Biomedical Engineering Reference
In-Depth Information
provided an accurate fitting to the experimental data at both low and high frequency for
the Fc-pepstatin/CNT/AuNP-modified electrode, as well as the subsequent binding event
with HIV-1 PR (Figure 4.32b). The binding of HIV-1 PR (10 pM) to the Fc-pepstatin/CNT/
AuNP-modified electrode led to an obvious change in
R
ct
. The Fc-pepstatin binding site
became almost saturated, since further increase in the HIV-1 PR concentration beyond this
level only effected a slight increase in
R
ct
. On the basis of this finding, the Fc-pepstatin/
CNT/AuNP-modified electrode together with 10 pM HIV-1 PR was used as a starting
point for testing the selected HIV-1 PR inhibitors. This result has demonstrated the pos-
sibility of using MWCNTs together with AuNPs and ferrocene-conjugate nanomaterials
in impedance spectroscopy for detecting HIV-1 protease and subsequent evaluation of the
enzyme inhibitors at picomolar levels.
Catalysts
The direct methanol fuel cell (DMFC) is commonly accepted as a potential material for
energy-generating devices because of its simple structure, liquid fuel, and environmen-
tal cleanliness [177,178]. However, the electrochemistry performance of DMFCs is greatly
hampered by the slowly oxidation rate of methanol. It is widely accepted that Pt surface
poisoning by CO-like species produced during methanol oxidation is the critical reason
for the low reaction rate. To solve this problem, Pt-based alloys (including PtRu and PtSn)
[179,180] and Pt/metal oxide composites (including Pt/SnO
2
and Pt/RuO
2
) [181-183] have
been used to increase the activity and CO tolerance of the catalysts. Song and Xiao [184]
utilized Pt, S, TiO
2
, and CNT composite as a catalyst in DMFC. As is generally accepted
that CO-like species can lead to Pt surface poisoning and reduce the rate of reaction, the
author introduced the Pt-S-TiO
2
/CNT electrode to improve the catalytic activity and CO
tolerance of Pt, as well as high electron and proton conductivities. The S-TiO
2
/CNTs were
prepared by an improved sol-gel and ethylene glycol reduction methods. The content of
sulfated TiO
2
in the S-TiO
2
/CNTs was 40 wt.%. The EIS studies were carried out in the
solution containing 1.0 M CH
3
OH and 1.0 M HClO
4
, as is shown in Figure 4.33.
From the Nyquist plot, the diameter of right semicircle is a measurement of the charge
transfer resistance, which is related to the reaction kinetics of charge transfer. The diame-
ter of right semicircle of Pt-S-TiO
2
/CNTs is smaller than that of Pt-TiO
2
/CNTs, indicating
1
2
Pt-S-TiO
2
/CNTs
Pt-TiO
2
/CNTs
35
30
25
20
15
10
5
2
1
0
0
10
20
30
40
50
60
Z'
(Ohm)
FIGURE 4.33
Electrochemistry Nyquist plot of impedance spectroscopy in 1 M CH
3
OH and 1 M HClO
4
solution at 0.4 V (sam-
ple: Pt-S-TiO
2
/CNTs and Pt-TiO
2
/CNTs). (From Song, H.,
J. Power Sources
, 195, 1610. With permission.) [184]
