DISSERTATION

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Results and Discussion
of the Rct. Moreover, the presence of additional DNA strands leads to an additional steric
hindrance decreasing the access of the redox mediator and contributes to an increase in Rct with
a strong dependence on ssDNA coverage. When the coverage is very low, additional DNA
strands do not notably alter the surface architecture and the redox mediator access is negligibly
hampered. At high ssDNA coverage which is however low enough to allow for maximum
hybridization efficiency, the approach of the redox mediator to the electrode surface is more
likely affected.
Nevertheless, due to the low persistence length of ssDNA it behaves as random coil lying on
top of the thiol passivation layer (Figure 3.10) still preventing the access of the redox mediator
to the electrode surface. The structure of the formed dsDNA is more rigid as compared to the
one of the ssDNA, leading to a more upright orientation of the dsDNA and facilitating the
approach of the redox species. The degree of this influence depends on the length of DNA
strands. Short DNA is expected to exhibit only a little impact while longer DNA causes a more
significant change of the electrode architecture.
Figure 3.10. Interfacial changes upon DNA hybridization. DNA obtains a more upright
orientation due to the rigidity of the dsDNA. Furthermore, the amount of the negative
charge increases and an additional steric hindrance arises due to an increased number of
strands. Thiol passivation layer was intentionally not shown for better clarity.
3.2 Importance of knowing the surface 40