Rapid Detection Of Bacteria In Food By SERS Based On Multifunctional Integrated Nanosensors

In recent years,food-borne diseases have become an important food safety problem in China and even the world.In order to ensure food safety,it is crucial to use reliable and effective methods to detect bacteria in food.The traditional detection methods for bacteria in food have cumbersome operation steps,high cost,time-consuming and labor-intensive,and are increasingly unable to meet the needs of fast,accurate and on-site detection of fast-moving food in today’s society.Therefore,the establishment of a simple,rapid and high-sensitivity detection method has good application prospects.In this study,a fast and specific detection method for Escherichia coli in food and a fast and non-specific detection method for a variety of bacteria in food were established by constructing a multifunctional integrated nanosensor,which laid a foundation for the in-depth study and rapid detection of bacteria in food using SERS technology in the future.In this paper,a multifunctional integrated nanosensor was firstly constructed.Multifunctional refers to the combination of magnetic enrichment technology,bacterial capture function and SERS technology.Magnetic nanoparticle Mn Fe2O4（MNP）was prepared by binary solvothermal method.Raman enhanced nano-shell（Ag）was coated on the core of magnetic nanoparticle（MNP）to form MNP@Ag core-shell structure.4-mercaptobenzoic acid（MBA）,the internal standard molecule of Raman,was modified on the surface of the shell by thiol chemical bond.The nanosensor is spherical nanoparticles with a particle size of 45 nm and it is a nanoscale multifunctional integrated nanosensor assembled with various components.Compared with traditional sandwich biosensors,our multifunctional integrated nanosensors require less raw materials,simple preparation steps,less loss during nanosensor fabrication,and high efficiency.The rapid and specific detection of Escherichia coli in food was explored in this study on the basis of the successful preparation of multifunctional integrated nanosensor.The prepared multifunctional integrated nanosensor was combined with Escherichia coli aptamer.Due to the specificity of the aptamer,Escherichia coli was captured by the nanosensor within 15 minutes.Using the Raman characteristic peak ratio of Escherichia coli and the internal standard molecule,the limit of detection is 10CFU/m L.It was applied to the detection of Escherichia coli in various liquid foods such as milk,juice,tea,and coffee.The recovery rate was 89%~110%,and the relative standard deviation was less than 1.7%.The nanosensor is easy to use,lower cost,high sensitivity and good reproducibility.Compared with traditional sandwich biosensors,the bacterial capture rate is also increased from the common 50~60% to 81%,which can realize simple and rapid detection of bacteria in food,and has great potential in practical applications.Based on the successful preparation of multifunctional integrated nanosensor,this study also conducts a preliminary study on the rapid and non-specific detection of various bacteria in food.Using the core-shell structure in the prepared magnetic enrichment SERS nanosensor,the Raman internal standard molecule mercaptophenylboronic acid（MPBA）was modified with thiol chemical bonds on the surface of the shell,and the non-specificity of MPBA to bacteria in food was used to combine and capture Escherichia coli（E.coli）,Lactococcus lactis（L.lactics）,and Bacillus subtilis（B.sub）in food samples.Three types of bacteria in food were captured by the nanosensor within 15 minutes,and the Raman characteristic peaks of the three types of bacteria in food and the Raman characteristic peaks of the internal standard molecule were obtained respectively.After normalization,OPLS-DA analysis was used for pattern recognition,which could be separated and identified three types of bacteria in food.After cross-validation,the average correct rate of the training set in this pattern recognition method is 96.6%,and the average correct rate of the test set is 91.3%.Applying it to the detection of milk,juice,tea and coffee food,the average values of R2 X,R2Y and Q2 are 0.909,0.808 and 0.509,respectively.Compared with traditional non-specific detection of multiple bacteria,this non-specific detection method has a short time to capture binding bacteria,and this pattern recognition method has high accuracy and good predictive ability,which also represents the development prospect of its application in the detection of more bacteria in food.