Biomedical Engineering Reference
In-Depth Information
CNTs, CNx-MWCNTs have larger surface-active, group-to-volume ratio, thermal stability,
superb electrical and mechanical properties [163-165]. Several reports studied the electro-
catalytic behavior of CNx-MWCNTs toward the glucose oxidase (GOx). Deng and Jian [166]
investigated the direct electron transfer of GOx at CNx-MWCNT-modified electrode and
its applications. CNx-MWCNTs suspension (3.5
μ
L) was dropped on the prepolished GCE
surface and dried at room temperature. The EIS experiments were carried out with 0.1 M
KCl solution containing 5 mM K
3
[Fe(CN)
6
]/K
4
[Fe(CN)
6
]. The frequency range is between
10
-2
and 10
5
Hz, and the amplitude of the potential is 5 mV. The Nyquist plots are shown
on Figure 4.31.
In Figure 4.31, the bare GCE shows an electron-transfer resistance of about 2800
Ω
, which
is larger than the CNx-MWCNT-modified GCE. It proves that the CNx-MWCNTs could
act as a good electron-transfer interface. Then, when the GOx was coated on the bare
electrode, the resistance increased significantly, which proved that the bulky GOx mol-
ecules blocked the electron exchange between the redox probe and electrode surface. After
GOx was absorbed on CNx-MWCNT-modified GCE, the semicircle diameter in Nyquist
plot was lower than CNx-GOx-modified GCE. The author explained that it could also
accelerate the electron transfer between the electroactive sites embedded in enzyme and
electrode.
The nucleotide sequence of the HIV-1 genome1 reveals that the HIV-1 virus encodes
an aspartic protease (HIV-1 PR), an essential enzyme for virion assembly and maturation
[167]. The enzyme will be inactivated because of mutation or chemical inhibition, leading
to the production of immature, noninfectious viral particles [168]. The approach to assay
HIV protease has been developed both in vitro and in vivo, including applying polypro-
tein or oligopeptide substrates, utilizing gel electrophoresis, as well as introducing high-
performance liquid chromatography for ascertaining the presence of cleavage product
[169-171]. These methods can only detect the inhibitor in the micromolar range, whereas
only a nanomolar or lower range of such drugs can be used in HIV-1 therapy [172]. EIS is a
quite efficient and highly sensitive electroanalytical method that can provide direct detec-
tion of immunospecies by measuring the change in impedance. Besides the convenience
and operation simplicity, EIS provides a nondestructive method to characterize the electri-
cal properties at biological interfaces [173,174]. Another application in HIV-1 PR detection
3200
2400
1600
c
800
d
a
0
b
0
3000
6000
9000
12000
Z'
(Ohm)
FIGURE 4.31
EIS of bare (a), CNx-MWCNTs (b), GOx (c), and GOx/CNx-MWCNTs (d) modified by GCEs in 0.1 M KCl solution.
(From Deng, C.,
Biosens. Bioelectron.
, 25, 373, 2009. With permission.) [161]
