Biomedical Engineering Reference
In-Depth Information
the reduction current at
0.30 V (vs. Ag/AgCl) with a detection limit of 100 nM. This
biosensor format was also applied to the determination of lactate and glucose by using
CNT-HRP-lactate oxidase or CNT-HRP-glucose oxidase-modified GC electrode.
Xu et al. [38] developed a hydrogen peroxide biosensor based on attractive characteris-
tics of the CNT. The MWCNT was used for the coimmobilization of HRP and the methyl-
ene blue (MB) mediator onto GC electrode surface. The biosensor can detect the hydrogen
peroxide as low as 1
M.
Zhang et al. [39] reported on the electrochemical behavior of monolayer film of myo-
globin (Myb) strongly adsorbed on MWCNT-modified GC electrode. MWCNT in the
biosensor promoted the direct electron transfer between Myb and the electrode surface.
The Myb on MWCNT behaves as an enzyme-like activity toward the electrochemical
reduction of nitric oxide. The unmediated MWCNT-Myb biosensor can detect as low as
80 nM nitric oxide.
Wang et al. [40] reported on the direct electrochemistry of catalase (Ct) at SWCNT-
modified gold electrodes. A solution of SWCNT dispersed in DMF was cast onto the gold
electrode. A well-defined redox wave corresponding to Fe(III)/Fe(II) redox center of the
heme group of Ct adsorbate was observed with a reduction-peak potential at
0.41 V.
The peak current linearly increased with Ct-enzyme concentration with a detection limit
of 4
M. The catalase-SWCNT modified electrode displayed a characteristic catalytic
wave upon addition of hydrogen peroxide.
13.4
DNA Hybridization Biosensors Based on CNTs
The development of rapid and simple DNA hybridization biosensors is very important in
clinical diagnostics for detecting genetic and infectious diseases. The DNA biosensor is
composed of a nucleic acid recognition layer, which is immobilized onto a signal transducer.
The role of the nucleic acid layer is to specifically hybridize with a complementary sequence
of DNA. Electrochemical DNA biosensor produces meaningful electrical signal upon
hybridization of a target DNA onto the DNA biosensor immobilized with a complementary
single-stranded (ss-) probe DNA. Recent advances in the electrochemical DNA biosensors
have been reviewed by Gooding [41]. The analytical performances of DNA biosensors can
be greatly enhanced by the use of CNT. Such improvements can be attributed to the
enhanced electrocatalytic activities of CNT toward the target DNA guanine base or the prod-
ucts of enzyme label. In addition, CNT can be used as a carrier platform for the immobi-
lization of DNA and multiple labels because CNTs have high conductivity and extremely
high surface-area-to-weight ratio.
13.4.1
DNA Hybridization Detection Based on Electroactive Label
CNT-enhanced electrochemical DNA hybridization biosensor has been reported by Cai et
al. [42] based on the use of redox intercalator daunomycin. A carboxylated MWCNT-
coated on a GC electrode was covalently linked to an amino-functionalized probe DNA.
Complementary target DNA was then hybridized into the probe DNA-functionalized
MWCNT, and the redox label daunomycin was intercalated into the double-stranded
DNA formed on MWCNT as shown in Figure 13.4 (left).
The redox label daunomycin was detected by differential pulse voltammetry. This DNA
biosensor allowed the detection of DNA up to 100 pM.
