DISSERTATION

________________________________________________________________ Experimental Work
Potential-assisted ssDNA immobilization was performed right after the electrode preparation,
in an electrochemical setup using small volumes (100-200 μL) as shown in Figure 5.5.
Measurements were performed in the same solution as the immobilization via incubation at
room temperature using different potential pulse profiles with various pulse durations. The total
duration of the immobilization process depended on the desired DNA coverage. In order to
remove unspecifically bound DNA from the electrode surface, electrodes were rinsed after
modification with the immobilization buffer.
5.7.3 Passivation by means of incubation
Passivation via incubation was done by placing the electrode in an Eppendorf tube containing
500 μL of a thiol derivative solution (in 10 mM PB, 20 mM K2SO4). The electrode was sealed
within the tube to prevent solution evaporation and kept in a thermo-mixer (HTC BioTech,
Germany) at 37 ºC for 19 h unless stated otherwise. Afterwards, the electrode was thoroughly
rinsed initially with absolute ethanol and then water to remove any loosely bound MCH.
5.7.4 Potential-assisted passivation
Potential-assisted passivation was performed using a 0.5/-0.2 V pulse profile with 10 ms pulse
duration. It was done in the same electrochemical setup as used for potential-assisted
immobilization (Figure 5.5). Passivation by MCH was done in a 10 mM solution with 10 mM
PB and 20 mM K2SO4, while passivation by MCU was performed in a 1 mM solution with 10
mM PB and 20 mM K2SO4. Measurements were performed at room temperature for 1 min
unless specified otherwise. In order to remove loosely bound thiols from the electrode surface,
the electrodes were rinsed with absolute ethanol and then water after modification.
5.8 Preparation of DNA chips
Prior to use, DNA chips were cleaned with piranha solution (cc. H2SO4 with 30 % H2O2, 3:1)
for 10 min. After thoroughly rinsing with water, the chips were electrochemically cleaned in
H2SO4 as explained in Chapter 5.3. Modification of chips was done using potential-assisted
procedures for immobilization, passivation and desorption. The detailed experiment sequence
is explained in Section 3.4.2.
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