Biomedical Engineering Reference
In-Depth Information
4
Nanosensing and Detection
4.1
Force Mapping
AFM has developed into a valuable tool for measuring molecular interactions. The
possibility of linking molecules to the probing tip provides a range of options to
probe molecular interactions between the probe on the AFM tip and the sample
surface (Hinterdorfer et al.
1996
; Baumgartner et al.
2000
; Yuan et al.
2000
; Zhang
et al.
2002
). In this way, membrane proteins can be probed on living cells. Using
such modifi ed cantilevers, adhesion forces were measured and mapped between
ligands and receptors on the surface of living cells (Fig.
8
) (Chen and Moy
2000
;
Fig. 8
Simultaneous acquisition of topography and elasticity images before and 10 and 45 min
after adding VEGF antibody (
top half
). Clustering of receptors can be observed both in topography
and elasticity maps (spots labeled 1-4).
Top histograms
show distribution of adhesion forces.
Bottom half
(
left
); adhesion forces between VEGF receptor and antibody (
a
), with distribution of
unbinding forces (
b
). Blocking peptide prevents the interaction (
c
). (
d
) Tapping mode image of
VEGF receptors on mica (
e
) and (
f
) show adhesion forces between VEGF receptor on endothelial
cell and antibody on tip without (
e
) and with (
f
) the presence of blocking peptide.
Bottom half
(
right
); AFM images of endothelial cells before (
a
) and after (
b
) addition of VEGF, showing
cytoskeletal reorganization. Fluorescence images showing the presence of Flk-1, a receptor for
VGEF (
c
,
d
) and control (
e
) with nonspecifi c antibody. For details, see Almqvist et al. (
2004
)
