Development and validation of an immunochromatographic test strip for rapid detection of doxycycline residues in swine muscle and liver

A one-step lateral flow immunochromatographic technique using colloidal gold-labelled monoclonal antibody (Mab) was developed for the rapid detection of doxycycline (DOX) residues in swine tissues. For this purpose, a Mab against DOX named as 2.3/3A6 with low cross-reactivity (CR) to other tetracyclines (TCs) was produced. The sensitivity of the test strip was as low as 7 ng/mL for DOX and the half maximal inhibitory concentration (IC₅₀) was calculated to be 22±2 ng/mL by relative optical density. The test can be completed within 10 min and the detection limit was 20 ng/mL in unaided visual assessment. Recoveries in samples spiked with DOX at concentrations of 20, 40 and 80 ng/g, were demonstrated to be from 81% to 95% for muscle samples and from 81% to 92% for liver samples. The intra-assay and inter-assay coefficients of variation (CVs) ranged from 3% to 6% and from 4% to 8%, respectively. Comparing with high performance liquid chromatography (HPLC) method in sensitivity and accuracy for the detection of DOX in swine tissues, the test strip showed good agreement. Therefore, the test strip is suitable for rapid and reliable determination of DOX residues in swine tissues semi-quantitatively or qualitatively.