Determination of ochratoxin A in wheat after clean-up through a DNA aptamer-based solid phase extraction column.

A DNA aptamer with high affinity and specificity to ochratoxin A (OTA) was conjugated to a coupling gel and used as sorbent for the preparation of solid phase extraction (SPE) columns. The SPE columns packed with 300μl oligosorbent (24nmol DNA) showed a linear (r=0.999) behaviour in the range of 0.4-500ng OTA. After optimisation of the extraction step, SPE columns were used for clean-up of OTA from wheat prior to liquid chromatographic (HPLC) analysis with fluorescence detection (FLD). Average recoveries from wheat samples spiked at levels of 0.5-50ng/g ranged from 74% to 88% (relative standard deviation <6%) with limits of detection and of quantification of 23 and 77pg/g, respectively. The comparative HPLC/FLD analyses of 33 naturally contaminated durum wheat samples cleaned-up on both aptamer-SPE and immunoaffinity (IMA) columns showed a good correlation (r=0.990). Aptamer-SPE columns could be re-used up to five times without any loss of performance.