An Electrochemical Immunoseneor For OTA Detection Using Single-Walled Carbon Nanotubes/Chitosan

Ochratoxins (OTs) are naturally found as secondary metabolites of Aspergillus ochraceus and Penicillium viridicatum. Among them, ochratoxin A (OTA) can contaminate a wide variety of foods and highly detrimental for human health. The highest OTA concentration in unprocesse cereals, soybean and their products permissible is defied to be 5 μg/kg by China’s National standard of the limit of fungal toxins in foods. Thus a simple, sensitive, efficient and rapid biosensor for OTA detection is extremely demanded. In this study, we presented an OTA electrochemical immunosensor which was based on an indirect competitive binding to a fixed quantity of OTA antibody between free OTA and ochratoxin A-bovine serum albumin (OTA-BSA). The OTA-BSA conjugate was firstly immobilized on a glass carbon electrode covered with functionalized single-walled carbon nanotubes/chitosan to obtain the electrochemical immunosensor. Then, diluted OTA antibody and OTA standard solution with a series of different concentration were added onto the surface of the modified OTA-BSA electrochemical immunosensor to perform the competition assay. After the competition, the alkaline phosphatase (ALP) labeled anti-mouse immunoglobulin G (IgG) secondary antibody (ALP-anti-antibody) was bound to the electrode surface. Electrochemical signal was produced through the catalytic hydrolysis between ALP and the substrate a-naphthyl phosphate (a-NP). This approach could quantitatively detect OTA from 0.01 to 100 ng/ml with a detection limit of 4 pg/ml which was lower than Italian specifications of OTA of 0.5 μg/kg in infants and children’s food. An immunosensor with excellent sensitivity, specificity and reproducibility was achieved and it could be regarded as a forceful tool for quantitative determination of OTA in security areas of food safety.