A competitive fluorescence assay based on free-complementary DNA for ochratoxin A detection

•A simple and efficient method based on free-complementary DNA was developed to detect ochratoxin A.•A lower detection limit and a higher sensitivity of the method were achieved due to the optimization of detection conditions.•The assay showed the potential and practical application for OTA detection in real food samples. An ultrasensitive, rapid, and specific method for Ochratoxin A (OTA) detection was designed using complementary sequence to aptamer as a target of molecular beacon (MB). The designed loop structure of the MB has the same sequence as the aptamer with a complementary DNA (cDNA) which translates the level of the target into a measurable response. The presence of the target holds aptamer at the corresponding amount and the additional cDNAs are consumed by unbound aptamers which avails free cDNAs that resulting in fluorescence rising due to unfolding of MBs. Under the optimized conditions, the fluorescence intensity increased linearly with OTA concentration over the range of 10 pg mL−1–1 µg mL−1 with the detection limit of 0.247 pg mL−1. The application of this assay in wheat sample in comparison with HPLC-MS/MS method, demonstrated that the new assay could be a potential sensing platform for OTA detection.