Biomedical Engineering Reference
In-Depth Information
A tBLM consisting of a 3-mercaptopropionic acid (MPA)
tethered to gold, with a bilayer of the positively charged lipid di-
methyldioctadecylammonium bromide (DODAB) on top, was used
to incorporate gramicidin.
154
The lipid bilayer was stabilized by
electrostatic interactions with the spacer. To this end, a pH of 8.6
was used to completely deprotonate the MPA monolayer, and the
ionic strength of the solution was kept sufficiently low by using
1,1-valent electrolytes of concentration less than 50 mM. The ion-
channel activity of gramicidin was verified by EIS upon simulating
the lipid bilayer by a resistance and a Warburg impedance in se-
ries, and by a capacitance in parallel with the first two elements.
The Warburg impedance was introduced to account for cation dif-
fusion in the bulk aqueous phase. The same tBLM was used to
incorporate the 25 kDa
Clavibacter
ion channel (CAC), which
exhibits anion selectivity.
155
CAC incorporation decreases the re-
sistance of the lipid bilayer from 3 to 5 times. The conductivity
induced by CAC increases exponentially with potential, and linear-
ly with chloride or with CAC concentration. Lipid bilayers formed
on gold-supported alkanethiol monolayers Z-functionalized with
an amino group were found to exhibit a film thickness more than
twice that on alkanethiol monolayers Z-functionalized with a car-
boxyl group, by using SPR.
11
Combining surface plasmon fluores-
cence spectroscopy (SPFS) with SPR by fluorescently labeling the
lipid films, the fluorescence intensity of the lipid bilayer on the
NH
2
surface was found to be almost three orders of magnitude
higher than that on the COOH surface. It was concluded that
many adsorbed vesicles were present on the NH
2
surface.
Another procedure for preparing spacer-bilayer assembies on
electrodes consists of anchoring a polyethyleneoxy hydrophilic
spacer to a hanging mercury drop electrode via a terminal sulfhy-
dryl anchoring group by immersing the mercury drop in an ethanol
solution of the spacer for about 20 min.
156
After extracting the
spacer-coated mercury drop from the ethanol solution, it is slowly
brought into contact with a lipid film previously spread on the sur-
face of an aqueous electrolyte, by taking care to keep the drop
neck in contact with the lipid reservoir. This disposition allows a
free exchange of lipid material between the lipid reservoir on the
surface of the aqueous electrolyte and the spacer-coated drop. This
procedure gives rise to the formation of a lipid bilayer in contact
Search WWH ::
Custom Search