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SNOM is a powerful microscopy technique that overcomes the Abbé diffraction limit.
Scanning near-field optical microscopy (SNOM) is one of the
family of scanning probe microscope techniques, which use a
small probe to scan across the surface and build up an image
line by line. The difference between a SNOM and other probe
microscopes is that optical information is collected from the
sample. A sharp micromachined tip is used that works like a
nano light source.
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The light source illuminates only a tiny part of the sample at any time.
The microscope works in the "near-field" because
the distance between the probe and the sample surface is so
much smaller than the wavelength of the light. This means that
high resolution optical information is available that is not
bound by the far-field diffraction limits. The fundamental advantage
is that the user gets a molecularly resolved optical and 3D
topographic image simultaneously. Thus the optical and topographical
features can easily be compared.
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Different types of SNOM probes can be used.
Different sorts of SNOM probes are available, which use different
types of control mechanisms to scan the surface. One option is
to use cantilevered probes, such as the ones that are used for
AFM. This has the advantage that the SNOM instrument is capable
of all the normal AFM scanning modes. The scanning and topography
measurement then works using the same principles as for a standard
AFM. |
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Many optical modes are available for SNOM microscopes.
SNOM can be used in many
of the modes of conventional optical microscopy, such as reflection,
transmission, scattered light or polarization contrast. The tip
can even be used for optical nanolithography. SNOM fluorescence
imaging has a great potential for life science applications. It
can be used to see single molecules in the topography and fluorescence
images, or to locate fluorescently labelled regions on cell membrane
surfaces, for example. |
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SNOM has been applied to a full range of biological samples.
SNOM imaging has been applied to many kinds of biological samples,
from single fluorescently labelled molecules such as DNA or proteins,
up to whole cells and chromosomes. SNOM is particularly suited
to labelling cell surface membrane proteins, since the illumination
depth is limited to tens of nanometers. This allows good discrimination
between proteins at the cell membrane and those in the cytoplasm.
Fluorescent labelling of chromosomes is also common, using FISH
or other techniques to label particular areas, which can then
be identified in the topography images. |
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