Biomedical Engineering Reference
In-Depth Information
Li et al. (22) describe the syntheses and electropolymerization of a series of new 3-
alkylthiophene derivatives functionalized with the maleimide, azide, and anhydride.
Despite the nucleophilic or electrophilic nature of the reactive groups, the synthesized
thiophene monomers exhibit rather good polymerizability, and the reactive groups with-
stand the polymerization conditions and are correctly incorporated into the resulting elec-
troactive polymers. The reactivity of the pendant reactive groups of the resulting polymers
to attach biomolecules was also investigated.
Syritski et al. (23) have described a technique to monitor ion transport in electrochemi-
cally synthesized inherently conducting polymer poly(3,4-ethylenedioxythiophene)
(PEDOT) induced by the redox switching of the polymer. Mass changes were monitored
by an electrochemical quartz crystal microbalance and scanning electrochemical
microscopy. Direct evidence of the exchange capability anions entrapped in the elec-
tropolymerized with Cl anion from the solution was found.
There have been several reports on new conducting films or mediators in the literature.
Ngamna et al. (24) have studied the properties of poly(2-methoxyaniline-5-sulfonic acid)
(PMAS), a water-soluble polymer, as a potential mediator for biosensors. Poly( L -Lysine)
(PLL) was added to the PMAS to make it water insoluble. Uniform and stable films were
fabricated on ITO-coated Mylar using 0.1% (w/v) PMAS and 0.05% (w/v) PLL.
Immobilization of enzyme horseradish peroxidase (HRP) onto the PMAS/PLL film was
also investigated. Amperometric responses were observed upon the addition of hydrogen
peroxide. HRP-immobilized concentration was optimized, and a linear response range
between 0.01 and 0.1 mM H 2 O 2 was observed.
Similarly Kros et al. (25) have produced electroactive membranes and investigated the
stability of PEDOT and polypyrrole as the electroactive component in amperometric
biosensors. PEDOT and polypyrrole were first synthesized in the pores of a track-etch
membrane by immersing the membrane into a solution of the corresponding monomer
and ferric chloride. Amperometric and resistance measurements, FT-IR spectroscopy, ESR
spectroscopy, and scanning electron microscopy were applied in the investigations. The
results indicated that polypyrrole was unsuitable as an electroactive component.
However, PEDOT was found to be superior for long-term applications in these novel elec-
troactive membranes.
Interpenetrating networks (IPNs) of polypyrroles/hydroxyethylmethacrylate hydrogels
have recently been prepared for enzyme entrapment in amperometric biosensor applica-
tions (26). The amperometric responses for hydrogen peroxide oxidation were evaluated.
Measurements were made of the amperometric responses via H 2 O 2 oxidation for each
biosensor. The biosensors were found to be more stable and sensitive compared to the con-
ventional approach. Conducting polymers films and 3D gels will continue to play an
important role in biosensor design configurations in the future.
7.1.6
Dendrimers
Dendrimers are 3D tree-like macromolecules. Figure 7.4 is a cartoon representation of a
dendrimeric structure. In a dendrimer, the branches are interlinked polymerized chains of
molecules, each of which generates new chains, all of which congregate to a core. Each
radial concentric region that is formed around the core is called a generation.
Since dendrimers are chemically synthesized, each structure can be tailored or tuned for
specific applications. The advantages offered are structural homogeneity and porosity and
a controllable composition with multiple homogeneous chain ends.
Modification or selection of appropriate chain ends can lead to specific properties such
as electric charge. The entire dendrimer can function as a polyelectrolyte. Control of the
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