| In this paper, a colloidal gold lateral flow strip assay was developed for detecting the 19-nortestosterone (19-NT). The assay was based on competitive principle of immunoassay and could judge the residue of 19-NT by visual colored result.The 19-nortestosterone was oximated by carboxymethoxylamine. Then the production coupled to bovine serum albumin (BSA) and ovalbumin (OVA) to synthesize immunogen NT-CMO-BSA and coating antigen NT-CMO-OVA respectively through mixed anhydride. The colloidal gold particle of about 18.6nm was obtained by reducing the gold chloride with sodium citrate. The optimum pH was between 8.6~ 9.8 and the optimum labeling rate of polyclonal antibody was 30μg/ml. Nitrocellulose membrane Purabind RP of Waterman, glass fiber glass 33 of Schleicher&Schuell, glass fiber CB-SB08, absorb pad and PVC board of Shanghai Biogold company were chosen to assemble immunochromatographic lateral flow strip. The colloidal gold-labeled anti-19-NT antibody was dispensed on the glass fiber glass 33 with 60μl/unit at 2×dilution. The test line and control line were separately dispensed with 0.5mg/ml 19-NT-OVA and 0.2mg/ml Goat-Rabbit IgG by Bio-dot XYZ3000. The detection limit of the strip was 180ng/ml for detecting the 19-NT standard solution and the detection limit was 200ng/ml for detecting the swine urine spiked with 19-NT. Through the quantitative analysis using ImageJ software, the detection limit was 25ng/ml.The advantages of this test strip were that the assay time was less than 15min, and the strip was suitable for on-site rapid test. The method and data provided by present study could offer a lead to further research into the applicability of gold labeled lateral flow strip assays for 19-NT and lay a foundation for developing test strip for detecting residues of other low molecule veterinary drugs in food.
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