Preparation And Application Of Novel Silver Micro-nanostructures SERS Substrates

As an in-situ and non-destructive detection technology,surface enhanced Raman spectroscopy（SERS）has been applied to food safety,environmental monitoring,criminal investigation,biomedicine and in-situ monitoring of reaction mechanism.It is found that the enhancement effect of SERS depends on the local surface plasmon resonance（LSPR）effect of noble metals.It is easy to achieve the precise regulation of LSPR by adjusting the shape,size and particle arrangement of noble metal nanostructures.Among many precious metal nanomaterials,silver nanomaterials have many advantages,such as simple synthesis process,various morphology and wide size range,which are widely used in the preparation of SERS substrates.Here we propose four new types of silver micro-nano structures,and their SERS performance is studied through their SERS detection effects on different probe molecules.1.The Ag-nanosheets（AgNST）-grafted carbon-fenced conductive Ag nanowires with3D scale-like nanostructure was successfully fabricated through a direct hydrothermal and chemical reduction.The fabricated nanostructure displayed the sensitive and reproducible surface-enhanced Raman scattering（SERS）responses.The SERS detection for the probing molecule（rhodamine 6G,R6G）with concentration as low as 10^-12 mol/L was obtained in a reproducible way,and the average enhancement factor was about 2.33×10⁵.In addition,glucose（0.001 mg/mL）aqueous solution can be easily detected.It shows that the material has great potential application value in disease diagnosis.2.The pyramid-shaped silver microstructure was successfully synthesized using a simple electrochemical deposition method.The prepared pyramid-shaped silver microstructure has high SERS activity,and its average enhancement factor（EF）is 9.1×10^-5.In addition,an excellent reproducibility is achieved resulting from a relative standard deviation of 7.9%,8.5%,7.3%,and 8.7%measured by four Raman shifts of R6G at 612,772,1363,and 1650 cm^-1,respectively,which is much lower than those of the commonly used SERS substrates.It shows that the pyramid-shaped silver microstructures SERS substrate has excellent reproducibility.And the as-prepared pyramid-shaped silver microstructures have been evolved as a sensitive SERS substrate for the detection of trace amounts of R6G and 3-mercaptopropionic acid（3-MPA）down to nanomolar and millimolar concentration.3.The coupling effect of precious metals and the surface of semiconductor materials can effectively improve the SERS activity of the substrate.Here,tetrabutyl titanate was used as the precursor to grow a compact TiO₂ nanocolumn array on FTO glass by hydrothermal method.Two methods of soaking with silver ammonia solution and reducing silver nitrate with trisodium citrate were used to deposit silver nanoparticles on the surface of TiO₂ nanopillars for preparation of TiO₂@AgNPs structure,thus,a highly sensitive noble metal-metal oxide semiconductor composite SERS substrate is obtained.R6G was used as probe molecule to detect SERS effects of substrate,and explore its enhancement effects and analyze the causes of their different enhancement effects.4.Silver nanowires（AgNWs）can act as effective surface-enhanced Raman spectroscopy（SERS）substrate to detect small molecules.However,AgNWs prepared by conventional polyol methods are often coated with a thin layer of polyvinylpyrrolidone（PVP）ligand as an insulating layer.And when AgNWs SERS substrate is prepared,silver nanowires will be formed an insulating layer to produce ill-defined AgNWs-PVP-AgNWs interface,limiting the plasmonic coupling among the stacked AgNWs.Therefore,sodium borohydride was used to completely remove the PVP ligand on the AgNWs surface at room temperature,which greatly improved the SERS activity of the AgNWs film.The SERS detection of R6G used with PVP AgNWs and without PVP AgNWs is 1.0×10^-9 and1.0×10^-15 M,and the average enhancement factor（EF）is about 0.86×10⁴ and 9.35×10⁴,respectively.The SERS detection of AgNWs for R6G,3-MPA and melamine with good recyclability in nanomolar and millimolar concentration can be easily detected.And the SERS substrate shows excellent recyclability.