| Surface-enhanced Raman scattering?SERS?is a highly efficient molecular spectroscopy technique and the molecular Raman signal is greatly enhanced by exciting the interaction between the surface and the molecules of the metal nanostructures.Therefore,SERS has been widely used to detect trance species,and even single studies in many fields,such as chemical,life science,and medical application.But,limited by the manipulation of nanostructures,the drift of instrument parameters and the uncertainty of the number of molecules,it is difficult to further improve the stability of SERS spectra.So,SERS quantitative analysis is an urgent problem to be solved.There are three major problems in the quantification process:signal fluctuation due to the non-uniformity of substrate;the orientation fluctuation of adsorbed molecular or chemical interaction leading to spectral instability;and uncertainty of the number of analytical molecules.And there are three types of solutions for the problem of substrate uniformity that play a major role:One is that an internal molecule is embedded into SERS substrates by a core-molecule-shell structure.But the preparation is very complicated,and the selection of the internal standard specie is limited by the preparation method.Another one is that an internal molecule is directly added into the analyte molecule.But,the internal standard species would affect and even replace the surface adsorption site of the analyte molecules.In addition,the latest reported one is that an internal standard specie is indeed in the SERS substrate itself.Based on our previous research,this paper mainly studies carbon nanotube/graphene/metal nanocomposite structure as SERS substrate.A self-calibration theoretical model is established by calibrating the molecular density information by 2D Raman characteristic peaks of the carbon nanotubes/graphene.This model reveals the mechanism of achieving SERS quantitative analysis and conducts experimental research.Specifically major work includes the following parts:?1?The modulation of plasmon resonance wavelength by Au and Ag nanoparticles?Au/AgNPs?has been studied.The self-assembly simple of AgNPs can reach more than109 analytical enhancement factors.At the same time,the method of thermal evaporation and annealing can form a relatively uniform single-layer Ag nano-island structure,and graphene?GE?acts as a protective layer and molecular adsorption platform for the substrate to increase substrate stability and uniformity.Meanwhile,the enhanced Raman spectrum of graphene has been studied,and the fluctuation of its signal reflects the volatility of the substrate.Furthermore,the principle of SERS quantitative analysis by internal standard method and its advantages in obtaining reliable molecular information have been expounded.?2?A carbon nanotube and AgNPs composite substrate?CNT-AgNPs?is reported,and the CNT has been used as an internal standard for the calibration of SERS intensity of analyte molecules.Preparation and characterization?SEM,EDS and Raman?of CNTs-AgNPs composite structures were studied.The composite structures can improve signal reliability and its'3D mesh-filled“hot spot”?high enhancement point?distribution can provide high sensitivity.The quantification of analyte molecules rhodamine 6G?R6G?has been demonstrated in an aqueous solution with the concentration of 10-9 to 10-7 M.Meanwhile,Raman mapping was used to investigated the stability of SERS spectra in a large scanning area and the probability distribution function was used to reduce the data error.As a result,the relative standard deviation?RSD?of its relative intensity k was reduced by half.Meanwhile,CNT-AgNPs samples have been used to detect N2 in natural air,indicating that such self-calibration method can further improve the reliability of the SERS analysis.?3?Self-calibration experiments of graphene-Ag nanohole composite substrate?GE-AgNHs?have been studied using 2D peak of grphene as an internal calibration to calibrate the concentration of analyte molecules.The results show that the self-calibrated substrate of GE-AgNHs can effectively reduce or even theoretically eliminate the effects of fluctuations in instrument fluctuations and substrate enhancement factors.On the one hand,the Raman mapping test show that the RSD value of the relative parameter k is reduced to half of the intensity of other typical Raman peaks;on the other hand,quantitative reliability analysis is performed on different concentrations of the R6G Raman mapping test.The results prove that the average relative intensity k increases with increasing concentration,and a good linear relationship between k and R6G concentrations is observed in the low concentration range of 10-10 to 10-15 M.?4?The reproducibility experiment of GE-AgNHs substrate have been also studied,the result indicates that it can effectively remove the adhering of R6G molecules on GE surface.Further analysis of the quantification of self-calibration experiments at high concentrations using CV molecules expose that there is a possible error in the self-calibration experiment at higher concentration due to molecular adsorption saturation and molecular layer thickness. |
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