A host of techniques are used to study these membrane systems. In this
book, discussion will be limited to widely used fluorescence techniques
such as FRAP, FRET, and FLIC, as well as a few surface-sensitive techniques such as AFM and QCM. There are a number of other important
methods, not covered in this section, for studying model bilayers such as
electron microscopy, which allows for the direct visualization of membranes in vivo, impedence spectroscopy, which allows for electrical
measurements of membranes that are important for understanding
neurons, as well as neutron and x-ray scattering techniques that are used
to probe the structure and periodicity of membranes. Several types of
model lipid bilayers can be fabricated and will be discussed in the next
few sections.
10.3.1 Black lipid membranes
Black lipid membranes are lipid bilayers formed in solution over a small
aperture, usually less than 1 mm in diameter. The hole is formed in a
hydrophobic material such as Teflon and is usually part of a wall separating two compartments that can be filled with aqueous solution (see
Figure 10.8a). The two most popular methods for black lipid formation
involve the painting of the lipid solution over the aperture or the formation of a folded bilayer. Painting is carried out with a small artist’s
paintbrush. The formation of folded lipid bilayers requires a container
with two compartments separated by a small aperture, and the solution
levels in each compartment must be controlled independently (Figure
10.8b). The desired solution is filled into each compartment and a
monolayer of phospholipid material is spread on top of one of the
compartments. The solution level containing the monolayer can be raised
and lowered over the aperture to deposit the bilayer.
Black lipid membranes have been used to study various biophysical
processes. Black lipid membranes are suspended in solution, where there
are no unwanted interferences of the membrane with an underlying
support. The absence of a support allows for transmembrane proteins to
be incorporated within the phospholipid bilayer such that they remain
fully mobile and active. The ability to insert single protein pores into black
lipid membranes allows for the creation of potential nanodevices. This
has been accomplished by Gu et al. (1999) through the use of genetically
modified a-hemolysin. a-Hemolysin mutants that can noncovalently
capture cyclodextrin molecules within their pores were created. A current
change is measured due to the restriction of the pore by cyclodextrin.
MODEL PHOSPHOLIPID BILAYER FORMATION AND CHARACTERIZATION 397
book, discussion will be limited to widely used fluorescence techniques
such as FRAP, FRET, and FLIC, as well as a few surface-sensitive techniques such as AFM and QCM. There are a number of other important
methods, not covered in this section, for studying model bilayers such as
electron microscopy, which allows for the direct visualization of membranes in vivo, impedence spectroscopy, which allows for electrical
measurements of membranes that are important for understanding
neurons, as well as neutron and x-ray scattering techniques that are used
to probe the structure and periodicity of membranes. Several types of
model lipid bilayers can be fabricated and will be discussed in the next
few sections.
10.3.1 Black lipid membranes
Black lipid membranes are lipid bilayers formed in solution over a small
aperture, usually less than 1 mm in diameter. The hole is formed in a
hydrophobic material such as Teflon and is usually part of a wall separating two compartments that can be filled with aqueous solution (see
Figure 10.8a). The two most popular methods for black lipid formation
involve the painting of the lipid solution over the aperture or the formation of a folded bilayer. Painting is carried out with a small artist’s
paintbrush. The formation of folded lipid bilayers requires a container
with two compartments separated by a small aperture, and the solution
levels in each compartment must be controlled independently (Figure
10.8b). The desired solution is filled into each compartment and a
monolayer of phospholipid material is spread on top of one of the
compartments. The solution level containing the monolayer can be raised
and lowered over the aperture to deposit the bilayer.
Black lipid membranes have been used to study various biophysical
processes. Black lipid membranes are suspended in solution, where there
are no unwanted interferences of the membrane with an underlying
support. The absence of a support allows for transmembrane proteins to
be incorporated within the phospholipid bilayer such that they remain
fully mobile and active. The ability to insert single protein pores into black
lipid membranes allows for the creation of potential nanodevices. This
has been accomplished by Gu et al. (1999) through the use of genetically
modified a-hemolysin. a-Hemolysin mutants that can noncovalently
capture cyclodextrin molecules within their pores were created. A current
change is measured due to the restriction of the pore by cyclodextrin.
MODEL PHOSPHOLIPID BILAYER FORMATION AND CHARACTERIZATION 397