Biomedical Engineering Reference
In-Depth Information
1.2
1.0
c
0.8
0.6
0.4
b
a
0.2
0.0
0
5
10
15
20
25
Concentration (ppm)
FIGURE 1.18
Inhibitory effect of (a) Zn(II), (b) Be(II), and (c) Bi(III) ions on the chemileuminescence signal from alkaline phos-
phatase. Reprinted with permission from Kamtekar, S., Pande, R., Ayyagari, M.S., Kaplan, D.L., Marx, K.A.,
Kumar, J., Tripathy, S.K.(1996). Trace Analysis of Zn(II), Be(II), and Bi(III) by Enzyme-Catalyzed
Chemileuminescence.
Anal. Chem.
68:216-220. Copyright (1996) American Chemical Society.
1.2.2.1 DNA Interaction With Electropolymerized Conducting Polymers—
Immobilization by Electrostatic Interactions
Conducting polymers are an interesting class of polymeric materials that have been inves-
tigated extensively. Most often they have been synthesized by chemical means. However,
the monomers possess oxidation potentials that allow them to be electropolymerized to
form conducting polymers at an electrode surface (54,55). Electropolymerization is pre-
ferred over synthetic chemical approaches since electropolymerization can be thought of
as a more Green Chemistry polymerization method. It eliminates the use of many harsh
chemicals involved in the chemical polymerization methods, although some solvents such
as acetonitrile are still needed to solubilize certain monomers. Once polymerized, con-
ducting polymers exhibit extensive electron delocalization between multiple monomer
units along the polymer backbone. In all cases, the extent of electron delocalization and the
degree of planarity depend upon the 3-D chain conformation of the particular polymer.
Take as an example polypyrrole. Scanning tunneling microscopy studies of polypyrrole
have demonstrated the presence of semicrystalline domains and the presence of helical
chain structures within these domains (56). When oxidized to form a cationic species, indi-
vidual positive-charged 'defects' are created in the electronic structure, as shown in Figure
1.19. Evidence for these structures has been obtained by ESR spectroscopy (57). These pos-
itive-charged defect structures are capable of migration along the highly conjugated back-
bone, giving rise to substantial electrical conductivity. This can range from 10
3
to 10
3
/cm for electropolymerized polypyrrole, depending upon synthesis conditions (58).
