DISSERTATION

_____________________________________________________________ Results and Discussion
Rct of ssDNA/MCH-modified electrodes with the Rct of an electrode modified only with MCH
under the same conditions that were used for the passivation of the surface. When the incubation
is done only for 15 min a minor increase in Rct is observed as compared with the MCH-modified
electrode implying that a negligible amount of DNA is immobilized. Rct increases notably after
2 h of incubation, however, by prolonging the incubation time to 4 and 8 h the immobilization
kinetics drastically slows down, which is manifested in the EIS plots as a small additional
increase in Rct.
In order to design a potential-assisted immobilization method that will lead to a significantly
improved immobilization kinetics and the formation of well-defined and reproducible DNAmodified
surfaces, the influence of several parameters on the behavior of DNA in the vicinity
of the electrode surface needs to be taken into consideration (Figure 3.19). As it was shown
earlier (Section 3.2.2), the pzc shifts to more negative potential values due to the modification
of the electrode with DNA. This shift requires a careful selection of the applied pulse potentials
to obtain control of the immobilization process.
Figure 3.19. Scheme representing dominating parameters influencing the behavior of
DNA at the electrode surface.
Furthermore, in order to understand the behavior of DNA at the surface of a polarized electrode
we need to observe the potential profile at the electrode surface developed upon applying a
certain potential. By applying a potential more positive or negative with respect to the pzc, an
excess charge is created on the metal side of the interface. As a response a double layer is
3.3 Importance of controlling the surface 53