GCEs were polished with 1 μm and 0.3 μm alumina slurries, sonicated for 5 min in ethanol and rinsed with ultrapure water. GCEs were activated in 0.1 M PBS at Concanamycin A 7.0 using cyclic voltammetry over the potential range from − 1.0 to + 1.0 V at a scan rate of 100 mV/s. Prior to the modification, CNTs were functionalized in concentrated HClO4 + HNO3 (3:7, v:v) for 5 h in an ultrasonic bath. Then, CNTs were filtered and washed with water and dried in air. 1 mg of functionalized CNTs and 0.1 mg of ATO nanoparticles were then dispersed in 5 mL of chloroform and sonicated in an ultrasonic bath for 30 min. 5 μL of the composite was cast on the surface of the electrode and then chloroform allowed to evaporate. Afterwards, the resulting electrode denoted as ATONPs/CNTs/GCE was extensively washed with ultrapure water. The modified electrode (ATONPs/CNTs/GCE) was reactivated in 0.1 M PBS at pH 7.0 by cyclic voltammetry over the range from − 0.6 to + 0.8 V at a scan rate of 100 mV/s. A schematic illustration of the preparation of the proposed electrode is given in Scheme 1.