New insights into the effect of pH on the mechanism of ofloxacin electrochemical detection in aqueous solution

Antibiotic contamination in water has become an increasingly serious problem that poses a potentially huge threat to human health. Ofloxacin (OFL) is a typical broad-spectrum quinolone antibiotic and is frequently detected in a wide variety of aquatic environments. Given its frequent contamination, the need for new electrochemical sensors to quickly and efficiently detect OFL in aquatic environments has attracted increasing attention. Solution pH is an important factor affecting the performance of electrochemical sensors. This work investigates OFL detection using graphene/glassy carbon electrodes (Gr/GCE) in phosphate-buffered saline across a range of pH (3-8). The molecular polarity analysis method was first used to reveal interactions between target contaminants and the electrode interface. The electrode properties and the polarity of OFL were studied using SEM, XPS, FT-IR spectrometry, zeta potentiometry and modelling calculation of molecular properties. Our results showed that OFL interacts with the surface of Gr/GCE via both hydrogen bonding and coulomb electrostatic forces. The electrical signal decreased more quickly in an alkaline than acidic environment, which was due to the differences between coulomb electrostatic and hydrogen bonding forces. These results also showed variations in the OFL peak current response under different pH conditions. Collectively, these findings provide a better foundation for the rapid identification of the optimal pH environment for the electrical analysis of contaminants like antibiotics in an aquatic environment.