Biomedical Engineering Reference
In-Depth Information
is lower than that, about 0.8-0.9 PF cm
-2
, of solvent-free BLMs,
thus denoting the incorporation of alkane molecules, and its re-
sistance (~0.5 M: cm
2
) is also lower. The potential range covered
by this solid-supported bilayer before its breakdown is appreciably
wider than that at conventional BLMs, attaining values as high as
1.5 V. Since the metal surface can be rough after cutting, it can
induce defects in the overlying lipid bilayer. These sBLMs, de-
vised by Tien, were used by this author and coworkers
141
to carry
out a feasibility study of an antigen-antibody reaction. The hepati-
tis B surface antigen was incorporated into the bilayer and was
then allowed to interact with the corresponding monoclonal anti-
body in the bathing solution. The antigen-antibody interaction re-
sults in a notable linear decrease in the bilayer resistance with an
increase in the antibody concentration, up to 50 ng mL
-1
. These
sBLMs were also used with the aim of realizing electrodes for
biosensor applications.
141
In this connection, nonbiological lipo-
soluble molecules such as ferrocene, tetracyanoquinodimethane
(TCNQ) and tetrathiafulvalene (TFF) were incorporated in the
bilayer and employed as electron carriers between the electrode
and a hydrophilic redox couple present in the aqueous solution.
142
As an example, vinyl-ferrocene incorporated in a platinum-
supported lipid bilayer acts as an electron carrier between the elec-
trode and the peripheral, water-soluble protein ferri-cytochrome
c
.
143
The lipid bilayer provides a natural, biocompatible, surface
for cytochrome
c
binding, with a resulting enhancement both in the
equilibrium constant for cytocrome
c
adsorption on the bilayer and
in the electron transfer rate between electrode and protein, with
respect to a gold electrode in the presence of bipyridyl.
144
Fuller-
ene C
60
incorporated in a lipid bilayer supported by ITO was
shown to facilitate electroreduction of ferricyanide ion and, upon
illumination, to accelerate the photoinduced electron transfer from
electron donors in solutions, (e.g., water, EDTA), to the elec-
trode.
145
In general, two possible mechanisms may be responsible for
transmembrane electron transport between the electrode and a hy-
drophilic, lipid insoluble, redox couple present in the aqueous so-
lution:
(1) a redox reaction at the bilayer/water boundary between the
hydrophilic redox couple and a lipophilic redox couple pre-
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