Electrochemistry of weakly adsorbed species: Voltammetric analysis of electron transfer between gold electrodes and Ru hexaamine electrostatically interacting with DNA duplexes

The Laviron formalism, developed for the case of strongly adsorbed species, is widely used for kinetic analysis of surface-confined electron transfer (ET) reactions and determination of ET rate constants k(s). However, its applicability and reliability for analysis of ET between electrodes and weakly adsorbed species is unclear. Here, we studied electrochemistry of Ru hexamine (RuHex) electrostatically interacting with double-stranded (ds) DNA tethered to gold electrodes through the alkanethiol linker. Electrostatic interactions between positively charged RuHex and negatively charged sugar-phosphate backbone of DNA are not strong and depend both on the solution ionic strength and the presence of RuHex in the bulk solution. In this work, electrochemistry of RuHex electrostatically bound to dsDNA strands was studied in the presence of 50 mu M RuHex by cyclic voltammetry and square wave voltammetry (SWV) and the values of k(s), were estimated by the Laviron and Komorsky-Lovric-Lovric methodologies, respectively. Direct comparative analysis of both procedures evidenced underestimation of the k(s) values obtained by the Laviron theory as compared to the Komorsky-Lovric-Lovric approach. Underestimation ranged between 40 and 50% and depended on the DNA surface coverage, being most pronounced at low surface concentrations of DNA, where the k(s) was maximal. The results evidence better suitability and reliability of SWV measurements in analysis of kinetics of ET reactions of weakly adsorbed species. 2013 Elsevier Ltd. All rights reserved.