Fluorometric aptamer based assay for ochratoxin A based on the use of exonuclease III

This study describes an aptamer based assay for the mycotoxin ochratoxin A (OTA). The method is based on the use of an OTA-specific aptamer, exonuclease (Exo) III, SYBR Gold as a fluorescent probe, and a complementary strand that specifically combines with the aptamer. In the presence of OTA, the aptamer and OTA hybridize, thereby resulting in the formation of ssDNA, which is not digested by Exo III. Intense fluorescence is observed after addition of SYBR Gold (best measured at excitation/emission wavelengths of 495/540 nm). Fluorescence increases linearly with the log of the OTA concentration in the range from 8 to 1000 ng · mL −1 . The detection limit is 4.7 ng·mL −1 . The assay was applied to the determination of OTA in diluted [2%( v /v)] red wine, and recoveries and RSDs ranged between 93.5% and 113.8%, and between 3.2% and 5.7%, respectively. In the presence of ochratoxin A (OTA), specific combinations of aptamer and OTA may occur and result in DNA double strands being untied, which avoids being digested by Exo III. Intense fluorescence is observed after SYBR Gold addition.