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Biophysical Journal 84:3218-3225 (2003)
© 2003 The Biophysical Society

AC Impedance Spectroscopy of Native DNA and M-DNA

Yi-Tao Long * {dagger}, Chen-Zhong Li * {dagger}, Heinz-Bernhard Kraatz * and Jeremy S. Lee {dagger}

* Department of Chemistry, University of Saskatchewan, Saskatoon, SK, Canada S7N 5C9; and {dagger} Department of Biochemistry, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5

Correspondence: Address reprint requests to Heinz-Bernhard Kraatz, Dept. of Chemistry, University of Saskatchewan, 10 Science Pl., Saskatoon, SK, Canada S7N 5C9; or Jeremy S. Lee, Dept. of Biochemistry, University of Saskatchewan, 107 Wiggins Rd., Saskatoon, SK, Canada S7N 5E5.

Monolayers of thiol-labeled DNA duplexes of 15, 20, and 30 basepairs were assembled on gold electrodes. Electron transfer was investigated by electrochemical impedance spectroscopy with Fe(CN)63-/4- as a redox probe. The spectra, in the form of Nyquist plots, were analyzed with a modified Randles circuit which included an additional component in parallel, Rx, for the resistance through the DNA. For native B-DNA Rx and Rct, the charge transfer resistance, both increase with increasing length. M-DNA was formed by the addition of Zn2+ at pH 8.6 and gave rise to characteristic changes in the Nyquist plots which were not observed upon addition of Mg2+ or at pH 7.0. Rx and Rct also increased with increasing duplex length for M-DNA but both were significantly lower compared to B-DNA. Therefore, electron transfer via the metal DNA film is faster than that of the native DNA film and certain metal ions can modulate the electrochemical properties of DNA monolayers. The results are consistent with an ion-assisted long-range polaron hopping mechanism for electron transfer.






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Copyright © 2003 by the Biophysical Society.