DISSERTATION

_____________________________________________________________ Results and Discussion
However, the selected potential values are not the only parameter that determine the efficiency
of the potential-assisted immobilization. Namely, after increasing the potential difference to
900 mV (pulse profile 0.5/-0.4 V) while keeping the pulse time at 10 ms no significant increase
in Rct is observed (data not shown) suggesting that the pulse duration needs to be adjusted with
respect to the selected pulse profile.
In order to demonstrate the effect of the pulse duration on the efficiency of immobilization,
different pulse times were investigated (1, 10, and 100 ms) keeping the total immobilization
time and the pulse profile constant (Figure 3.23). The total duration was 5 min and the 0.5/-0.2
V pulse profile was used. Decreasing the pulse time to 1 ms significantly increases the number
of cycles to 150,000 for the total immobilization time of 5 min. However, at 1ms pulse time the
lowest Rct was obtained among all tested pulse times. When the pulse duration is prolonged to
10 ms and the number of cycles is 15,000, a significant increase in the immobilization efficiency
is observed as shown in a substantial increase in Rct. By prolonging the pulse duration even
more to 100 ms, only 1,500 cycles are completed and Rct again drops to lower values.
Figure 3.23. Comparison of different pulse durations used for potential-assisted DNA
immobilization. ssDNA immobilization was performed for 5 min using the 0.5/-0.2 V pulse
profile with 1, 10 and 100 ms pulse duration. MCH passivation and EIS measurements
were performed as stated in Figures 3.7 and 3.8. Figure adapted from ref. 5 .
3.3 Importance of controlling the surface 58