Layer-by-Layer Combination of MWCNTs and Poly(ferulic acid) as Electrochemical Platform for Hesperidin Quantification

The electrochemical polymerization of suitable monomers is a powerful way to create voltammetric sensors with improved responses to a target analyte. Nonconductive polymers based on phenolic acids were successfully combined with carbon nanomaterials to obtain sufficient conductivity and high surface area of the electrode. Glassy carbon electrodes (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and electropolymerized ferulic acid (FA) were developed for the sensitive quantification of hesperidin. The optimized conditions of FA electropolymerization in basic medium (15 cycles from -0.2 to 1.0 V at 100 mV s^-1 in 250 µmol L^-1 monomer solution in 0.1 mol L^-1 NaOH) were found using the voltammetric response of hesperidin. The polymer-modified electrode exhibited a high electroactive surface area (1.14 ± 0.05 cm² vs. 0.75 ± 0.03 and 0.089 ± 0.003 cm² for MWCNTs/GCE and bare GCE, respectively) and decreased in the charge transfer resistance (21.4 ± 0.9 kΩ vs. 72 ± 3 kΩ for bare GCE). Under optimized conditions, hesperidin linear dynamic ranges of 0.025-1.0 and 1.0-10 µmol L^-1 with a detection limit of 7.0 nmol L^-1 were achieved, which were the best ones among those reported to date. The developed electrode was tested on orange juice and compared with chromatography.

Electrochemical Sensors Based on the Electropolymerized Natural Phenolic Antioxidants and Their Analytical Application

The design and fabrication of novel electrochemical sensors with high analytical and operational characteristics are one of the sustainable trends in modern analytical chemistry. Polymeric film formation by the electropolymerization of suitable monomers is one of the methods of sensors fabrication. Among a wide range of the substances able to polymerize, the phenolic ones are of theoretical and practical interest. The attention is focused on the sensors based on the electropolymerized natural phenolic antioxidants and their analytical application. The typical electropolymerization reaction schemes are discussed. Phenol electropolymerization leads to insulating coverage formation. Therefore, a combination of electropolymerized natural phenolic antioxidants and carbon nanomaterials as modifiers is of special interest. Carbon nanomaterials provide conductivity and a high working surface area of the electrode, while the polymeric film properties affect the selectivity and sensitivity of the sensor response for the target analyte or the group of structurally related compounds. The possibility of guided changes in the electrochemical response for the improvement of target compounds' analytical characteristics has appeared. The analytical capabilities of sensors based on electropolymerized natural phenolic antioxidants and their future development in this field are discussed.