Electrosynthesis of toluidine blue on Fe3O4 nanoparticles modified electrodes in a deep eutectic solvent for the electrochemical determination of neurotransmitter epinephrine

Abstract

The electrochemical methodology is important and challenging for rapid, simple, low-cost, sensitive, selective and reliable determination of biomolecules to diagnose and treat diseases. Our work presents the combination of the catalytic ability of a toluidine blue (TB) redox polymer and the important physical and chemical properties of Fe3O4 nanoparticles (Fe3O4NPs) to develop a new disposable sensor with advanced analytical performancecharacteristics for the determination of EP. Fe3O4NPs combined with poly(toluidine blue) (PTB) redox polymer film on a PGE support have been developed involving electropolymerization of TB in deep eutectic solvents (DES), which is a green solvent. Scanning electron microscopy (SEM) was used to evaluate the effect of the electrode composition on the surface morphology of the nanostructured PTB films, being correlated with the electrochemical characteristics observed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). It has been shown that combining Fe3O4NPs with PTB synthesized in DES improves the analytical properties of the sensor more than using each modifier individually due to synergistic effects. The analytical performance of PTBethaline-HCl/Fe3O4/PGE was evaluated for epinephrine (EP) reduction in the presence of an excess dopamine (DA) by DPV. The proposed sensor was used to determine EP using the reduction peak as a voltammetric signal instead of the oxidation peak usually employed to minimize possible interfering effects in biological samples. The developed sensor showed good response with high sensitivity (9.26 µA µM−1 cm−2), low detection limit (0.05 µM), wide linear range (0.19–20 µM), and excellent reproducibility (RSD 1.7 %) and repeatability (RSD 2.9 %). The practical applicability of the proposed sensor has been successfully tested for the quantification of EP in human serum and injection ampoule samples. This is a very promising analytical method for monitoring the level of EP in real samples.