Biomedical Engineering Reference
In-Depth Information
Figure 10.17c
and
Tables 10.10
and
10.11
show the increase in the affinity,
K
(
¼k
/
k
d
) with an
increase in the ratio of the fractal dimensions,
D
f
/
D
fd
. For the data shown in
Figure 10.17c
,
the affinity,
K
(
¼
k
/
k
d
) is given by:
4
:
95
0
:
837
K
ð¼
k
=
k
d
Þ¼ð
1
:
189
0
:
629
Þð
D
f
=
D
fd
Þ
ð
10
:
11c
Þ
The fit is good. Only three data points are available. The availability of more data points
would lead to a more reliable fit. The affinity,
K
, is very sensitive to the ratio of the fractal
dimensions,
D
f
/
D
fd
, as noted by the close to fifth (equal to 4.95) order of dependence
exhibited.
10.4 Conclusions
A fractal analysis is presented for the binding and dissociation (wherever applicable) of dif-
ferent gases on different biosensor surfaces. Both single- and dual-fractal analysis are used.
The dual-fractal analysis is used only when the single-fractal analysis does not provide an
adequate fit. Corel Quattro Pro 8.0 (1989) was used to fit the data. The fractal analysis is used
to analyze (a) the binding of LPG to zinc oxide films prepared by the spray pyrolysis method
onto a glass substrate (
Shinde et al., 2007
), (b) the binding and dissociation of different NH
3
concentrations in air to a sol-gel derived thin film biosensor (
Roy et al., 2005
), (c) binding of
NH
3
in air to an optical fiber-based evanescent sensor (
Cao and Duan, 2005
), (d) binding to a
nc-Fe
3
O
4
/Si-NPA humidity sensor (
Wang and Li, 2005
), and (e) the binding and dissociation
of different methanol concentrations in ppm) to a polyimide thin layer biosensor (
Manera
et al., 2006
).
The binding rate coefficients are quite sensitive to the degree of heterogeneity or the fractal
dimension on, for example, (a) the ZnO films sprayed on glass substrates for the detection of
0.2 volume percent LPG in the gas phase (
Shinde et al., 2007
), (b) the binding of NH
3
to a
sol-gel derived thin film biosensor where the influence of presintering temperature was ana-
lyzed (
Roy et al., 2005
), (c) the binding of NH
3
in air to a sol-gel derived thin film biosensor
where the influence of film thickness was analyzed (
Roy et al., 2005
), (d) during reversibility
studies on an ammonia sensor, and during studies that analyzed the influence of different car-
rier gases (N
2
, air, and argon) for the detection of ammonia by an ammonia sensor (
Cao and
Duan, 2005
), (e) during humidity sensing using a composite thin film by coating a nc-Fe
3
O
4
on a Si-NPA (
Wang and Li, 2005
), and (f) the binding of different concentrations of ppm
methanol in air to a polyimide thin layer biosensor (
Manera et al., 2007
). Similar results
are presented for the dissociation rate coefficients, wherever applicable.
The detection of different gases (analyte) present in air and in different carrier gases using the
different types of biosensors provides one with an idea of what is available in the literature
and what gases may be detected. Of course, these constitute only a small section of the
