Study On Micro/Nanostructure Composite SERS Substrates And Its Applications

Surface-enhanced Raman spectroscopy(SERS),as an ultrasensitive trace detection tool,has great potential applications in many fields.The key to the implementation of SERS is to construct high-performance substrates(chips).For the substrate preparation,cost-effective,time-consuming and large-scale fabrication of substrates with high SERS activity and signal uniformity has always been the goal of researchers.For the application,SERS is generally only suitable for detecting molecules that have a large intrinsic Raman scattering cross section and are adsorbed on the substrate surface.For small gaseous molecules with low Raman activity and high mobility,it is difficult to directly detect and study their interactions with the substrate surface by SERS.In addition,due to the ultrasensitive sensing properties of SERS,slight variations in the intensity of the "hot spots" on the substrate and the measuring conditions can cause large fluctuations in the obtained signal.As a result,it is difficult to perform accurate quantitative SERS analysis.Aiming at the above bottlenecks in SERS,including the preparation of high-performance substrates,detection and research of small gaseous molecules,and quantitative SERS analysis,this paper focuses on the design and preparation of SERS substrates and explores their application performance.The innovative achievements of this thesis are as follows:(1)Based on the solvent method,an flower-like Au/CuS micro/nanostructured particle thin film SERS substrate was obtained to achieve high sensitivity,high stability and recyclable SERS detection.The micro/nanostructured particle is composed of CuS nanopetals with curved surfaces and cross-linked with each other,and the surfaces of which are loaded with high-density and radially distributed Au nanotips.By assembling this micro/nanostructured particle,a SERS substrate is constructed.This SERS substrates can detect rhodamine 6G(R6G)molecule below 10’10 M and its calculated enhancement factor reach 107.Furthermore,it is especially suitable for practical on-site detection in combination with a hand-held Raman spectrometer,showing good signal reproducibility(RSD<5%).In addition,the analytes adsorbed on the substrate surface can be degraded by light irradiation to achieve perfect regeneration of the SERS substrate.(2)Based on laser ablation in liquid,a PbO nanosheet/Au nanoparticle thin film composite SERS substrate was obtained to realize ultrasensitive detection of H2S gas.The PbO nanosheets in the composite SERS substrate can effectively capture gaseous H2S molecules and induce the in situ conversion of the nanosheets into PbS nanosheets.By monitoring the SERS signal changes of the substrate before and after exposure to H2S gas,the rapid SERS-based detection of trace H2S gas is realized.The response to H2S is less than 10 s,and the detection limit concentration is less than 1 ppb.In addition,this composite SERS substrate can be recycled by heating the used substrate.This work presents the reusable SERS substrate for the efficient detection of trace gaseous H2S(3)Based on the silicon internal standard quantification strategy,a silver-coated silicon nanocone array substrate was designed,and the on-site quantitative SERS was established.A uniform and ordered silver-coated silicon nanocone array was prepared by depositing Ag on the colloidal sphere template-assisted etched Si nanocone array.It has been demonstrated that the Si underneath the Ag coating in the substrate can respond to the measuring parameters’ fluctuations synchronously with and similarly to the analyte adsorbed on the substrate surface,and the normalization with Si Raman signals can well eliminate the fluctuations in measurements,achieving the highly reproducible measurements(mostly,<5%in signal fluctuations)and accurate quantitative SERS analyses.The validity of this strategy has been demonstrated with 4aminothiophenol(4-ATP),crystal violet(CV)and R6G as typical analytes.This study provides a new practical chip and the reliable quantitative SERS for the field-detection of real samples.(4)Based on the Au/Si nanocone array substrate,the molecular evolution routine of NO2 on the Au surface in the atmospheric environment was revealed.According to spectroscopic measurements,it is found that when NO2 contacts the Au surface in the atmospheric environment,chemisorbed NO2 will be rapidly formed,and after a few minutes of induction period,the chemisorbed NO2 would evolve into NO[Au(NO3)4].Subsequently,the generated NO[Au(NO3)4]is decomposed into O2,NO,adsorbed NO2,-OH and HNO3 by pyrolysis or deliquescence.The molecular evolution process of NO2 on Au surface is elaborated according to DFT simulation calculation and measurement spectrum.This work provides spectroscopic evidence for the molecular evolution of NO2 on the Au surface,deepening the understanding the interaction mechanism between NO2 and metal.