Biomedical Engineering Reference
In-Depth Information
of dependence between four and a half and five (equal to 4.71) on the fractal dimension,
D
f2
,
or the degree of heterogeneity that exists on the biosensor surface. This indicates that the
binding rate coefficient,
k
2
, is very sensitive to the degree of heterogeneity that exists on
the biosensor surface.
Wang and Li (2005)
recently analyzed the structural and capacitive humidity sensing pro-
perties of nc-Fe
3
O
4
/Si-NPA. These authors fabricated a composite thin film by coating nc-
Fe
3
O
4
on a Si-NPA. These authors report that this showed a regular hierarchical structure that
comprised of the pillar array in the micron dimension, and a nanoporous structure in the film
of Fe
3
O
4
. These authors point out that their humidity sensors were made based on the nc-
Fe
3
O
4
/Si-NPA system.
Wang and Li (2005)
further explain that several kinds of porous ceramic films have been
analyzed to help develop miniaturized and integrated humidity sensors (
Traversa, 1995;
Traversa et al., 1996; Nahar and Khanna, 1998; Qu et al., 2000
). In these cases,
Wang and
Li (2005)
point out that the solution of an appropriate substrate along with suitable morpho-
logy is the key to obtaining good sensing properties. For example,
Bisi et al. (2000)
report that
porous silicon fabricated by traditional anodization exhibits an integral sponge structure. This
apparently leads to a relatively lengthy response time.
Xu et al. (2005)
had reported earlier
that these response times could be improved by fabricating a micron/nanometer composite
structure, that is, the Si-NPA.
Wang and Li (2005)
report that magnetite is a traditional humidity sensing material. These
authors combined the properties of Fe
3
O
4
and the unique structure of Si-NPA. nc-Fe
3
O
4
was spin coated on Si-NPA, and this was then used as the humidity sensor.
Figure 10.14
shows the RH (relative humidity) increasing progress (binding), that is the time
response of the nc-Fe
3
O
4
/SI-NPA sensor (
Wang and Li, 2005
). A single-fractal analysis is
adequate to describe the “binding” kinetics. In this case the binding rate coefficient,
k
,is
equal to 0.000996
0.0938.
These authors point out that their nc-Fe
3
O
4
/SI-NPA sensor exhibits high sensitivity, a high
output signal intensity, and short response times.
0.000089, and the fractal dimension,
D
f
, is equal to 2.2716
Manera et al. (2007)
recently reported that polymer-based materials are being increasingly
used for gas applications. Polymers based on polyaniline, polythiophene, and polypyrrole
exhibit good transport and optical sensing properties at room temperature (
Rellas et al.,
1999; Nicolas-Debarnot and Poncin-Epaillard, 2003; De Melo et al., 2005
).
Manera et al.
(2007)
analyzed the sensing properties of polyimide thin films using the surface plasmon res-
onance (SPR) technique. These authors further indicate that polyimides are a class of organic
polymers that find applications in the area of microelectronics industry as films, varnishes,
adhesives, and matrix resins. This is because of their thermal and chemical stability as well
as their resistance to mechanical deformation at high temperature (
Ghosh and Mittal, 1996;
