Electrochemical determination of fisetin using gold electrodes modified with thiol self-assembled monolayers

Abstract

The electro-oxidation of fisetin (FIS) at gold electrodes modified with self-assembled monolayers (SAM) is studied in 15% dimethylsulfoxide +85% phosphate buffer solutions of different pH using cyclic and square wave voltammetries. Gold electrodes were modified with 2-mercaptoethanesulfonic acid (2-MES) and 4-mercaptophenol (4-MP). Both modified electrodes were characterized by reductive desorption, electrochemical impedance spectroscopy, contact angle measurements, and by the determination of the apparent surface pKa.The FIS first oxidation peak showed an electrode process controlled by diffusion at 2-MES modified gold electrodes, while the electrode process showed a diffusion/adsorption mixed control at 4-MP modified gold electrodes. Square wave voltammetry was used to perform the FIS quantitative determination at both modified electrodes using the commercial reagent. Calibration curves were linear in the concentration range from 1×10−7 to 1×10−4M and from 1×10−6 to 1×10−5M for 2-MES and 4-MP SAM modified electrodes, respectively. Limits of detection for a 3:1 signal to noise ratio were 5×10−8M (14.3ppb) and 5×10−7M (143ppb) for 2-MES and 4-MP modified electrodes, respectively. The reproducibility and the repeatability were 2.2% and 0.5% for 2-MES SAM modified electrodes, and 1.6% and 1.3% for 4-MP SAM modified electrodes, respectively.