A fluorometric aptamer-based assay for ochratoxin A using magnetic separation and a cationic conjugated fluorescent polymer

A fluorometric aptamer-based assay for ochratoxin A (OTA) is described. It is making use of magnetic separation and a cationic conjugated fluorescent polymer. Amino-tagged aptamer (Apt) against OTA is immobilized on magnetic beads (MBs) to form a conjugate of type Apt-MBs. The immobilized aptamer is partially complementary to carboxyfluorescein-labeled DNA which binds to the Apt-MBs via hybridization if OTA is absent. Only few FAM-DNA will remain in the supernatant after magnetic separation, and only weak fluorescence resonance energy transfer (FRET) occurs on addition of the fluorescent polymer. If, however, OTA is present, it will bind to the aptamer and prevent the hybridization between Apt-DNA and FAM-DNA. This results in the presence of large amounts of FAM-DNA in the supernatant after magnetic separation. On addition of fluorescent polymer, efficient FRET occurs from the polymer to FAM-DNA. Fluorescence, best measured at excitation/emission peaks of 370/530 nm, increases with increasing concentrations of OTA. This assay is highly sensitive and selective. The detection limit is as low as 0.11 ng mL(-1). This is 6 times lower than the aptamer assay without using the fluorescent polymer. Conceivably, this method has a wider scope in that it may be extended to other mycotoxins by simply changing the aptamer.