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There are a huge number of potential applications of force
spectroscopy, so only an overview is possible here. Virtually
any sample can be studied using force spectroscopy, and different
interactions or tip coatings and shapes will all give complementary
information about the sample.
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Molecular interactions
When
molecules are attached to the tip and/or the sample, the stretching,
unfolding or adhesion of single molecules can be studied. Long
chain molecules, such as DNA or dextran can be stretched between
the tip and the sample. The stiffness, persistence length and
internal molecular transitions can be studied. The melting transition
in DNA can be seen as the backbone rearranges under raised tension. |
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| Molecules with complex
3-dimensional structure, such as many proteins, can be unfolded
in a controlled way so that the structural units can be investigated.
Titin and bacteriorhodopsin are examples of proteins that have
been intensively studied. Membrane proteins can be pulled out
of the membrane, and the "popping" out of individual
alpha-helices has been seen. |
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The adhesion can be measured between molecules attached to
the tip and to the sample. These can be antibodies and antigens
or other receptor-ligand pairs. The adhesive forces can be measured
and mapped over the surface, and information extracted about
the energy and kinetics of the binding. These techniques have
also been applied to the binding between complementary and mismatched
DNA strands.
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Cellular mechanics and interactions
The viscoelastic response of cells can be studied by using the
cantilever to indent the cell. On living cells, the changes
in mechanical properties can be seen as the cell divides, or
when drugs such as cytochalasin, which disrupts the cytoskeleton,
are added. Mechanosensitive cells such as osteoblasts or ear
cells can be stimulated with the cantilever, and the response
monitored. Adhesion maps over the surface are also possible
to investigate the distribution of receptors.
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