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patients. The observed CFTR density of non-CF RBC is in good correlation to
electrical measurements in Calu-3 cells, a human airway epithelial cell line.
11
6.1.6
Topography and Recognion Imaging of Human RBCs
TREC
allows mapping of topographical details of a specimen and
simultaneous investigation of the distribution of proteins on the surface (see
also
Chapter 7
). To provide a speciic recognition, an antibody is covalently
bound to the scanning AFM tip. While oscillating over the surface, the AFM
tip approaches the surface that contains cognate antigen, and an antibody-
antigen bond is formed. During a subsequent retraction of the tip, the bond
will cause a measurable tension. Since topographical features affect only the
lower part of the oscillation, the latter is used for the piezo feedback loop.
In contrast, the molecular recognition inluences only the upper part of
the oscillation, which is separated in an electronic circuit for localizing the
recorded recognition images provide structural and chemical information of
the investigated surface.
12,13
Figure 6.7.
TREC working principle. A ligand functionalized AFM tip is oscillated
over the sample surface. The lower part of the amplitude is used for driving the AFM
feedback loop, resulting in the topography image, whereas the upper part is affected
by molecular recognition, yielding a simultaneously acquired recognition image.
14
out of the membranes with 10-12 nm in height, representing the membrane
proteins. The structures were comparable with the topography of membrane
proteins obtained with standard AFM. Visualization at single-molecule level
was achieved without compromising its topographic imaging performance,
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