Colorimetric aptasensor for the sensitive detection of ochratoxin A based on a triple cascade amplification strategy

Ochratoxin A(OTA), a highly toxic mycotoxin commonly found in food, poses a serious threat to health even at low concentrations. Developing a sensitive, accurate, simple, and cost-effective detection method is of great significance for food safety and quality control. Herein, a triple cascade amplification strategy was used to construct the colorimetric assay for the detection of OTA, where the amplification process consists of an entropy-driven DNA circuit (EDC), a catalytic hairpin assembly (CHA), and Mg2+-assisted DNAzyme catalysis (MNAzyme). Through the specific binding of ochratoxin A (OTA) and its aptamer, an initiator strand is released to initiate upstream EDC and then produce a new trigger unit that motivates downstream CHA to generate MNAzyme, which further cleaves the substrate strand to induce the formation of G-quadruplex/hemin DNAzyme as a signal readout. The aptasensor was shown to detect OTA, with a low detection limit of 8.7 fM and good selectivity. The developed method could be used as a highly colorimetric aptasensor for the detection of OTA in spiked rice samples.