JPK instruments nanowizard afm - Imaging Modes

JPK Instruments NanoWizard
®
Handbook Version 2.2a
27
5.3 Imaging modes
The two main modes used to image cells are contact mode and intermittent contact
mode. The choice of mode will depend, in part, on user preference, but there are
some indicators for which will be the best choice.
Contact mode Intermittent contact mode
Pros
Enhances visualization
of subsurface cytoskeletal
structures in both living and fixed cells
Better suited for the imaging of cells with steep
edges, i.e. high cell body or dendrites
Allows faster scan speeds on flatter cells
Less lateral disruption during the scanning
process
Less predominance of submembranous
structure (for imaging of features other than
subsurface cytoskeleton)
Phase images showing material p
roperties
available
The amplitude may remain quite constant even if
the cantilever bends somewhat due to material
adsorbing, for example. This would cause a
force offset in contact mode, but not immediately
in IC mode.
Cons
Flexible objects will move l
aterally, in the scan
direction (this will happen in all imaging modes
but is exacerbated in contact mode)
The user must monitor the scan closely to ensure
that the imaging conditions remain optimal and
the applied force does not increase too much due
to deflection drift
Responds less well to steep height changes -
such as sides of dendrites or the side of the cell
body, which can complicate imaging whole cells
More susceptible to complications due to a sticky
sample or substrate
For soft cantilevers wit
h low resonant
frequencies, the scan speeds may be rather
limited, since the data collection rate can be in
the range of the oscillation frequency for soft
cantilevers. The feedback system will require
several oscillation cycles to accurately determine
the amplitude of the oscillation.
Comments
In contact mode the applied force is directly
related to the spring constant of the cantilever and
the deflection setpoint. A softer cantilever (lower
spring constant) and a lower setpoint value will
apply a lower
force and should therefore in
general give better imaging, particularly for living
cells
In intermittent contact mode, the applied force is
not so directly related to the spring constant of
the cantilever, since the imaging sensitivity
depends on the reso
nance properties of the
cantilever. A slightly stiffer cantilever may have
a better resonant behavior
and hence give more
sensitive imaging. A higher resonance
frequency will also enable faster imaging.