Design Of Metal Nanostructures With Two-dimensional Materials As Spacers And Its Application In SERS

Raman spectroscopy is produced by inelastic light scattering which caused by molecular vibratio.It can provide fingerprint information for molecular diagnosis.However,the inherent scattering intensity of conventional Raman spectroscopy is extremely weak,and the general light intensity can only reach 10^-10of the incident light intensity,which limits its application range.Surface enhanced Raman spectroscopy not only provides fingerprint information for target detection molecules,but also provides more abundant molecular structure information.And it can achieve ultrasensitive,real-time and in situ detection at the single molecular level.It is a very powerful trace detection tool.At present,different types of zero-dimensional and one-dimensional metal nanostructures are widely used in SERS substrates,such as zero-dimensional single isolated nanospheres,one-dimensional nanowires or nanorods.However,the low dimensional space mode metal nanostructures limit the production of high density"hot spots"and the poor regulation,which limits the further improvement of SERS substrate detection sensitivity.Compared with low-dimensional modes,two-and three-dimensional(2D and 3D)metal nanostructures have better optical property tunability and can be widely used in SERS quantitative sensing field.At the same time,2D materials have the characteristics of stability,uniformity,high light transmission,smooth and uniform surface,no suspended bond structure,which can not only prevent the direct contact between layer and layer metal nanostructures,but also be beneficial to the uniform adsorption of detection molecules,effectively inhibit background fluorescence,and improve signal sensitivity.Based on the 2D spacer metal layer,we designed several SERS substrates with high sensitivity and stability,and studied their properties in detail as follows:(1)A two-dimensional Au nanoparticle/Mo S₂/Au nanoparticle(Au NP/Mo S₂/Au NP)composite structure with molybdenum disulfide film as molecular adsorbent was provided by repeated annealing method.This method provides enlarged Au NP density with much smaller gap spacing,and thus dramatically increases the density and intensity of hot spot.The Mo S₂films distribute among the hot spots,which is beneficial for uniform molecular adsorption,and further increases the sensitivity of the SERS substrate.The finite difference time domain method is used to simulate the base structure and the simulation results are consistent with the experimental results.Three kinds of molecules(R6G,CV and MG)were used to evaluate the SERS substrate.Ultra-sensitive,highly repetitive,and stable SERS signals were obtained,and enhanced factors reached 1.79×10⁹,which would promote the application process of SERS technology in quantitative analysis and detection.(2)A multilayered Ag nanoparticle(Ag NP)/graphene coupled to an underlying Cu film system(MAg NP-Cu F)was designed,which can be used as an effective SERS substrates realizing ultra-sensitive detection for toxic molecules(R6G,CV and thiram)and in-situ monitoring the plasmon-driven reaction for p-nitrothiophenol(PNTP)to p,p'-dimercaptobenzene(DMAB)conversion.The mechanism of ultra-sensitive SERS response and catalytic reaction is investigated via Ag NP/graphene layer-dependent experiments.With the help of finite time domain difference method,the multi-dimensional surface plasmons coupling of MAg NP-Cu F structure was theoretically confirmed.The research found that the intensity and density“hot spot”can be effectively manipulated by the number of plasmonic layers,and the bottom Cu film could also reflect the scattered and excitation beam and would further enhance the Raman signal.Moreover,the MAg NP-Cu F exhibits outstanding performance in stability and reproducibility.We believe that this concept of multilayered plasmonic structures would be widely used not only in the field of SERS but also in the wider research in photocatalysis.