DISSERTATION

_____________________________________________________________ Results and Discussion
EIS was employed for label-free detection of DNA hybridization. Even though this technique
is very sensitive to surface modification, it is not yet sensitive enough to achieve the desired
sensitivity. On the other hand, the use of compounds that are able to intercalate into the DNA
helix is very promising. One of the main advantages of intercalators is that these molecules can
be used universally with any given DNA sequence. This significantly decreases the complexity
of the system and allows for the application in multiple probe DNA chips. Therefore, this
chapter focuses on the investigation of a new intercalation compound, an acridine orange based
intercalator (AO) conjugated with glucose oxidase (GOx) from Aspergillus niger.
Synthesis of a ferrocenyl labelled intercalation compound for the detection of double stranded
DNA (dsDNA) was reported recently 102 . However, this strategy is limited by low currents in
case of low dsDNA coverages due to the oxidation of the 1e - redox-species, i.e., the ferrocene
derivative. On the other hand, redox-enzyme conjugated intercalation compounds offer much
higher efficiency at low dsDNA coverages due to the intrinsic catalytic amplification by
catalytic redox-conversion of a specific substrate and thus the continuous recycling of a redox
mediator/redox probe by the enzyme. DNA hybridization detection schemes based on redoxenzymes
modified with an intercalation compound were previously reported 103,104 in which the
authors used the well-known biotin-streptavidin chemistry. By constructing an intercalator that
is covalently bound to an enzyme, one assay preparation step is avoided as compared to
previously described intercalator-enzyme conjugates 103,104 ) in the DNA detection scheme.
Figure 3.51. Scheme of the synthesized acridine orange-glucose oxidase intercalating
compound.
Since acridine orange is a well-established intercalator selective towards dsDNA 105,106 it was
chosen as a basis to synthesize an intercalator-enzyme conjugate. Glucose oxidase is a widely
3.5 Intercalation as a DNA detection technique 97