Sensitive fluorescence immunoassay on the basis of the fluorescence quenching effects of quantum dots for the determination of norfloxacin in animal-origin foods

A highly sensitive and reliable fluorescence immunoassay based on the fluorescence quenching (FQ) effect of quantum dots (QDs) was developed for the sensitive detection of norfloxacin (NOR) in animal-origin foods. Briefly, the enzymatic formation of horseradish peroxidase (HRP) in conventional ELISA effectively quenched the fluorescence of QDs through inner-filter effect (IFE) and fluorescence resonance energy transfer (FRET), and then the absorption signal of conventional ELISA was transformed to fluorescent signals, resulting in a higher sensitivity for NOR detection in animal-origin foods. The detection limit of NOR in this developed method was 0.20 μg L−1 in standard solution, which was 12-fold more sensitive than conventional ELISA (2.50 μg L−1). The results of specificity analysis revealed that the proposed method could not only be used for the detection of NOR, but also for the other 9 structural analogues. The recovery rates of NOR-spiked animal-origin foods ranged from 88.11 % to 108.16 %, with CV values of 1.95 %–18.03 %. In addition, the established method had good consistency with the commercial ELISA kits and HPLC, indicating the accuracy of the developed method for the detection of NOR in real samples. In conclusion, the established fluorescence immunoassay was sensitive and facile, and could be alternatively used for the determination of NOR residues in animal-origin foods.