Biology Reference
In-Depth Information
tetroxide complexes, can be incorporated into DNA strands outside
the recognition sites or onto a secondary capture probe to be
measuredelectrochemicallyfordeterminationoftheamountofDNA
hybridization(Fig.14.2B(a)).Enzymereportertagshavebeenfound
usefulindetectionstrategiesduetothecatalyticsignalamplification
from substrate turnover, and have also been used as reporter labels
in magnetic-based DNA assays (Fig. 14.2B(b)). These have been
reported either as an enzyme-linked immunoassay or by directly
linkingthe enzymelabel to a secondary DNA probe.
14.2.4
Layer-by-Layer Immobilization Techniques
Thesequentialchargeinversionofalternatingpolycation/polyanion
solutions to form multilayers, known as layer-by-layer assembly, is
a simple and e
cient technique to form biologically active surfaces.
Severalstudieshaveusedthelayer-by-layertechniquetoimmobilize
DNA functionalized multiwalled carbon nanotubes (MWCNT) with
nanoparticles that result in effective electrochemical DNA sensors.
InonereportcovalentattachmentofAunanoparticlesandMWCNTs
was accomplished by first successively carboxylating the nanotubes
followed by cross-linking aminothiol groups to introduce thiol
functionalities [16]. Thiolated nanotubes were then adsorbed onto
a gold electrode followed by adsorption of gold nanoparticles. This
processwasrepeated6timesuntilafinallayerofgoldnanoparticles
wasusedtoadsorbprobeDNA.Inanotherconfiguration,cysteamine
wasfirstattachedtothegoldelectrodeandactedasamolecularglue
to covalently attach carbodiimide ester-activated COOH-MWCNT
followed by treatment with a cysteamine/AuNP solution [17].
The additional cysteamine would subsequently conjugate to the
activated MWCNT while its free sulfur group would attach to
the gold nanoparticles. This process was then repeated to create
an alternating MWCNT/gold nanoparticle film with a controlled
number of bilayers. A final layer of cysteamine/silver nanoparticles
and activated MWCNT was used to covalently attach NH
2
-DNA
probes to create a reproducible and stable biosensor. In both
these works, detection of the DNA was carried out by monitoring
the voltammetric detection of the DNA intercalator doxorubicin
following the hybridizationevent.
