Self-calibration Properties Of Carbon Nanotube/Silver As Surface-enehanced Raman Scattering Substrate

Surface-enhanced Raman scattering(SERS)is another major discovery since the discovery of Raman scattering by Indian scientist Raman in 1928,which can effectively amplify Raman scattered light.Because of its high sensitivity and high selectivity,it has become a powerful detection method in many fields such as life medicine,food safety,and pharmaceutical science.However,in practical applications,due to the temperature drift of the instrument,the uncertainty of the number of adsorbed molecules on the substrate surface,the difficulty of controlling the nanostructure,the instability of chemical enhancement,and the poor reproducibility,the SERS technology is still in qualitative or semi-quantitative analysis status.Exploring to improve the accuracy of SERS quantitative detection is one of the current researches focuses.The methods for quantitative detection of SERS are mainly divided into three categories.(1)Quantitative analysis by improving the uniformity of the substrate:with the advancement of science and technology,nano-processing technology with more mature,more uniform and orderly substrate make quantitative analysis possible.(2)Internal standard method:the concentration of the analyte molecules is obtained by calculating the ratio of the internal standard molecules to the Raman peaks of the analyte molecules.The method includes three modes:an external addition mode,a core-internal standard molecule-shell mode,and a substrate self-calibration mode.(3)Data analysis method:the molecular concentration information can be obtained by analyzing and processing the peak height or area of the Raman data.In this paper,the substrate self-calibration mode in the internal standard method is used,and carbon nanotubes(CNTs)are used as internal standards to prepare a carbon nanotube/silver nanoparticle composite structure SERS substrate,which realizes self-calibration experiments of a variety of probe molecules.The self-calibration theory model,sturectures,simulations,and experiments are carried on.Main works are as follows:(1)The self-calibration mechanism of the internal standard method was studied.The research status of quantitative analysis using internal standard method at home and abroad was analyzed.The formula calculation reflects the self-calibration mechanism of the k value method(k is the ratio of the Raman peak intensity of the analyte molecule to the Raman peak intensity of the internal standard molecule).At the same time,the requirements for the selection of internal standard were put forward.(2)Structural design and process realization:a carbon nanotube/silver nanoparticle composite structure substrate(CNTs/Ag1/Ag2)was designed.At the same time,two schemes were used to prepare the CNTs/Ag1/Ag2 substrate.Firstly,the prepared CNTs/Ag1 was combined with Ag2 by a hybrid ultrasonic method;secondly,the Ag2was modified onto the CNTs/Ag1 substrate by vacuum filtration.By changing the amount of Ag2 added in CNTs/Ag1,the number of silver nanoparticles in the CNTs/Ag1/Ag2 substrate was adjusted,and the influence of the number of"hot spots"between silver nanoparticles and silver nanoparticles on the results of quantitative analysis was analyzed.The results show that as the distribution density of silver nanoparticles increases,the"hot spots"that have no enhancement effect on internal standards also increase,and the number of probe molecules falling into this type of"hot spots"also increases.In the end,the linear fitting of the normalized k value decreases and the quantitative precision decreases during the quantitative analysis.(3)The self-calibration experiments of CNTs/Ag1/Ag2 substrates prepared by the hybrid ultrasonic method were systematically studied.The structure design,preparation process and simulation results of the substrate are introduced in detail.UV-VIS-NIR spectrophotometer,scanning electron microscopy(SEM)and micro confocal Raman Spectroscopy were used to absorption test,surface morphology characterization and Raman characterization of CNTs/Ag1/Ag2 substrate.With Crystal Violet(CV),Rhodamine 6G(R6G)and Malachite Green(MG)as probe molecules,the detection limit of CNTs/Ag1/Ag2 substrate can reach 10^-15 mol/l(R6G),and the enhancement factor(EF)is as high as 5.75×10¹¹.Quantitative detection of three probe molecules of R6G,CV,and MG was achieved.The linear fitting degree R² are 99.62%,99.15%,and95.13%,and the relative standard deviation(RSD)ranges of the normalized ratio k were0.110?0.257,0.183?0.278,and 0.177?0.229.The RSD value of the k value and the RSD value of the corresponding Raman intensity have decreased by almost half.(4)The structure design,preparation process and detection experiment of carbon nanotube array/silver nanoparticle(CNTA/AgNPs)composite structure substrate were studied.The substrate of CNTA/AgNPs was prepared by vacuum evaporation and high temperature annealing,which greatly improved the uniformity of the substrate.Surface morphology and Raman characterization were performed by SEM and Raman spectrometer.CNTA/AgNPs substrate has a detection limit of 10^-6 mol/l for R6G as a probe molecule.Based on the SEM image of the substrate and the experimental results,the problems in the quantitative analysis of the substrate are analyzed.