Sensitive immunoassay of Listeria monocytogenes with highly fluorescent bioconjugated silica nanoparticles probe

In this paper, a sensitive immunoassay method was proposed for Listeria monocytogenes detection by using highly fluorescent bioconjugated nanoparticles probe. (FITC-IgG)-doped fluorescent silica nanoparticles (fsNPs) firstly were synthesized by a microemulsion method and characterized by TEM and fluorescent spectra. Then the prepared fsNPs were conjugated with polyclonal rabbit anti-L. monocytogenes antibody (pAb) and used as indicator probe. A sandwich-type immune affinity reaction between polyclonal rabbit anti-L. monocytogenes antibody coated onto microplate wells, target bacteria and the fsNPs-antibody conjugates subsequently was conducted to detect target L. monocytogenes and assemble the indicator probe onto the wells. The target L. monocytogenes was measured by the fluorescent signals of the assembled indicator probes. Under the optimal conditions, the calibration graph of fluorescent intensity is proportional to the amount of target bacteria over the range of 50-10,320 CFU/mL with a detection limit of 50 CFU/mL. The proposed method has been successfully applied to detect L. monocytogenes in food samples offering the advantages of sensitivity, simplicity, and stability.