An amplified electrochemical aptasensor for ochratoxin A based on DNAzyme-mediated DNA walker

In this work, a novel signal-on electrochemical aptasensor was designed for ochratoxin A (OTA) detection based on DNAzyme-mediated DNA walker. Double-stranded DNA (dsDNA), formed by the hybridization between OTA aptamer and DNA walker, and Hairpin DNA (HP) containing adenosine ribonucleotide (rA) site were immobilized on the electrode surface. In the presence of OTA, the competitive binding of OTA with aptamer caused dsDNA to dissociate, resulting in that DNAzyme sequence in DNA walker was exposed. With the addition of Ag+, DNAzyme-mediated DNA walker was activated and sheared HP on the electrode surface cyclically, which reduced the negative charge density and improved the transfer rate on the electrode surface for signal amplification. The peak current increased by 4.58 times with addition of Ag+ than that without addition of Ag+. The proposed aptasensor exhibited a good linear relationship in the OTA concentrations from 0.001 ng/mL to 5 ng/mL, and the limit of detection was 0.1 pg/mL. The aptasensor showed good anti-interference toward AFB(1), FB1, and ZEN. The aptasensor was applied to detect OTA in spiked corn samples and wine samples, and the average recoveries were 94.5%-97.7% and 92.0%-97.8%, respectively.