution of the structure,which proved that the design of the three-dimensional nanostructure can effectively improve the optical capture efficiency and made the near-field and far-field effects combine with each other,so that the SERS substrate had high SERS activity.These will greatly facilitate the widespread availability of SERS in biological and chemical detection.