Research And Application Of New SERS Substrate In Food Safety Detection

Nothing matters more than foods to humans, for foods are the very physical basis on which human survival and development depend. Food safety is closely related to human health and has profound impact on public health safety, prosperity and stability in any nation. Food safety means ensuring there is nothing toxic or harmful in foods in order to protect human bodies from any injury.Food safety has become a public concern in the international community. Testing of food safety mainly involves pesticides, residues of veterinary drugs, excessive hormones, and illegally-used additives, which are still tested and analyzed using conventional methods, such as HPLC、GC、GC-MS、LC-MS. Despite their high sensitivity, good reproducibility and wide application, these approaches leave much to be desired, such as the need to for professional operators, the complicated and time-consuming pre-processing of samples. Therefore, it is of great importance to establish a simple but efficient testing method for analysis of pesticides, residues of veterinary drugs, over-use of hormones and illegal-used additives.It was not until the 1990 s that Raman spectroscopy became widely used in the field of food safety. With the popularization of near infrared wavelength laser and the commercialization of Raman spectroscopes, Raman spectroscopy has made a big stride in its application to food safety. As a highly sensitive means of indication, the use of SERS technologies in the testing and analysis of pesticides, veterinary drugs, hormones and illegal addictives has been increasingly studied. Following the appearance of SERS phenomena, the selection and preparation of active SERS substrates have become the key technology to obtain high-quality SERS signals. This technology not only determines whether SERS signals can be generated, the quality of the intensity of SERS signals, and whether the substrates are stable and reproducible. This paper is intended to introduce a new type of substrate Fe3O4@Si O2@Ag flower, on which a large number of experiments have been conducted to explore its application to food safety. Research covered by this paper is summarizedas follows:1. A new type of substrate Fe3O4@Si O2@Ag flower was prepared.. The synthetic method was simple and efficient, and the structure of the preparation was uniform, dispersible and magnetically responsive. Among the components of Fe3O4@Si O2@Ag flower naoparticles, Fe3O4@Si O2 magnetic nanoparticles serve as the core that is sufficiently magnetic. They can be collected easily with external magnets in the process of preparation or washing so that such time-consuming methods as configuration and filtering can be dispensed with. Chemical electroplating mediated by stannous chloride can allow the surface of Fe3O4@Si O2 to produce homogeneous and dense silver seeds which favor the subsequent growth of flowery ~ 6 ~silver crusts. At the same time, the thick Si O2 crusts can make magnetic particles highly dispersible while ensuring the assembly of magnetic particles in the course of synthesis under ultra-sound conditions. As a result, the dispersion and structural homogeneity of Fe3O4@Si O2 magnetic nanoparticles can be achieved. The Fe3O4@Si O2@Ag flower SERS substrate displays not only the property of samples of microsatellite enrichment by magnetic beads, but the optic and chemical property of silver nanomaterials. The flowery silver crusts are easy to modify chemically and can serve as effective multi-functional nanomaterials.2. The homogeneity, stability and repeatability of a new type of SERS substrate were investigated. Results of experiments suggest that this SERS substrate is quite uniform, with an RSD of 5.31%. The intensity of SERS signals is not only relatively homogeneous and repeatable to some extent, but remains stable in a period of two months. Testing was performed of PATP, melamine, thiram, sudan I and sudan III.3. The SERS substrate was chemically modified. Alkanethiol of three types and different lengths were linked to Ag via the thiol group so that dense hydrophobic self-organized layers were formed on the surface of the substrate in order to enrich the molecules of the tested substance. While Raman signals were amplified, the molecules of the tested substance that possessed hydrophobic groups were enriched in the liquid so as to obtain stronger Raman signals of the tested substance. It was found that the 1-hexanethiol-modified SERS substrate was able to lead to stronger enhancement than 1-dodecanethiol and octadecanethiol. Our experiments proved that 1-hexanethiol-modified Fe3O4@Si O2 magnetic nanoparticles combined with Nanorods could enhance SERS more effectively while making up for the decrease of hot structure on the SERS substrate that was caused by adsorption of alkanethiol to the surface of silver crusts. The homogeneity, stability and repeatability of the joint substrate was studied.4. The structure of four types of antibiotics and estrogenics was optimized using Gaussian 09 package. Besides, the simulated Raman spectrum for calculations of molecules of these antibiotics and estrogenics was obtained. With reference to Raman and SERS peaks from experiments, the characteristic peaks of each antibiotics and female hormone were determined; the vibration peaks of each Raman spectrum were identified.5. This joint substrate was used in the testing of four types of antibiotics and estrogenics. It was observed that the Raman peak intensity of samples had a good linear relationship with the log-log diagram of the intensity. Principal component analysis of multivariate statistics was made of Raman peaks of the mixed antibiotics and estrogenics so that antibiotics and estrogenics were separated and identified.6. Pretreatment methods of eight types of labeled milk were compared. The high recovery of analytes, effective separation of analytes from interferents, user-friendliness and economy have made solid phase extraction(SPE) the first choice for pretreatment of milk. The combination of SPE, SERS substrate and the handheld Raman spectrometer was used in testing four types of antibiotics and estrogenics in milk samples before the linear range of Raman peaks of these antibiotics and estrogenics was made available. It was found that the peak intensity had a good linear relationship with the concentration of samples and that the recovery was comparatively high. Based on the range of measurement of the recovery rate and RSD, it was found that Fe3O4@Si O2-Ag-C6 combined with the Nanorods SERS substrate enriched and enhanced estrogenics in milk more effectively than it did antibiotics in milk, which might be related to the molecular structure of samples.Throughout full text of this article, there are three following innovations:(1) Innovation of preparation method of SERS substrate.(2) Innovation of 1-hexanethiol-modified Fe3O4@Si O2 magnetic nanoparticles combined with Nanorods.(3) Innovation of application to the detection of real samples by surface enhanced Raman spectroscopy.