Voltammetric sensors based on the electropolymerized phenolic acids or triphenylmethane dyes for the antioxidant analysis

Sensors with the electrochemically formed polymeric films as sensitive layer are of high interest in electroanalysis. Various monomers are successfully used for the sensors creation in particular compounds with phenolic moiety. Among them, natural phenolic acids and triphenylmethane dyes forming non-conductive polymeric coverages are of interest. Therefore, carbon nanomaterials are successfully applied as a platform for further electropolymerization of a suitable monomer. Phenolic acids (gallic and ellagic) and triphenylmethane dyes (thymolphthalein and aluminon) have been studied as monomers. Their potentiodynamic electropolymerization conditions (monomer concentration, supporting electrolyte type and pH, potential scan rate and range, number of cycles) on the surface of glassy carbon electrode (GCE) modified with multi- or functionalized single-walled carbon nanotubes and carbon nanofibers have been optimized. The electrode surface has been characterized with SEM, cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). Polymeric coverages exhibit porous structure with the shape of particles and their aggregates (folded structure with pores and channels in the case of polyaluminon) deposited on the surface of carbon nanomaterials. Modified electrodes have shown increase of the electroactive surface area and statistically significant decrease of the charge transfer resistance in comparison to bare GCE. The electrodes have shown a sensitive and selective response to different classes of the antioxidants (capsaicinoids, flavanones (hesperidin and naringin) and flavonols (rutin and quercetin)). The electrooxidation parameters of the antioxidants have been found. Under conditions of differential pulse voltammetry, the electrodes act as sensitive and selective sensors for capsaicinoids, flavanones and flavonols including possibility of the simultaneous quantification. The analytical characteristics obtained are improved vs. reported earlier for other electrochemical sensors. The practical applicability of the sensors has been demonstrated on food and plant samples. Thus, electropolymerized phenol-containing compound/carbon nanomaterial composites can be considered as a promising sensing platform in the antioxidants electroanalysis.