HIGH-RESOLUTION ATOMIC FORCE MICROSCOPY OF NATIVE MEMBRANES - Life at the Nanoscale: Atomic Force Microscopy of Live Cells - page 35

compared to the native case. More importantly, in the cataract membranes
connexons were absent at the edges of the AQP0 arrays and in the membrane
in general ( Fig. 2.8d ) . The absence of connexons in lens membranes obviously
led to the fusion and malformation of AQP0 domains and failure of intercellular
communication in the tissue ( Fig. 2.8e , r ight). As connexons function as ion,
metabolite and waste channels between neighbouring cells, their absence is
certainly responsible for the breakdown of the microcirculation system 68 in
the lens tissue, thus causing cell death and leading to lens opaciication.
2.5 HIGHSPEED AFM STUDIES OF THE DYNAMICS OF
BIOMOLECULES
AFM 77 is a powerful tool for the characterization of biological molecules,
providing high-resolution topographic data of biological molecules
under physiological buffer conditions at room temperature and ambient
pressure. This capability of imaging in conditions where biomolecules are
functional makes AFM the ideal technique for characterizing the dynamics
of biomolecules. As a matter of fact, only three years after the invention
of AFM in 1986 the irst observations of the dynamic clotting aggregation
processes were performed; 78 few other studies were performed over the next
years on antibody binding processes 79 and DNA-protein interactions. 80,81
After that period AFM was perhaps less used to study dynamic processes
of biomolecules mainly because of the limitation of the imaging speed of
conventional AFMs that is around one minute per image. Such an imaging
rate is simply too slow for capturing the dynamics of most biomolecular
processes. Therefore, the AFM has mainly been used for structural studies
of native proteins or as a force-measurement tool. 1 To expand the use of AFM
for the study of the dynamics of biomolecules, a signiicant increase of the
imaging speed is required.
In response to the need for faster imaging rates, a new generation of faster
high-speed (HS) atomic force microscopes have been developed in recent
years. The key feature of this new generation of AFMs is the increase of the
speed of response of the moving components of the AFM setups, in particular
the probe and the piezoelectric stage. The increase of speed of the moving
components is obtained by reducing their dimensions. 82 Different research
groups have been active on this development. 83-88 Best performances on
biomolecule imaging to date range around an imaging speed of 30 ms per
frame with about 150 x 150 pixels (for more details, see Chapter 8 ). 89
The principle of the AFM is based on the force of interaction between
the probe and the sample. For successful imaging of biomolecules, the force