Flexible Potentiometric Sensor System for Non-Invasive Determination of Antioxidant Activity of Human Skin: Application for Evaluating the Effectiveness of Phytocosmetic Products

In contemporary bioanalysis, monitoring the antioxidant activity (AOA) of the human skin is used to assess stresses, nutrition, cosmetics, and certain skin diseases. Non-invasive methods for skin AOA monitoring have certain advantages over invasive methods, namely cost-effectiveness, lower labor intensity, reduced risk of infection, and obtaining results in the real-time mode. This study presents a new flexible potentiometric sensor system (FPSS) for non-invasive determination of the human skin AOA, which is based on flexible film electrodes (FFEs) and membrane containing a mediator ([Fe(CN)6]3–/4–). Low-cost available materials and scalable technologies were used for FFEs manufacturing. The indicator FFE was fabricated based on polyethylene terephthalate (PET) film and carbon veil (CV) by single-sided hot lamination. The reference FFE was fabricated based on PET film and silver paint by using screen printing, which was followed by the electrodeposition of precipitate containing a mixture of silver chloride and silver ferricyanide (SCSF). The three-electrode configuration of the FPSS, including two indicator FFEs (CV/PET) and one reference FFE (SCSF/Ag/PET), has been successfully used for measuring the skin AOA and evaluating the impact of phytocosmetic products. FPSS provides reproducible (RSD ≤ 7%) and accurate (recovery of antioxidants is almost 100%) results, which allows forecasting its broad applicability in human skin AOA monitoring as well as for evaluating the effectiveness of topically and orally applied antioxidants.