| In recent years,surface-enhanced Raman scattering?SERS?technology has become a very powerful tool in surface analysis,biosensing,and medical diagnosis due to its advantages of high sensitivity,specificity,and non-destructive testing.During the actual detection process,the detection sensitivity and repeatability of the Raman signal of the target molecules are important indicators to measure the detection level.The excellent detection ability is related to many factors,the most important of which are the SERS activity of the substrates,the uniformity of the substrate structure,and the repeatability from batches.Studies have shown that the SERS activity of the substrate is mainly determined by the abnormal amplifying ability for the incident electromagnetic field based on the surface structure.This amplified electromagnetic field can enhance the Raman scattering signal of the target molecules by more than a million times.Among them,micro-nano“hot spot”structures?sub-nano-scale nano-gap,nano-tips,nano-cavities,etc.?with local surface plasmon resonance?LSPR?characteristics are the key to obtaining ultra-strong electromagnetic fields.Therefore,the construction of uniform“hot-spot”structure has become an important research project to obtain uniform and repeatable SERS signals.In this paper,from the perspective of methodologies for preparing a SERS substrate with uniform nanostructure,various configurations of metal nanoarray structures were obtained in different ways,and a large-area uniform construction of the SERS substrate structure was achieved.The experimental method used in this paper not only reduces the cost,but also effectively improves the detection uniformity and repeatability of the SERS signal of the target molecules,which provides the possibility for the commercialization of the SERS substrate.The specific research results are as follows:?1?Inspired by the“dropping funnel”phenomenon,we fabricated close arranged Au NP arrays by combining oil/water interface assembly with convective assembly,and transferred the interfacial Au NPs film to solid substrates without disturbance.By controlling the dropping rate of the funnel,the gold nanoparticle film formed by potential energy equilibrium assembly at the oil-water interface began to drop off and was transferred in situ to the solid substrate at the bottom of the funnel without disturbance.Combined with the morphology observation of gold nanoparticles,we discussed the influence of the contact angle between the substrate and the interface film on the film transfer integrity while maintaining the funnel dropping speed a constant.Finally,we employed the Au NPs array film obtained under optimized conditions as the active SERS substrate for the detection of Crystal Violet?CV?molecule.The SERS Mapping and the relative standard deviation?RSD?statistics of the Raman intensity of the CV molecules both show that the Au NPs array obtained by this two-step method of disturbance-free self-assembly can be used as a uniform SERS substrate;?2?In order to fabricate the metal nanoarray structure with SERS activity more controllably,we obtained uniform metal-covered polymer nanopillar arrays by combining with nano-pouring and thermal evaporation deposition technology by using porous anodized aluminum oxide?AAO?as templates.We firstly poured polymer precursor solutions into the channels with different sizes,and re-engraved polymer nanopillars with different inter-nanopillar gaps and diameters by the thermal curing process;then,after removing the template,Ag films with different thicknesses were deposited on the tops of the nanopillars.The Ag film deposition furtherly adjusted the gap between the nanopillars and we finally obtained a highly uniform plasma structure with different SERS activities.We performed structural stability and SERS performance analysis by means of scanning electron microscope?SEM?,atomic force microscope?AFM?,and SERS mapping.Using CV and Rhodamine 6G molecules as the analytes,the RSD values of 4%at 1169 cm-1 for CV molecules and 8.1%for R6G molecules at 1355 cm-1 mode were obtained,showing excellent SERS uniformity.In addition,the flexible substrate can be more flexibly attached to the surface with complex morphologies and has certain potential for commercialization;?3?Preparation of hierarchical metallic nanoparticle arrays by“confined spheroidization”.Inspired by the spatial confinement effect in the preparation of polymer nanopillars,we confined the process of“annealing and spheroidizing”of metal materials at high temperatures in the holes of the AAO template and developed a novel“limited spheroidizing”method,and successfully obtained the periodic hierarchical metallic nanoparticle array.Inside each nanopore,larger-sized nanoparticles were formed due to the 3D“volume confinement”,while smaller-sized nanoparticles were formed on the pore wall due to the 2D“linear confinement”.We discussed the effects of metal deposition thickness,template size,and metal species on the size of the nanoparticles,and compared the SERS Properties of the as-prepared nanostructures by conducting electromagnetic field simulations of the prepared hierarchical metallic nanoparticle arrays with COMSOL theoretical analysis software.Using CV as probe molecules,the SERS uniformity and repeatability of the substrate were characterized.This work prepared a large-area metallic nanoparticle arrays by a simple one-step method,which would have important reference significance in the development of periodic nanomaterials;?4?Simple construction of large-area Au&Ag composite nanoarray structure with high SERS activity.Taking advantage of the above idea of“confined spheroidization”,we firstly obtained uniform Ag nanoparticle arrays through the annealing process by selecting a template with appropriate size;then the periodic Au&Ag composite nanoarrays with high SERS activity were obtained by in-situ substitution by employing the as-prepared Ag nanoparticle arrays as the reaction template.Through SEM,EDS and SERS detection analysis,it was found that the SERS activity of composite nanostructures was much higher than that of the pure Ag nanoparticle arrays after confined spheroidization.We speculated that the significant improvement of SERS activity was due to the synergistic effect of Au and Ag,and the electromagnetic field coupling enhancement generated by the special cascade structure.In addition,it was found that under different reaction times,the composite nanostructures obtained after 15 min in situ substitution had better SERS activity.This kind of structure not only showed outstanding detection sensitivity and signal homogeneity for dye molecules?Crystal Violet?CV?,methylene blue?MB?,malachite green?MG?,rhodamine 6G?R6G?,all with RSD values of SERS signal less than 10%?,but also obtained a good linear relationship for trace detection of anticancer drug molecule—6-mercaptopurine?6-MP?.This novel route greatly simplifies the preparation process of periodic composite nanomaterials and provides a new idea for the preparation of multi-component metallic nanostructures. |
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