Massive use of antibiotics in veterinary medicine has led to their accumulation in meat and dairy products. Consumption of antibiotic-contaminated food can trigger the development of antibiotic-resistant bacteria, endangering human lives. Among antibiotics, the oxytetracycline (OTC) family of antibiotics is most widely used in veterinary medicine. Strict control of the antibiotics in food necessitates the development of fast and effective methods for OTC detection, for instance, in milk. One of the most promising approaches to OTC detection is based on the use of specially designed DNA aptamers. These DNA aptamers are relatively short, 15-60 bases, nucleotides folded in the solution in a 3D structure, forming a binding site for the target antibiotic. Aptamers can be chemically modified for attachment to sensor electrodes. In this work, we investigated the electrochemical detection of OTC using DNA aptamers specific to OTC that have been covalently immobilized onto the nanocomposite surface of a glassy carbon electrode with electrodeposited reduced graphene oxide and multiwalled carbon nanotubes. Differential pulse voltammetry, DPV, in the presentence of a ferri/ferrocyanide redox couple was used as an internal standard and to monitor the redox current. In the presence of OTC, the amplitude of DPV decreased, evidencing the blocking of charge transfer. After system optimization, we reached the limit of detection of 0,45 ng OTC /ml, which is 200 times lower than the maximum residue limit established by the European Commission of 100 ng OTC /mg.

This work was funded under the European Union’s Horizon 2020 research and innovation program through the Marie Skłodowska-Curie grant agreement No. 101007299 (T.H.), the Science Agency VEGA, project No. 1/0445/23 (T.H.). Part of the project was sponsored by the Center for Nanophase Materials Sciences (CNMS), user proCNMS2022-A-01196, which is a US Department of Energy Office of Science User Facility at Oak Ridge National Laboratory.