Study-on Preparation And SERS Properties Of Ordered Inorganic Nano Films

Ultrasensitive detection of biological substances and chemicals has important significance in the fields of science and technology,such as biomolecular diagnosis,environmental monitoring,materials and analytical chemistry.Among various kinds of analysis technology,surface-enhanced Raman scattering?SERS?has become one of the most effective method for the detection of trace molecules due to its high sensitivity and molecular specificity.However,we still need to make great efforts to improve the stability,reproducibility and reduce the cost of the SERS substrate,which can realize it's widely used in our real life.Besides,employ assembly technology or search for new base materials has become a focus of our research.After ordered assembly,the nano materials shows enhancement in detection efficiency and long-term stability.What's more,it is a more effective way to reduce costs by using semiconductor material to replace the precious metal substrate.In this paper,the nano materials with uniform morphology were synthesized by using polyol,hydrothermal and polymer template methods,and then assembled into a variety of uniform and ordered nano films through Langmuir-Blodgett?LB?technique,three-phase interface and vertical deposition methods.The morphologies,crystal phase and spectra of these films were characterized.Furthermore,the application of SERS was also studied.The research results are summarized as follows:1.Firstly,Ag nanowires?AgNWs?were prepared in polyol system.Then a simple and controllable LB technique was introduced to assemble AgNWs@GO-AgNPs composite film.The graphene oxide?GO?-shielded AgNW film was used as a large-area uniform and long-term stable SERS substrate,while the Ag nanoparticles?AgNPs?decorated on the outside surface of GO layers can increase the roughness of the film to provide more SERS active sites.What's more,as a subnanometer spacer,GO creates a uniform nanogap between AgNPs and AgNWs that can form more "hot spots" in the nanocomposite film.By virtue of these advantages,the AgNWs@GO-AgNPs composite film exhibits a highly sensitive SERS measure with a detection limit of rhodamine 6G?R6G?as low as 10-13 M.Besides,we also investigated the catalytic activity of the AgNWs@GO-AgNPs composite film for the reduction of 4-nitrophenol?4-NP?as a probe reaction,and the improvement of catalytic activity are mainly attributed to the synergistic effect of AgNPs and AgNWs on or in the film.The investigation displays a new avenue for the development of high efficient,excellent performance and long-term stable GO-protected orderly film based on LB technology for the biosensor and catalyst.2.Here,a non-stoichiometric semiconductor metal oxide,W₁₈O₄₉,was used as a novel SERS substrate instead of noble metal.The W₁₈O₄₉ nanowires with relatively uniform morphologies were synthesized by the hydrothermal reaction.Then the W₁₈O₄₉ ordered nanowire film was fabricated by three-phase interface approach.When W₁₈O₄₉ ordered nano wire film was used for the SERS detection of organic dyes,we found that the non-stoichiometric W₁₈O₄₉ nanowires which have more oxygen vacancies than WO₃ exhibit higher SERS signal.As a SERS substrate,the W₁₈O₄₉ nanowires have a Raman response to various probe molecules,such as basic fuchsin?FB?,methylene blue?MB?and rhodamine B?RB?.And the detection limit of RB is 10^-7 M which is close to that of the precious metal without the "hot spot".The relative standard deviation of reproducibility on this film substrate was only 9.7%.Therefore,as a new non-noble metal SERS substrate,the film provides an important inspiration for its wide application in the detection of pollutants.3.Three dimensional ordered TiO₂ inverse opal substrate?IOS?thin films were prepared effectively by vertical deposition method using opal photonic crystal assembled by polystyrene?PS?spheres as template.Then,CdSe were used to sensitize the TiO₂ IOS and finally the ordered and uniform CdSe-TiO₂ IOS composite films were synthesized successfully.The synergistic effect of slow photons and multiple scattering effects of TiO₂ IOS and CdSe sensitization,leads to the enhancement sensitivity of the CdSe-TiO₂ IOS composite film as a SERS substrate.And when the thin film was employed as a SERS substrate to detect MB,the detection limit can reach as low as 7×10?-9? M.From the experiment results,we found that the absorption spectrum of the film was extended from ultraviolet region to visible region,and the band gap becomes narrower.Compared with the pure TiO₂ IOS,the photocurrent density of the composite film has a 2.16-fold increase,owning to the suppression of the recombination rate of photo-generated electrons and holes.The CdSe-TiO₂ IOS composite film possesses bifunction,which can used as an ordered SERS substrate with high sensitivity and low cost,and its high photocurrent density provides an experimental basis for the study of solar cells.