Magneto Immunofluorescence Assay for Quinolone Detection in Bovine Milk

Quinolone is a family of widely prescript antibiotics in veterinary medicine. Their excessive use can be causative of quinolone residues in foodstuffs of animal origin. Therefore, a magneto immunofluorescence assay in microwell plate has been developed and validated to screen quinolone in bovine milk. The assay is based on an indirect competitive method where the quinolone in the milk sample competed with the quinolone immobilized on magnetic beads for the anti-quinolone antibody. Then, an anti-IgG antibody–labeled peroxidase and their respective substrates were added and the fluorescent signal was indirectly related with the quinolone concentration. Recoveries of quinolones from 82 to 102% were obtained in skimmed, whole, and raw milk samples in concordance with the results obtained by a reference method. Seven quinolones were evaluated quantitatively by the method, obtaining limits of detection of 10 μg L −1 for ciprofloxacin and marbofloxacin, 13 μg L −1 for enrofloxacin and danofloxacin, 22 μg L −1 for norfloxacin, 29 μg L −1 for sarafloxacin, and 30 μg L −1 for ofloxacin. For the screening detection of quinolones, ciprofloxacin was used as model with decision limit (CCα) and detection capability (CCβ) of 103 and 106 μg L −1 , respectively. High cross-reactivity (> 100%) was obtained to all assayed quinolones while negligible cross-reactivity (