DISSERTATION

______________________________________________________________________ Introduction
carbonaceous materials and glass substrates was extensively investigated for the covalent
immobilization of DNA.
Figure 1.9. Schematic representation of DNA immobilization by physisorption via a)
bases, b) the phosphate backbone, c) covalent immobilization, d) chemisorption, and e)
biotin-streptavidin immobilization.
Chemisorption of thiol tethered DNA on noble metals (typically gold) occurs by the selfassembly
process that is explained in Section 1.1. This method is widely used for the
preparation of DNA sensors due to its simplicity and the formation of a relatively strong Au-S
bond (Figure 1.9, d). Biotin-streptavidin immobilization was also employed for grafting of
DNA. It occurs through two steps, namely biotinylation of either the surface or the DNA
followed by binding of the streptavidin-modified counterpart (DNA or surface, respectively)
and formation of a very strong biotin-streptavidin conjugate (Figure 1.9, e). Nevertheless, since
the surface is usually biotinylated by chemisorption of biotin-terminated SAMs, the strength of
the modification is determined by the Au-S bond strength.
1.3 DNA immobilization 17