E-DNA sensors for convenient, label-free electrochemical detection of hybridization

We review the development of reagentless, electrochemical sensors for the sequence-specific detection of nucleic acids that are based on the target-induced folding or unfolding of electrode-bound oligonucleotides. These devices, which are sometimes termed E-DNA sensors, are comprised of an oligonucleotide probe modified on one terminus with a redox reporter and attached to an electrode at the other. Hybridization of this probe DNA to a target oligonucleotide influences the rate at which the redox reporter collides with the electrode, leading to a detectable change in redox current. Because all sensing elements of this method are strongly linked to the interrogating electrode, E-DNA sensors are label-free, operationally convenient and readily reusable. As E-DNA signaling is predicated on a binding-specific change in the dynamics of the probe DNA (rather than simply monitoring the adsorption of a target to the sensor surface) and because electroactive contaminants (interferents) are relatively rare, this class of sensors is notably resistant to false positives arising from the non-specific adsorption of interferents, and performs well even when challenged directly with blood serum, soil and other complex sample matrices. We review the history of and recent advances in this promising DNA and RNA detection approach.