Aptamer-modified pencil graphite electrodes for the impedimetric determination of ochratoxin A

Ochratoxin A (OTA), a widespread food contaminant, is considered as one of the most hazardous mycotoxins commonly occurring in beer. Herein, we describe a novel impedimetric aptasensor based on Pencil Graphite Electrodes (PGE) for the analysis of OTA. Taking advantage of its affordability and high active surface area, a PGE was modified with a specific aptamer, to achieve sensitive detection of OTA. This strategy relies on the target-induced increase in the electron transfer resistance (R-ct) upon OTA recognition using ferro/ferricyanide as a redox probe. With the addition of OTA, the formation of OTA-aptamer complex resulted in an increase of Act. The change of R-ct strongly depends on OTA concentration, which is applied for mycotoxin quantification. An acceptable linear range was obtained from 0.1 to 2.0 ng mL(-1) with a very good limit of detection as low as 0,1 ng mL(-1). This simple-to-design aptasensor was successfully tested in spiked beer samples, with OTA concentrations in the range of 0.4-1.6 ng mL(-1), attesting a recovery percentage of 93.4 +/- 6.6%. It also showed a high level of stability and reproducibility thanks to the electro-grafting method via in-situ generation of 4-carboxyphenyl diazonium salts. This PGE-based platform is a versatile approach for the design of low-cost aptasensors for food safety control.