Study On Preparation Of Flower-like Silver Nanostructures Based On Liquid Crystal And Enhancement Properties Of Raman Spectrum

With the advantages of simplicity,fast and high detection sensitivity,Surface-enhanced Raman scattering（SERS）technique has great application potential in spot rapid diagnosis fields.At present,the main problems in the application of SERS materials are:（a）poor consistency of spectra caused by the surface distribution of enhanced materials,（b）poor time stability caused by metal surface oxidation,and（c）the complex preparation method and high cost of uniformly stable SERS materials.To solve these problems,this paper carries out the research work.SERS material was prepared with lyotropic liquid crystal soft template and electrochemical deposition.Optimizing experimental conditions for the control of the nucleation and reaction rate,the optimal preparation conditions are obtained as:5 V electrodeposition voltage,0.3 mol/L AgNO₃ solution concentration,and 3 hours electrodeposition reaction time.Then,the SERS material is prepared and the silver nano-flower has the size of 2-3μm,which is composed with 20 nm sheet petals and other irregular small petals.Rhodamine 6G was also used as a probe molecule,and the Raman enhancement factor is computed to be up to 8.3×10⁵.The effects of the nanostructure distribution and the number of hotspots were studied within the laser spot area on the consistency of Raman spectrum.To 10,20,and 40μm laser spot sizes,an empirical formulaI=1.3 r^1.6 was obtained by fitting the measured data,which describes the relation between the surface coverage and Raman spectrum intensity.Then,based on the acquired equation,the reference surface coverage should be selected and then,all the spectral intensities with different surface coverages were attributed to the reference surface coverage.Thus,the effect of the surface coverage will be eliminated by recalculating the spectral intensities corresponding to the reference surface coverage.The experimental results shown that the spectral coefficient of variation were decreased to about 6%for different substrates,and the Raman spectral consistency is increased to be up to 5 times.The spectral consistency of the SERS materials was further improved.Larger detection laser spot area,higher spectral consistency.While the laser spot size in enlarged from 10μm to 40μm,the coefficient of variation of the spectrum is decreased from 6.2%to 2.3%.It was also found that,for the same detection region,multiple measuring and averaging the Raman spectra may improve the spectral consistency of the SERS materials further.When seven measurements were averaged,the coefficient of variation was decreased from 6%to 3.2%.Different to the ordinary method which achieve the long-time stability of SERS material by optimizing the material structure,a novel method is proposed to achieve the good time stability of SERS material by changing its external environment to block the oxidation reaction.The validation experiment scheme was given and three contrast groups were set as air,vacuum,and argon groups.Each group contains 3SERS materials which is prepared with the same condition and then,divided into 12sub-regions to obtain 11 groups of Raman spectra data within six months.Finally,the Raman spectral intensities reducing according to the time with different storage environments were obtained and the effectiveness of the proposed method may be confirmed.Through the research work of this thesis,the silver nano-flower enhancement material is fabricated with the uniform distribution and low-cost.And,the consistency of Raman spectra was significantly improved with the result of the spectrum coefficient of variation is downed to about 2%.Moreover,the simple method to improve the time stability was proposed,and a specific experimental verification scheme was presented.This research work not only promotes the practical application of SERS material in trace detection,but also accelerates its practical and productization process.