Dual-Color Upconversion Nanoparticles (UCNPs)-Based Fluorescent Immunoassay Probes for Sensitive Sensing Foodborne Pathogens

Rare earth-doped upconversion nanoparticles (UCNPs) have promising potential in biodetection due to their peculiar frequency upconverting capabilities and high detection sensitivity. Here, we report a novel dual-color UCNP-based bacterium-sensing biosensor for simultaneously Escherichia coli and Staphylococcus aureus detection using UCNP as a fluorescence marker and conjugated with antibodies as the specific molecular recognition probe. Dual-color UCNPs were fabricated via varying lanthanide dopants to acquire the well-separated emission peaks. When E. coli and S. aureus were added into the reaction system, the recognition probes would capture the target bacteria through the specific binding of antibody. Then, the fluorescence intensities decreased (∆ I = I o -I ) were observed to increase linearly with the rising concentration of the E. coli (664 nm) and S. aureus (806 nm) from 47 to 47 × 10 6  cfu mL −1 ( R 2  = 0.98) and 64 to 64 × 10 6  cfu mL −1 ( R 2  = 0.97), respectively, resulting in the relatively low limit of 13 and 15 cfu mL −1 for E. coli and S. aureus . Furthermore, this UCNP-based bacterium-sensing biosensor could also be successfully applied to simultaneously detect E. coli and S. aureus in adulterated meat and milk samples.