Aptamer based photometric assay for the antibiotic sulfadimethoxine based on the inhibition and reactivation of the peroxidase-like activity of gold nanoparticles

It is known that gold nanoparticles (AuNPs) possess peroxidase-like activity. They can catalyze the oxidation of 3,3,5,5-tetramethylbenzidine by H 2 O 2 which leads to a color change from red to blue. It is shown here that the peroxidase-like activity of AuNPs can be inhibited by passivating its surface passivation with a ssDNA aptamer against sulfadimethoxine. If, however, the target molecule (sulfadimethoxine) is present, the aptamer is desorbed from the AuNPs surface, and this results in the reactivation of the catalytic property of the AuNPs. The color change of the solution (from purple to blue) is related to the analyte concentration, and this can be judged visually or by UV-visible absorptiometry at 650 nm. The assay, under optimized conditions, has a detection limit of 10 ng·mL −1 of sulfadimethoxine, and the calibration plot is linear over a rather wide concentration range (0.01–1000 μg·mL −1 ). The assay can be performed within