Optical waveguide lightmode spectroscopy technique–based immunosensor development for deoxynivalenol determination in wheat samples

Contamination by deoxynivalenol (DON), a trichothecene mycotoxin produced by Fusarium species, occurs in cereals worldwide; therefore, efforts have been made toward the development of rapid and sensitive methods for the detection of this compound. In our investigation, optical waveguide lightmode spectroscopy (OWLS) technique has been applied to label-free detection of DON in both competitive and in direct immunoassay formats using DON-specific polyclonal antibodies. After immobilizing the antibody or the antigen conjugate for the direct or indirect measurement, the sensor chip was used in a flow-injection analyzer system. The direct method was found to result in an unstable sensor response and sensitivity insufficient to determine DON in different grains. In contrast, a competitive immunosensor format provided reproducible quantitative detection in the sub-ppt range. For competitive sensor investigation with the sensitized chip, first the optimal dilution rate of polyclonal antibodies was determined. For the measurements, antibody stock solution was diluted to 8 μg mL−1. During the competitive measurement, standard solutions were mixed with the antibodies at the appropriate concentration, and the mixture was incubated for 1 min and injected into the OWLS system. The sensitive detection range of the competitive detection method was between 0.01 and 50 ng mL−1. After the establishment of the indirect method, spiked wheat flour samples were investigated. Results obtained with spiked samples showed that OWLS detection has a potential for quick determination of DON in wheat samples.