Biomedical Engineering Reference
In-Depth Information
been slower. But, we are at the beginning of a new era in membrane protein engineering
based on the accelerating acquisition of structural information, a better understanding of
molecular motion in membrane proteins, technical improvements in membrane protein
refolding, and the application of computational approaches developed for soluble proteins.
In addition, the next 5 years should see further advances in the applications of engineered
channels and pores, notably in therapeutics and sensor technology. Li et al. (80) have been
investigating applications of nanopore membranes in analytical chemistry—specifically in
membrane-based bioseparations, in electroanalytical chemistry, and in the development of
new approaches to biosensor design. Membranes that have conically shaped pores (as
opposed to the more conventional cylindrical shape) may offer some advantages for these
applications. They describe a plasma-etch method that converts cylindrical nanopores in
track-etched polymeric membranes into conically shaped pores. The key advantage of the
conical pore shape is a dramatic enhancement in the rate of transport through the mem-
brane, relative to an analogous cylindrical pore membrane. They have demonstrated this
by measuring the ionic resistances of the plasma-etched conical pore membranes.
Goryll et al. (81) present a method to fabricate an aperture in a silicon wafer that can be
used to suspend a freestanding lipid bilayer membrane. The design offers the feature of
scalability of the aperture size into the submicron range. Lipid bilayer membranes formed
across the aperture in the oxidized silicon substrate show a gigaohm sealing resistance.
The stability of these membranes allowed the insertion of a nanometer-sized ion channel
protein (OmpF porin) and the measurement of voltage-dependent gating that can be
expected from a working porin ion channel.
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