A screening lateral flow immunochromatographic assay for on-site detection of okadaic acid in shellfish products

A lateral flow immunochromatographic (LFIC) test strip based on a colloidal gold–monoclonal antibody (McAb) conjugate was developed for on-site rapid detection of okadaic acid (OA) in shellfish. It applies a competitive format using an immobilized toxin conjugate and free toxin present in samples. The McAb against OA was conjugated with 20-nm colloidal gold as detector reagent. The toxin in the sample competed with the immobilized toxin to bind to the gold conjugated with McAb. The colloidal gold/McAb/toxin mobile complex was not captured by OA–bovine serum albumin (BSA) on the test line, but it was captured by goat anti-mouse immunoglobulin G (IgG) on the control line. The color density of the test line correlated with the concentration of toxin in the range of 10–50 ng ml−1. The qualitative detection limit of 150 μg kg−1 sample was close to the European Union (EU) regulatory limit (160 μg kg−1). Therefore, these strips were able to directly and qualitatively estimate the consuming safety of shellfish. They require no equipment because of available visual results, and they screened numerous samples within 10 min. The results were further confirmed by high-performance liquid chromatography tandem mass spectrometry (HPLC–MS/MS). As a food safety screening tool, the test strips are convenient and useful to rapidly on-site test the presence of OA in shellfish products.