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