Regulation Of The Surface Structure Of Magnetic Gold Composite Microspheres And Study On Its SERS Performance

Surface-enhanced Raman scattering?SERS?means that when the molecules to be detected were adsorbed on the rough metal surface,especially the noble metal surface,the Raman scattering signal was greatly enhanced.In view of the close relationship between the Raman signal and the molecular structure of the adsorbed substance,it has a unique fingerprint signal and can identify different molecules with high sensitivity.Therefore,SERS technology,as an analytical method with great potential application value,has been widely used in environmental detection,including biological analysis,food hygiene,public safety and other research fields.Since the SERS signal of the analytes were heavily dependent on the components,structure and morphology of SERS substrate.Therefore,the control synthesis of SERS substrate was the key to achieve high-performance SERS analysis and detection.Now,SERS substrate was mainly divided into two types:array membrane type SERS substrate and particle type SERS substrate.Compared with the ordered membrane type SERS substrate,the particle type SERS substrate has become a research hotspot for many scientific researchers due to its advantages such as simple preparation and abundant surface-active hot spots.Compared with silver nanoparticles,gold nanoparticles have better stability,biological compatibility and other advantages.At present,gold nanoparticles such as triangular gold nanoplates and gold nanorods.because of their cutting-edge structure,presented strong SERS properties,especially the SERS properties will be further amplified when these particles formed a gap structure during the process of assembly.However,when using gold nanoplates or gold nanorods as SERS substrate to detect the substances in the solution,it was necessary to combine and separate the gold nanoparticles with the detected substances in the solution,and separate the nanoparticles through centrifugation or filtration,which was relatively complex and easy to cause losses.Combining the noble metal nanoparticles with superparamagnetic Fe₃O₄ microspheres did not only simplified the operation by using magnetic separation technology,but also enabled the magnetic composite particles to aggregate to form new active hot spots under the action of external magnetic field,further enhancing the overall SERS performance of the substrate.Concerning magnetic based SERS substrates,while the magnetic microsphere surface realized the noble metal shell coating,the regulation of the surface structure of the magnetic substrate noble metal composite microsphere is the key of preparing the high-performance magnetic based SERS substrate.In this paper,the surface structure of magnetic gold composite microspheres is taken as the research object.By referring to the previous research results of gold nanoplates and gold nanorods,the reaction rate of the precursor is firstly regulated to inhibit homogeneous nucleation and the heterogeneous deposition of noble metals on the surface of magnetic microspheres is realized.Secondly,according to the experimental reaction system,suitable surface morphology control reagents were found,and on this basis,the reaction parameters were regulated to realize the assembly of gold nanoplates and nanorods on the surface of magnetic microspheres.Finally,using CV as the probe molecule and combining with SERS performance characterization,the structure of the product was optimized to achieve the development of magnetic based SERS substrate with high performance.The specific research content is as follows:1.Fe₃O₄@SiO₂ composite microspheres as the core,in the surface modification of gold nanoparticles?about 3 nm in diameter?,as the growth center,and then to explore the different kinds of reducing agent such as ascorbic acid,hydroxylamine hydrochloride,catechol,L-dopa influence on gold shell growth.then the introduction of Br^-as shape-directing agent,achieve the growth of gold shell lamellar structure.Through experimental comparison and analysis,it is found that the synergistic effect of L-dopa and Br^-is the key to the synthesis of gold nanoplates.The influence of reaction temperature and concentration of reagent on the morphology was further investigated.The surface of Fe₃O₄@SiO₂ composite microspheres was successfully synthesized by adjusting the reaction conditions.Using CV?crystal violet?as Raman probe,the SERS properties of different surface structures were analyzed,and the magnetic based gold nanoplates composite microspheres SERS substrate with the best performance was obtained,and its detection limit concentration for crystal violet was up to 10^-1010 M,and the enhancement factor was 5.7×10⁵.Compared with the gold nanoplates,the detection performance is improved by 10 times while the separation efficiency is improved.The improvement of the performance may come from the new active hot spots formed by the gold nanoplates crossing when the microspheres are concentrated.2.The aggregation cross of gold nanorods can easily introduce active hot spots and further improve the tip density of the magnetic core surface for the achievement of higher performance detection.Taking this as the starting point,combined with the growth process of gold nanoplates in the previous chapter,the control synthesis of magnetic gold nanorods composite microspheres was explored in detail.Firstly,in view of the role of Ag⁺in the growth process of gold nanorods,silver nanoparticles?about 10 nm in diameter?were introduced into the surface of Fe₃O₄@SiO₂ composite microspheres to achieve the uniform release of Ag⁺in the reaction process.Secondly,levodopa was selected as a reducing agent to further investigate the influence of reaction temperature,reagent concentration and other factors on the morphology.By adjusting the reaction conditions,the surface of Fe₃O₄@SiO₂ composite microspheres was successfully synthesized with different gold nanorod assembly structures.Using CV as Raman probe,the SERS properties of different structures were analyzed,and the SERS substrate of magnetic gold nanoplates composite microspheres with the best performance was obtained,and the limit concentration for detection of crystal violet was up to 10^-1111 M,and the enhancement factor was 3.2×10⁶.Compared with gold nanoplates,its detection performance is improved by 10 times,which is an order of magnitude higher than the detection performance of magnetic gold nanorods composite microspheres.It is speculated that the reason lies in the fact that the synthesized product has the surface structure of high-density gold nanorods and introduces more active hotspots in the aggregation and intersection.