| Surface enhanced Raman scattering(SERS)is an advanced surface analysis technique that can enhance the Raman scattering signal of molecules adsorbed on or in the vicinity of metal surface enormously.Due to its accurate speed,high sensitivity,and good selectivity,SERS technique shows important application prospects in the fields of chemistry,biology,medical treatment,environmental detection and food safety,which is one of the current hot research fields.However,it is known that the uniform,repeatable,and stable SERS active substrate are key of making SERS technique a routine analytical tool.This article is mainly divided into four parts:In chapter 1,Raman spectroscopy,SERS technique,printed SERS active substrates and their research status were introduced.On this basis,the research target,research contents and research programme were proposed.In chapter 2,the silver nanoarrays SERS active substrate was fabricated by inkjet printing silver ink and thermal treatment on the surface of the optical disk grating.Optical microscope,scanning electron microscope,and atomic force microscopy were used to characterize the surface morphology,microstructure and surface roughness of the samples.The results showed that the grooves and ridges of the gratings were evenly covered with silver nanoparticles.The periodic grating structures were not changed before and after coating,and the surface roughness altered accordingly with the depth of the characteristic groove.Rhodamine 6G(R6G)was used as the probe molecule,and then SERS activity,uniformity,stability and reproducibility of the silver nanoarrays SERS active substrate were studied by a confocal microscopic Raman spectrometer.The effects of polarization Raman,laser wavelength and other factors on the SERS activity of the silver nanoarrays have been investigated.The testing method that the incident laser perpendicular to the sample surface and collecting scattered signals from all directions was adopted.Compared with 785 and 638 nm,the best SERS response was obtainedwhen the laser wavelength was 532 nm.The uniformity of SERS mapping showed that the relative standard deviation values of 2500 and 6480 points were 8.35% and11.53% for the 610 cm-1 peak,respectively.The SERS spectral lines of R6 G were continuously tested.The decay rate of absolute intensity decreased month by month,but spectral lines still had strong SERS activity after eight months.The relative standard deviation value of the eight silver nanoarrays SERS active substrates prepared under the same conditions was 10.21%.In chapter 3,the finite-difference time-domain method was used to simulate the electric field diagram by solving the three-dimensional Maxwell's equations.According to the data of particle diameter,spacing,grating period and other data obtained from the experiment,models were built on the grating and planar surface to simulate the local electric field distribution of the silver nanoparticles and explain the electromagnetic enhancement mechanism.It was found that the silver/grating substrate had a higher SERS enhancement ability than the silver/planar substrate due to the high-density hot spots of the periodic gratings.In chapter 4,it was found that the optimal drying temperature for preparing the the silver nanoarrays was 100 ? by optimizing the process parameters and testing conditions.Based on the SERS activity of the silver nanoarrays,the illegal food additives such as malachite green and melamine were successfully qualitative and semi-quantitative detection: when the detectable concentration of the malachite green aqueous solution was 5×10-7 mol/L,its characteristic peaks can still be distinguished well.Melamine doped in infant and adult milk powder solutions was detected directly with a detection concentration as low as 1.2 mg/L.The concentration of melamine in the milk powder solution had a good linear relationship with the absolute intensity of the characteristic peak,and the correlation coefficient reached 0.9968 in the range of1.2 to 100 mg/L. |
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