Study On Preparation Of Monodisperse Silver Nanoparticles And Application For Highly Reproducible SERS Quantitative Detection

Surface-enhanced Raman Scattering(SERS)is a powerful molecular fingerprint technology with high sensitivity,high selectivity,non-invasive detection and other characteristics.It can dynamically acquire the unique fingerprint information of molecular structures.SERS provides new strategies for biological analysis and in-situ detection and has broad applications in the fields of biochemistry,life sciences,environmental monitoring,and food safety supervision.As the most commonly used plasma-enhanced substrate,nano-silver can efficiently amplify the Raman scattering of probe molecules,and the SERS effect is significant.However,the poor reproducibility of SERS detection has always been an important problem hindering the quantitative analysis application of SERS.To this end,on the one hand,prepares monodisperse nano-silver to ensure good reproducibility of SERS detection through the SERS substrate.On the other hand,the change in SERS signal caused by the specific reaction of the target is used as the basis for SERS quantification to eliminate the influence of various interference factors on determination of the target.This article first studied and compared three different methods of preparing nano-silver,and obtained monodisperse quasi-spherical nano-silver with different sizes.And using Rhodamine B(Rh B)as the Raman probe molecule,the SERS test conditions were optimized to ensure the high reproducibility of SERS detection.In the end,based on the nanosilver that can catalyze the degradation of Rh B by hydrogen peroxide(H₂O₂),highly reproducible SERS quantitative detection of medium H₂O₂in real milk samples was realized by in-situ monitoring of the change in the SERS signal intensity of Rh B molecules during the catalytic reaction.The main research studies include:(1)Preparation of monodisperse nano-silver.Using a step-by-step method,the p H value was adjusted to control the nucleation and growth rate of nano-silver,realizing a fast nucleation and a slow growth mode,synthesizing uniformly dispersed spherical nano-silver sol.By using ascorbic acid(AA)/sodium citrate(SC)reduction method,monodisperse quasi-spherical nano-silver was directly prepared in water in the presence of additional anion Cl^-.Chloride and silver ions form a new soluble silver precursor in the reaction medium.Concentration and redox potential regulate the redox activity of the silver precursor,and control the size and shape of the nano-silver.Using the seed-mediated growth method,the AA was used to reduce the silver-ammonia complex in the aqueous solution.And the size of Ag NPs was precisely adjusted by changing the amount of the nano-silver seed.Thereof,quasi-spherical silver nanoparticles of 75nm and 125nm were prepared.(2)Research on optimization of SERS detection based on nano-silver.Rhodamine B molecule is used as the SERS probe to optimize the SERS detection of nano-silver.In this experiment,nano-silver aggregates under the acceleration of acid solution and salt solution.By monitoring the changes of the Raman probe molecule Rh B with the enhanced SERS signal of nano-silver aggregation,the effects of different sizes of nano-silver,nano-silver concentration,and nano-silver aggregation(different anions/cations,p H,salt concentration,mixing time,etc.)The effect of Rh B probe molecule on SERS,and the repeatability of the substrate and the linear range of SERS detection have been studied.The results show that the higher the concentration of nano-silver,the better the effect of SERS;but the high concentration of nano-silver will cause a large amount of aggregation and affect SERS.The SERS performance is the best when the nano-silver size is of 23 nm,the coagulant is of 7m M HCl(p H 3)and 20 m M Na Cl,and the mixing time is 10 min.The linear correlation coefficient R of SERS detection in the concentration range of 0.2-0.6?M Rh B is 0.9984,the least relative standard deviation(RSD)is 2.91%.(3)Study of highly reproducible SERS quantitative detection application--determination of H₂O₂in milk.Using 23nm monodisperse quasi-spherical nano-silver with rhodamine B as the probe molecule,the study of nano-silver catalyzing the degradation of rhodamine B by H₂O₂under acidic conditions was passed The relationship between the change of Rh B probe molecule SERS and the concentration of H₂O₂,quantitative detection of H₂O₂.The catalytic activity of nano-silver comes from the adsorption and electron transfer of the substrate on the surface of nano-silver.The nano-silver exhibits peroxidase-like activity at low p H,catalyzing the alkaline decomposition of H₂O₂on the metal surface by the generation of hydroxyl radical(·OH)as as the main active substance to degrade Rh B.The results show that hydrochloric acid is used as a coagulant to simplify the system,the concentration of hydrochloric acid is in the range of 2.0?10.0 m M,and the enhanced Rh B molecule SERS signal after 10 minutes of nano-silver aggregation is relatively stable and then H₂O₂is detected.The detection result of nano-silver aggregation in the sensor is There is no obvious change,and the reproducibility and specificity of the sensor are good.The logarithm of H₂O₂concentration in the range of 0.5×10^-6?1.0×10^-3M has a linear relationship with the change of SERS intensity(620cm^-1)?I/I₀,and the sensor is used in milk for standard addition recovery detection,and the recoveries were between 94%and 114%.