DISSERTATION

_____________________________________________________________ Results and Discussion
can be detected for dsDNA-modified electrodes (right column) than for the negative control
(left column). This shows that the 14-atom-long and flexible tether between the AO-moiety and
the enzyme allows for an at least partial intercalation of AO into dsDNA. AO-GOx is able to
intercalate into dsDNA and upon addition of glucose, the enzyme catalyzes the oxidation of
glucose to gluconolactone. The reduced enzyme transfers the electrons via a ferricyanide to the
electrode surface. The obtained catalytic current proves the presence of AO-GOx and with this
DNA hybridization.
Figure 3.56. Background corrected and normalized currents measured with ssDNA/MCU
(left) and dsDNA/MCU (right) electrodes exposed to AO-GOx solution upon addition of
glucose (40 mM) into the electrolyte solution. Chronoamperometric detection was
performed in 10 mM PB containing 450 mM K2SO4 and 1 mM ferricyanide at an applied
potential of +400 mV (vs. Ag/AgCl/3 M KCl). Preparation of electrodes was performed as
explained in Figure 4.55. Error bars represent standard deviation between measurements
(n = 3).
It should be noted that the absolute currents vary for different electrodes, however, the ratio
between the currents obtained for dsDNA and ssDNA-modified electrodes is rather constant
(see error bar for the left column). Therefore, following the developed procedure, well defined
DNA-modified surfaces are obtained that ensure a high signal-to-noise ratio. The conversion of
glucose by the enzyme and the continuous regeneration of the redox probe ensure a high signal
amplification. Thus, the novel sensing platform allows for the clear differentiation between dsand
ssDNA even at low surface coverages.
3.5 Intercalation as a DNA detection technique 103