Biology Reference
In-Depth Information
signal DNA labeled on the surface of Au-NPs. In order to amplify
the detection signals, the Au-NPs were also modified with CdS-NPs.
Since a single Au-NP could be loaded with hundreds of signal DNA
probe strands, a significant amplification for the detection of target
DNA was achieved. The hybridization events were monitored by
measuring the Cd ions dissolved from the hybrids using differential
pulse voltammetry (DPV). The peak current values increased with
the target DNA concentration in the range 1.0
×
10
−
14
to 1.0
×
10
−
15
M was achieved. Two-
base mismatched sequences showed weaker peak current and non-
complementary sequencesgave no response at all.
Another recent approach [51] consisted of the construction
of a DNA sandwich electrochemical biosensor based on the use
of PbS-NPs attached to AuNPs/bio-bar code-modified magnetic
microbeads (MBs). The magnetic carriers containing PbS-NPs
labeled DNA probe were immersed in an electrochemical cell
containing 1.0 M HNO
3
and the released Pb
2
+
was measured by
anodic stripping voltammetry (ASV) at a mercury film electrode
(MFE). The target DNA gave a linear response in the range from
2.0
×
10
−
14
Mto1.0
×
10
−
12
M, with a detection limit of 5.0
×
10
−
15
M.
Similar detection strategies involve immobilization of DNA-
modified Au-NPs onto the working electrode surface through
hybridization, and the use of molecules binding to DNA as
electrochemical labels. As an example, Miao
et al.
[52] described a
sensing strategy for the detection of glutathione in fetal calf serum
based on the use of two Au electrodes and two complementary
oligonucleotides (Fig. 4.9). The surface of one AuE is modified
with one of the two oligonucleotides and then immersed in the
glutathione solution where, due to the ligand release effect, the
oligonucleotides are replaced by glutathione. When the second AuE
is immersed in the solution, the released oligonucleotide molecules
are immobilized onto this electrode surface. Then, Au-NPs modified
withthecomplementaryoligonucleotideareaddedandimmobilized
ontothiselectrodesurfacethroughhybridization.Largenumbersof
[Ru(NH
3
)
6
]
3
+
are then localized onto the electrode surface via the
electrostatic interaction between the electrochemical species and
oligonucleotide molecules. Since the Au-NPs amplify the detection
10
−
13
, and a detection limit of 4.2
×
