DISSERTATION

_____________________________________________________________ Results and Discussion
Figure 3.29. Nyquist plots with typical Rct values obtained by comparing the potentialassisted
immobilization method with immobilization performed by simple incubation or
supported by applying a constant potential. MCH passivation was done by incubation for
19 h at 37 °C.
Besides the ability of the potential-assisted immobilization method to tremendously accelerate
the immobilization kinetics and to achieve much higher DNA coverages in a shorter time as
compared to the incubation method or applications of constant potentials, a high reproducibility
of the surface modification needs to be attained. Figure 3.30 presents average Rct values
obtained with the potential-assisted immobilization method using different pulse profiles. In all
cases Rct values are obtained with a standard deviation below 5 %, showing that the developed
immobilization protocol leads to a highly reproducible surface modification. Thus, the
envisaged ssDNA surface coverage can be pre-selected by choosing the number of applied
potential pulse cycles.
Looking at the results presented in this chapter it can be concluded that understanding the
behavior of ssDNA in front of the electrode surface affected by the surrounding electrolyte and
the polarization of the electrode is essential for the development of highly reproducible DNAmodified
surfaces. The developed potential pulse-assisted immobilization strategy leads to
high-quality DNA-modified surfaces helping by this to overcome difficulties in DNA sensor
3.3 Importance of controlling the surface 65