Construction Of High-efficient Surface-enhanced Raman Scattering (SERS) Substrates And Their Properties And Applications

Surface-enhanced Raman scattering （SERS） has a high surface sensitivity andgood selectivity. It has been widely used in materials science, biomedicine andelectrochemistry. SERS offers a tremendous enhancement of Raman signals overorders of million magnitude due to the attendance of noble metal nanomaterials.Constructing SERS substrates with high activity is one of important subjects inSERS studies. It is believed that the strong enhancement of a SERS substrateoriginates from abundant of “hot spots” composed by nano-sized gap-typedconfigurations. The construction of SERS substrates with abundant of “hot spots” isan absolutely important goal in the development of SERS substrates. The “hot spots”SERS substrate can be applied for SERS sensing chips and trace detections. Basedon the spectroscopic characteristics and promising applications of highly activeSERS substrates, this thesis is outlined as follow:1. Construction of Composite Surface-Enhanced Raman Scattering（SERS） Substrates by Silver Nanoparticle AssemblyMetal-molecule-metal sandwich structures on quartz slides were constructed bythe self-assembly of Ag nanoparticles with various shapes via p-aminothiophenol（PATP） molecules as linkers. These sandwich structures were characterized bySERS spectroscopy using different excitation lasers.The results demonstrated that SERS intensities of PATP in sandwich structureswere much stronger than those on silver nanoparticle monolayers, duo to the EMfield coupling between two layers of silver nanospheres. And the large SERSintensities appeared when the SPR peaks of SERS substrates well matched excitationlines. 2. Highly efficient construction of oriented sandwich structures forsurface-enhanced Raman scatteringTo solve the problem of low achievement in fabricating sandwich SERSsubstrates, a highly efficient sandwich structure was demonstrated by the orientedassembly of metal nanoparticles （NPs） on a periodic hexagonal array of metalnanoprisms with1,4-benzenedithiol （1,4-BDT） as linkers. The metal nanoprismarray was prepared by vacuum deposition of metal on a close-packed polystyrenenanosphere pre-patterned substrate. The metal nanoprism array presents differentsurface properties from the pits left from the removal of polystyrene nanospheres,which causes linkers to selectively adsorb on the metal nanoprism array andsequentially leads to the oriented immobilization of the second-layer metal NPs,avoiding mismatched orientation. The sandwich structure greatly increases theachievement of ’hot spots’ to almost100%of all the metal nanoprisms and enables alarge amplification of SERS signals by a factor of ten. The enhancement activities ofsandwich SERS substrates were evaluated under different excitation wavelengths byexperiment and theory.This study proved that the SERS intensities of sandwich structures are higher,which clearly indicates that sandwich structures provide more hot spots for SERSvia the electromagnetic field coupling between two layers of metal NPs. Moreover,The SERS intensities are stronger when the excitation wavelength is close to themaximum of the plasmonic band.3．Highly Efficient Construction of Silver Nanosphere Dimers on Poly（dimethylsiloxane） Sheets for Surface-Enhanced Raman ScatteringA highly-efficient and low-cost way to synthesize silver nanosphere dimers wasdeveloped on a flexible poly（dimethyl siloxane）（PDMS） sheet by using a stepwiseupright assembly method for the “hot spots” SERS study. The first silvernanoparticle layer is almost entirely embedded in PDMS and the second-layeredsilver nanoparticles directionally position the tops of the embedded particles. Thedimer （hot spots） yield in a well-defined upright orientation is almost50%. Thelocally confined EM field enhancement was presented by finite-difference time-domain （FDTD） simulation. Their SERS ability was evaluated by detectingdifferent concentrations of4-Mpy, and the incident angle-related excitation modewas discussed.The analysis of the localized electric field distributions of the silver nanospheredimer presents that the strongest electric field coupling appears at the gap of twonanospheres when the incident angle is about45degree and its intensity achieves400times enhancement. The SERS intensities on nanodimers were much strongerdue to the electromagnetic field coupling of nanoparticle-nanoparticle. By using thisnovel SERS substrate, the lowest detection concentration for4-mercaptopyridine is4.0×10¹⁴M. And we can see that the EFs of over107are reached. The nanodimerstructure has higher EFs relative to the nanosphere monolayer.