Construction And Application Of SERS Platform Based On Two-dimensional Periodic Array

The quantitative detection and identification of ultra-low concentration biological and chemical molecules is a research hotspot in the fields of medical diagnosis,environmental science,homeland security and so on.Molecular detection techniques are usually based on optics,electrochemistry,electronics or gravimetric methods.Among these methods,surface-enhanced Raman spectroscopy（SERS）is considered to be one of the most reliable,sensitive and selective non-destructive molecular analysis techniques.It performs molecular analysis by amplifying the electromagnetic field and establishing a charge transfer state between the chemisorbed analyte molecules and the SERS active platform.Unfortunately,the applicability of SERS is quite limited,mainly due to the lack of good repeatability and stability of the current SERS platform and the lack of high sensitivity.At present,precious metal nanoparticles such as gold,silver and copper are widely used in the active platform of surface-enhanced Raman scattering.Although their application in SERS is economical and simple,the SERS signals are inconsistent because of their poor controllability of structure and limited hot spot detection area.Therefore,in the past few years,researchers have focused on building a structural,material and dimensional composite SERS platform,which can increase the adsorption of analyte molecules,increase structural coupling and promote the formation of multi-dimensional hot spots.However,at present,the manufacture of composite SERS platform is mostly expensive,and the technical requirements are very high.Therefore,the preparation of a more economical and convenient composite SERS platform is of great significance not only to broaden the application of surface-enhanced Raman spectroscopy,but also to broaden the application field of this kind of SERS platform.This paper has carried out three parts of research:（1）SERS substrate of two-dimensional curved crater composite array and its anti-counterfeiting application.We combine self-assembly technology,magnetron sputtering technology and plasma etching technology to construct a multi-layer curved surface"crater"structure with orderly curved surface and random distribution of"crater"potholes.Through experiments,the following optimal conditions can be obtained:sputtering 100 nm Ag on silicon substrate and then etching 5 min.Under these conditions,the SERS strength of the substrate will reach the maximum,which is two orders of magnitude higher than that of the untreated substrate,and consistent with the results obtained by digital simulation of FDTD.The shape of the structure obtained under this condition is more complete,and it is more convenient to be used as the map of anti-counterfeiting coding.The number of potholes,the average diameter of potholes and the ratio of the covering surface of potholes in this field are statistically calculated to form a unique three-stage anti-counterfeiting code.At the same time,combined with the SERS spectrum of the substrate,the anti-counterfeiting bar code is further compiled according to the difference of peak position and strength.The preparation of this kind of composite structure SERS substrate not only broadens the application field of substrate,but also provides an idea for the preparation of economical and simple SERS composite structure substrate.（2）Design of Ag/TiO₂/Ag multilayer composite nanoarray structure with adjustable SERS activity.In this part,we combine nano-etching technology with magnetron sputtering technology to prepare a series of nanostructure substrates with evolutionary structure.Ag/TiO₂/Ag composites are introduced into this composite structure.Inspired by the composite of curved surface nanostructures and potholes,we follow the idea of structural composite in this chapter.The surface nanostructures are combined with nano-stars,nano-rings,nano-disks and other structures,and then the composite of materials is introduced,hoping to further enhance the regulation of SERS properties.The combination of TiO₂ and Ag and the electron transfer property of TiO₂ further enhance the activity of SERS.Deposition,plasma etching and transfer are carrying out on a closely packed polystyrene（PS）colloidal sphere（200 nm）array.Due to the shadow effect between colloidal spheres and metal particles introduced by deposition,a series of Ag/TiO₂/Ag nanostructure arrays with adjustable nanostructures can be obtained,such as nano-cap（NC）,nano-cap-star（NCS）and nano-particle-disk（NPD）.These nano-arrays with rough surfaces and evolutable structures can continuously adjust optical plasmon resonance and reconstruct SERS hotspots on a large scale,which have potential applications in surface science,chemical detection and nanophotonics.（3）Preparation and in situ SERS study of Nano-flakes structure in curved surface array.By means of two-dimensional periodic nano-pattern array and chemical growth induced by 4-MBA molecules,we have developed an Ag"nano-flakes structure"array with three-dimensional high-density SERS hot spots by secondary growth of new hot spots on the existing structure hotspots.The nano-petals grown by this structure are filled in the gap structure of the nano-sphere array,so that the gap with the original scale of hundreds of nanometers is reduced to dozens or even several nanometers,which adds a new dense gap hot spot for the gap which is unable to produce SERS enhancement because of the large distance.the structure has strong SERS performance,and the SERS intensity reaches the maximum when the structure reaches saturation.At the same time,in order to further the growth mechanism of three-dimensional Ag nanoflowers with high density in order to obtain SERS substrates with excellent performance,we chose factors including light radiation,molecules and environmental gases to track the formation mechanism of silver nanoflakes.In-situ Raman observations and theoretical analysis show that aromatic small molecules with carboxyl groups play an important role in the local surface plasmon resonance（LSPR）driven silver nanoscale reaction,which provides a new way for the reconstruction of high-density hot spots in nanostructured SERS substrates.