Ultrasensitive\nAnalysis of Escherichia\ncoli O157:H7 Based on Immunomagnetic Separation and\nLabeled Surface-Enhanced Raman Scattering with Minimized False Positive\nIdentifications

It is a big challenge to monitor pathogens in food with\nhigh selectivity.\nIn this study, we reported an ultrasensitive method for Escherichia coli O157:H7 detection based on immunomagnetic\nseparation and labeled surface-enhanced Raman scattering (SERS). The\nbacterium was identified by heterogeneous recognition elements, monoclonal\nantibody (mAb), and aptamer. E. coli O157:H7 was separated and enriched by magnetic nanoparticles modified\nby mAb, and then a plasmonic nanostructure functionalized by aptamers\nwith embedded Raman tags and interior gaps was utilized for further\ndiscrimination and detection. The selectivity was enhanced by two\nbinding sites. The higher Raman enhancement was obtained by strong\nlocal electromagnetic field oscillation in the gap and the firm embedment\nof 4-mercaptopyridine (4-Mpy). Optimum experiments created that SERS\nsignals of 4-Mpy at 1010 cm<sup>–1</sup> had a good linearity\nwith E. coli O157:H7 at a large range\nof 10 to 10<sup>7</sup> CFU/mL with a limit of detection of 2 CFU/mL.\nThis method has great potential for on-site food pathogenic bacterial\ndetection.