DISSERTATION

_____________________________________________________________ Results and Discussion
3.3 Importance of controlling the surface
The most popular strategy for the immobilization of thiolated molecules on gold surfaces is a
spontaneous formation of Au-S bonds via self-assembly achieved by a simple immersion of the
gold electrode into a solution containing a desired thiol 66 . This strategy is widely used for both
SAM formation of alkylthiols and immobilization of thiolated DNA. The aim of SAM
formation of alkylthiols is generally to achieve the highest possible coverage and to obtain
compact layers with a high blocking ability. On the other hand, desired DNA coverage depends
on the envisaged DNA detection strategy and it can range from low to high coverages 66,84,85 .
Nevertheless, in order to obtain high coverage of thiolated molecules long incubation times are
required, ranging from several hours to days 13-15 . In contrast, low DNA coverages can be
obtained in a short time, but with the drawback of significant variation of densities 67 .
Therefore, a new immobilization strategy needs to be introduced that allows to reproducibly
control the surface modification in a desired manner and what is equally important, in a very
short time. The new approach needs to eliminate the dependence on the spontaneous selfassembly
that is very long and lacks reproducibility. Thus, the possibility of surface control by
potential-assisted surface modification was investigated using both thiolated DNA and
alkylthiols as examples of intrinsically charged and uncharged molecules, respectively.
Furthermore, with the aim of using the envisaged potential pulse-assisted immobilization
method for the preparation of DNA arrays, this approach has to allow array modification with
multiple DNA probes. Due to the need for an electrochemical system (reference and counter
electrodes in addition to the chip working electrode) to perform potential pulsing and the size
of the individual electrodes on an array (usually μm dimensions) it is obvious that more than
one electrode of the array needs to be exposed to the solution used for modification. Therefore,
to prevent crosstalk between electrodes, each electrode needs to be cleaned prior to the
modification. Thus, potential pulse-assisted cleaning of Au modified surfaces was investigated
with the aim to regenerate Au surfaces within a very short time, while not causing any damage
to the surface.
3.3 Importance of controlling the surface 50