Determination of Oxytetracycline by a Graphene—Gold Nanoparticle-Based Colorimetric Aptamer Sensor

A colorimetric aptamer sensor for the determination of oxytetracycline was developed based on the controllable peroxidase-like catalysis of a graphene/gold nanoparticle hybrid and the high affinity between oxytetracycline aptamers and oxytetracycline. The oxytetracycline aptamer was a single-stranded DNA sequence that was adsorbed on the interface of the hybrid, resulting in inhibition of the catalysis. The aptamer–oxytetracycline complex formed spontaneously following the addition of oxytetracycline, escaped from the hybrid, and recovered the catalytic ability that was inhibited by the aptamer. In the presence of hydrogen peroxide, the recovered hybrid oxidized a colorimetric reagent, causing a concomitant change in color. The whole process did not involve labeling and the color change was readily observed. This method provided a linear dynamic range for oxytetracycline from 0.17 to 0.50 µM with a detection limit of 91 nM and a quantification limit of 0.17 µM. In addition, the selectivity of the sensor was confirmed in the presence of high concentrations of potential interferents. This work is expected to encourage the development of additional simple and visible sensors for the determination of other pollutants.