Research On Fiber SERS Probe Based On Gold And Silver Nanostructure Arra

Surface-enhanced Raman scattering（SERS）,as a molecular detection technology,can obtain the"fingerprint information"of target analytes with high sensitivity,even to the single molecule level,and has been widely used in Surface physics,biology,chemistry,nanomaterials and other fields.Especially,with the development of fiber sensing technology,fiber probes based on SERS have also received great attention.Compared with the traditional SERS detection,the fiber-optic SERS probes prepared by depositing the precious metal nanostructure on the fiber facet have lower cost and good repeatability.Most importantly,the fiber-optic SERS probes can realize real-time,in-situ and remote detection.The electromagnetic field strength on the surface of the structure and the SERS signals can be greatly enhanced by the periodic metal nanostructures prepared on the optical fiber facet with uniformly distributed high-density"hot spots",such as metal nanocap arrays.Meanwhile,the fiber-optic SERS probes based on metal nanostructures can effectively generate heat after laser irradiation,drive and guide the liquid convection in the analytical solution to accelerate the desorption of probe molecules from the"hot spot"of metal nanostructures,so as to achieve effective self-cleaning of the fiber probes,which is conducive to providing the possibility for reproducibility analysis and quantitative analysis in SERS detection.In this paper,three highly ordered metal nanocap arrays were prepared on the optical fiber facet by the combination of nanosphere lithography and vacuum thermal evaporation.The prepared optical fiber SERS probe was used to realize the highly sensitive detection of probe molecules such as 4-aminothiophenol（4-ATP）.The main research work is as follows:（1）Nanosphere lithography was used to prepare fiber-optic SERS probes based on Au nanocap arrays.Polystyrene（PS）microspheres are firstly arranged in a highly ordered hexagonal tight array through self-assembly at the gas-liquid interface,and transferred to the optical fiber facet.Then,gold film is deposited by vacuum thermal evaporation technology to prepare a regular and ordered Au nanocap array on the PS microsphere array.The morphology of the Au nanocap array on the fiber-optic probe was characterized and analyzed by scanning electron microscopy（SEM）.The results show that Au nanocaps prepared on the optical fiber facet presents a highly ordered hexagonal tight array with good periodicity and reproducibility.The electric field distribution and hot spot distribution of the manufacturing structure were simulated and analyzed by using finite difference time domain（FDTD）method,and the results showed that the adjacent nanocap gaps can produce strong hot spot effect.Using 4-ATP as the probe molecule,the experimental results showed that the fiber-optic SERS probes had excellent detection sensitivity.（2）The fiber-optic SERS probe based on Ag/Au nanocap arrays was prepared on the basis of Au nanocap arrays.The fiber-optic SERS probes based on Ag/Au bimetallic composite structure have the advantages of both the chemical stability of gold nanomaterials and the strong SERS activity of silver nanomaterials.SEM characterization and FDTD simulation showed that the Ag/Au bimetallic nanocap arrays had obvious spatial stereoscopic structure,and the coupling of Ag/Au bilayer can greatly increase the hot spot intensity of the gap between adjacent metal nanocaps.The Ag/Au bimetallic nanocap array was used as SERS base to detect environmental pollutants such as 4-aminothiophenol,rhodamine 6G,and methylene blue.It was found that the fiber-optic SERS probes based on Ag/Au nanocap array prepared had good detection repeatability and high sensitivity,and had a good prospect in practical application.（3）Based on Au nanocap arrays,the fiber-optic SERS probes based on Au nanocap arrays with Ag nanoshells decorated on the fiber facet were fabricated by performing a second PS microspheres self-assembly and metal nanofilm deposition.Through the characterization of the fiber-optic SERS probe surface morphology,it was found that the Au nanocaps were closely arranged on the optical fiber facet,while there were nanogaps between the Ag nanoshells on the gold nanocaps.The FDTD simulation shows that the nanogaps between the Ag nanoshells and the Au nanocap can generate strong hot spot effect,significantly improve the local electromagnetic field intensity,thus displaying better SERS effect.The results also showed that a visible SERS peak characteristic of 4-ATP could be observed at concentrations as low as 10^-8 M,exhibiting an excellent SERS sensitivity.