DISSERTATION

_____________________________________________________________ Results and Discussion
electrostatically, a maximal hybridization efficiency of ideally 100 % is obtained providing a
sufficient concentration of tDNA. Therefore, an increase of the ssDNA coverage leads to an
increase in the hybridization yield and in the current signal obtained from labelled tDNA
(observed for DNA immobilization up to 2 min). However, further increase of the ssDNA
concentration causes a steric and electrostatic hindrance depending on the ionic strength
towards the hybridization process and the efficiency of hybridization decreases leading to a
lower signal. Therefore, for the employed detection scheme (hybridization with Fc-tDNA, 20-
mer probe DNA) the optimal ssDNA coverage is around 2-3 × 10 12 molecules/cm 2 , achieved
by immobilization of ssDNA for 2 min using the developed potential-assisted immobilization
method.
Figure 3.47. a) CV characterization of the surface during sensor preparation, and b)
FSCV measurements before and after hybridization of the ssDNA/MCU-modified electrode
with Fc-tDNA. ssDNA immobilization: 10 mM PB, 450 mM K2SO4, 1 µM DNA; p.a.
immobilization (0.5/-0.2 V vs. Ag/AgCl/3 M KCl, 10 ms pulse duration), 2 min. MCU
passivation: 10 mM PB, 20 mM K2SO4, 1 mM MCU (30 % ethanol), 0.5/-0.2 V vs.
Ag/AgCl/3 M KCl (10 ms), 1 min. CV and FSCV measurements were performed as
explained in Figure 3.46.
This chapter demonstrates that using the developed potential-pulse assisted immobilization
technique DNA sensor preparation can be done in as little as 3 min depending on the desired
DNA coverage. Compared to the standard sensor preparation praxis where surface modification
3.4 Potential-assisted preparation of DNA sensors 89