Hexachloroiridate(IV) as a redox probe for the electrochemical discrimination of B-DNA and M-DNA monolayers on gold

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Switzerland), 2008-06, Vol.617 (1), p.71-77
• Main Authors: Dinsmore, Michael J., Lee, Jeremy S.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Biosensors; Biotechnology; DNA monolayers; Electrochemical impedance spectroscopy; Fundamental and applied biological sciences. Psychology; Hexachloroiridate; M-DNA; Methods. Procedures. Technologies; Various methods and equipments
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/j.jelechem.2008.01.018

This paper demonstrates the effectiveness of using the IrCl 6 2 - / 3 - redox couple to investigate DNA monolayers, and compares the potential advantages of this system to the standard Fe(CN) 6 3 - / 4 - redox couple. B-DNA monolayers were converted to M-DNA by incubation in buffer containing 0.4 mM Zn 2+ at pH 8.6 and studied by cyclic voltammetry (CV), impedance spectroscopy (IS) and chronoamperometry (CA) with IrCl 6 2 - / 3 - . Compared to B-DNA, M-DNA showed significant changes in CV, IS and CA spectra. However, only small changes were observed when the monolayers were incubated in Mg 2+ at pH 8.6 or in Zn 2+ at pH 6.0. The heterorgeneous electron-transfer rate ( k ET) between the redox probe and the surface of a bare gold electrode was determined to be 5.7 × 10 −3 cm/s. For a B-DNA modified electrode, the k ET through the monolayer was too slow to be measured. However, under M-DNA conditions, a k ET of 1.5 × 10 −3 cm/s was reached. As well, the percent change in resistance to charge transfer, measured by IS, was used to illustrate the dependence of M-DNA formation on pH. This result is consistent with Zn 2+ ions replacing the imino protons on thymine and guanine residues. The IrCl 6 2 - / 3 - redox couple was also effective in differentiating between single-stranded and double-stranded DNA during de-hybridization and rehybridization experiments.