In this article, a novel aptasensor for ochratoxin A (OTA) detection based on screen-printed carbon electrode (SPCE) modified with polythionine (PTH) and iridium oxide nanoparticles (IrO2 NPs) is presented. The electrotransducer surface is modified with an electropolymerized film of PTH followed by the assembly of IrO2 NPs that aminated aptamer selective to OTA is exchanged with the citrate ions surrounding IrO2 NPs via electrostatic interactions with the same surface. Electrochemical impedance spectroscopy (EIS) in the presence of [Fe(CN)6]-3/-4 redox probe is employed to characterize each step in the aptasensor assay and also for label-free detection of OTA in a range between 0.01-100 nM obtaining one of the lowest limit of detection reported so far for label-free impedimetric detection of OTA (14 pM; 5.65 ng/kg). The reported system also exhibits a high reproducibility, a good performance with a white wine sample, and an excellent specificity against another toxin present in real samples.
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