Chemistry Reference
In-Depth Information
FIGURE 8.18
(a) CVs for dendrimer
8
/glucose-oxidase/carbon paste electrode, in pH 7.0
sodiumphosphate buffer (with 0.1MKCl) solution, with no glucose present (dotted line), and in
presence of 0.1M glucose (solid line). (b) Steady-state polarization curves of the dendrimers/
glucose oxidase/carbon paste electrodes in the presence of 25
m
M glucose. (c) Variation of the
steady-state current of the dendrimers/glucose-oxidase/carbon paste electrodes with glucose
concentration (at
รพ
350mV vs. SCE). Adapted from Losada et al. [42].
flexible silicon-containing branches (Figure 8.1) can serve to wire electrically the
enzyme [26,35,42].
In order to test the capability of ferrocenyl dendrimers
to act as
electron-mediating species, a study of the efficiency of dendrimer/glucose-oxidase/
carbon paste electrodes was carried out. The most significant results are illustrated in
Figure 8.18. Cyclic voltammograms of these carbon paste electrodes show an
electrochemical behavior indicative of enzyme-dependent catalytic reduction of the
ferricinium cations. The electrodes are clearly sensitive to small changes in glucose
concentration and display a good response over long periods of time. Dependence of
glucose response on dendrimer structure was examined. It has been found, from the
calibration curves and the results of Michaelis-Menten analysis that for equimole-
cular amounts of ferrocene moieties, octanuclear dendrimers
1
,
2
,
7
, and
8
, possessing
the longest organsilicon branches, mediate electron transfer more efficiently than the
relay systems based on tetranuclear dendrimers
2
and
8
1
and
7
. In addition, it is clear that
dendrimers
in which the ferrocenyl units are attached to the dendritic
framework through a two methylene flexible spacer are more effective at mediating
electron transfer between reduced glucose oxidase (GOx) and the carbon paste
electrode than the corresponding dendrimers of same nuclearity
7
and
8
1
and
2
. These results
