An oligosorbent-based aptamer affinity column for selective extraction of aflatoxin B-2 prior to HPLC with fluorometric detection

The article describes an aptamer affinity column for selective solid-phase extraction of aflatoxin B-2 (AFB(2)). Amino-modified aptamer against AFB(2) was immobilized on CNBr-activated Sepharose through a covalent bond. The effects of oligosorbents based on 3'-or 5'-amino-modified sequences with a C6 or a C7 spacer arm were evaluated by UV spectroscopy at 260 nm. The extraction recovery was evaluated by HPLC with fluorometric detection. The extraction of AFB(2) was optimized. Under the optimum conditions, the aptamer affinity column has a linear response to AFB(2) in the range of 0.5-80 ng, with a capacity of 84.6 ng. Control supports without immobilized aptamers and a nonspecific oligosorbent immobilized with a negative control oligonucleotide were studied in order to demonstrate selectivity. The method was tested with spiked peanut sample (0.5-50 mu g.kg(-1) AFB(2)) and gave average recoveries of 80.9% and a mean relative standard deviation of 1.9%. The limit of detection is 25 pg.mL(-1). This is much lower than the maximum residue limits suggested by the European Union. The columns can be re-used up to five times without any loss of performance. The oligosorbent was also applied to clean-up of AFB(2) from peanut sample extracts before HPLC analysis. Results were further confirmed by ultra-fast liquid chromatography with tandem mass spectrometry. Conceivably, the method may also be applied to other samples, such as food, agricultural products, and traditional Chinese medicines.