| Surface-enhanced Raman spectroscopy（SERS）has been widely used in disease diagnosis,drug research,biological testing and food safety as a simple,efficient,highly sensitive and chemically specific technique that can provide fingerprint information about an analyte.The"hot spots"effect of SERS substrates has been a major research problem in SERS detection.Conventional dry SERS assays tend to produce a"coffee ring"effect on the substrate,resulting in poor reproducibility and uncontrollable"hot spots"in the substrate.Traditional solution SERS methods also produce"hot spots"that are difficult to control and have poor reproducibility.Dynamic surface Raman spectroscopy（D-SERS）solves the shortcomings of the traditional method and makes the substrate with highly sensitive"hot spots",but since D-SERS is a dynamic process,the best"hot spots"are very short.However,since D-SERS is a dynamic process,its optimal"hot spots"are short-lived and difficult to operate in practical applications.Therefore,in this thesis,we propose a new solvent-induced SERS enhancement strategy（SI-SERS）to solve the shortcomings of the traditional SERS detection method,by the mechanism of different solubility of QSS in different solutions.After the uniform adsorption of AuNPs on the surface of QSS,the composition of the solution in which QSS is located is changed by adding an appropriate amount of ethanol solvent to reduce its solubility in the solution,resulting in a controlled shrinkage phenomenon,which in turn regulates the spacing between AuNPs on the surface of QSS,resulting in the formation of high-density,dynamically controlled,highly stable and highly sensitive SERS"hot spots",and the actual detection in different environments is achieved by changing the nature of surface nanoparticles.It has been successfully applied to the detection of biomarkers in human saliva.The details of the study are as follows.（1）A novel solvent-induced SERS-based strategy and its substrate preparation were explored in this work.After the uniform adsorption of AuNPs on the QSS surface through electrostatic interaction,the controlled shrinkage of QSS occurs due to the decrease of QSS solubility in the mixed solution after the addition of ethanol solvent by the property of QSS fully dissolved in pure aqueous solution,and the distance between AuNPs is controlled by changing the concentration of added ethanol solvent to form many high-density and stable"The SI-SERS platform can avoid the effect of"coffee ring"and contribute uniform and outstanding Raman signals for the target samples.In this work,the electromagnetic field distribution of QSS@AuNPs substrates was also simulated by FDTD solution software to verify the SI-SERS effect.Finally,the SI-SERS-based method for the determination of smoking addiction marker molecule SCN-using QSS@AuNPs substrate can reach LOD of 10-10 M with a linear range of detection concentration from 10-7 M to 10-10 M.This method is reliable,simple,fast,convenient,and applicable to the trace detection of solution state samples in various environments.（2）On the basis of Work 1,hydrophobic treated silver nanoparticles were introduced to enable the optimized QSS@AuNPs/NDM-AgNPs substrate to detect analytes in both oil and water phases on the same microsphere,which also inherited the advantages of the original substrate and enabled a broader range of analyte systems to be tested.In this work,by fixing the QSS at the oil-water two-phase interface and using the pressure of the upper liquid,AuNPs were added to the upper liquid so that the upper hemisphere of the QSS was uniformly adsorbed with AuNPs,and after placing it in the NDM-AgNPs mixed solution,the other half of the QSS spheres were adsorbed with NDM-NPs to obtain the QSS@AuNPs/NDM-AgNPs substrate.In addition,the electromagnetic field distribution of QSS@AuNPs/NDM-AgNPs substrate was simulated by FDTD solution software to verify the SI-SERS effect.Finally,the SI-SERS method based QSS@AuNPs/NDM-AgNPs substrate was used to determine SCN-and cortisol in saliva,and the LOD could reach 10-10 M and 10-8 M,and the linear range of detection concentration was 10-7 M to 10-10 M and 10-5 M to10-8 M.The method is reliable,simple,fast,and convenient,compared with Work I,the substrate is applicable to a wider range of systems to be tested. |
