Preparation Of Flexible SERS Substrate And Its Application In Detection Of Pesticide Residue In Fruits And Vegetables

With the increasing demand for fruits and vegetables,the problem of pesticide residues in fruits and vegetables has attracted widespread attention.Because eating fruits and vegetables contaminated with pesticides can lead to potential health problems,there is an urgent need for a fast,convenient,ultra-high sensitive analytical methods are used to detect pesticides and pesticide residues in fruits and vegetables to ensure environmental and food safety.In this paper,for the purpose of ultra-sensitive non-destructive detection of pesticide residues on the surface of fruits and vegetables,a flexible surface-enhanced Raman scattering（SERS）substrate was prepared by loading silver nanoparticles in chitosan and methylcellulose matrix.Methods,the rapid sampling and detection of the pesticides triazophos and thirams on the surface of fruits and vegetables have been realized.The main research contents and conclusions are as follows:The first part is based on the preparation of a three-dimensional flexible SERS substrate based on the loading of silver nanoparticles on chitosan foam,which is applied to detect the pesticide triazophos in fruit and vegetable samples.The chitosan film SERS substrate can detect the pesticide triazophos by directly wiping the solid surface.The film substrate used Nile blue A（NBA）as the Raman probe molecule,which can detect NBA solutions as low as 10^-12M.The chitosan film substrate can also quantitatively detect triazophos with a wide linear range of 0.2～1 ppb and a low detection limit of 80 ppt.Furthermore,the substrates were stable and exhibited high sensitivity after 5 weeks of storage at room temperature.The substrate has been successfully applied to the detection of real samples such as apple,cabbage,lettuce,green onion,etc.Therefore,this simple and efficient SERS substrate has great potential for pesticide sensing applications.In the second part,a flexible material with in situ growth of silver nanoparticles（Ag NPs）in methylcellulose（MC）matrix was prepared as a SERS substrate,and the SERS performance of the MC/Ag NPs thin film substrate was investigated and applied to the rapid detection of the thiram on the surface of cucumber and tomato.The SERS substrate can detect NBA probe molecule as low as 10^-8M.The substrate still showed good SERS signal intensity after two months of storage.The MC/Ag NPs thin film substrate can quantitatively detect thirams,which not only has high sensitivity,but also can detect thirams as low as 0.24 mg/L,and also shows a good linear relationship between the concentrations of 0.024～24 mg/L.In addition,the MC/Ag NPs thin film SERS substrate can realize the rapid sampling and detection of thiram on tomato and cucumber peels without any other conditions.These results indicate that the MC/Ag NPs thin film SERS substrate has great application value for the rapid detection of pesticides in food.