Nanogapped Fe₃O₄@Au Surface-Enhanced Raman Scattering Tags for the Multiplex Detection of Bacteria on an Immunochromatographic Strip

Herein, we present an ultrasensitive surface-enhanced Raman scattering (SERS)-based immunochromatographic assay (ICA) for the multiplex detection of foodborne bacteria in food samples by using nanogapped Fe₃O₄@Au (Mag@Au) as multifunctional SERS tags. The Mag@Au tags with multiple surface hotspots were integrated into the ICA system for the first time to provide a superior SERS signal for ICA analysis, high stability for complex samples, and magnetic enrichment ability for target pathogens. Visible test lines were successfully introduced by mixing bovine serum albumin (BSA)-coated gold nanoparticles (Au@BSA) with detection antibodies, which can facilitate the accurate positioning of test zones for quantitative SERS analysis. The magnetic SERS-ICA can achieve simultaneous and quantitative detection of Salmonella typhimurium and Staphylococcus aureus in 30 min with low limits of detection of 12 and 9 cells mL^-1, respectively. The proposed method further demonstrated good stability and accuracy in various food samples and thus possesses great potential for on-site and sensitive monitoring of bacteria.