Gold Nanoparticle/Nanobody\nImmunochromatographic Strip\nfor Detection of 19-Nortestosterone

19-nortestosterone (19-NT) is recognized as a highly\neffective\nanabolic steroid that is banned in animal products because of its\nnegative impact on human health. Despite legal prohibitions, 19-NT\nis still abused, driven by its commercial benefits. In this study,\na gold nanoparticle immunochromatographic assay (GICA) utilizing nanobodies\n(Nb) has been developed for the efficient, rapid, and sensitive detection\nof 19-NT. Specifically, anti-19-NT-Nb2F7 coupled gold nanoparticles\nand optimized a variety of detection conditions for GICA, including\npH, concentration of Nb2F7, and amount of probe. Under optimal conditions,\nthe Nb2F7-based GICA could rapidly and sensitively detect 19-NT within\n10 min, with a limit of detection (LOD) as low as 0.08 ng/mL. Moreover,\nthis method exhibited good recovery and stability for detecting 19-NT\nin pig urine and bovine urine, which was correlated well with standard\nUPLC-MS/MS. Overall, this Nb2F7-based GICA is well-suited for on-site\nscreening of 19-NT in animal urine products, providing a rapid, cost-effective,\nand user-friendly alternative to traditional assay.