Genetically Engineered Nanobody–Recombinant Antibody Colloidal Gold Strip for Ultrasensitive Atrazine Detection in Fruits and Vegetables

Colloidal gold immunochromatography (CG‐ICA) is distinguished by its cost‐effectiveness and rapid detection capabilities. However, its key recognition components—antigens and antibodies—are typically produced through chemical synthesis or ascites induction techniques. These methods often lead to batch‐to‐batch variability and the risk of cell line loss, thereby limiting the production efficiency of antigens and antibodies. In this study, using atrazine as the target analyte, a novel colloidal gold test strip, AId/rAb‐ICA (Anti‐Idiotypic nanobody/recombinant full‐length antibody‐immunochromatographic assay), was successfully developed by employing an anti‐idiotypic nanobody (AI‐Nb‐66) and a recombinant full‐length antibody (ATR‐rAb) to replace the traditional antigen‒antibody pair in CG‒ICA. The detection limit (LOD) of this test strip was 0.31 ng/mL. It was successfully validated in apples, celery, and scallions, with recovery rates ranging from 82.45% to 103.60% and coefficients of variation (CVs) not exceeding 7.80%. This study offers a new approach for atrazine detection and the development of colloidal gold test strips.