A highly sensitive and specific polyclonal antibody-based enzyme-linked immunosorbent assay for detection of antibiotic olaquindox in animal feed samples

The use of olaquindox (OLA) as an additive in animal feedstuffs has been prohibited in the European Union and many other countries. In this study, a highly sensitive and specific indirect competitive enzyme-linked immunosorbent assay (ELISA) for determination of OLA in animal feed samples was developed. OLA was activated by N′N-carbonyldiimidazole and coupled with bovine serum albumin (BSA) and ovalbumin (OVA). It was found that the sensitivity and specificity of the two antisera were very similar, with the IC₅₀ values of 16 ng mL⁻¹ and 19 ng mL⁻¹, respectively. Cross-reactivity was less than 35% for four structurally related compounds and no recognition of five other antibiotics was observed. The better antiserum I was selected for further experiments, for example testing stability, solvent effect, accuracy, and precision. The IC₅₀ value for eight standard curves was in the range 12–18 ng mL⁻¹ and the LOD at a signal-to-noise ratio of 3 (S/N = 3) was 0.31 ± 0.11 ng mL⁻¹. The ELISA tolerated 5% methanol without significant influence on IC₅₀ value. The recoveries of spiked OLA in five different animal feed types including auxin, pig complex feed, fish complex feed, broiler concentrated feed, and pig premix feed were in the range 88.3–119.0% and the intra-assay relative standard deviation (RSD) was within 4.7–33.5% (n = 3). The ELISA for unspiked feed samples was confirmed by high-performance liquid chromatography (HPLC), with a high correlation coefficient of 0.9862 (n = 5). The proposed ELISA could be a feasible quantitative/screening method for OLA analysis in feed samples with the properties of high sensitivity, specificity, simplicity of sample pretreatment, high sample throughput, and low expense. Figure Polyclonal antibody based ELISA for detection of olaquindox