DISSERTATION

______________________________________________________________________ Introduction
on a chip 4 . Since electrochemical detection results directly into an electric signal, there is no
need for an expensive transduction equipment 56 . Electrochemical transduction of the
hybridization event can be divided into direct and indirect DNA detection.
Direct DNA detection relies either on changes in the electrical properties of the interface caused
by hybridization or a direct oxidation of nucleic bases 48 . In the 1960s Paleček and coworkers
pioneered the work on direct reduction and oxidation of DNA at a mercury electrode 46 (Figure
1.14). Later, the oxidation of purine bases of DNA was achieved using carbon, gold, indium tin
oxide and polymer-coated electrodes 56 . Since guanine is the most redox active from all DNA
bases, its oxidation was studied the most. Even though this method is quite sensitive, its main
drawback are high background currents due to the high potentials required for direct DNA
oxidation.
Figure 1.14. Reduction (red) and oxidation (blue) sites of DNA bases for direct DNA
electrochemical detection. Figure adapted with permission from ref. 59 . Copyright (2012)
American Chemical Society.
Electrochemical impedance spectroscopy (EIS) was extensively used to follow changes in the
interface properties upon hybridization. The method measures the change in the faradaic
impedance in the presence of redox species resulting from the hybridization event. Different
strategies have been used for the amplification of the signal.
Indirect DNA detection can be achieved through the use of electrochemical mediators, redox
active indicators that non-covalently interact with dsDNA, labelling of the probe or target DNA
or using sandwich type assays (Figure 1.15).
1.4 Hybridization detection 23