Fluorometric determination of okadaic acid using a truncated aptamer.

Okadaic acid (OKA), a marine toxin produced by dinoflagellates, is responsible for most human diarrhetic shellfish poisoning-associated health disorders. A competitive displacement assay for OKA is described here. An OKA-binding aptamer was truncated with two sequences, one labeled with 6-carboxyfluorescein (FAM), and one with a quencher. On addition of OKA, it will bind to the aptamer and green fluorescence pops up because label and quencher become spatially separated. One of the truncated aptamers exhibis an excellent binding capability (Kd 2.77 nM) for OKA compared to its full-length aptamer (526 nM). The selectivity of the assay was proven by the successful fluorometric determination of OKA in the presence of common diarrhoetic toxins and in shellfish extracts. The detection limit is as low as 39 pg·mL. Graphical abstract Schematic representation of the competitive displacement assay for okadaic acid (OKA). The OKA-binding aptamer is truncated with two parts, one labeled with 6-carboxyfluorescein (FAM), and one with a quencher. On addition of OKA, green fluorescence pops up because label and quencher become spatially separated.