Figure 1.

To investigate the electron transfer kinetics of DNA duplexes, we designed redox-reporter-modified guanine-free, guanine-rich, and mismatch-containing constructs attached via one end to a mercaptohexanol monolayer on a gold electrode. As the redox reporter (labeled “R”), we use methylene blue, which is commonly used to monitor through-DNA electron transfer.^{16,17,19,20,22,35,36,43,51} To measure the rate of transfer fromsuch constructs, we use chronoamperometry, an approach that determines electron transfer kinetics with improved precision than can generally be achieved by the previously employed voltammetric techniques.⁵² Shown, for example, are current decays measured for a 16-base DNA sequence in its single- and double-stranded forms. Fitting these to a single-exponential decay returns k_app = 150 ± 3 s⁻¹ for the single-stranded constructcontaining only adenine and thymine and k_app = 2.8 ± 0.9 s⁻¹ when its complement is added (at 100 nM) and the system is allowed to hybridize. (The “error bar” intervals quoted for these numbers as well as those reported or illustrated elsewhere in this paper reflect 95% confidence intervals estimated from replicate measurements conducted on 12 independently fabricated electrodes.)