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

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 x 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 (Y= 1993.86X - 6812.17, R-2 = 0.9947) was obtained with a wide linear range (5 x 10(4) to 5 x 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.