| Surface-enhanced Raman spectroscopy provides structural information such as molecular vibrations and rotations,and has features such as fast detection,no labeling of samples,and the ability to detect samples in aqueous solutions.This technique is suitable for the detection of biological samples,but they are easily damaged by direct irradiation with high optical power excitation light,which can lead to inaccurate results or even failure to detect the SERS signal.For the non-destructive testing of biological samples,this thesis proposes a SERS substrate structure based on polymeric flat-plate waveguides with gold nanoparticles(Au NPs).To avoid damage to the sample caused by direct excitation light,the substrate uses the abrupt field of a flat-plate waveguide to excite a"hot spot"around the gold nanoparticles to enhance the Raman signal.The substrate uses long-range detection to increase the distance between the light and the sample molecules using the long-range transmission of the flat-plate waveguide,cumulatively increasing the Raman signal,while improving the repeatability of the Raman signal using the long-range averaging effect.The polymer-based flat-plate waveguide-AuNPs SERS substrate proposed in this thesis has important applications in the detection of biological samples.This thesis focuses on the design and optimization of polymeric flat-plate waveguide-AuNPs SERS substrates,on the basis of which processing and fabrication,performance testing and application experiments have been completed,as follows.1.The polymeric flat plate waveguide-AuNPs SERS substrate structure was optimally designed with PDMS as the waveguide core,CYTOP as the waveguide lower cladding and the sample solution as the waveguide upper cladding,with gold nanoparticles distributed in the sample solution.The structure was simulated and analysed using COMSOL Multiphysics software and the structural parameters were optimised.The effects of gold nanoparticle particle size and polymer waveguide core thickness on the substrate enhancement performance and transmission loss were investigated,and the simulation analysis of waveguide core thickness errors during substrate fabrication was carried out.The study shows that the maximum enhancement factor of 2.5×105 can be achieved with a theoretical simulation at a particle size of 50nm and a waveguide core thickness of 3000 nm,which results in a maximum local field enhancement and a small substrate loss.2.The fabrication process of polymer flat-plate waveguide-AuNPs SERS substrate was investigated,the process parameters were optimized,the relationship between the homogenization thickness and the rotational speed of the waveguide nucleus PDMS was determined,and the flatness of the surface of the flat-plate waveguide and the fabrication of gold nanoparticles were examined.The results showed that the average thickness of PDMS waveguide nuclei was 3000±50 nm at 4050 r/min,and the Relative Standard Deviation(RSD)was 0.62%,indicates that the polymer flat waveguide has good surface flatness.The peak UV-Vis absorption spectrum of the gold sol was at 535nm and the particle size of the gold sol was about 50 nm.The polymeric optical flat plate waveguide with AuNPs SERS substrate was fabricated to meet the theoretical simulation conditions.3.A SERS signal long-range detection experimental system was built for SERS substrate performance and application testing of polymeric flat-plate waveguide-Au NPs.The effect of substrate transmission length on the enhanced signal intensity,as well as key performance indicators such as detection limit,enhancement factor and repeatability were tested using rhodamine 6G as the detection sample,and application tests on biological samples were completed.The optimum transmission distance of the polymeric flat waveguide-AuNPs SERS substrate was 9.6 mm,and the detection limit of the rhodamine 6G molecule was 10-7 mol/L with an enhancement factor of 4.3×104.The RSD of the characteristic peaks of rhodamine 6G was around 3%with good repeatability.The detection of L-tryptophan in 10-3 mol/L biological samples was achieved,indicating that the substrate is capable of achieving non-destructive detection of biological samples. |
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