JPK instruments nanowizard afm - Applications

JPK Instruments NanoWizard
®
Handbook Version 2.2a
11
2.7 Applications
Molecules and membrane surfaces
The highest resolution images are usually obtained on single molecules
immobilized on a surface such as glass or mica. It is possibl
e to study protein
sub-structure and organization, 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.
One of the most important factors in high resolution imaging is the sample
preparation, that the sample should be very clean and firmly adsorbed to the
substrate.
DNA
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 e
ffects of different drugs or conditions on
the cell morphology and behavior
. 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 high
est 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.
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
m
anipulate molecules or parts of the sample, or even to dissect the sample on a
nanometer 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 oxidize
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 labeled
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 applic
ations
page for the NanoWizard
®
AFM and the NanoWizard
®
image gallery on the JPK
website contain more examples of the range of AFM applications and experiments
that are possible.
www.jpk.com