The Study Of SERS Quantitative Detection Of Contaminant In Food Based On Gold-silver Core-shell Nanostructures Substrate

With the rapid development of SERS technology,the application of SERS technology in various fields has become wider,especially in field of food testing.However,the SERS method is still challenging to achieve quantitative detection.In this thesis,two gold-silver core-shell nanostructures were synthesized by the seed-mediated growth method.In combination with internal standard method,two functional SERS substrates with high repeatability was designed and constructed and rapid quantitative analysis of contaminants in food matrix were realized.In order to improve the accuracy of experiments and theoretical studies,it is of great significance to prepare regular-shaped nanocrystals.Combined with the seed growth method and oxidation etching technology,highly spherical gold-silver core-shell nanospheres(Au@Ag NSs)with tunable diameter and uniform shape in the range of 24 nm?87 nm were synthesized at room temperature.In the preparation progress,the etching degree is only related to the amount of etching agent,and the thickness of the silver shell could be effectively controlled by changing the amount of etching agent.Using the interface self-assembly technology,Au@Ag NSs were assembled into a densely arranged two-dimensional monolayer film.The SERS performance of Au@Ag NSs monolayer film was evaluated by the calculation of analysis enhancement factor.The results show that as the diameter of the gold-silver core-shell nanospheres increases,the analysis enhancement factor increases significantly.In addition,the electromagnetic field dist ribution of Au@Ag NSs periodic array has been simulated by Mie theory and FDTD software.The theoretical simulation has good agreement with the experimental results.Au@Ag NSs with excellent SERS performance were used as assembly unit.The internal standard molecules with Raman activity were modified as signal calibration,and Au@Ag NSs were assembled on the filter paper using the liquid/liquid interface assembly technology.A novel SERS substrate for quantitative detection of pollutants in complex matrices was fabricated.In meantime,a convenient and flexible strategy for constructing a paper-based SERS sensor was developed.A precise pattern of nanoparticles on filter paper could be achieved by using a dropper and a mask to transfer and assemble Au@Ag NSs monolayer.On this basis,the paper-fluidic SERS sensor was fabricated by cutting and packaging for two detection modes,i.e.,lateral-flow and vertical-flow.Both detection modes integrated sample pretreatment with SERS detection were applied to accurate ly detect the thiram in complex sample of orange juice with pulp.Due to the calibration by the internal standard,the determination coefficient of the sample concentration and Raman intensity fitting curve was increased from 0.96 to 0.99.Aiming at anisotropic nanostructures with excellent performance,a simple method for preparing gold-silver core-shell nanorods(Au@Ag NRs)with adjustable width and length was proposed and the SERS performance of the self-assembled monolayer film was studied.Specifically,gold nanodipyramids(Au NDPs)of three various widths from 25 nm to 42 nm were prepared by overgrowth along the radial orientation,and together with Au NDPs as seed,silver was deposited in the axial orientation to successfully obtain core-shell Au@Ag NRs with diverse length from73 nm to 157 nm.Combined with FDTD simulation,the morphology,optical properties and SERS properties of the synthesized Au/Ag NRs were systematically studied.The results showed that the Au@Ag NRs with larger width and longer length had the best SERS enhancement effect,which provided the experimental and theoretical basis for the preparation of efficient SERS substrate.Based on Au@Ag NRs with excellent SERS performance,combined with specially designed homemade equipment and capillary,a portable and highly reproducible capillary-based SERS detection platform was developed for rapid on-site SERS detection.The SERS detection platform was composed of a capillary with Au@Ag NRs adsorbed on the inner wall and a detection bracket,which can effectively and non-destructively extract samples.Additionally,the higher sensitivity of the capillary SERS substrate could be attributed to the fact that there are more nanoparticles and SERS hot spots in the capillary cylindrical structure i n the effective laser excitation region.Finally,in-situ extraction and quantitative analysis of the residual fungicides(malachite green and crystal violet)on shell surface were achieved using the capillary SERS detection platform.The determination coefficient of the sample concentration and Raman intensity fitting curve was increased from 0.96 to 0.99 by the calibration of the internal standard.