Amperometric aptasensor for ochratoxin A based on the use of a gold electrode modified with aptamer, complementary DNA, SWCNTs and the redox marker Methylene Blue

The authors describe an amperometric aptasensor for the mycotoxin ochrotoxin A (OTA). It is based on the use of a modified gold electrode containing aptamer (Apt) as the sensing ligand, Methylene Blue (MB) as the redox indicator, single-walled carbon nanotubes (SWCNTs) as electrochemical signal amplifiers, and complementary strands of aptamer (CSs) as assisting DNA. In the absence of OTA, the duplex formed between Apt and CSs on the electrode remains intact. Thus, a strong electrochemical signal is observed due to the presence of the redox marker MB in the duplex. If OTA is added, the duplex will be disassembled and MB and SWCNTs will be released from the surface of the gold electrode. Hence, the electrochemical signal is weakened. The method is highly specificity for OTA and has a limit of detection as low as 52 pM. The aptasensor was successfully applied to the determination of OTA in (spiked) serum and grape juice samples where it shows LODs of 134 and 58 pM, respectively.