A novel electrochemical aptasensor based on rolling circle amplification-driven Ag plus -DNAzyme amplification for ochratoxin A detection

Ochratoxin A (OTA), a hazardous mycotoxin, is widely found in food ingredients and processed products, hence an urgent need to establish a sensitive and reliable low-level OTA detection method. Herein, a novel trochemical aptasensor was prepared by designing OTA-mediated formation of DNA circular probes to tiate rolling circle amplification (RCA) reaction, RCA-driven Ag +-DNAzyme as signal amplification strategy, simultaneously. Streptavidin-modified magnetic beads (SA-MBs) and biotin-modified aptamer (Bio-Apt) were bonded, then padlock and primer were added to form padlock-primer-Apt-MBs. In the absence of OTA, padlock-primer can not be detached from MBs to initiate the subsequent RCA reaction, so the methylene blue-labeled hairpin (Hp-MB) with rA site can not be cleaved, leading to a large original current. When OTA present, the aptamer preferentially combined with OTA, resulting in the detachment of the padlock-primer. Then DNA circular probe was formed as padlock further hybridized with primer under the function of T4 ase. Then, DNA circular probe generated long DNA strands with repetitive Ag +-DNAzyme sequences, which can cleave Hp-MB, causing a decrease in MB signal. The developed sensor had a good linear relationship the range of 5 x 10 -4 to 50 ng/mL and the detection limit was as low as 38 fg/mL for OTA. This strategy was suitable for OTA detection in corn flour and red wine, which exhibits good potential application in actual samples.