Using PANI|In₂O₃ Composite for Indirect Electrochemical Detection of Diclofenac Sodium via Polyaniline Oxidation Peak

The unusual electrochemical, catalytic, and electronic properties of conductive polymer composites with metal oxides, owing to their synergistic effects, have attracted continued interest in the past decade for diverse applications in electroanalysis and electrocatalysis. Herein, we present a novel method for indirect determination of diclofenac (DCF) sodium using a PANI|In₂O₃ composite. A glassy carbon electrode (GCE) modified with a thin PANI|In₂O₃ layer was synthesized by cyclic voltammetry (CV) from a 0.3 M H₂SO₄ solution. Electrochemical impedance spectroscopy (EIS) measurements demonstrated that the PANI|In₂O₃ composite has a significantly higher R_ct value 624.0 Ω than the pure polyaniline film (14.0 Ω). CVs of bare GCE demonstrated the irreversible oxidation of diclofenac, characterized by an anodic peak at a potential of 0.6 V. Differential pulse voltammograms (DPVs) of DCF on a GCE|PANI electrode showed two pronounced anodic peaks (j_pa), which were responsible for the electrochemical oxidation of polyaniline (I) and oxidation of DCF (II). Modification with In₂O₃ dramatically decreased the current density of peak II by inhibiting the oxidation of DCF, and on the contrary, it increased the intensity of peak I tens of times. The GC|PANI|In₂O₃ electrode can be used as an electrochemical sensor for the determination of diclofenac at low concentrations between 1 × 10^–6 M to 1 × 10^–4 M, and j_pa – C_DCF has a correlation coefficient of 0.95. The GC|PANI|In₂O₃ material exhibited a limit of detection of 181 nM and a linear range of 1–100 µM for the DCF sensor.