Fabrication And SERS Effect Of Silver-based Surface-enhanced Raman Spectroscopy Substrates

Raman spectroscopy belong to the molecular vibrational spectrum and can reflect the characteristic structure of the molecule.However,the intensity of Raman scattering effect is very weak,Which is only about 10-10 of the incident light in generally.If we want to study the Raman spectrum of molecules which adsorbed on the surface of the object,we need to take some measures to enhance the scattering effect.Therefore,surface-enhanced Raman spectroscopy has been invented.The enhancement effect related to rough surfaces such as gold,silver,copper and so on are named surface-enhanced Raman scattering effect,and the corresponding spectrum is called surface-enhanced Raman spectroscopy(SERS).Surface-enhanced Raman spectroscopy is widely used in many industry fields such as materials,petroleum,chemistry,polymer,biology,environment and geology.Because the material and surface morphology of the substrate are essential for detecting molecules effectively,the preparation of surface-enhanced Raman spectroscopy substrates has always been a hot topic in this field.In this paper,Silver SERS substrates with three morphologies(silver particle,silver island membrane and silver bowl-like substrate)were studied.The main innovations are as follows:(1)A convenient and rapid synthesis method using ascorbic acid as a reducing agent to reduce silver nitrate was proposed to prepare spherical,urchin-like and flower-like silver particle.The effects of silver nitrate concentration,ascorbic acid concentration,temperature and pH on the morphology of silver particle were studied.As the concentration of silver nitrate increased,the morphology of the silver particle changed from sphere to urchin and became flower-like finally,and the size of the silver particle also increased.As the concentration of ascorbic acid increased,the surface of the silver particle gradually became smooth and the size of the silver particle decreased.With the increase of reaction temperature,the morphology of silver particle gradually became irregular shape.The result showed that the optimal reaction temperature was at 0℃ and 20℃.As the pH increased,the silver particle gradually became non-uniform and the particle size also decreased.Silver particle prepared by different concentrations of silver nitrate was used as the SERS substrate,and R6G was used as the probe molecule to carry out Raman detection on the substrate.The results showed that the silver particle prepared with the concentration of silver nitrate of 0.1 mol/L and Vc concentration of 0.077 mol/L have the best enhancement effect,and the detection limit of R6G can reach 1×10-6 mol/L.The substrate was used to detected thiram double,the detection limit was 1×10-8 mol/L and has good repeatability.(2)An ordered silver island film SERS substrate was designed and prepared.The silver island film was prepared by using the Stober method to prepare SiO2 nanosphere as a mask.With the increase of the volume of n-hexanol,the particle size of SiO2 nanosphere increased gradually,and the particle size ranged from 330 nm to 470 nm;With the increase of the volume of TEOS,the particle size of SiO2 nanosphere was also increased gradually,and the particle size ranged from 420 nm to 470 nm;With the increase of the volume of the ethanol in solvents,the quality of SiO2 opal structure became worse and its internal arrangement became disordered gradually;It was found that the quality of opal structure was the best,the inner arrangement was orderly and the structure was dense hexagonal when evaporation temperature was 70℃ and pure water was used as solvent.When the R6G and thiram were detected that the silver island membrane was used as SERS,the detection limits were 1×10-7 mol/L and 1×10-8 mol/L respectively,and has shown higher repeatability.(3)A flexible silver bowl shape was prepared as SERS substrate.The silver bowl was used as the SERS substrate,and the R6G and thiram were detected.The detection limits were 1×10-8 mol/L and 1×10-9 mol/L respectively.It was found that the silver bowl-shaped substrate has better SERS enhancement effect than the silver particle of different morphologies and the silver island film substrate.Also it has a good repeatability.