A highly sensitive impedimetric label free immunosensor for Ochratoxin measurement in cocoa beans

• An impedimetric label free immunosensor for Ochratoxin A detection was developed.
• Protein A/G was used for the oriented formation of anti-OTA on the electrode surface.
• AFM analysis showed an ordered a highly dense anti-OTA surface.
• The detection limit obtained (0.1 ng/ml) was suitable for European OTA limits.

In this work the development and optimization of an impedimetric label free immunosensor for the detection of Ochratoxin A (OTA) is reported.Two antibody immobilization methods (oriented and not oriented) were compared highlighting a lower limit of detection (5 pg/ml) for the not oriented immobilization but a closer linear range in contrast to oriented anti-OTA immunosensors which showed linearity in the range of 0.01–5 ng/mL OTA. The analysis of the Atomic Force Microscopy (AFM) images showed two different nanostructures indicating that the use of oriented immobilization created a more ordered and highly dense antibody surface. Finally the oriented immunosensor was used to quantify OTA in spiked cocoa bean samples and the results were compared with those registered with competitive ELISA kit. The immunosensor was sensitive to OTA lower than 2 μg/kg that represents the lower acceptable limit of OTA established by European legislation for the common food products.