Biomedical Engineering Reference
In-Depth Information
In view of the well-known lysing effect of D-hemolysin on
biomembranes, we cannot exclude a similar effect on these
tBLMs, with membrane breakdown.
By replacing the lipoic acid residue of DPTL with a trichloro-
propyl-silane group, a supramolecule (DPTTC) was obtained,
which was self-assembled on a SiO
2
surface via the trichlorosilane
tether.
174
The SiO
2
layer was very thin (about 0.2 nm), being the
native oxide layer of a highly p-doped silicon wafer. Consequent-
ly, a tBLM obtained by forming a lipid monolayer on top of the
DPTTC monolayer tethered to the silicon wafer could be investi-
gated by EIS. The impedance spectrum of the resulting tBLM was
simulated by two RC meshes in series, with the omnipresent solu-
tion resistance
R
:
in series with them. The two RC meshes simu-
lated the oxide layer and the lipid bilayer tethered to it, respective-
ly. The functionality of this tBLM was tested by verifying the ion-
channel activity and ion selectivity of valinomycin and gramicidin.
Valinomycin decreases the resistance of the lipid bilayer in the
presence of KCl by three orders of magnitude, while the corre-
sponding capacitance remains practically unaltered. The highly
insulating properties of this tBLM have potential for biosensing
applications on semiconductor chips. A tBLM was also formed on
aluminum oxide (AlO
x
) sputtered on template-stripped gold.
175
An
anchor-lipid
was immobilized on the AlO
x
film, about 2.7 nm
thick, via Langmuir-Blodgett transfer. The anchor-lipid differs
from DPTL by the replacement of the lipoic acid residue with a -
P=O(OEt)
2
group for anchoring to the AlO
x
surface. A DPhyPC
monolayer was deposited on top of the anchor-lipid monolayer by
vesicle fusion. The natural porosity of the AlO
x
film, not visible at
AFM, was intended to enlarge the ionic reservoir beneath this
tBLM. The thin AlO
x
film on gold allowed an EIS and SPR char-
acterization of the system. The impedance spectrum of the tBLM
was fitted by a parallel combination of a resistance and a constant
phase element (instead of a capacitance), in series with the electro-
lyte resistance,
R
:
. The lipid bilayer had a resistance of about 17
M: cm
2
and a capacitance of 10 PF cm
-2
. The resistance is similar
to that of gold-supported tBLMs, but the capacitance is one order
of magnitude higher. This suggests that the tBLM adheres to some
extent to the pores of the AlO
x
layer. Incorporation of valinomycin
in the lipid bilayer decreases its resistance by more than one order
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