Colloidal gold-based immunochromatographic strip assay for the rapid detection of diminazene in milk

Diminazene (DIM) is widely used to treat trypanosomiasis in livestock, but its residues in animal products can cause food safety problems. Thus, a rapid colloidal gold-based immunochromatographic strip assay was established to analyse DIM residue in milk samples. A highly sensitive and specific monoclonal antibody (mAb) against DIM was produced with a new synthetic immunogen by the active ester method. The titre of the prepared antibody was up to 1:1.0 × 10⁶, the affinity constant was 2.2 × 10⁸ L mol^-1 and the half-maximal inhibitory concentration (IC₅₀) was 0.4 ng mL^-1 based on enzyme-linked immunosorbent assay (ELISA). Then, the colloidal gold-labelled mAb probe was successfully prepared and used for preparing the immunochromatographic strip. The strip showed high sensitivity and specificity, the IC₅₀ for DIM was 5.2 ng mL^-1, the limit of detection was 1.2 ng mL^-1 and the linear range of detection was 1.8-15.4 ng mL^-1. The average recoveries ranged from 89.5% to 91.7%, and coefficients of variation were 6.6-7.2%. The immunochromatographic strip assay can be employed in the rapid detection of DIM residue in milk samples.