Functionalized Au MBA @Ag Nanoparticles as an Optical and SERS Dual Probe in a Lateral Flow Strip for the Quantitative Detection of Escherichia coli O157:H7

Abstract A method combining surface‐enhanced Raman scattering (SERS) with a lateral flow strip (LFS) was developed for the quantitative and sensitive analysis of Escherichia coli O157:H7. Au MBA @Ag nanoparticles were prepared as SERS probes, and 4‐methylthiobenzoic acid (MBA) as a Raman reporter was inserted into the interior gap of the Au@Ag core‐shell nanoparticles, which replaced the Au nanoparticles that serve as SERS nanotags in traditional LFS. Using this developed SERS‐LFS, the presence of the target bacteria could be tested through the appearance of a red band on the test line. Furthermore, quantitative analysis of E. coli O157:H7 was achieved by measuring the specific Raman intensity of MBA on the test line. The sensitivity of this SERS‐LFS biosensor is 5 × 10 4 CFU/mL of E. coli O157:H7, which is 10‐fold higher than that of a naked eye‐based colorimetric LFS. This quantitative detection of E. coli O157:H7 ( = 1993.86 − 6812.17, R 2 = 0.9947) was obtained with a wide linear range (5 × 10 4 to 5 × 10 8 ) due to the signal enhancement of the SERS nanotags. In addition, the SERS‐LFS could differentiate E. coli O157:H7 from closely related bacterial species or nontarget contaminants, suggesting high specificity of this assay. The applicability of SERS‐LFS to the analysis of E. coli O157:H7 in milk, chicken breast, and beef was also validated, indicating that the sensitivity was not disturbed by the food matrix. In summary, the SERS‐LFS developed in this study could be a powerful tool for the quantitative and sensitive screening of E. coli O157:H7 in a food matrix. Practical Application This study demonstrates that a surface‐enhanced Raman scattering (SERS)‐based lateral flow strip (LFS) could be used as a rapid and sensitive method for Escherichia coli O157:H7 detection. Furthermore, this SERS‐based LFS could achieve quantitative detection of the target, eliminating the defect of the traditional colloidal gold LFS, which is not quantifiable.