High-performance electrochemical sensing of tetracycline via functionalised reduced graphene oxide nanocomposites

• rGO-ES-Pd nanocomposite-based sensor developed for tetracycline detection. • Sensor shows high sensitivity (LOD: 1.51 × 10 −7 M) and broad linear range (0.01–5.0 μM). • Emeraldine salt and palladium nanoparticles enhance electron transfer and matrix selectivity. • The method exhibits low interference from ibuprofen, erythromycin, and amoxicillin. • Sensor validated in urine, river water, and wastewater with high reproducibility. The detection of antibiotic residues, particularly tetracyclines (TC), is crucial due to their potential risks to public health and environmental safety. This study reports the development of a selective and sensitive electrochemical sensor based on reduced graphene oxide functionalized with emeraldine salt and palladium nanoparticles (rGO-ES-Pd) for the detection of TC in simulated samples, urine, surface water, and wastewater. The rGO-ES-Pd nanocomposite was synthesised via a wet chemical method and drop-cast onto a glassy carbon electrode (GCE) to fabricate the rGO-ES-Pd/GCE sensor. To evaluate the impact of different polyaniline oxidation states, three additional nanocomposites, rGO-EB-Pd (emeraldine base), rGO-PG-Pd (pernigraniline), and rGO-LE-Pd (leucoemeraldine), were also prepared and tested. Comprehensive characterisation was performed using transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Among the tested nanocomposites, the rGO-ES-Pd/GCE sensor exhibited the highest electrocatalytic activity for TC detection, with a pH-dependent peak current response in the potential range of 0.1–0.4 V. The sensor demonstrated a wide linear detection range (0.01–5.0 × 10 −6 M) and a low detection limit (1.51 × 10 −7 M). Selectivity studies in the presence of common interfering substances, ibuprofen, erythromycin, and amoxicillin, revealed minimal interference and a low relative standard deviation (RSD) of 3.29 %, confirming the robustness of the sensor. The developed electrochemical method was successfully applied to detect TC in real environmental (river water, wastewater influent) and biological (urine) samples, showing excellent reproducibility and long-term stability.