Design And Fabrication Of High Performance 3D Nanostructure SERS Probes And Trace Molecular Detection

Surface-enhanced Raman scattering(SERS)is a nondestructive,highly sensitive and rapid spectroscopic technique for the detection of trace substances.The coupling between local surface plasmon resonance(LSPR)and surface plasmon polaritons(SPP)can be significantly enhanced by optimizing the nanostructures pattern to enhance the intensity of electromagnetic field,which is an important new way to obtain high-performance SERS probes.In this dissertation,a new kind of high performance SERS probe with 3D structure/metal particles was designed for detection of trace mercury ions.The new mold design method was used to realize the SERS probe with low cost,high homogeneity and batch preparation by the procedure of nanoimprint lithography(NIL).The probe successfully realized the high precision and rapid detection of trace mercury ions in water.The main contents are as follows:Based on the current research on SERS effect,through theoretical calculation of finite difference time domain(FDTD),mathematical analysis and SERS experiment,a variety of coupling effects such as SPP and LSPR which could lead to electric field enhancement were quantitatively studied.The optimal structure of the coupling enhancement effect of SPP and LSPR under different parameters of each structure was successfully obtained through the normalization of elimination spectrum,and the hexagon structure(h316,g190)with excellent theoretical detection limit was obtained,and the correctness of the simulation was verified by the trace detection of R6G molecule.The SERS probe designed was prepared by NIL,for the imprint transfer of single large size pattern and large range of multiple patterns,combined with the finite element analysis,the methods of"double layer mold"and"double layer mold+modular segmentation composite mold"were designed respectively to optimize the surface stress distribution of the mold pattern area under force balance state.The"double layer mold"method improved the average stress of the central area of the pattern and significantly promoted the uniformity of the large area of the imprint structure.Adopting the method of"double layer mold+modular segmentation composite mold"method,under the premise that the overall regional stress increased by several orders of magnitude,the stress value RSD in the high stress zone was only 1.91%.The large size pattern of 3mm and the large range multiple patterns of 2 inches and 4 inches were completed imprint respectively,which proved the effectiveness of this mold design method.The rapid step-by-step quality analysis of the probe was completed by using two-step detection methods:optical hue extraction and rapid signal processing analysis.After signal test and data quick analysis,the SERS probe has high detection sensitivity and high signal uniformity.The SERS probe realized the detection limit for Rhodamine 6G(R6G)model molecule of 3.76×10^-12 M,an enhancement factor(EF)of up to 2.5×10⁸ and a uniformity of7.04%.Furthermore,the detection limit of the probe for mercury ions was only 5.0×10^-11 M(10 ppt)with a good linear relationship(R²=0.985)ranging from 5.0×10^-11 M to 5.0×10^-5 M,which was quite prominent for Hg ions detection.It is great significant for the efficient and high-quality processing of high-performance SERS probe as well as its preparation and practical application.