Rapid Detection of Escherichia coli O157:H7 in Fresh Lettuce Based on Localized Surface Plasmon Resonance Combined with Immunomagnetic Separation

This study presents a method for rapid detection of Escherichia coli O157:H7 in fresh lettuce based on the properties of target separation and localized surface plasmon resonance of immunomagnetic nanoparticles. The multifunctional immunomagnetic nanoparticles enabling simultaneous separation and detection were prepared by synthesizing magnetic nanoparticles (ca. 10 nm in diameter) composed of an iron oxide (Fe3O4) core and gold shell and then conjugating these nanoparticles with the anti-E. coli O157:H7 antibodies. The application of multifunctional immunomagnetic nanoparticles for detecting E. coli O157:H7 in a lettuce matrix allowed detection of the presence of <1 log CFU mL(-1) without prior enrichment. In contrast, the detection limit of the conventional plating method was 2.74 log CFU mL(-1). The method, which requires no preenrichment, provides an alternative to conventional microbiological detection methods and can be used as a rapid screening tool for a large number of food samples.