Highly sensitive impedimetric immunosensor for OTA detection

Ochratoxin-A (OTA) is a mycotoxin which is produced by moulds that grow on crops in the field or in storage. OTA can be present in food and feedstuffs (derivates) and the Agency for Research on Cancer (IARC) has classified OTA as possibly carcinogenic to humans. For these reasons its determination by easy and rapid analytical methods is required. At present, the official methods of OTA determination in food samples is the high performance liquid chromatography (HPLC) and gas chromatography (GC). However this kind of analyses are expensive, complex and requires experienced staff. The Enzyme-linked immunosorbent assays (ELISA) are used with screening purpose of OTA, but their major limit is to provide many false positives and negatives. The electrochemical immunosensor can be an interesting analytical method for OTA determination thanks to the high sensitivity of electrochemical techniques. In this work a label-free impedimetric immunosensor for sensitive detection of OTA was reported. To achieve a greater sensitivity of the immunosensor, the immobilization of anti-Ochratoxin A antibody on gold electrode surface was carried out coupling self-assembled monolayer (SAM) and protein A/G which allows the immobilization of antibody in an convenient oriented way which favours the antigen-antibody interaction. The Electrochemical Impedance Spectroscopy (EIS) was used to probe the features of the surface-modified electrode: it is a sensitive technique that monitors the electrical response of the system studied after application of a periodic small amplitude AC signal. The analysis of the system response provides information concerning the electrical behaviour of the interface and the interaction antibody - antigen occurring on it. Due to the specific immuno-interaction at the immunosensor surface, the Impedance changes; in particular, it can be seen that the Electron Transfer Resistance (Rct) values decrease with increase in the concentration of OTA in the range of 0.01-5.00 ng/mL. Moreover, the developed OTA immunosensor showed a high sensitivity, specificity and a good reproducibility. Relevance In this study a decrease of charge transfer resistance (Rct) was found with the increasing of OTA concentration. Limit of detection (LOD) of label free impedimetric immunosensor developed was 10 ng/L.