|
Molecules and membrane surfaces
IThe highest resolution images are usually obtained on single
molecules immobilised on a surface such as glass or mica. It
is possible to study protein sub-structure and organisation,
particularly in 2-dimensional protein crystals. This can also
be successful with membrane proteins, in conditions that would
not allow 3-dimensional crystallization for standard structural
investigations. Long molecules such as DNA or glycoproteins
can be studied to measure intrinsic properties such as the persistence
length, or interactions with bound proteins. The molecules do
not need coating or staining and can be imaged in air or liquid.
Molecules can be studied in action, for example enzymes such
as collagenase or amylase digesting their substrate.
|
DNA image
Protein crystal |
|
Cell imaging
AFM has many advantages for cell imaging, since the cells can
be imaged at high resolution in physiological conditions, in
buffer or medium. Living cells can be imaged, and this has led
to studies of the effects of different drugs or conditions on
the cell morphology and behaviour. Cells infected with parasites
or viruses have also been studied. The details of the cytoskeleton
are usually visible in the images of live cells, while fixed
cells show the highest resolution features of the membrane surface.
Many possibilities open up if the AFM can be mounted on an inverted
optical microscope, so that DIC or fluorescence images can be
compared with the 3-dimensional topographic information, or
the maps of the mechanical properties of the cell surface.
|
Cell imaging
AFM and optical |
Other modes and interactions
Apart from simply imaging, AFM cantilevers can be used in many
other modes of interaction with the surface. The tip can be used
to pattern the surface, move and manipulate molecules or parts
of the sample, or even to dissect the sample on a nanometre scale.Nanolithography
is possible, for example by applying a bias voltage and using
the natural water capillary that forms between the tip and sample
in air to oxidise patterns on the surface. With modified cantilever
tip surfaces, molecules on the tip can be patterned onto the surface,
or molecules on the surface can be picked up and moved around.
The tip can be used to image normally, and then higher forces
applied to cut through parts of the sample, for example to dissect
a labelled part from a chromosome. |
|
|
There are as many applications for AFM as there are biological
samples, so it is beyond the scope of this introduction to give
a full picture here. The applications page for the NanoWizard®
AFM and the NanoWizard® image gallery contain more examples
of the range of AFM applications and experiments that are possible.
|
|
|
|
