Mechanistic and analytical insights onto the electrochemical sensing of ofloxacin using a functionalized carbon nanotube as electrode material

Ofloxacin, a widely used fluoroquinolone antibiotic, exhibits broad-spectrum activity by inhibiting bacterial topoisomerase enzymes. Due to its widespread presence in pharmaceutical products, biological matrices, and environmental samples particularly in aquatic systems, its accurate and sensitive detection is essential to ensure public health and environmental safety. In this study, we report the development of a novel, simple, selective, and highly sensitive voltammetric sensor for the determination of ofloxacin in pharmaceutical and real-world samples. A functionalized multi-walled carbon nanotube paste electrode (f-MWCNTPE) was employed for the electrochemical oxidation and quantification of ofloxacin using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Electrochemical measurements were conducted in 0.1 M phosphate buffer solution (PBS) at a scan rate of 0.1 Vs −1 , with a pulse period of 0.1 s and an accumulation time of 60 min. The sensor demonstrated a low detection limit of 10 × 10 −9 M and exhibited excellent selectivity in the presence of common interfering ions. The oxidation mode of ofloxacin molecule at the f-MWCNT's paste electrode was characterized as irreversible and adsorption controlled electrochemical process that involved the loss of 2 electrons from the piperazinyl part of ofloxacin molecule, yielding a distinct anodic peak at +0.85 V at pH 5. This redox reaction between ofloxacin molecule and electrode surface generated a measurable anodic current of 72 μA, the intensity of which was directly proportional to the concentration of ofloxacin in solution. It is pertinent to mention that with the increase in pH the peak current increased and reach to a maximum of 72 μA at pH 5 and then tend to decrease up to pH 10. Similarly, the potential gradually shifted from pH 2 to pH 10, which showed Nernstian behavior. Furthermore, the proposed sensor was successfully applied to the quantification of ofloxacin in pharmaceutical tablets and urine samples, achieving high recovery rates. Owing to its low cost, ease of fabrication, and renewability, this sensor presents a promising tool for routine monitoring of ofloxacin in diverse analytical contexts. • f-MWCNT based paste electrode was developed for electrochemical detection of ofloxacin. • Characterization reveals the surface modification of the MWCNTPE after functionalization. • Randle-Sevcik equation was used to determine the electrochemical surface area (9.8 cm 2 ) • The developed sensor enables rapid, sensitive and selective detection of ofloxacin. • Study offers valuable insights for scalability and commercialization with a LOD of 10x10 -9 M.