Fast and Accurate Determination of Minute Ochratoxin A Levels in Cereal Flours: Towards Application at the Field †

Abstract

Ochratoxins are a group of mycotoxins produced as secondary metabolites by several fungi of Aspergillus and Penicillium species. Ochratoxin A (OTA) is the most toxic member of the group and can be found in a large variety of widely consumed foods, such as coffee, cocoa, wine, and flour. Reliable determination of OTA levels in food samples is therefore indispensable to ensure compliance with MRLs set by national/European regulations and minimize health risks for consumers. In the current study, a label-free biosensor based on white light reflectance spectroscopy (WLRS) for the rapid and accurate determination of OTA in cereal flour samples is demonstrated. A Si chip with a 1-μm-thick thermal SiO2 on top plays the role of transducer after the immobilization of an OTA–protein conjugate on its surface. For the assay, a mixture of an in-house-developed anti-OTA antibody with the calibrators or the samples is injected over the chip surface, followed by reaction with a secondary biotinylated antibody and streptavidin for signal amplification. The label-free, real-time monitoring of immunoreactions occurring on the SiO2/Si chip surface is achieved by recording the shift in the reflected interference spectrum caused by the immunoreactions. This shift is converted through appropriate mathematical processing to an effective biomolecular adlayer thickness. After optimization, the sensor is capable of detecting OTA in wheat flour samples at concentrations as low as 60 pg/mL within 25 min. The assay is repeatable, with intra- and inter-assay CVs ≤5.9% and ≤9.0%, respectively. The assay’s excellent analytical characteristics and short analysis time, in combination with the small size of the device, render the proposed WLRS system ideal for the quantitative determination of minute OTA levels at the point-of-need.