Simultaneous detection of Staphylococcus aureus and Salmonella typhimurium using multicolor time-resolved fluorescence nanoparticles as labels.

Foodborne illnesses caused by Staphylococcus aureus and Salmonella typhimurium are common public health issues worldwide, affecting both developing and developed countries. In this study, aptamers labeled with multicolor lanthanide-doped time-resolved fluorescence (TRFL) nanoparticles were used as signal probes, and immobilized by Fe3O4 magnetic nanoparticles were used as the capture probes. The signal probes were bonded onto the captured bacteria by the recognition of aptamer to form the sandwich-type complex. Under the optimal conditions, TRFL intensity at 544nm was used to quantify S. typhimurium (y=10,213×-12,208.92, R2=0.9922) and TRFL intensity at 615nm for S. aureus (y=4803.20×-1933.87, R2=0.9982) in the range of 102-105CFU/ml. Due to the magnetic separation and concentration of Fe3O4 nanoparticles, detection limits of the developed method were found to be 15, 20CFU/ml for S. typhimurium and S. aureus, respectively. The application of this bioassay in milk was also investigated, and results were consistent with those of plate-counting method. Therefore, this simple and rapid method owns a great potential in the application for the multiplex analysis in food safety.