Investigation Of Surface-enhanced Raman Scattering Substrate For Detection Of Thiram

Since its discovery in the 1970 s,surface enhanced Raman scattering(SERS)has been receiving the growing interest in a variety of areas due to its inherent merits such as the fingerprint properties of vibrational spectroscopic,ultrahigh sensitivity,non-destructive detection feature and the even single molecule detection.Especially,SERS has been proved to be an extremely powerful analytical tool for any forms of sample,for example,liquid and gaseous status These features makes SERS one of the most powerful and promising techniques for non-destructive,on-site and analysis as well as chemical and biological substances.SERS also has been applied to various areas such as environmental monitoring,material characterization,medical science,food safety and the defense of public security.High-quality active substrates is absolutely essential to SERS,therefore we focus on designing and fabrication of substrates with high quality.In this paper,we designed and fabricated two types of flexible substrates and the SERS activity of these substrates are evaluated by using R6 G as the probe molecule.Then,we used the prepared substrates to detect the pesticide residue: thiram.Firstly,we have prepared the flexible PDMS-Ag SERS substrate with periodic microstructure array based on the template method.The SEM and AFM characterizations results show that the PDMS-Ag SERS substrates are in a high degree of uniformity.In the meantime,the parameters of experiment are optimized before studying the SERS activity of PDMS-Ag substrate.The results indicate that the PDMS-Ag substrate with micro structure array(M-structure)has exhibit larger Raman signal enhancement than ones with flat structure(F-structure),due to the surface plasmonic effect.When the thickness of silver film on the PDMS-Ag surface is 40 nm,it shows the optimal Raman signal enhancement,which is consistent with the results of theoretical simulation.Secondly,PE-CVD method was employed to prepare the GNWs substrate with growth anisotropy and nano flower shape,then the GNWs-Ag substrate was prepared by magnetron sputtering deposition.The SEM image shows that the three-dimensional structure of GNWs with large specific surface area,the distribution of silver nanoparticles or silver film on the surface of GNWs are uniform and they can produce a large number of hot spots.It indicates that the GNWs substrate exhibit a certain degree of SERS enhancement effect,which belongs to the chemical enhancement.Owing to the synergistic effect of chemical enhancement and electromagnetic enhancement,the Raman signal enhancement of GNWs-Ag substrate is larger than the GNWs substrate.In addition,the theoretical simulation analysis shows that the silver nanoparticles on both sides of graphene sheet can enhance the local electromagnetic field.When the thickness of silver film on GNWs-Ag substrate is 10 nm,it demonstrates the optimal Raman signal enhancement.Finally,these two kinds of substrates are employed to detect the thiram in ethanol at series concentrations,the results show that the detection limit of these two kinds of substrate are 10 ppb and 50 ppb respectively,which are far below the limit value of Environmental Protection Agency(EPA).Moreover,there is a good linear relationship that the correlation coefficients were 0.9798 and 0.9257 respectively.The Raman mapping results shows that the two kinds of substrate used in for analysis of thiram exhibit good repeatability and stability.By the comparison with normal Raman spectrum and SERS spectrum of thiram,it is observed that S-S bond of thiram molecules are cleaved due to the catalytic action of silver nano material.The SERS study of thiram is carried out at several adsorption concentrations,revealing that two different coordination complexes are possibly adsorbed on surface of silver with different geometries such as monodentate or bidentate.In summary,the combination of these two kinds of substrate and the portable Raman spectrometer,to achieve the fast and simple detection of environmental pollutants;PDMS-Ag substrate can be integrated into the microfluidic channel,which can realize the combination of SERS technology and the microfluidic technology;GNWs-Ag substrate can be used for detection of environmental pollutants with high efficiency by forming the ?-? conjugation between the substrate and the target molecule.With the continuous optimization of the performance of SERS substrate,the two kinds of substrate could be potentially used in practical detection application in environmental pollutants monitoring areas.