DISSERTATION

_____________________________________________________________ Results and Discussion
only a slightly higher Rct value is observed. Furthermore, the resulting blocking of the electrode
surface is much lower than in the case of potential pulse-assisted DNA immobilization (Figure
3.28).
Figure 3.28. Comparison of the potential pulse-assisted immobilization method with
immobilization at constant potentials. ssDNA-modified electrodes were characterized
using a) EIS and b) CV. ssDNA-modified electrodes were obtained by potential-assisted
DNA immobilization using the 0.5/-0.2 V pulse profile with 10 ms pulse duration and by
applying a constant potential of -0.2 V or 0.5 V vs. Ag/AgCl/3 M KCl for 15 min. ssDNA
immobilization was performed in 10 mM PB with 450 mM K2SO4 and 1 µM ssDNA. EIS
measurements were performed as stated in Figure 3.7. CVs were performed in 10 mM
PB, 20 mM K2SO4 containing 5 mM of K3[Fe(CN)6] and K4[Fe(CN)6] at 100 mV/s scan
rate.
Finally, ssDNA/MCH-modified electrodes obtained by DNA immobilization using the
potential pulse-assisted method (0.5/-0.2 V vs. Ag/AgCl/3 M KCl, 10 ms pulse duration) or
immobilization supported by a constant positive potential (0.5 V vs. Ag/AgCl/3 M KCl) were
compared (Figure 3.29). The total immobilization and passivation times were kept constant. As
expected, the Rct value obtained by applying 0.5 V during immobilization is comparable to the
Rct value obtained for immobilization performed by a simple incubation. Furthermore, this
amount is significantly lower as compared to the potential-pulse assisted immobilization, which
additionally supports the suggested mechanism behind the developed approach.
3.3 Importance of controlling the surface 64