Biomedical Engineering Reference
In-Depth Information
paramagnetic properties at room temperature. The PB-modified nanoparticles were then
immobilized on the surface of glassy carbon electrode and applied to construct a sensor.
The sensor has potential to be applied as a mediator-less biosensor for the redox enzyme-
based reactions. The above studies indicate the versatile applications of magnetic sensing.
Thus magnetic biosensors are rapidly coming on-stream.
7.1.4
Smart Polymer Composites, Fabrics, and Textiles
A recent interesting area of biosensor design is the utilization of flexible substrates such as
plastic film, which can lead to shape-selective or wearable biosensors (15). In particular,
the combination of polymers with carbon nanotubes has been applied to form composites
with interesting properties. Reinforced epoxy composites have been fabricated with mul-
tiwalled nanotubes (16). Fangming et al. (17) used a coagulation method to induce better
dispersion of single-walled nanotubes (SWNTs) in a polymer matrix to produce
SWNT/poly(methyl methacrylate) PMMA composites. These composites had superior
elastic modulus, electrical conductivity, and thermal stability. Chang et al. (18) used in situ
polymerization technique to fabricate nanotube-polypyrrole nanocomposites with better
conductivity than polypyrrole alone. These were made by using ultrasonic energy to dis-
perse the nanotubes in the solvent and incorporate them into composites. In another study
(19) nanotube-based composites were fabricated using an electrospinning technique. The
addition of CNTs led to an improvement in strain-sensing capabilities of the sensors.
Smart textiles can be produced by in situ polymerization of the conducting polymers
such as polypyrrole or polyaniline in the presence of the textile. The simultaneous poly-
merization and deposition of the polymer on the fabric avoid the need for further pro-
cessing. The resulting fabrics are conductive and they have found applications in medical
monitoring. Brady et al. (15) report on the development and characterization of polypyr-
role-polyurethane foam-based material. Sawicka et al. (20) have prepared electrospun bio-
composite nanofibers and applied them in a biosensor for urea. Nanocomposite fibers of
urease and polyvinylpyrrolidone were first prepared by the electrospinning technique.
Fast response and sensitivity to low concentrations of urea and a versatile design were the
key advantages noted.
7.1.5
Conducting Films and Gels
Conducting materials such as polyaniline, polythiophene, and polypyrrole have been
previously quite frequently applied in biosensor design and investigations. The main advan-
tages of these materials are: (i) they possess the electrical conductivity similar to metals and
the mechanical properties of polymers; (ii) they form thin films that can be applied to entrap
biomolecules while minimizing the mass transfer resistance, thus leading to very small
response times; and (iii) electropolymerization can be applied to form the films. Thus, these
materials can easily be applied in the design of electrochemical biosensors.
New advances in conducting film applications have been reported including the
preparation of hybrid 3D structures. For instance, Ionescu et al. (21) report on the prepa-
ration of novel pyrrole-alginate gels. In situ electrochemical polymerization of the linked
pyrrole groups was carried out at 0.93 V, which led to the formation of a composite
polypyrrole-gel matrix. This gel was found to be superior in terms of enzyme retention as
well as increased alginate stability in the presence of phosphate anions unlike the natural
alginate gel. Thus, such conducting gels can be applied for enzyme retention and electro-
chemical reactions. Biosensors based on GOD-based composite alginate were also
developed by these authors.
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