Fabrication of electrochemical theophylline sensor based on manganese oxide nanoparticles/ionic liquid/chitosan nanocomposite modified glassy carbon electrode

In this study, the preparation of a glassy carbon (GC) electrode modified with chitosan/NH2-ionic liquid/manganese oxide nanoparticles (Chit/NH2-IL/MnOx) was described for electrocatalytic detection of theophylline (TP). First, chitosan hydrogel (Chit) was electrodeposited on the GC electrode surface at a constant potential (−1.5 V) in acidic solution. Then, the previously synthesized amine-terminated 1-(3-Aminopropyl)-3-methylimidazolium bromide ionic liquid (NH2-IL) was covalently attached to the modified electrode via glutaraldehyde (GA) as linking agent. Finally, manganese oxide (MnOx) nanoparticles were electrodeposited onto the Chit/NH2-IL film by potential cycling between −1.0 and 1.7 V in Mn(CH3COO)2·4H2O neutral aqueous solution. Electrochemical behavior of the modified electrode was evaluated by cyclic voltammetry (CV) technique. The charge transfer coefficient (α) and electron transfer rate constant (ks) for MnOOH/MnO2 redox couple were calculated to be 0.35 and 1.62 s−1, respectively. The resulting system brings new capabilities for electrochemical sensing through combining the advantages of IL and MnOx nanoparticles. The differential pulse voltammetric (DPV) results indicated the high ability of GC/Chit/NH2-IL/MnOx modified electrode to catalyze the oxidation of TP. DPV determination of TP in acetate buffer solution (pH 5) gave linear responses over the concentration range up to 120 μM with the detection limit of 50 nM and sensitivity of 804 nA μM−1. Furthermore, the applicability of the sensor for TP analysis in pharmaceutical samples has been successfully demonstrated.