| In the fields of food safety,water quality and biomedical detection,there is huge demand for fast,real-time,non-destructive and high-precision measurements of analytes.Raman scattering is of interest because of its ability to provide a unique"fingerprint"information about molecules.However,due to the small Raman scattering cross section,leading to the very weak Raman signal,the application in ultra-micro concentration detection,small sample volumes and label-free biological specimens detection has been challenged in various ways.The emergence of surface-enhanced Raman scattering（SERS）technique has effectively solved the problem of weak Raman scattering signal.The traditional surface-enhanced Raman scattering technique relies on expensive large Raman spectrometers and requires sampling and testing in the laboratory,which cannot adapt to the actual requirements of field measurements,and is also difficult to adapt to the current needs of high-precision quantitative testing.By combining fiber optic sensing technology with surface-enhanced Raman scattering,the excitation and collection efficiency of the detected samples can be greatly improved,which makes it possible to measure with high sensitivity by portable Raman spectrometer,bringing new opportunities for fast Raman detection.In this thesis,we combined SERS and fiber optic sensing technology to prepare AuNPs（gold nanoparticles）-hollow-core fiber composite structure SERS probes,and conducted experimental studies on the parameters affecting their detection performance,as well as carried out preliminary explorations on the challenges of high-precision quantitative analysis in Raman spectroscopy.Main works are as follows:（1）For the study of quantitative analysis of ethanol solutions,when calibrated by the ethanol intrinsic peak level(1041 cm-1,1083 cm-1,1267 cm-1,1446 cm-1)ratio method.The standard curve established by using the characteristic peak at 1446 cm-1（CH3-asymmetric distortion）as the reference peak at 88%～99.7%concentration can more accurately invert the concentration of ethanol,the highest fitting accuracy is 0.996.At the significance levelαof0.05,the joint hypothesis test（F-test）and test of temporal stability（t-test）show that there is no more significant difference between the overall variance and the test variance as well as the slope of the fitted curve.When CCl4is used as an internal standard,the standard curve with Raman peak at 446 cm-1（A1non-simplex state）as the internal standard peak(207 cm-1,306cm-1,446 cm-1)at 76.5%～86.7%concentration of the mixed solution has higher stability and accuracy,the highest fitting accuracy is 0.999.（2）Study of the effect of optical parameters and waveguide structure on SERS enhancement with hollow core fiber,uses hollow core fibers with lengths of 50 cm and diameters of 128μm and 210μm respectively,the focal spot size was 158μm measured at a focal length of 8 mm.The output optical power versus laser output current is measured for each of the two parameters of the fiber,and the current 0.8 m A can be obtained as the output optical power threshold,at this time,the optical output power of 128μm hollow-core fiber reaches its maximum value,which is about 30 m W.Without Raman enhancement,the fiber optic probe is inserted into the sample at a depth of 2 cm,the limit of detection of 128μm hollow core fiber for R6G is 10-5M,and the analytical enhancement factor AEFfiberof waveguide structure is calculated as 81.55.（3）Experimental study on Raman enhancement of AuNPs-hollow-core fiber composite structures,by studying the effect of fiber length on SERS enhancement effect,we obtained that the SERS enhancement effect is proportional to the fiber length in the range of 0～50 cm.In the experiments on the effect of gold sol and coagulant density on SERS intensity,it was found that the best Raman enhancement effect was achieved when the volume ratio of gold sol to R6G was 1:6,and the highest Raman scattering intensity was achieved when the volume ratio of gold sol to R6G and coagulant was 1:6:2.The RSD of the Raman peak intensity signal at 1344 cm-1was calculated to be 2.38%and 7.11%for the self-cleaning and repeatability experimental tests,respectively.Comprehensive experiments demonstrated that the probe reached a minimum detection limit of 10-15M for R6G molecules and a total enhancement factor of 108. |
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