Label-free ochratoxin A electrochemical aptasensor based on target-induced noncovalent assembly of peroxidase-like graphitic carbon nitride nanosheet

The development of simple, fast and sensitive aptasensor for OTA plays an important role in food safety due to its severe toxicity. In this research, taking advantage of the intrinsic peroxidase-like activity of g-C3N4 nanosheet (g-CNNS) and its high affinity toward signal-strand DNA, a label-free electrochemical OTA aptasensor was fabricated. There is an outstanding property that the aptasensor did not require labeled aptamer and immobilization of g-CNNS compared with previous g-CNNS-based aptasensors. The presence of OTA induced the conformational change of the aptamer, and then g-CNNS noncovalently assembled with the free complementary strand on the electrode via π-π interaction. The captured g-CNNS catalyzed the oxidation of H2O2 to amplify current signal. As a result, this aptasensor realized the detection limit of 0.073 nM, and was also employed to assay OTA in the real samples, including red wines, juices and corns. More importantly, the development of this label-free electrochemical aptasensor opens up the application of g-CNNS as the peroxidase-mimicking DNAzyme.