Bifunctional nanobody facilitates a colorimetric and fluorescent dual-mode immunoassay of Staphylococcal enterotoxin A.

Immunoassay is a diagnostic tool based on the specific binding of antibodies and antigens with widespread applications. Nonetheless, several research obstacles, like poor specific antibodies, the poisonous reagents and unstable results, still remain challenges. Herein, we innovatively reported a colorimetric and fluorescent dual-mode immunoassay based on the bifunctional nanobody for SEA detection. Benefiting from the advantages of nanobodies, the bifunctional protein with both recognition and catalysis was built to identify and catalyze with efficiency to generate the first colorimetric signal. Meanwhile, the introduction of quinine as the natural source of the second fluorescent signal greatly improved the stability and safety of detection. In addition, the proposed method was successfully applied to detecting SEA in food samples with high accuracy and stability. This study integrated the bifunctional nanobody with eco-friendly fluorescent product to provide a specific and green platform for the detection of foodborne toxins.