Biomedical Engineering Reference
In-Depth Information
peaks of these mixtures yield well-formed single peaks at mole
fractions close to 100% of any of the two pure components,
whereas two partially overlapping peaks are observed at interme-
diate mole fractions. This indicates that phase separation takes
place over an intermediate mole fraction range. No tBLMs were
observed by EIS when trying to fuse vesicles on tethered mixed
monolayers with thiolipid mole fractions below this intermediate
mole fraction range. These results were confirmed by friction
AFM images in air, recorded with a hydrophilic cantilever tip.
Hydrophobic heightened domains due to repulsion between the tip
and the hydrophobic thiolipid were observed at intermediate mole
fractions.
A relatively high resistance of 0.1 M: cm 2 was attained by
fabricating a micropatterned monolayer of a thiolated triethylene-
oxy chain covalently bound to a cholesteryl group, whose hydro-
phobic surface was covered by a lipid monolayer formed by vesi-
cle splitting and spreading; 5 this micropatterned film had 15 Pm u
15 Pm square holes filled with a mercaptoethanol monolayer,
whose hydrophilic surface was covered by a lipid bilayer formed
by vesicle unrolling and spreading. The square holes filled with the
short mercaptoethanol molecules and the lipid bilayer on top are
believed to be preferential sites for the incorporation of integral
proteins. In fact, the rigidity of the cholesteryl groups and their
anchorage to the electrode via the thiolated triethyleneoxy chain
make the mixed cholesteryl/lipid bilayer less suitable for protein
incorporation than the liquid-crystalline lipid bilayer on top of the
mercaptoethanol monolayer. Biofunctionality of this tBLM was
confirmed by incorporation of the ionophore valinomycin and the
channel-forming peptide gramicidin, which exhibited the expected
ion selectivity. Instead of using a microcontact printing on gold, an
alternative approach consisted in transferring a mixture of a thio-
lipid and of palmitic acid to a gold substrate by the Langmuir-
Blodgett technique. The regularly distributed domains of palmitic
acid on gold were then washed away in a suitable solvent, while
the covalently bound thiolipid was not removed; the resulting do-
mains of bare gold were then filled with a mercaptoethanol mono-
layer. 89 Besides microcontact printing and Langmuir-Blodgett
transfer of phase-separated thiolipid monolayers, deep-UV photoli-
thography was employed for patterning thiol layers on gold surfac-
es. 204
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