DISSERTATION

________________________________________________________________ Experimental Work
is the real surface area of the electrode. In all experiments with the exception of multi-electrode
chip measurements 2 mm diameter gold electrodes were used having a geometrical surface area
of 0.0314 cm 2 and a real surface area calculated as explained in Section 5.3. The surface
coverage is obtained in mol/cm 2 .
Finally, to determine the amount of DNA molecules the following equation should be used:
where NDNA is DNA coverage obtained in molecules/cm 2 .
N DNA = Γ × N A (5.9)
5.11 Intercalation
Intercalation of AO-GOx was carried out at room temperature for 15 min by drop casting 10
µL of the intercalator solution (in 100 mM PB) on ssDNA/thiol or dsDNA/thiol-modified
electrodes. The electrode was subsequently rinsed with 10 mM PB containing 450 mM K2SO4
to remove unspecifically bound intercalator molecules.
Chronoamperometric measurements were performed in a 10 mM PB with 450 mM K2SO4
solution containing 1 mM ferricyanide that was purged with Ar for at least 30 min prior to
experiments. During measurements a constant potential of +400 mV (vs. Ag/AgCl/3 M KCl)
was applied and after stabilization of the background current 40 mM glucose was injected to
assure enzyme saturation. Measurements were done under argon atmosphere.
5.12 Methods
5.12.1 Electrochemical impedance spectroscopy
Impedance is a measure of the resistance of the system towards an alternating current and it
extends the concept of resistance to AC circuits. It is a complex function that can be represented
in two ways (Figure 5.6), namely by the real and the imaginary impedance components or by
the modulus and the phase shift:
Z = Z ′ + jZ ′′ (5.10)
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