Fluorometric aptamer-based determination of ochratoxin A based on the use of graphene oxide and RNase H-aided amplification

The authors describe a fluorometric assay for ochratoxin A (OTA) that is based on the use of graphene oxide and RNase H-aided amplification. On addition of OTA, cAPT is replaced from the APT/cAPT hybridization complex and then hybridizes with RNA labeled with a fluorophore at the 5'-end. Eventually, the fluorophore is released by RNase H cleavage. As the concentration of OTA increases, more cAPTs are displaced, this leading to fluorescence enhancement (best measured at excitation/emission wavelengths of 495/515 nm). This RNase H-assisted cycle response results in strong signal amplification. The limit of detection, calculated on the basis of a signal to noise ratio of 3, is 0.08 ng.mL(-1). Response is linear in the 0.08-200 ng.mL(-1) OTA concentration range. The method is highly selective for OTA over ochratoxin B and aflatoxin B-1. It was applied to the determination of OTA in red wine samples spiked at levels of 1, 7, and 50 ng.mL(-1), and the recoveries ranged from 90.9 to 112%.