A Pt-loaded magnetic covalent organic framework with dual enzymatic activity for nanozyme-linked immunosorbent assay of SEB

Staphylococcal enterotoxin B (SEB) is a major pathogenic factor in foodborne diseases, and its rapid and sensitive detection is crucial for early warning of food safety risks and public health protection. In this study, a colorimetric immunosensing system for SEB detection was constructed based on a magnetic covalent organic framework (COF) composite loaded with platinum nanoparticles (Pt NPs) that exhibit dual enzymatic activities. The effective loading of Pt NPs endows the composite with excellent peroxidase (POD) and oxidase (OXD)-like activities. The COF matrix not only provides abundant binding sites for Pt NP dispersion but also enhances substrate adsorption, thereby significantly improving catalytic efficiency. By introducing an Fe3O4 core, the nanocomposite enables facile preparation of antibody–nanoparticle conjugates through separation and enrichment functions. The Fe3O4@COF@Pt nanocomposite demonstrates excellent peroxidase- and oxidase-like activities, capable of decomposing H2O2 and O2 to generate hydroxyl radicals (˙OH) and superoxide anions (O2˙−), which catalyze the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) into blue oxidized TMB (OXTMB), resulting in a visible color change for signal output. The sensor achieves specific detection by utilizing its peroxidase-mimicking activity, exhibiting a linear detection range of 1–200 ng mL−1 with a detection limit as low as 0.395 ng mL−1. This nanozyme-linked immunosorbent assay (NLISA) based on Fe3O4@COF@Pt offers a highly sensitive and convenient platform for SEB detection.