Fabrication Of Precious Metal Micro-nano Structure SERS Substrates And Their Performances

Surface enhanced Raman scattering(SERS)spectroscopy has ultra high sensitivity to the probe molecules adsorbed on the surface of metal particles,and is capable of analyzing and identifying the structure,adsorption state and other aspects of information of the probe molecules.In addition,SERS has the advantages of good selectivity and weak interference from water and fluorescent signals.So,SERS technology has the widespread application prospect in analysis,chemistry,environmental science and biomedical fields.However,whether SERS technology can be implemented more widely,largely depends on the activity,uniformity and reproducibility of SRES substrates.Therefore,the study of the preparation of various types of SERS substrates has been one of the focuss of SERS research fields.This desertation not only focuses on the development of new and highly active SERS substrates,but also studies the influence of different factors on the activity and performance of the SERS substrates.The main research contents and innovations of this work include the following four parts:1.Polyvinylpyrrolidone-protected silver nanoparticles of different nanostructures were prepared by the method of electrostatic self-assembly.The SERS properties of the nanocube monolayer were the best,and these protected silver nanoparticles were also proved to have good biocompatibility.Polyvinylpyrrolidone-protected silver nanostructures of various shapes,including nanocubes,nanospheres and hybrid shapes with nanospheres and nanorods,on the surface of glass or Si substrates are prepared by using electrostatic self-assembly.The PVP-protected silver nanocubes films have better SERS activity with an order of magnitude larger enhancement factors than the PVP-protected silver nanospheres films and the PVP-protected silver hybrid shapes films,which is confirmed by our numerical simulations.The uniformity and reproducibility of the SERS signals on PVP-Ag NCs film are tested by point-to-point and batch-to-batch measurements.Meanwhile,the PVP-Ag films are also shown to be an excellent SERS substrate with good biocompatibility for hemoglobin detection.It is shown that the PVP-Ag NCs films can be used as excellent SERS substrate with good activity,uniformity,reproducibility and biocompatibility and are promising for a myriad of chemical and biochemical sensing applications.2.Ag nanocubes/4-aminothiophenol/smooth platinum film sandwich structure was constructed,the effect of Pt film thickness on the intensity of the Raman signal was realized,and the experimental results were confirmed by theoretical simulation.The proposed sandwich structure is shown to exhibit better performance than the Ag nanocubes only as SERS substrate.The dependence of the Raman signal intensity on the thickness of the Pt films is examined.It is shown that the Raman signal increases with the thickness of the Pt films from 42 to 90 nm,suggesting the electromagnetic coupling of the localized surface plasmons of the Ag nanocubes with the surface plasmon polaritons of the underneath Pt film,which is confirmed by our numerical simulations.The SERS enhancement factor in Ag nanocubes/4-aminothiophenol/smooth platinum film sandwich structure is estimated to be(4.1±0.2)×106 for a Pt film of 90 nm.The implication of the present observation is enormous because it strongly suggests that the inherent obstaclesto the more wide spread use of SERS can be overcome by the judicious use of SERS-active nanoparticles directly or indirectly.3.Put forward a new green and simple preparation method of Ag-Fe3O4 nanocomposites,a magnetic assembly method is used to make the surface "hot spot"dense SERS substrate,the contribution of Fe3O4 to the plasma resonance of the composite is significantly demonstrated by experiments.Ag-Fe3O4 nanocomposites were synthesized by the redox reaction between Ag2O and Fe(OH)2 in the absence of additional reductant at moderate temperature and atmospheric condition.The as-synthesized Ag-Fe3O4 nanocomposites are assembled into an orderly arrayed SERS substrate holding clean and reproducible properties with an applied external magnetic field.4-mercaptobenzoic acid is chosen as the probe molecule to test the enhancement factors,uniformity and reproducibility of the SERS substrate.Experimental results indicate that the EF of 4-MBA on our proposed SERS substrate is up to 5.2×106 and the detection limit is down to?10-10 M.The SERS spectra of 4-MBA molecules were randomly collected from a number of positions on the substrate and six Ag-Fe3O4 nanocomposites substrates are measured with the same procedure.It is shown that the SERS substrate have the good uniformity and reproducibility with low standard deviation,indicating our proposed Ag-Fe3O4 nanocomposites with external magnetic field control abilities have potential applications in the fields of magnetic separation and SERS techniques.In particular,this study also provides a new strategy for fabrication of magnetic noble metal NPs and a new route in eliminating the single-use problem of traditional SERS substrates.4.We proposed a facile green synthesis system to synthesize large-scale Ag hemi-mesoparticles monolayer on Cu foil.Ag hemi-mesoparticles have different surface morphologies on their surfaces,including ridge-like,meatball-like,and fluffy-like shapes.In the reaction,silver nitrate was reduced by copper at room temperature in dimethyl sulfoxide via the galvanic displacement reaction.The different surface morphologies of the Ag hemi-mesoparticles were adjusted by changing the reaction time,and the hemi-mesoparticle surface formed fluffy-spherical nanoprotrusions at longer reaction time.At the same time,we explored the growth mechanism of silver hemi-mesoparticles with different surface morphologies.With 4-mercaptobenzoic acid as Raman probe molecules,the fluffy-like silver hemi-mesoparticles monolayer with the best activity of surface enhanced Raman scattering(SERS),the enhancement factor is up to 7.33 x 107 and the detection limit can reach 10-10 M.SERS measurements demonstrate that these Ag hemi-mesoparticles can serve as sensitive SERS substrates.At the same time,using finite element method,the distribution of the localized electromagnetic field near the particle surface was simulated to verify the enhanced mechanism.This study helps us to understand the relationship between morphology Ag hemi-mesoparicles and the properties of SERS.