Biomedical Engineering Reference
In-Depth Information
Ru(bpy)
3+
G
e
−
Intercalation
e
−
Gox
Ru(bpy)
2+
NH
NH
O=C
O=C
O=C
O=C
N
H
N
H
FIGURE 13.4
Carbon nanotube electrode array for the detection of DNA hybridization. Left: use of electroactive interaction
compound. Right: use of Ru(bpy)
3
2+
a mediator for the oxidation of guanine base.
Similarly, SWCNT-based DNA biosensor has been reported in connection with the use
of electroactive ferrocene label [43]. In the biosensor, single-stranded probe DNA was
covalently linked to the carboxylated SWCNT aligned on a gold electrode. A ferrocene-
labeled complementary target DNA was then hybridized with the probe DNA on an elec-
trode to produce a reversible cyclic voltammogram of ferrocene.
13.4.2
DNA Hybridization Detection Based on Guanine Oxidation
Wang group reported on an electrochemical DNA hybridization biosensor based on the
guanine oxidation. High surface area of CNT-modified electrode has been shown to per-
mit the adsorptive accumulation of the guanine and greatly enhance the sensitivity of the
electrochemical detection of DNA, which permits a label-free DNA analysis [44]. A simi-
lar enhancement of the guanine oxidation in DNA was reported by Pedano and Rivas [45].
The CNT paste electrode was suitable for adsorptive stripping potentiometric measure-
ment of trace levels (ng/L) of nucleic acids.
Similarly, an array of vertically aligned MWCNT with Ru(bpy)
3
2+
-mediated guanine oxi-
dation has been shown useful for ultrasensitive detection of DNA hybridization [46] as shown
in Figure 13.4 (right). The hybridization of subattomole DNA targets was detected by this
method, showing several orders of magnitude improvement in sensitivity compared to the
conventional methods where the DNA was immobilized using self-assembled monolayers.
13.4.3
DNA Hybridization Detection Based on Enzyme Label
In general, enzymes generating electroactive products are widely used as amplification
labels in the assay of DNA hybridization or specific antigen-antibody interaction. Wang
group [47] reported on the use of functionalized CNTs as carriers for multiple enzyme
labels for electrochemical DNA hybridization detection and immunosensing. In these
