Synthesis And Application Of Flexible SERS Substrate With Internal Standard

Surface-enhanced Raman spectroscopy（SERS）is an ultra-sensitive labeling free analysis technique,which provides unique chemical and structural fingerprint information.However,the use of SERS for reliable quantification analysis remains a great challenge because the reproducibility of Raman signals is generally unsatisfactory.The poor reproducibility was due to the non-uniformity of SERS substrate and the irregular adsorption of probe molecules on the surface of nanoparticles.Various interference may also affect the stability of Raman signal,such as temperature,humidity and laser power.Therefore,it is of great significance to develop a method to improve the reliability of SERS detection.Recent reports have shown that the use of internal standard can effectively improve the reproducibility of non-uniform SERS substrates.Prussian blue is a highly sensitive and backless resonant Raman label,and its unique Raman label（C≡N）signal is located in the Raman silent area of 1800-2300 cm^-1,avoiding the optical noise produced by endogenous molecules in the fingerprint area(300-1800 cm^-1),making it an ideal Raman internal standard.Based on the above research,this paper mainly carries out the following two parts of work:（1）Using cotton as supporting material,flexible SERS substrate Au/PB/Cotton was constructed by electrostatic self-assembly of gold nanoparticles（Au NPs）with positive charge and Prussian blue nanoparticles（PB NPs）with negative charge on the surface of cotton cloth through simple impregnation method.The detection limit of ciprofloxacin（CPX）on this substrate was 9.06×10^-8 mol/L,and the linear range was10^-5-10^-3 mol/L.For quantitative analysis,we use internal standard molecules to correct Raman wave signals in real time,and the linear correlation coefficient（R²）increased from 0.9838 to 0.9999.At the same time,the relative standard deviations（RSD）of spot-to-spot and batch-to-batch reproducibility were reduced from 19.81%and 13.58%to 6.07%and 5.18%,respectively,by internal standard correction for microenvironment and instrumental factors,which significantly improved the uniformity and reproducibility of the substrate and provided the possibility for reliable quantitative analysis.In addition,the recovery of CPX on the surface of chicken wings was 90.29%.（2）Polymer polyvinyl alcohol（PVA）was used as the supporting material,and PVA/PB/Au film was formed through electrostatic self-assembly by taking advantage of the different charged properties of Au NPs and PB NPs.The accuracy of 4-MBA quantitative analysis was improved through the correction of internal standard,and the R² was increased from 0.9675 to 0.9974 in the linear range of 10^-6-10^-3 mol/L.The detection limit of Malachite green was 2.87×10^-8 mol/L,and the linear range was10^-7-10^-4 mol/L.The effect of microenvironment and other factors were corrected by internal standard,and the R² was increased from 0.9647 to 0.9832.At the same time,the internal standard effectively corrected the fluctuation of SERS signal caused by the change of measuring conditions and the inhomogeneity of the plasma array,thus improving the reproducibility and accuracy of SERS sensing.RSD of spot-to-spot and batch-to-batch reproducibility decreased from 11.99%and 25.02%to 4.74%and9.39%,respectively.Compared with traditional SERS chips,the reproducibility of Raman signal on internal standard modified SERS substrate was significantly improved.In addition,the recoveries of MG were 85.76%,84.12%and 92.60%,respectively.Notably,the flexible SERS substrate can still maintain great stability within 90 days...