Intercalative Stacking: A Critical Feature of DNA Charge-Transport Electrochemistry
In electrochemistry experiments on DNA-modified electrodes, features of the redox probe that determine efficient charge transport through DNA-modified surfaces have been explored using methylene blue (MB^+) and Ru(NH_3)_6^(3+) as DNA-binding redox probes. The electrochemistry of these molecules is studied as a function of ionic strength to determine the necessity of tight binding to DNA and the number of electrons involved in the redox reaction; on the DNA surface, MB^+ displays 2e^-/1H^+ electrochemistry (pH 7) and Ru(NH^3)_6^(3+) displays 1e^- electrochemistry. We examine also the effect of electrode surface passivation and the effect of the mode (intercalation or electrostatic) of MB^+ and Ru(NH_3)_6^(3+) binding to DNA to highlight the importance of intercalation for reduction by a DNA-mediated charge-transport pathway. Furthermore, in experiments in which MB^+ is covalently linked to the DNA through a σ-bonded tether and the ionic strength is varied, it is demonstrated that intercalative stacking rather than covalent σ-bonding is essential for efficient reduction of MB^+. The results presented here therefore establish that efficient charge transport to the DNA-binding moiety in DNA films requires intercalative stacking and is mediated by the DNA base pair array.
© 2003 American Chemical Society. Received 13 June 2003. Published online 2 October 2003. Published in print 1 October 2003. We are grateful to the National Institutes of Health (Grant GM61077) for their financial support of this research. In addition, we thank the Parsons Foundation for fellowship support (E.M.B.)
Published - jp030753i.pdf