Quantum dot-labeled phage-encoded RBP 55 as a fluorescent nanoprobe for sensitive and specific detection of Salmonella in food matrices

As a commonly pathogenic bacterium, the rapid detection of Salmonella outbreaks and assurance of food safety require a highly efficient detection method. Herein, a novel approach to Salmonella detection using quantum dot-labeled phage-encoded RBP 55 as a fluorescent nanoprobe is reported. RBP 55, a novel phage receptor binding protein (RBP), was identified and characterized from phage STP55. RBP 55 was functionalized onto quantum dots (QDs) to form fluorescent nanoprobes. The assay was based on the combination of immunomagnetic separation and RBP 55-QDs, which formed a sandwich composite structure. The results showed a good linear correlation between the fluorescence values and the concentration of Salmonella (101-107 CFU/mL) with a low detection limit of 2 CFU/mL within 2 h. The method was used to successfully detect Salmonella in spiked food samples. This approach can be used for the simultaneous detection of multiple pathogens by labeling different phage-encoded RBPs using polychromatic QDs in the future.