Al2O3 microparticles immobilized on glassy‑carbon electrode as catalytic sites for the electrochemical oxidation and high detectability of naproxen: Experimental and simulation insights

Abstract

This work demonstrates that Al2O3 microparticles immobilized on a glassy‑carbon electrode (GCE) anticipate the electrochemical oxidation of naproxen in 150 mV and increases its oxidation current, resulting in a highly sensitive sensor. Considering their non-conducting nature, we suggest that Al2O3 microparticles act as adsorption sites that alter the electrochemical oxidation pathway of naproxen by adsorbing its intermediate(s) and facilitating the electron transfer at the GCE surface. Interestingly, the voltammetric results obtained for ibuprofen (presents similar chemical structure and electrochemical oxidation mechanism) indicated the same facilitated electron transfer that suggests that the interaction between naproxen (or ibuprofen) with Al2O3 microparticles occurs via the carboxylic group, which is removed after the first electron transfer according to the proposed mechanism. Molecular dynamics simulations showed stronger interaction of naproxen than ibuprofen with alumina sites which may explain the respective facilitated electron transfer. Moreover, a stronger interaction of a major electrochemical oxidation product of naproxen with alumina was confirmed by simulation and explains the electrode fouling occurred when more positive potentials (+1.4 V instead of +1.0 V vs. Ag/AgCl/KClsat) were applied for the naproxen amperometric detection. The alumina-modified GCE surface presented a detection limit of 12 nmol L−1 with a linear range between 50 and 500 nmol L−1 for naproxen determination (Edet = +1.0 V). These sensing characteristics are superior in comparison with electrodes modified with carbon nanotubes and their composites. Hence, a simpler protocol for electrode modification using a non-conducting material can provide a highly sensitive sensor for naproxen due to its catalytic properties facilitating the electron transfer between naproxen (or ibuprofen) and GCE.