DISSERTATION

______________________________________________________________________ Introduction
Surface modification is the process of altering of the material surface by implementing
new and desired characteristics to it. Molecular self-assembly, a process of high-level intermolecular
orientation and organization without an outer force, is a powerful tool for surface
modification. Self-assembled monolayers (SAMs) have a wide range of applications 1 , but
whether they are used for regulation of the surface wettability, as a protection layer in corrosion
inhibition, or surface functionalization for binding proteins, DNA or cells, the main requirement
in all their applications is the control of the modification process. For example, depending on
the envisaged application, the desired coverage of the layer can significantly differ.
Furthermore, the choice of numerous parameters determines both the rate and the duration of
the modification process resulting in the desired coverage.
One of the biggest applications of SAMs is in the development of biosensors. DNA
hybridization detection and DNA sensors are becoming tremendously important in diagnostics
as a result of the continuous advancement of the Human Genome Project 2,3 . A DNA sensor
usually consists of a single stranded DNA grafted on an electrode surface, essential for the
recognition of the complementary target DNA present in a sample under investigation. The
recognition process occurs by hybridization between these two DNA strands, which is
converted into a signal by the transducer part of the DNA biosensor. Transduction of the signal
can be done by different techniques – optically, piezoelectrically and electrochemically. In
recent years the development of electrochemical DNA biosensors is in the spotlight, due to their
operating simplicity, possibility of miniaturization, and thus portability, and low cost, which
makes them very attractive for mass production. Continuous investigation of fundamental
issues, such as surface characterization, tailoring of interfaces and DNA recognition, along with
the progress in the field of microfabrication will lead to powerful, yet easy-to-use DNA
diagnostic products 4 .
The sensitivity and selectivity of DNA biosensors is highly dependent on the quality of the
prepared DNA sensing surface. In order to tailor the desired DNA sensing surfaces for
envisaged sensing platforms it is of utmost importance to understand processes occurring at the
electrode during the surface modification 5 . Only in this way properties of the surface can be
controlled in a reproducible manner on a desired time scale.
The following sections will present the current state of the art in the field of self-assembly and
DNA sensing, including some historical aspects related to the “molecule of life”.
2