Development of an Indirect Chemiluminescent Competitive ELISA to Detect Danofloxacin Residues in Milk

Glucose oxidase-induced colorimetric immunoassay for qualitative detection of danofloxacin based on iron (Ⅱ) chelation reaction with phenanthroline

In this study, we developed a competitive colorimetric immunoassay for qualitative detection of DAN based on oxidation of iron (Ⅱ) (Fe²⁺) in the presence of glucose oxidase (GOx) and color change induced by Fe²⁺-phenanthroline (Phen) chromogenic system. Streptavidin (SA) acted as a linker between biotinylated anti-DAN-monoantibody (bio-mAb) and biotinylated GOx (bio-GOx) to form the immunocomplexes bio-mAb-SA-bio-GOx. In the absence of DAN, the immunocomplexes bio-mAb-SA-bio-GOx combining with coated DAN-ovalbumin (DAN-OVA) will be immobilized and catalyze glucose to produce H₂O₂. Fe²⁺ is oxidized to Fe³⁺ by H₂O₂, giving rise to a colorless result. In the presence of DAN, Fe²⁺ produces a chelation reaction with Phen, leading to orange-red color. Under optimal conditions, the detection limit (LOD) by naked eyes was 2.5 ng mL^-1 in milk, chicken, beef, and pork samples. Low LOD, no matrix effect, and no signal reader requirement make it possibly applied to quickly screen DAN on site.

Silver nanoprism-based plasmonic ELISA for sensitive detection of fluoroquinolones

Fluoroquinolones are synthetic antibiotics that are commonly used in animal husbandry, and the consumption of animal products with fluoroquinolone residues has imposed a serious threat to human health. Here, we report a plasmonic enzyme-linked immunosorbent assay (pELISA) method based on oxidative etching of silver nanoprisms (AgNPRs) for the quantitative and qualitative detection of danofloxacin (DAN), a fluoroquinolone antibiotic. AgNPRs that undergo colorimetric changes upon oxidative etching by H2O2 serve as the signal transducer in our design. An indirect competitive pELISA was constructed by introducing biotinylated monoclonal antibody (mAb), streptavidin and biotinylated glucose oxidase, which catalyzes the generation of H2O2 for etching AgNPRs. The quantitative detection limit of the proposed method was 0.24 ng mL-1 for DAN. The qualitative detection limit for DAN reached 0.32 ng mL-1, which was 32-fold lower than that of the assay using 3,3',5,5'-tetramethylbenzidine (TMB) as the signal transducer. The average recoveries of DAN in milk ranged from 103% to 121%, with a coefficient of variation of 0.6-3.41%. The recovery results were further confirmed using liquid chromatography-tandem mass spectrometry. In summary, the proposed AgNPR-etching pELISA exhibits high sensitivity, good accuracy and excellent reliability for the quantitative and qualitative detection of DAN in milk.