Page 239 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

224 Principles and Methods

100 nm EHT = 10.00 kV Signal A = InLens Date : 22 Apr 2005
Meg = 264.46 KX WD = 6 mm Photo No. = 9641 Time : 17:09.07
Figure 6.3 Scanning electron microscopy (SEM) of platform of nan-
otube ensemble, in which the carbon nanotubes (CNTs) are verti-
cally oriented, periodically spaced, and readily accessible from the
top and the bottom. The multiwalled carbon nanotubes are 50 nm
in diameter, have walls of 3 nm thickness, and exhibit an exposed
length of 60 nm, a total length of 10 m, and a center-to-center
spacing of 100 nm between adjacent tubes.

published elsewhere [66]. This unique configuration has allowed the
specific covalent linkage of glucose oxidase, as well as NADH peroxidase,
at the nanotube tips and noncovalently to the sidewalls, with high cov-
erage (Figure 6.4). These electrodes have been used to characterize the
electrochemical profile of the immobilized enzymes by cyclic voltametry
and chronoamperometry measurements, attesting to the active state of
the enzymes after immobilization [56, 59, 67].

Figure 6.4 SEM of glucose oxi-
dase labeled with gold nanopar-
ticles, covalently linked to the
tips of highly ordered carbon nan-
otubes (CNTs). In the array, the
specific localization of the enzyme
to the tips is possible through
reaction with carboxyl groups
formed by acid etching, then acti-
100 nm vated by conventional EDC/NHS
chemistry (description in text).