Biology Reference
In-Depth Information
catalyzes the hydrolytic cleavage of the substrate, resulting in
the removal of the substrate strand along with the DNA bio-
bar code and the bound [Ru(NH
3
)
6
]
3
+
from the Au electrode
surface. The release of Ru(NH
3
)
3
6
results in lower electrochemical
signal of Ru(NH
3
)
3
6
confined to the electrode surface. Because each
nanoparticle carries a large number of DNA strands that bind to the
signal transducer molecule Ru(NH
3
)
3
6
, the use of DNA-Au bio-bar
codes enhances the detection sensitivity by 5 times, enabling the
detectionofPb
2
+
ataverylowlevel(1nM).TheDPVsignalresponse
of the DNAzyme sensor is negligible for other divalent metal ions,
indicating that the sensor is highly selective for Pb
2
+
. Table 4.4
summarizes recent works found in the literature for genosensors
makinguseofAu-NPsascarriersforotherNPsorotherelectroactive
species.
4.3.2
Detection Strategies Involving Direct Participation
of Au-NPs in the Generation of the
Electrochemical Signal
Other detection strategies involve direct participation of Au-
NPs in the generation of the electroanalytical signal used for
quantification of target DNA. These include the detection systems
based on Au-NPs dissolving, label-free electrochemical impedance
and conductimetric detection approaches, different methodologies
for signal enhancement by precipitation of silver or even gold onto
Au-NP-DNA conjugates and Au-NP enlargement strategies. Some
illustrative examples of these strategies are discussed below.
4.3.2.1 Detection based on Au-NPs' acidic or
electrochemical dissolving
This detection procedure is based on the oxidative dissolution of
the Au-NPs bound to DNA into aqueous Au ions followed by their
electrochemical sensing. Chemical dissolution of the Au-NP tags has
been mainly carried out with a HBr/Br
2
solution, this step being
followed by accumulation and stripping analysis of the resulting
Au(III) ions. Due to the high toxicity of the HBr/Br
2
solution, other
oxidation methods have been also employed.
