| Agricultural products and food biosafety issue has caused widespread concern around the world, because of the illegal addition of melamine or the pollution of foodborne pathogens. To meet the demand for Disease Control and Prevention, finding a stable, convenient, rapid, sensitive, specific and cost-effective detection technique has become the target of production and regulatory authorities. Due to its high sensitivity, high resolution, no damage to the sample, Surface-enhanced Raman spectroscopy (SERS) has become a hot method in the field of research and detection. According to the theory and application of SERS technology, a number of SERS detection technologies have been established. However, this technology of SERS detection has not yet been able to be productized in a wide range of application. The study still needs further improvement and optimization.The quality of SERS substrate is directly related to the sensitivity and stability of the sample detection. As a SERS substrate, metal sol has the advantage of simple preparation andrelatively high SERS enhancement factor, which can meet the requirements of general application.In this paper, several pure metal sol and composite SERS substrate were prepared with the use of gold, silver sol and hydrophilic silica as a base material. Melamine and three foodborne pathogens (E.coli BL21, Serratia marcescens ATCC8039 and Bacillus subtilis var ATCC9372) were detected and analyzed with Raman equipment. The main goal is to lay the foundation for the subsequent SERS detection and practical application.The thesis is mainly divided into four parts:1. IntroductionThis paper presents an overview of SERS. The type, preparation methods and the advantages and disadvantages of SERS substrates are reviewed. The present situation and detection methods of SERS technique in the detection of melamine and foodborne pathogens are reviewed.2. Preparation of SERS substrateAg nanoparticles (AgNPs), gold/silver core-shell nanorods (Au@Ag NRs) and nano composite material (SiO2-Au@Ag) which was prepared though the connection of silica and Au@Ag NPs were succesfully prepared. The prepared structures were characterized and analyzed with the use of transmission electron microscopy and UV spectrophotometer. These nanostructures were used as SERS substrates in the following experiments.3. The detection of evaluation of melamineSERS effect of produced substrates were evaluated preliminarily with p-aminothiophenol (PATP) as a small testing molecule. The composite substrate (SiO2-100nmAu@Ag) with good SERS performance was selected and its detection limit for PATP was 10-10 M. A linear relationship between the SERS intensity at 1075 cm-1 and the logarithm of concentration is observed from 10-10 M to 10-7 M and the correlation coefficient is calculated to be 0.9537. The composite substrate (SiO2-100nmAu@Ag) was used to detect the illegal addition of melamine in milky products and the detection limit is 10 ppb. A linear relationship between the SERS intensity at 680 cm-1 and the logarithm of concentration is observed from lOppb to 10000ppb and the correlation coefficient is calculated to be 0.9292.4. The application of SERS substrate for the detection of foodborne pathogensThe composite nanostructure (SiO2-100nmAu@Ag) was simply mixed with pathogens and cultured for 3 hours at 37℃,400 rpm. Afterwards, a small drop of the cultured product was dropped onto silicon and the Raman spectroscopy was detected. Three foodborne pathogens (E.coli BL21, Serratia marcescens ATCC8039 and Bacillus subtilis var ATCC9372) were detected. The detection limit for these pathogens was as low as 104 CFU/mL. These three kinds of pathogens were successfully distinguished though the analysis of Raman spectroscopy. A linear relationship was also observed between the SERS intensity and the logarithm of concentration ranging from 104 to 106 CFU/mL. The correlation coefficient is 0.9499 for E.coli BL21,0.9794 for Serratia marcescens ATCC8039 and 0.8330 for Bacillus subtilis var ATCC9372. |
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