An ultrasensitive HRP labeled competitive aptasensor for oxytetracycline detection based on grapheme oxide–polyaniline composites as the signal amplifiers

In this work, we explored an amplification strategy which was based on graphene oxide–polyaniline (GO–PANI) and horseradish peroxidase (HRP) to construct the competitive aptasensor for ultrasensitive detection of oxytetracycline (OTC). In the protocol, the GO–PANI film was immobilized on the surface of the electrodes. Then, gold nanoparticles (AuNPs) were electrodeposited on the electrode surface using a constant potential stripping technique. The selected aptamer which had high affinity and specificity for OTC was used as a capture probe and labeled with HRP. The linear response to OTC concentration of the developed aptasensor was in the range of 4.0 × 10−6 mg L−1 to 1.0 mg L−1. The detection limit (LOD) of 2.3 × 10−6 mg L−1 was obtained (S/N = 3). In addition to good repeatability and stability, the proposed aptamer sensor also showed the advantages of low background current and high sensitivity to examine OTC in real samples.