Fabrication of a novel electrochemical aptasensor based on conductive polymers and graphite sheet for measuring tetracycline antibiotic in milk, egg, and honey

In this research, an electrochemical aptasensor was made for the detection of tetracycline (TET) antibiotic in food samples. The graphite sheet was modified for the first time by electrochemical co-polymerization of anthranilic acid and aniline, which increases the active surface and electrical conductivity of the electrode and is also a suitable substrate for covalent bonding with aptamers. This electrode was examined and characterized by electrochemical methods, Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), and X-ray energy dispersive (EDS) techniques. Then, the Apt-TET aptamer sequence was self-assembled on the electrode to increase the selectivity of the electrode response. The optimization of important parameters including the TET detection time, aptamer immobilization time, and Apt-TET aptamer concentration was performed. The aptasensor was used to measure the TET by differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) techniques in 0.1 M KCl solution in the presence of Fe(CN)₆^4−/3- redox prob. The proposed aptasensor has a very wide linear range from 1 × 10⁻⁶ to 1 × 10⁻¹⁶ M with a detection limit of 3.3 × 10⁻¹⁷ M. The developed aptasensor was successfully applied for the determination of TET in milk, egg, and honey samples.