Monoclonal Antibody-Based ELISA and Colloidal Gold Immunoassay for Detecting 19-Nortestosterone Residue in Animal Tissues

Abstract

This article presents the generation of monoclonal antibodies (mAbs) with high specificity against 19-nortestosterone (NT) through cell fusion techniques and the development of a mAb-based indirect competitive ELISA (icELISA) method and colloidal gold-based immuno-chromatographic assay to detect NT residues in beef and pork samples. A modified carbodiimide method was employed to synthesize the artificial antigen, and BALB/c mice were used to produce anti-NT mAbs. On the basis of the checkerboard titration, an indirect competitive ELISA standard curve was established. This assay was sensitive and had a linear range from 0.03 to 38 ng/mL in phosphate buffered saline (PBS), with IC₅₀ and LOD values of 0.52 ng/mL and 0.01 ng/mL, respectively. Of all the competitive analogues, the produced mAb exhibited a high cross-reactivity to 17α-nortestosterone (83.6%), the main metabolite of NT in animal tissues. Except for moderate cross-reactivities with trenbolone (22.6%) and β-boldenone (13.8%), the other interference to the assay was negligible (R² = 0.9945) and in pork (R² = 0.9977). Therefore, the combination of two immunoassays provides a useful screening method for quantitative or qualitative detection of NT residues in animal-origin products.