DISSERTATION

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Results and Discussion
3.1 Importance of preparing the surface. Criteria for cleanliness
Building of the automatic polishing machine was the author’s idea. The machine was
constructed by Dr. Kirill Sliozberg. Optimization of the mechanical cleaning procedure was
done by the author.
Even though the surface preparation is cardinally important for the quality and reproducibility
of the measurements especially in the field of biosensors and self-assembly, it is often
underestimated and neglected. Due to the nanoscale size of the DNA strands and its charge,
surface architecture is a parameter that can significantly increase the sensitivity of a DNA
sensor 68 . Depending on the surface pDNA loading can be higher or lower.
Even though the interest of the thesis was not to investigate the influence of the surface
roughness and the size of the furrows on the biosensor performance, special attention was given
to the surface cleaning with the aim to improve the reproducibility of measurements. The
preparation of electrodes consisted of several steps:
- Mechanical cleaning using an automatic polishing machine
- Electrochemical cleaning in H2SO4
- Characterization of the surface by electrochemical impedance spectroscopy (EIS)
- Characterization of the surface by cyclic voltammetry (CV)
By reproducibly preparing the surfaces using an automatic polishing machine (polishing setup
and procedure are explained in Section 5.3) the quality of the prepared electrodes was
significantly improved in comparison with a previously used manual polishing procedure
(Figures 3.1 and 3.2). Moreover, a reproducible roughness was achieved as one of prerequisites
for minimal signal deviation between experiments. This allowed exclusion of the surface
properties as one of the possible parameters affecting the already complex results.
3.1 Importance of preparing the surface. Criteria for cleanliness 30