Sensitive detection of the okadaic acid marine toxin in shellfish by Au@Pt NPs/horseradish peroxidase dual catalysis immunoassay

Abstract

Based on the catalysis enhancement strategy of Au@Pt nanoparticles (Au@Pt NPs) and horseradish peroxidase (HRP) related to the TMB–H₂O₂ indicator, a sensitive colorimetric immunoassay was established for trace okadaic acid (OA) detection. The anti-OA monoclonal antibody (McAb) with a high K_aff constant was prepared and modified on Au@Pt NPs. Through grafting the HRP conjugated goat anti-mouse IgG antibody (IgG) on Au@Pt/McAb, bifunctional composites with Au@Pt–Ab and HRP were prepared and adopted. Characteristics including morphology, specificity and catalytic performance were evaluated. Under the optimal conditions, the sensitivity of the resultant enzyme immunoassay was significantly improved, and a low limit of detection (LOD) of OA was achieved at 0.04 ng mL⁻¹ (equivalent to 0.6 μg kg⁻¹ in mussel tissue), which was better than that of most HRP or Au/HRP enzyme-linked immunosorbent assays. When applied to fortified shellfish samples (e.g. oysters, mussels and clams), the recoveries ranging from 98.3 ± 2.3% to 106.0 ± 9.0% were acceptable and comparable with those of the LC-MS method. Acceptable precision was achieved with a variation coefficient (CV) of 2.3–8.4%. The method provides a promising alternative for the highly sensitive detection of the OA marine toxin at trace levels.