Structure Design And Performance Evaluation Of Efficient SERS Substrate Based On 3D Micro-nano Composite Structure

Surface Enhanced Raman Scattering（SERS）is a molecular-specific spectroscopy technique that exhibits high sensitivity,fast response,and no damage towards test objects.It has demonstrated unique advantages in various fields including analytical chemistry,food safety,environmental monitoring,biological sciences,etc.SERS performance is dependent on physical and chemical properties of base material.Therefore,exploring the structure and mechanism of the base material can promote the application of SERS.In this dissertation,a rigid and flexible SERS substrate of three-dimensional composite micro/nano structure composite metal nanoparticles was designed and constructed.It exhibits high sensitivity,good uniformity and strong stability.Based on performance analysis,the main physical mechanism of material system to enhance SERS activity was well described by simulation.Main research content and conclusions are as below.Firstly,semi-sphere shielding effect of the Ag NPs@nanoparticle three-dimensional composite SERS substrate was investigated through numerical simulation and experimental studies.Through constructing Ag NPs@SiO₂ and Ag NPs@ZnO three-dimensional simulation models,the effect of varying the number of Ag NPs on the surface of oxide nanospheres on the enhancement characteristics of composite sphere’s surface electromagnetic field was investigated.Simulation results showed that a large number of Ag NPs generated localized surface plasmon resonance（LSPR）,forming shielding effect on the upper half-sphere of SiO₂.A similar simulated structure,Ag NPs/SiO₂ nano-composite structure,was then prepared,and SERS performance of the Ag NPs@SiO₂nanosphere composite was tested based on microstructural characterization.Experimental results demonstrated that probe molecules below the Ag NPs/SiO₂ hemisphere lost resonance interaction,leading to a decrease in Raman signal intensity and thus validating the theoretical analysis.Secondly,Ag NPs/ZnO NFs three-dimensional composite substrates were constructed on various materials.The incident laser beam effectively oscillated multiple times within the three-dimensional structure of ZnO NFs,and the three-dimensional structure of ZnO NFs,which extended in all directions and overlapped spatially,optimized the spatial distribution of Ag nanoparticles.The layered step structure at the hexagonal pyramid end of ZnO crystal facilitated the retention of Ag NPs and target molecules,thereby creating a high-density three-dimensional active"hotspot"and exhibiting excellent SERS activity.The Ag NPs/ZnO NFs/Sithree-dimensional composite substrate achieved a detection limit of R6G molecules of 10^-14 M,and the testing results demonstrated good uniformity and reproducibility of the substrate.Furthermore,an optically transparent polymer PMMA was introduced onto the surface of Ag nanostructures and assembled on a ZnO nanotower array with layered nano-steps to form an Ag NPs@PMMA/ZnO NTs/Sisubstrate.This substrate achieved a detection limit of R6G molecules of 10^-18 m.Raman tests on 20 arbitrary points and 10 batches of the same substrate presented relative standard deviations of the peak intensity at 611 cm^-1 of 4.32%and 5.50%,respectively,indicating good uniformity and reproducibility of the substrate.The SERS intensity remained stable after 6 months of storage in air,indicating good storage stability of the substrate.Simulation analysis revealed the resonant characteristics of particles within the layers,between the layers,and at the top of nanotower under different electric field polarization directions.This has elucidated the physical mechanism of the excellent performance of the substrate resulting from resonance formation in all directions by the tower-type array of substrate material.Moreover,the introduction of PMMA not only enhanced the stability of silver particles,but also prevented direct contact between Ag nanoparticles,enabling the formation of equipotential bodies.The high dielectric constant of PMMA also contributed to the generation of a highly local electric field around the metal nanoparticles.Finally,with Ag NPs/ZnO NFs/Sithree-dimensional composite rigid substrate as the template,the Ag NPs/ZnO NFs active nanocomposite structure was transferred from the rigid surface to the flexible tape surface through the"past-peel"process.The Ag NPs/ZnO NFs/Tape 3D flexible substrate was formed,showing good in-situ detection ability and strong mechanical stability.Ag NPs/ZnO NFs/Tape flexible substrates were used for in-situ detection of the R6G in river water,and the CV residues on the surface of shrimp.Trace analysis of 10^-8 M and 10^-7 M was achieved,respectively.The substrate preparation process is relatively simple,with relatively low energy consumption,and with good stability on the silicon substrate.The three-dimensional structure can be transfered onto tape just before using,which ensures good shelf storage stability.The prepared Ag NPs/ZnO NFs/Tape 3D flexible substrate has practical application prospect in field trace analysis of food safety,environmental monitoring,homeland security,etc.