DISSERTATION

________________________________________________________________ Experimental Work
to be conducted under saturation of the redox marker. That is, the method works under the
assumption that [Ru(NH3)6] 3+ exchanges all counterions screening the DNA.
Figure 5.10. Cyclic voltammogram of a bare gold electrode immersed in 10 mM PB
containing 20 mM K2SO4 and 100 μM [Ru(NH3)6]Cl3 in the potential window -0.4 to 0.1
V (vs. Ag/AgCl/3 M KCl) at 100 mV/s scan rate.
In order to measure the charge, a potential step is applied from a potential at which a negligible
reduction of the redox mediator is observed (0 V vs. Ag/AgCl/3 M KCl, Figure 5.10) to a
potential that corresponds to the diffusion limited current for the reduction of all surface
confined redox species (-0.4 V vs. Ag/AgCl/3 M KCl, Figure 5.10). Initially, the charge is
measured in a background solution without the redox marker, to obtain the double layer charge.
Subsequently, the measurement is repeated in the same solution containing additionally the
redox molecule [Ru(NH3)6] 3+ . The charge measured in this solution is given by the integrated
Cottrell equation:
Q = 2nFAD 1
2 C ∗
π 1 2
t 1 2 + Q dl + nFAΓ 0
(5.16)
where D is the diffusion coefficient of the redox molecule (cm 2 /s), C* is the bulk concentration
of [Ru(NH3)6] 3+ (mol/mL), Qdl is the double layer charge and the term nFAΓ0 is the charge
related to the reduction of surface confined species. Making an assumption that the double layer
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