DISSERTATION

_____________________________________________________________
Results and Discussion
3.2 Importance of knowing the surface
In order to tailor optimal DNA-modified surfaces for the envisaged sensing platforms it is of
utmost importance to understand processes occurring at the electrode surface during the DNA
assay build-up. Only in this way, the properties of the surface can be controlled in a reproducible
manner. Electrochemical impedance spectroscopy is an excellent technique for this due to
which it gained a wide popularity in the field of bioelectroanalysis 70,71 . It is a non-destructive
technique allowing one to monitor surface modification without altering the system’s response.
Moreover, due to its sensitivity it is a great tool for following very subtle changes in the surface
architecture. EIS is a very informative technique that allows in depth investigation of processes
occurring at the electrified interface by sequentially following each step of the build-up of DNA
assays 5,72 .
Furthermore, to understand the behavior of DNA strands in front of an electrode surface we
need to investigate not only physico-chemical properties of the DNA itself but it is essential to
also observe the electrode and the surrounding solution as important components of the system.
Since the DNA is essentially a negatively charged polyelectrolyte (depending on the ionic
strength of the surrounding solution), the charge of the surface has a significant impact on the
behavior of DNA at the interface. Therefore, it is of great importance to know how the surface
is polarized (positive or negative) upon application of different potentials. Consequently, the
potential of zero charge (pzc) of the bare polycrystalline electrode was determined.
Additionally, the influence of the surface modification with DNA on the pzc was also
investigated.
3.2 Importance of knowing the surface 34