Poly(methylene blue)-ternary deep eutectic solvent/Au nanoparticle modified electrodes as novel electrochemical sensors: Optimization, characterization and application

A new electrochemical sensor based on a nanocomposite formed by the electroactive redox polymer poly(methylene blue) (PMB) formed in a ternary deep eutectic solvent (DES) mixture, and gold nanoparticles (AuNP) was developed. The polymerisation of MB was carried out by potential cycling in ternary DES formed by choline chloride, ethylene glycol and fructose, containing 84% of the choline chloride: ethylene glycol mixture, in the presence of an acid dopant. The composition of the AuNP-chitosan dispersion was optimized by studying the effect of different concentrations of the nanoparticles and the polymer in the dispersion on the PMB film growth. The nanocomposite films obtained under different conditions were characterized by cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The nanocomposite with the best characteristics was also obtained in aqueous media for comparison. The nanocomposite-based sensor formed by AuNP and PMB in DES was used for determining ascorbic acid (AA) and 5-aminosalicylic acid (5-ASA) by fixed potential amperometry at +0.20 V in 0.10 mol L−1 KCl and at +0.40 V in Britton-Robinson buffer at pH 7, respectively. Limits of detection of 0.40 μmol L−1 and 0.064 μmol L−1 were obtained for AA and 5-ASA, respectively, with the PMBDES/AuNP/GCE. The sensor was successfully applied to determine both analytes in pharmaceutical samples.