Fluorescence Polarization Immunoassay for Rapid, Accurate and Sensitive Determination of Ochratoxin A in Wheat

A sensitive and accurate fluorescence polarization (FP) immunoassay has been developed for the determination of ochratoxin A (OTA) in naturally contaminated wheat samples. A fluorescein-labeled OTA tracer was synthesized, and its binding response with three monoclonal antibodies was tested. The most sensitive competitive FP immunoassay showed an IC50 value of 0.48 ng/mL with a negligible cross-reactivity for ochratoxin B (1.7 %) and no cross-reactivity with other mycotoxins commonly occurring in wheat. The wheat sample was extracted with acetonitrile/water (60:40, v/v) and purified by a rapid solid-phase extraction procedure using an aminopropyl column prior to the FP immunoassay. The overall time of analysis was less than 20 min. The average recovery from spiked wheat samples (3 to 10 mu g/kg) was 87 %, with relative standard deviations generally lower than 6 %. Limits of detection and quantification were 0.8 and 2.0 mu g/kg, respectively. The trueness of the method was assessed by using two reference materials for OTA showing good accuracy and precision. A good correlation (r = 0.995) was observed between OTA contamination of 19 naturally contaminated wheat samples analyzed by both FP immunoassay and high-performance liquid chromatography/immunoaffinity clean-up used as reference method. These results show that the developed FP method is suitable for high-throughput screening, as well as for reliable quantitative determination of OTA in wheat at level far below the EU regulatory limits.