A fluorescent cascade amplification method for sensitive detection of Salmonella based on magnetic Fe3O4 nanoparticles and hybridization chain reaction

We developed a fluorescence sensor based on hybridization chain reaction (HCR) and Fe3O4 nanoparticles for the detection of Salmonella, common pathogen related to numerous food poisoning outbreaks. In this study, a pair of specific primers based on invA of Salmonella was designed and used in asymmetric polymerase chain reaction (aPCR) to produce a long target single-stranded DNA (ssDNA) that was captured by biotin-probe labeled magnetic beads (MBs) forming the MBs-ssDNA. The target ssDNA triggered HCR amplification with the two carboxyfluorescein (FAM) labeled DNA hairpin reporter probes (H1-FAM, H2-FAM) that enabled the measurements of the fluorescence intensities from the resulting ssDNA∼(H1-FAM ∼H2-FAM)n. The Fe3O4 nanoparticles were used to isolate the target ssDNA which hybridized with the reporter probes and led to decreased background signal that resulted in a detection limit of 7.4 × 101 CFU/mL in buffer and 6.9 × 102 CFU/g in spiked lettuce. The method developed also showed excellent selectivity over several common foodborne pathogens. The Fe3O4 nanoparticles capture coupled with fluorescence detection sensor showed promise for the detection of Salmonella.