Electrochemical Analysis of Ion Channels and Transporters in Pore-Suspending Membranes - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 278

LUVs to established pore-spanning membranes, which are partial-
ly ruptured and thus leaky, refurbished the insulating properties.
We demonstrated that the absolute value of the impedance of pore-
spanning lipid bilayers increased by one order of magnitude four
hours after LUVs were added. 35
Interestingly, not all pore-spanning membrane preparations
resulted in an impedance spectrum as shown in Fig. 4 A . In many
cases, two dispersions were monitored that changed during the
vesicle incubation process, as observed in the impedance spectra
shown in Fig. 5 A .
To analyse these data, three degenerate networks are conceiv-
able ( Fig. 5 C ). Two Ohmic resistors and capacitors, respectively,
account for the two observed dispersions in series to a resistor that
reflects the electrolyte resistance R el . Data analysis based on the
three networks provided very similar values for each parameter
and, hence, they cannot be distinguished. Over the course of an
incubation period of 22 hours, as indicated by the arrow in Fig. 5
A , the two dispersions merge into one. We hypothesize that, within
the first stage of bilayer formation, the LUVs fuse only partially
( Fig. 5 B ). This intermediate state of hemi-fused liposomes could
be modelled by two RC -elements in series to each other ( Fig. 5 B ),
characterising the electrical properties of the membrane interfaces.
( ii ) Impedance Analysis of Pore-Suspending Membranes on
Porous Alumina with Partially Opened Pore Bottoms
Despite the promising electrical properties and long-term sta-
bility of these pore-spanning membranes, they suffered from very
long formation times of up to 24 hours. Especially when prote-
oliposomes are applied, a fast preparation is desired, as some pro-
teins denature, thus losing their function within a few hours. We
assumed that the area where the sealing ring contacts the porous
substrate is crucial for current leakage. Thus, we altered the sur-
face of the porous substrates with a total area of 0.314 cm 2 in a
way that only a small fraction of the barrier oxide within the seal-
ing ring area is fully removed (0.079 cm 2 ), while the rest of the
pores remain sealed with alumina ( Fig. 6 ).