Biology Reference
In-Depth Information
Figure 7.1.
Schematic representation of different DNA immobilization
strategies: (a) covalent attachment of ODN thiols or disulfides by self-
assembly onto gold surfaces resulting in Au-S bond formation; (b) imm-
obilization by adsorption relies on electrostatic interactions between
negatively charged sugar-phosphate backbone of DNA and positively
charged electrode surface, and/or the interaction with the nucleobases; (c)
a
nity binding of biotinylated oligonucleotides onto streptavidin modified
electrode surfaces.
(Fig. 7.1). The immobilization is essential for the development of
a robust biosensing interface and maintaining control over the
immobilization step is necessary to ensure proper orientation,
accessibility, and stability of the capture strands on the sensor
surface. We begin our review with an overview of immobilization
strategies that havebeen successfully employed in DNA biosensors.
7.2.1
Covalent Attachment
A number of covalent immobilization methods have been reported.
Amongthem,theself-assemblyofthiolordisulfidecontainingODNs
onto a gold surfaces is probably the most popular immobilization
strategy, as shown in Fig. 7.1. Thiols react with Au resulting in
the formation of a gold-thiol linkage as indicated in the following
equation:R-SH
+
Au
→
R-S-Au
+
e
+
H
+
.
For example, Mirkin has demonstrated that Fc-ODN films
attached through a gold-thiol linkage display reversible redox
behavior[7].Inaddition,thesurfacecoverageofaDNAprobecanbe
controlledusingalkylthioldiluents,asshowninFig.7.2.Thesurface
coverage of a ss-DNA capture strand has a dramatic effect on the
hybridization e
ciency since su
cient space between the capture
