Biomedical Engineering Reference
In-Depth Information
Fig. 6
Imaging of triple-helical collagen I with AFM. The inset magnifi es one collagen molecule
(
left
). Other panels show collagenase binding to collagen molecules. Images are taken before col-
lagen addition (
a
), immediately after collagenase addition (
b
), and 4 min later (
c
). Globular parti-
cles bound to collagen are indicated by
arrows
;
thick arrows
show sites, where collagen was
broken after collagenase binding. For details, see Lin et al.
1999
track neuronal death and neuritic arborization optically during AFM imaging
(Fig.
5
, left panel). Such optical techniques have so far been a better temporal reso-
lution, since the AFM imaging of a whole cell is time consuming. Further develop-
ments in fast-scanning AFM systems will be able to study such processes with
subsecond time resolution, a large improvement over the conventional AFM scans
that take several minutes to collect.
3.3
Single Molecule Imaging and Manipulation
Since single molecules can be imaged routinely in AFM, it is feasible to use the
AFM to image real-time processes of molecules' interaction with each other. For
instance, proteolysis of collagen was observed using AFM (Fig.
6
) (Lin et al.
1999
) .
Such processes are typically monitored using SDS-PAGE which gives little
information about the real-time activity and the 3D structural information of the
binding of the enzyme to the molecules. Single collagenase binding events to col-
lagen could be imaged; digestion of collagen could be followed.
With the possibility of monitoring single molecules comes the advantage of
being able to manipulate the molecules as well. By tethering antibodies to the AFM
tip, and after bringing the tip in contact with the sample of interest, the antigen in
the sample can not only be detected, but also unfolded. For instance, bacteriorho-
dopsin molecules could be extracted from purple membrane and unraveled by pull-
ing with the AFM tip (Kienberger et al.
2005
) .
3.4
Mapping Polymer Electrical Activity and Structure
There has been a large commercial and scientifi c interest in conjugated polymer
blends. Such polymer systems have a wide range of applications ranging from
microactuators (Jager et al.
2000
) to chemical sensors (Hagleitner et al.
2001
) and
