Immunomagnetic separation and Listeria monocytogenes detection with surfaceenhanced Raman scattering

Abstract

Background/aim: We aimed to develop a rapid method to enumerate Listeria monocytogenes (L. monocytogenes) utilizing magneticnanoparticle based preconcentration and surface-enhanced Raman spectroscopy measurements.Materials and methods: Biological activities of magnetic Au-nanoparticles have been observed to have the high biocompatibility, and asample immunosensor model has been designed to use avidin attached Au-nanoparticles for L. monocytogenes detection. Staphylococcusaureus (S. aureus) and Salmonella typhimurium (S. typhimurium) bacteria cultures were chosen for control studies. Antimicrobialactivity studies have been done to identify bio-compatibility and bio-characterization of the Au-nanoparticles in our previous study andcapturing efficiencies to bacterial surfaces have been also investigated.Results: We constructed the calibration graphs in various population density of L. monocytogenes as 2.2 × 101 to 2.2 × 106 cfu/mL andthe capture efficiency was found to be 75%. After the optimization procedures, population density of L. monocytogenes and Ramansignal intensity showed a good linear correlation (R2 = 0.991) between 102 to 106 cfu/mL L. monocytogenes. The presented sandwich assayprovides low detection limits and limit of quantification as 12 cfu/mL and 37 cfu/mL, respectively. We also compared the experimentalresults with reference plate-counting methods and the practical utility of the proposed assay is demonstrated using milk samples.Conclusion: It is focused on the enumeration of L. monocytogenes in milk samples and the comparision of results of milk analysisobtained by the proposed SERS method and by plate counting method stay in food agreement. In the present study, all parameterswere optimized to select SERS-based immunoassay method for L. monocytogenes bacteria to ensure LOD, selectivity, precision andrepeatablity.