Biomedical Engineering Reference
In-Depth Information
(
a
)
(
b
)
(
c
)
(
d
)
Figure 11.14
Top-down and cross-sectional SEM images of NPG electrodes obtained
at er dealloying (A, C) a uniformly sputtered Au-Ag ilm and (B, D) a non-uniformly
sputtered Au-Ag ilm, in 70% (w/v) nitric acid at 38 C for 15 min. (Reprinted with
permission from ref [74])
area (A
geo
) and the area available for the immobilization of a macromol-
ecule (A
macro
), in that case cytochrome c, were measured. A
real
was 28 times
that of A
geo
and A
macro
was 40% of the A
real
. h is indicates that NPG has a
much higher surface area than l at electrodes and the size of some nano-
pores were inaccessible to cytochrome c, as a large macromolecule, due to
steric hindrances. A
macro
for non-uniform alloy was even smaller. However,
the surface available for immobilization of macromolecules was multiple
times of that available on l at electrodes.
Kai
et al.
directly grew 3D NPG onto a Ti substrate by the chemical
reduction of an Au precursor under a hydrothermal condition [75]. h e
morphology and composition of the fabricated NPG was characterized
by SEM, X-ray photoelectron spectroscopy (XPS), and energy-dispersive
X-ray (EDX) spectroscopy (Figure 11.15). h ey immobilized redox active
protein hemoglobin (Hb) onto NPG network as a supporting matrix
and studied the direct electrochemistry of Hb and catalytic reduction
of H
2
O
2
by Hb.
In another study, Li
et al.
[76] arranged a label-free amperometric
immunosensor for detection of human serum chorionic gonadotropin
(hCG) that is a glycoprotein hormone used as a marker for testicular and
ovarian cancers. h ey immobilized hCG on NPG foils and used hydroqui-
none (HQ) redox species as indicator.
h e outer surface of NPG could be covered with smart polymers
to construct a controlled-release system with potentially exceptional
