The mechanism responsible for electron transport within layers of redox DNA anchored to electrodes has been extensively studied over the last twenty years, but remains controversial. Herein, we thoroughly study the electrochemical behavior of a series of short, model, ferrocene (Fc) end-labeled dT oligonucleotides, terminally attached to gold electrodes, using high scan rate cyclic voltammetry complemented by molecular dynamics simulations. We evidence that the electrochemical response of both single-stranded and duplexed oligonucleotides is controlled by the electron transfer kinetics at the electrode, obeying Marcus theory, but with reorganization energies considerably lowered by the attachment of the ferrocene to the electrode via the DNA chain. This so far unreported effect, that we attribute to a slower relaxation of water around Fc, uniquely shapes the electrochemical response of Fc-DNA strands and, being markedly dissimilar for single-stranded and duplexed DNA, contributes to the signaling mechanism of E-DNA sensors.
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