Electrochemistry of Biomimetic Membranes - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 207

these proteins with their associated water-soluble proteins (e.g.,
incorporation of rhodopsin and its interaction with the G-protein
transducin 149 , incorporation of cytochrome c oxidase and its inter-
action with cytochrome c.) 150 This allowed the authors to distin-
guish conditions under which nonspecific electrostatic interactions
prevail over those characterized by the predominance of specific
hydrophobic interactions. Salamon and Tollin have subsequently
improved the technique by interposing a thin dielectric layer of
SiO 2 , acting as a waveguide, between the silver layer and the lipid
bilayer, which was now self-assembled on the hydrophilic SiO 2
surface. 151 This system allows an estimate of the refractive index
and the extinction coefficient of the composite film not only with
p -polarized light (i.e., in the direction perpendicular to the bilayer
plane), as in conventional SPR, but also with s -polarized light, i.e.,
in the direction parallel to the bilayer plane. These parameters
measure the anisotropic character of the lipid membrane structure.
This technique, called coupled plasmon-waveguide resonance
spectroscopy (PWR), has provided useful pieces of information on
the structural changes accompanying the incorporation in a lipid
bilayer of the integral protein cytochrome b 6 f and its interaction
with the peripheral, water-soluble protein plastocyanin; 152 the
structural changes involved in the incorporation of different recep-
tors and in their ligand binding have also been investigated. The
PWR spectroscopy has also been used to monitor the formation of
microdomains in mixed sphingomyelin-DOPC mixtures (called
lipid rafts) and the sorting of receptors into each microdomain. 153
The microdomain size evaluated from the lateral resolution of the
PWR sensor is very high (100-300 Pm). While providing useful
structural information on (lipid bilayer) - (integral protein) - (pe-
ripheral protein) systems, this technique cannot provide direct evi-
dence for the functional activity of these systems and a verification
that the differential capacitance of the lipid film is that expected
for a well-behaved lipid bilayer.

5. Tethered Bilayer Lipid Membranes (tBLMs)

As a rule, tethered bilayer lipid membranes refer to architectures in
which the lipid bilayer is separated from the support through a
monomolecular layer tethered to the support via a sulfhydryl or
disulfide group (for gold, silver or mercury supports) or via a