A sensitive SERS-based assay technique for accurate detection of foodborne pathogens without interference

The accurate and sensitive detection of foodborne pathogens is critical for timely food quality supervision and human health. To address this issue, herein, we developed a simple and novel surface-enhanced Raman scattering (SERS) assay using p-mercaptobenzoic acid (MBN)-modified gold nanoparticles (Au NPs) and magnetic beads for interference-free detection of Escherichia coli (E. coli). This assay technique cleverly reduced silver ions (Ag⁺) on the surface of E. coli (bacteria@Ag NPs), and the functionalized magnetic beads (capture probes) captured and enriched bacteria@Ag NPs, forming the structure of the capture probes-bacteria@Ag NPs. Then, the capture probes-bacteria@Ag NPs were dissolved in the acidic medium, and the Ag NPs on the surface of E. coli was converted to Ag⁺ again. Due to the special coordination between Ag⁺ and MBN-modified Au NPs (functionalized Au NPs), the SERS intensity of MBN exhibited a positive correlation with the E. coli concentration, and the SERS detection assay of E. coli was established. The signal of the functionalized Au NPs located at 2228 cm^-1 perfectly avoided the spectral overlap with coexisting materials in the Raman fingerprint region, which ensured the accuracy of the technique. The controlled aggregation of the functionalized Au NPs ensured the reproducibility and reliability of the detection system; the emergence of MBs greatly reduced the reaction time and made sure the operation was rapid, simple and portable. The limit of detection (LOD) for E. coli was as low as 10 cfu mL^-1, and the detection assay was successfully applied for the detection of E. coli in bottled water and milk. As a sensitive and accurate analytical technique for the detection of pathogens, this SERS-based method has great potential to be applied in the field of food safety.