Biology Reference
In-Depth Information
SCFS techniques include micropipettes, laser tweezers, magnetic tweezers
and AFM.
Several
, including the step pressure technique
16
and the biomembrane force-probe (BFP),
micropipette techniques
have been developed that
operate both at the cellular and molecular level. These methods were applied
to study single-molecule interactions, membrane tether formation from
single cells and overall cell adhesion.
21
However, whereas the step pressure
technique
17-20
is characterised by a low force resolution (≈100 pN), the BFP
is applicable over a rather limited range of forces (≈0.1 to 1000 pN).
16,17,22
Disadvantageously, this force range does not allow to monitor the formation
of higher-ordered adhesive structures.
60
Optical tweezers
16
have been employed to measure the interaction of cells
with functionalized microspheres.
23,24
Alternatively, whole cells have been
trapped in laser beams, and their adhesion to functionalized substrates
has been probed. The conined force detection range of optical tweezers
(0.1-100 pN)
limits their applicability mainly to single-molecule studies.
Moreover, the high laser intensity at the focus of the beam can cause local
temperature increase, which may damage cells.
25
25
have also been applied to measure cell-substrate
interactions. In these experiments, a substrate-coated magnetic microsphere
is brought into contact with a cell and detached by generating a magnetic
ield.
Magnetic tweezers
Alternatively, a bead-coupled cell can be probed on an adhesive
substrate.
26
Similar to optical tweezers, the force detection range of the two
latter magnetic tweezer setups (0.01-100 pN)
25
limits their applicability
to single-molecule studies. Recently, a novel magnetic tweezer setup was
introduced that allows applying forces of up to 100 nN to magnetic beads.
25
27
This later setup designed to measure rather high forces is suficient to study
the rupture of complex cell adhesion sites. However, it shows a rather poor
force sensitivity that hardly enables to detect adhesive forces of single
CAMs. To sum up, the SCFS techniques described are restricted either to the
analysis of single-molecule interactions or to the detection of overall cell
adhesion at lower force resolution. In the following, we will introduce the
principles and advantages of AFM-based SCFS to characterize the adhesion
of single cells to molecular resolution.
10.3 AFMBASED SCFS
AFM-based SCFS is the most versatile among the mentioned SCFS techniques
since it allows the largest range of forces, from ≈5 pN to about 100 nN, to
be measured.
In this setup, a cell is attached to an AFM cantilever, and the
adhesive strength to a protein-coated surface (
Fig. 10.1a
)
or another cell
(
Fig. 10.1c
) is quantiied.
28
29-31
Alternatively, the cantilever is functionalized
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