Electropolymerized dyes as sensing layer for natural phenolic antioxidants of essential oils

Essential oils are widely used in aromatherapy, food and pharmaceutical industries. They contain a range of electroactive components in particular natural phenolic antioxidants like eugenol, trans-anethole, thymol, carvacrol, and vanillin. Therefore, sensitive voltammetric determination of these compounds is of practical interest. To solve this problem, sensors based on the electropolymerized dyes have been developed. Pyrogallol red, equimolar mixture of phenolic red and p-coumaric acid, thymolphthalein, bromocresol purple have been used as monomers for the formation of non-conductive coverages as confirmed by cyclic voltammetry data. Polymer layer improves the selectivity and sensitivity of sensors to target analytes. Layer-by-layer combination with carbon nanomaterials (single- or multi-walled nanotubes) has been applied to provide sufficient electroconductivity of the electrodes. The effect of electropolymerization conditions has been studied on the basis of target phenolic antioxidants response. The surface and electron transfer parameters of the developed sensors have been characterized by scanning electron microscopy, voltammetry, and electrochemical impedance spectroscopy. The sensors have been used in quantification of eugenol, trans-anethole, thymol, carvacrol, and vanillin under conditions of differential pulse voltammetry in Britton-Robinson buffer. The detection limits in the range of 0.037–0.730 μM have been achieved. The analytical characteristics of the sensors are comparable or improved vs. existing ones. The major advantage of the sensors developed is high selectivity of response in the presence of other natural phenolic antioxidants.