Detection Of Common Preservatives By Enhanced Raman Spectroscopy Based On Composite Substrate

Diet is one of the most basic human needs.The preservation of food has always been an important issue in the development of human history.With the development and progress of science and technology,various preservatives are favored and widely used by the food industry because of their simple,efficient and economic characteristics.However,in order to reduce costs,cover up poor quality and extend the shelf life,some illegal businesses may add illegal preservatives to food,endangering the health of consumers.For example,sodium thiocyanate is a major illegal preservative for milk.Salicylic acid,benzoic acid and other widely used preservatives are considered safe,but if they are used in excess in food,they will also cause damage to health and have potential risks.Therefore,it is necessary to developed an accurate and sensitive detection method to supervise the preservatives.The Raman signal of preservatives such as sodium thiocyanate,salicylic acid and benzoic acid is very weak,so it is difficult to detect the signal at low concentration.Therefore,it is necessary to rely on surface enhanced Raman spectroscopy(SERS)technology to enhance the Raman signal of the object to be tested.Therefore,it is necessary to design and prepare a suitable SERS substrate for the object to be tested.The composite SERS substrate prepared by combining the traditional nano gold and silver substrate with other materials will have better performance and be more suitable for complex detection environment,it has the value of applying it to the detection of preservatives.Based on surface enhanced Raman spectroscopy,three composite SERS substrates were designed and prepared to realize the qualitative and quantitative detection of three preservatives: sodium thiocyanate,salicylic acid and benzoic acid.1.Detection of sodium thiocyanate based on the composite SERS substrate of silver and metal organic framework materials.In this study,relying on the excellent porosity and large specific surface area of MIL-101(Fe)material,it can effectively adsorb sodium thiocyanate molecules and keep sodium thiocyanate in the hot spot area of nano silver on the surface,so as to greatly enhance the SERS signal of sodium thiocyanate.In the experiment,sodium thiocyanate was detected in water and milk environment respectively,and the limits of detection in water and milk were calculated to be 18.5 μg/L and 96.3 μg/L respectively,the results show that the method can accurately and sensitively detect sodium thiocyanate in milk.2.Detection of salicylic acid based on cysteamine functionalized silver composite SERS substrate.In this work,cysteamine molecules were selected as ligands according to the carboxyl functional groups contained in salicylic acid,and cysteamine modified functionalized nano silver was synthesized as SERS substrate by using the strong binding between cysteamine sulfhydryl end and silver.The free amino end of cysteamine was positively charged,it can capture salicylic acid molecules into the hot spot region of nano silver,which improves the enhancement of salicylic acid SERS signal by the substrate.Then salicylic acid was detected by SERS in water and carbonated beverage environment.The limits of detection in water and beverage were 24.69 μg/L and 751.38 μg/L respectively,indicating that the method has strong detection ability and good accuracy.3.Detection of benzoic acid based on composite SERS substrate of silver and polyvinylpyrrolidone.In this work,a benzoic acid detection method using nano silver coated with PVP as SERS substrate was proposed.PVP forms a coated structure outside the nano silver particles through the combination of pyrrolidone ring and nano silver surface.The coated PVP layer can not only act as a surface stabilizer to prevent the aggregation of nano silver,but also capture benzoic acid molecules into the hot spot area of nano silver,so as to enhance its SERS signal.The substrate was used for SERS test of benzoic acid in water.The linear relationship was good at low concentration,and the limit of detection was as low as 115μg/L,far lower than the national standard.By synthesizing three kinds of composite SERS substrates,this study successfully achieved the concentration detection of three preservatives,established a preservative detection method based on SERS technology,expanded the application scope of SERS technology in the field of food detection,and provided technical support for effectively monitoring the safety of preservatives.