Designing an aptamer based magnetic and upconversion nanoparticles conjugated fluorescence sensor for screening Escherichia coli in food

The study assembles a highly sensitive upconversion fluorescence sensor for screening Escherichia coli (E. coli) in food. The principle of the strategy was based on the specific matching between two aptamers embedded magnetic nanoparticles (MNPs) and cDNA-upconversion nanoparticles (UCNPs). The fluorescence emission intensity of the MNPs-aptamer-cDNA-UCNPs conjugate system gradually decreased upon rise in the E coli levels. This change was regarded as a concentration equivalent for E coli at 662 nm. The morphology, crystallinity, vibrational and electronic characterization for the formed MNPs-aptamer-cDNA-UCNPs conjugate were safely assigned. Under the optimum conditions, the fluorescence sensor achieved a lower limit of detection (10 cfu mL−1) in the linear range of 58–58 × 106 cfu mL−1. Furthermore, the applicability of the proposed sensor to detect E coli was examined in adulterated pork samples. The strategy was also validated by a standard plate count method with satisfactory recovery (p > 0.05).