The Application Of Surface Enhanced Raman In Food Safety Detection Based On Ag Nanoparticles/Porous Anodized Alumina Membrane

With the improvement of people's living standards,food safety issues have become the focus of social attention.Similarly,food safety testing technology has become the focus of researchers.At present,the traditional detection techniques mainly include thin layer chromatography,high performance liquid chromatography?HPLC?,gas chromatography,enzyme-linked immunosorbent assay,and liquid chromatography-tandem mass spectrometry?LC-MS?.These methods usually require expensive instruments,professional operators,complicated detection process,and long time-consuming.Surface enhanced Raman spectroscopy?SERS?,as a new type of rapid detection technology,carries a wealth of chemical fingerprint information.Because of advantages of high sensitivity,simple operation,convenient equipment carrying,and trace non-destructive testing,it has attracted extensive attention from researchers in food safety testing.In recent years,porous anodized aluminum?PAA?membranes have the advantages of perfect chemical and mechanical stability,high pore density,and controllable shape and size.If it is combined with electrochemical detection technology,spectroscopy technology,it can not only amplify the ion spectrum signal by several orders of magnitude,but also has excellent detection sensitivity.In this study,PAA membrane was used as a Raman substrate,and then its surface was functionalized to develop an enhanced surface Raman technology for detecting illegal additives and aflatoxin B₁ in food.The main content of this article includes the following three aspects.1.Detection of illegal additives in food via surface enhanced Raman spectroscopy based on the aggregation of Ag nanoparticlesAg nanoparticles?AgNPs?with strong SERS hot spots were prepared by one-pot method to reduce Ag ions with citrate.Transmission electron microscopy?TEM?and UV-vis spectrophotometer were used to characterize Ag nanoparticles,and portable Raman spectroscopy was used to detect signals of SERS substrates.The sample pretreatment was simplified via addition of trichloroacetic acid as a protein precipitant and nanoparticle coagulant.The standard addition method and the ultraviolet spectrophotometric method were used to calibrate the SERS substrate for detecting contaminants.The experimental plan was optimized,the linear range was determined,and the detection limit was calculated.The results show that the particle size of the prepared AgNPs is about 50 nm.The Raman enhancement effect is the best in Ti plate,as the concentration of Na Cl and Na OH is 4 mol/L,the ratio of AgNPs to sample is1:2.The linear range of this method for detecting melamine is 0.2-10 mg/L,and the detection limit is 0.08 mg/L.The sensor has good repeatability?RSD=4.34%?.When detecting sodium thiocyanate in milk,the reaction time is optimized for 6 minutes and the range of linear detection sodium thiocyanate is 10 to 100 mg/L,and the calculated detection limit is 0.04 mg/L.2.Detection of AFB₁ via surface enhanced Raman spectroscopy based on the surface of two-dimensional nanochannelThe PAA membrane was prepared by the secondary anodization method.Amino group was covered on the surface of the PAA membrane by silanization.AFB₁aptamer was modified on the surface of the PAA membrane by the condensation reaction of the amino group and the aldehyde group to construct a sensor substrate.The AgNPs with Raman enhanced signal was prepared by reducing sodium nitrate with sodium citrate.After the surface was functionalized,it was combined with the surface of the PAA membrane to form a biosensor the AFB₁concentration in the sample was detected.TEM,UV-vis spectrophotometer and convenient Raman spectrometer were used to obtain the characteristics of samples.When AFB₁ does not exist in the system,the aptamer recognizes short-stranded DNA,resulting in a"zipper"structure.This structure fixes AgNPs on the surface of the PAA membrane to cause the aggregation of AgNPs,which generates a strong SERS signal.When the competitive AFB₁ is added,the aptamer will preferentially bind to AFB₁,resulting the short-stranded DNA to unwind.The AgNPs attached to the PAA membrane also fell off,resulting in a decrease in the Raman signal.The results show that the pore diameter of the prepared PAA membrane is about 20 nm,and the particle size of AgNPs is about 50 nm.Both of them successfully modified AFB₁ aptamer and complementary DNA molecules with aptamer.The linear range of the prepared AgNPs-PAA biosensor is 0.01 to 10 ng/m L,and the detection limit is 0.009 ng/m L.The sensor has good repeatability?RSD=11.14%?and selectivity.Compared with aflatoxin B₁,the Raman signal of other mycotoxins?aflatoxin B₂,aflatoxin G₁ and ochratoxin A?did not change significantly.3.Preparation of three-dimensional array nanochannel SERS sensor and its application in AFB₁ detectionThree-dimensional array nanochannels were prepared by cyclic pulse method.The experimental protocol was optimized by varying the PEG molecular weight,PEG concentration?20%,30%,35%?and phosphoric acid etching time?5 min,10 min,13min,15 min,17 min?.SEM and convenient Raman spectrometer were used to characterize the three-dimensional structure.Three-dimensional PAA membrane was used as the substrate to prepare the AgNPs-three-dimensional PAA biosensor,and placed it in an electrochemical workstation for electromigration.Ag/Ag Cl electrode is used as the working electrode in the solution to be tested,and a potential is applied on both sides of the sensors.AFB₁ quickly reached the membrane surface with the direction of electromigration,causing AgNPs to fall off,and the Raman signal decreased.When 30%PEG with a molecular weight of 6000 and oxidative etching time of 15 min,the three-dimensional PAA membrane has the most uniform transverse pore size.The pore diameter is about 30 nm and the hole spacing is 120 nm.Using it as a template,carbon nanotubes were also deposited horizontally and vertically.Due to the impact of COVID-19,the subsequent application of the three-dimensional PAA membrane biosensor in AFB₁ detection cannot be carried out as planned and will be completed by subsequent graduate students.