Biomedical Engineering Reference
In-Depth Information
ing an enhanced robustness under acidic conditions and at high
temperatures (up to 100°C). To self-assemble a TEL monolayer
(which corresponds to a phospholipid bilayer) on the surface of the
coated gold, it is just sufficient to raise the level of the electrolyte,
on whose surface a TEL has been previously spread, above the
orifice level. The electrochemical properties and the stabilities of
the DPhyPC bilayers and of the TEL monolayers were verified by
EIS, upon fitting the data by a simple RC mesh. In fact, for practi-
cal purposes, the resistance
R
:
of the electrolyte could be neglect-
ed. The specific capacitances were 0.53 and 0.69 PF cm
-2
for
DPhyPC bilayers and 0.75 and 0.77 PF cm
-2
for TEL monolayers
resting on SbpA and SUM, respectively. Membrane resistances of
up to 80 M: cm
2
were observed for DPhyPC bilayers on SbpA. In
addition, lipid bilayers supported by SbpA exhibited a long-term
robustness of up to two days. Upon incorporating the voltage-
gated ion channel alamethicin at open circuit, the membrane re-
sistance dropped from about 80 M: cm
2
to about 950 : cm
2
,
whereas the capacitance did not change. Subsequent addition of
the inhibitor amiloride caused a modest increase in resistance. The
ion-channel activity of the ion carrier valinomycin and its selec-
tivity toward K
+
ions with respect to Na
+
ions were also verified.
In a different approach, the gold support was replaced by an
aqueous electrolyte.
235
In this case, the polyethylene plastic sheet
was folded in half and interposed between two compartments. An
orifice was punched in the two adjacent plastic sheets and a piece
of SUM was placed over the aperture, between the two sheets,
with the S-layer covered side turned toward the cis compartment
(
Fig. 22c
). Both compartments were filled to just above the aper-
ture with an aqueous electrolyte; a DPhyPC-(dipalmitoyl-
phosphatidic acid) lipid bilayer was then formed on the cis side of
the SUM by the same modified Langmuir-Blodgett procedure pre-
viously described. For comparison, an unsupported, conventional
BLM was also formed across the aperture using the same lipid
mixture and the same Langmuir-Blodgett technique. Conventional
BLMs and SUM-supported lipid bilayers showed a specific ca-
pacitance of 0.6-0.7 PF cm
-2
. The S-layer produced a stabilizing
effect on the lipid bilayer. Thus, the dielectric breakdown voltage
of the conventional BLM was 220 mV, whereas the SUM-
supported lipid bilayer did not rupture upon application of three
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