An ultrasensitive fluorescent biosensor using high gradient magnetic separation and quantum dots for fast detection of foodborne pathogenic bacteria

Rapid screening of contaminated foods is the key to prevent and control the outbreaks of foodborne diseases. In this study, a novel fluorescent biosensor was developed for ultrasensitive and rapid detection of E. coli O157:H7. The proposed fluorescent biosensor used the double-layer channel with the immune magnetic nanoparticles (MNPs) for specific separation and efficient concentration of the target bacteria, and the immune quantum dots (QDs) with the portable optical system for quantitative detection of the bacteria. First, the bacteria were captured by the immune MNPs in the channel at the presence of the high gradient magnetic fields (HGMFs) to form the MNP-bacteria complexes. Then, the immune QDs were used to react with the target bacteria to form the MNP-bacteria-QDs complexes in the channel. Finally, the enriched complexes were collected and detected using the portable optical system to obtain the fluorescence intensity for final determination of the E. coli O157:H7 cells in the sample. This proposed biosensor was demonstrated to be able to detect E. coli O157:H7 as low as 14 CFU/mL within 2 h. The recovery of E. coli in the spiked milk samples ranged from 95.92% to 108.15%, indicating that it was capable of detecting E. coli in real samples. Besides, this proposed biosensor was able to detect the bacteria in the volume of 10 mL, and has the potential to detect the bacteria in a larger volume to increase the sensitivity.