Biomedical Engineering Reference
In-Depth Information
F
max
Approach
200
No rupture with adhesion
Single-tether rupture
Double-tether rupture
150
100
50
0
-50
-100
Bond ruptures
-150
0
50
100
150
Probe displacement (nm)
FIGURE 4.7
Three withdraw parts force curves are shown and a typical approach part in
measurements of interactions between biotin and streptavidin is indicated by the legend in
the figure. One force curve has adsorption at the surface. Two other curves show rupture
events that are removed from the surface of substrate as illustrated by a cartoon in the fig-
ure. (Reproduced from Guo, S. L. et al. 2010b.
Journal of the American Chemical Society
.
132 (28):9681-9687.)
AFM tip
Te t h e r e d
biomolecules
R
l
rms
Substrate
FIGURE 4.8
Cartoon illustrating formation of multiple bonds between molecules tethered
by polymeric linkers to the atomic force spectroscopy tip and recognition partners that are
closely packed on the substrate.
one molecule:
2
R
l
rms
N
max
≈
(4.1)
where
R
is the radius of the tip curvature. Thus, if molecules are tethered to the
probe with radius of curvature of 25 nm with polymeric linkers with the end-to-
end distance of 5 nm then upto 10 bonds might be formed during one probe-sample
contact (assuming that recognition partners on the substrate are relatively small and
densely packed). Such large number of bonds impedes accurate data analysis. In
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