Based On Two-dimensional Colloidal Crystals To Construct A Multi-dimensional High-density Hot Spot Effect SERS Active Substrate And Performance Research

Surface Enhanced Raman Spectroscopy(SERS)technology,as a spectral detection for chemical and biological analysis,has advantages such as low analyte usage,high detection throughput,fast detection speed,and effective avoidance of biological autofluorescence.Many areas such as chemical sensing,biosensing and detection of harmful chemicals have good application prospects.Researchers generally believe that the Raman signal of analyte molecules on SERS active substrates was enhanced by plasma "hot spots",which were local electromagnetic field enhancements caused by the collective oscillation of free electrons in noble metals such as Au,Ag,Cu or transition metals.The obtained electromagnetic field was coupled to obtain a stronger Raman signal.It is a key to construct a SERS active substrate with high sensitivity,high stability and reusability.The ordered structure of two-dimensional colloidal crystals has been extensively studied as a substrate due to its good absorption of light,and the close-packed structure can ensure the repeatability and uniformity of the Raman signal of the analyte molecule.The combination of the periodic electric field and the optical field of the coinage metal(such as Au/Ag/Cu)can significantly enhance the spectral signals of the analyte(such as fluorescence,infrared and Raman signals).On the other hand,semiconductor materials with nanostructures(such as ZnO,Cu2O,TiO2,etc.)can enhance the charge transfer in the SERS process due to their hole-to-electron pairs that can be generated by light irradiation.If noble metal nanoparticle and semiconductor composites are used as SERS active substrate,enhanced the charge transfer between the surface of the substrate and the analyte molecules.Moreover,due to the excellent photocatalytic properties of the semiconductor material,the probe molecules adsorbed on the surface of the substrate can be photodecomposed to achieve multiple reusability of the substrate.Therefore,it is particularly important to realize the construction of a highly sensitive substrate,especially combining the excellent interface properties of substrate having a certain micro/nano structure,the substrate can be better reproducible and reusable.Based upon the above research background,this thesis proposes a method for efficiently constructing a SERS-active substrate with high-density hot-spot effect.Polymer microgel particles were used to construct two-dimensional colloidal crystals,which bring the unique single-layer ordered structure with excellent optical properties and soft template properties.The colloidal crystal/Au composite substrate was obtained by an ion sputtering method which is easy to realize large-area deposition.Regulated the microenvironment of the microgel particles to control the dispersed aggregation state of the Au nanoparticles on the substrate.The electromagnetic field coupling effect of the active substrate was changed to realize the construction of a highly enhanced reusable SERS active substrate.On this basis,the two-dimensional colloidal crystal was used as a template to assist the hydrothermal growth of the ZnO nanorod array.A ZnO nanorod array structure having different surface topography was prepared.The construction of SERS active substrates with three-dimensional hot spot distribution effects was achieved by assembling Au NPs by ion sputtering.Finally,the SERS performance and enhancement mechanism of the substrates were studied by using Rhodamine 6G(R6G)as the probe molecule.This thesis mainly consists of the following three parts:(1)This study proposes an approach for constructing a SERS-active substrate material having a high density of hot spot effects.A regular two-dimensional colloidal crystal structure was assembled by gas-liquid interface using the Poly(styrene-co-N-isopropylacrylamide)@polyacrylic acid(PSN@PAA)microgel particles as building blocks.Ion sputtering obtained the colloidal crystal/Au composite film.The aggregation of Au nanoparticles on the surface of the colloidal crystal and the SERS performance of the substrate was adjusted by the amount of sodium citrate in the methanol solution.The results showed that the addition of sodium citrate solution make the Au nanoparticles had a certain shrinkage effect,which created a gap between Au and Au NPs,and improves the SERS performance of the active substrate.Constructed SERS-active substrate has an enhancement of 105 orders of magnitude with a detection limit of 10-9 M,and the substrate has good reproducibility and reusability.It has potential application in the fields of dye molecule detection,chemical sensing and catalysis.(2)The ZnO nanorod array structure was used two-dimensional colloidal crystal structure as a template by hydrothermal synthesis.The ZnO nanorods were hydrothermally grown with zinc nitrate hexahydrate as the source of Zn.Different hydrothermal growth times buring the different surface morphology of the substrate.The results showed that the polymer microgel particles contribute to the enrichment and fixation of the precursor.A shorter nanorod array structure with a certain hydrophilicity was obtained by 30 mins growth.As the growth time increases,the surface of the array structure becomes more hydrophobic.The SERS performance of the constructed substrate becomes stronger as the deposition time of the Au nanoparticles increases.(3)Different structures of zinc oxide nanorod structures were grown on the PSN@PAA/Au substrate by hydrothermal synthesis.A colloid/Au/ZnO/Au composite substrate having a three-dimensional hot spot distribution was obtained by ion sputtering.The Au nanoparticles of different size aggregation states were obtained by adjusting the Au NPs sputtering time to construct a SERS active substrate with multi-dimensional hot spot distribution and electromagnetic field enhancement(EM)and chemical enhancement(CE)mechanisms.The results showed that the constructed active substrate had an enhancement factor of 10V orders of magnitude,a lower detection limit of 10-10 M and better signal reproducibility.The SERS performance of R6G molecules in different solvents can be achieved by hydrophilic and hydrophobic properties of the surface of the substrate.The SERS-active substrate constructed in this research has good application prospects in the fields of chemical biosensing,catalysis and photoelectric conversion.