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 (C-dl) and the observed surface coverage (Gamma(obs)). The high electrochemical activity in connection with low C-dl made it possible to apply the Aul vertical bar I-(ads)vertical bar 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 mu M with a sensitivity of 2.39 nA mu M-1 cm(-2) and a detection limit of 1.0 mu M (S/N = 3). Kinetic studies using the rotating disk electrode revealed that the mediated oxidation of NADH on the Aul vertical bar I-(ads)vertical bar 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 x 10(2) M-1 s(-1) (C-NADH -> 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. (c) 2008 Elsevier Ltd. All rights reserved.