Preparation, characterization and electrocatalytic properties of an iodine|lignin-modified gold electrode

Hydrolytic lignin (HL) was adsorbed from an aqueous/organic solution on bare and iodine-modified gold electrode. Subsequent electrooxidation of the lignin adsorbate generated redox-active quinone-based groups in the biopolymer structure, exhibiting high reversibility during potential cycling and fast electron transfer kinetics. The presence of the chemisorbed iodine layer on the supporting gold electrode had a pronounced effect on the electrochemical properties of the final modified electrode in terms of double-layer capacitance (Cdl) and the observed surface coverage (Γobs). The high electrochemical activity in connection with low Cdl made it possible to apply the Au|I(ads)|HL electrode as a fast-responding and sensitive electrochemical sensor for NADH. When tested in the amperometric mode at a constant potential of +0.4 V vs. Ag/AgCl, the modified electrode showed a linear current–concentration response over the range of 5–120 μM with a sensitivity of 2.39 nA μM−1 cm−2 and a detection limit of 1.0 μM (S/N = 3). Kinetic studies using the rotating disk electrode revealed that the mediated oxidation of NADH on the Au|I(ads)|HL electrode was limited by the second order reaction of the analyte molecules with o-quinone moieties with a rate constant of ca. 4.7 × 102 M−1 s−1 (CNADH → 0). The modified electrode showed high resistivity against fouling and retained ca. 65% activity after storage in phosphate buffer (pH 7.4) at room temperature for 1 week.