Ultrasensitive multichannel immunochromatographic assay for rapid detection of foodborne bacteria based on two-dimensional film-like SERS labels.

Rapid and sensitive detection of multiple foodborne bacteria without DNA amplification is still challenging. Here, we proposed an immunochromatographic assay (ICA) with multiplex analysis ability and high sensitivity for direct detection of bacteria in real food samples, based on an improved surface-enhanced Raman scattering (SERS) sensing strategy. Multifunctional Au shell-coated graphene oxide nanosheets (GO@Au) were fabricated and for the first time introduced into the ICA system as a two-dimensional film-like SERS label, which possessed huge surface area, excellent stability, and superior SERS activity. Different from the conventional spherical nanotags, the antibody-conjugated GO@Au nanosheet effectively and rapidly adhered to bacterial cells, improved the dispersibility of bacteria-nanolabel complexes on the ICA strips, and provided numerous stable hotspots for SERS signal enhancement. The combination of GO@Au labels and the ICA system achieved the multiplex and ultrasensitive determination of three major foodborne pathogens, namely, Staphylococcus aureus, Escherichia coli O157:H7, and Salmonella typhimurium, in a single test, with low detection limits (8, 10, and 10 cells/mL) and short detection time (20 min). The proposed biosensor demonstrated high stability and good accuracy in various food samples and is thus a promising tool for the rapid identification of bacteria.