Preparation And Properties Of SERS Substrates Based On Ordered Array Structure

Surface-enhanced Raman spectroscopy has been used as an efficient detection tool in many fields due to the properties of high sensitivity,low cost and non-destructive.And the preparation for surface-enhanced Raman scattering(SERS)substrates has been focus of research in this field.The ordered array structure with uniform distribution of hot spots has attracted close attention.The reported preparation methods can be summarized as top-down processing method and bottom-up self-assembly method.Compared with the top-down processing technology,the bottom-up self-assembly method is cheap to prepare and reduces the controllable range to order of nanometers.On the enhancement mechanism,although ordered arrays can provide highly reproducible Raman signals,the sensitivity is weak,which is mainly due to the sparse hot spots formed by ordered array,such as metal film coated nanospheres(FON).In addition,the compatibility of ordered array SERS substrates is limited in practical applications.For example,rigid SERS substrates cannot accommodate in-situ detection of curved surface.On the contrary,flexible SERS substrates have poorer support than rigid substrates.Therefore,there is still a challenge to develop an ultra-sensitive,highly reproducible and universal SERS substrate through a simple and low-cost method.This paper is devoted to developing an ultra-sensitive and highly compatible SERS substrate based on in-depth research on Raman enhancement mechanism for ordered array,and then exploring the SERS application in environmental analysis,catalytic reaction.The main contents are as follows:(1)By combining self-assembled monolayer AuNPs with SiO2 opal structure,the binary "island" array(BISA)is constructed as SERS substrate,which has periodic high-density hot spots.The enhancement factor(EF)reaches 3.74 × 1010,and the Raman signal intensity deviation is less than 8%.In addition,FDTD simulation indicates that the BISA structure provides geometric conditions to increase the density and intensity of SERS hot spots with periodic distribution.Due to the excellent catalysis of AuNPs(hot carriers generated by excitation light),the catalytic reaction of 4-ATP to DMAB was achieved with real-time SERS measurement on BISA substrate.Since the catalytic efficiency is related to the number of AuNPs,the photocatalytic activity can be adjusted by changing diameter of SiO2 spheres(2)The AuNPs placed in hemispherical honeycomb array structure(PIHHN)was introduced by multi-step assembly strategy.The PIHHN substrate enables omnidirectional,ultra-sensitive,and reproducible SERS detection.The detection ability of R6G is as low as 10-15 M,and the RSD of signal does not exceed 5.8%.FDTD simulation indicates that compared with hemispherical honeycomb array,the addition of AuNPs will further focus light field on the gap and produce coupling between gap resonance and cavity resonance to obtain stronger electromagnetic field enhancement.In addition,more hot spots are created between AuNPs and metal cavity to increase the density of hotspots.When the substrate is tilted by 75 degrees,the SERS signal strength is only attenuated by half.When the substrate is bent at 60 degrees,the SERS signal remains stable.Based on this property,on-field detection of contaminated soil can be achieved,and pollutants down to 0.5 ppb can be detected.(3)By investigating the effect of organic ligands on the assembly behavior of OA-Au,it can be found the appropriate content of organic ligands will prolong the thermal vibration time of OA-Au at evaporation front,which form an ordered structure.The patterning of OA-Au superlattice is realized by inkjet printing technology,which can be used as multiplex SERS chip.In addition,the solid substrate was transformed to liquid substrate,which can obtain a large-area continuous superlattice.The OA-Au superlattice can be transferred to substrate with any shape or different properties by the contact method,which expands the application range of SERS substrate,which is expected to realize the on-demand preparation for SERS substrate.