Biomedical Engineering Reference
In-Depth Information
Fig. 14
AFM used to “draw”
lines of oxidized thiol groups
on silicon chips. Such groups
are reactive to free thiols.
The image shows beta-
galactosidase linked
to such oxidized thiol lines.
For details, see Pavlovic
et al. (
2003
)
Another method to selectively position, for instance, protein molecules on surfaces
with high resolution is to use the AFM tip to locally oxidize a surface to create a
reactive group that can bond to the biomolecules of interest. For instance, 3-mercap-
topropyltrimethoxysilane can be used to thiolate a silicon wafer, after which the
AFM tip can be used to locally oxidize the thiol groups into thiolsulfi nates/thiolsul-
fonates. The latter groups are reactive and covalently bind to free thiol groups on
biomolecules ( Fig.
14
) (Pavlovic et al.
2003
). Beta-galactosidase, an enzyme rich in
exposed and structurally now-essential free thiol groups, was linked covalently to
silicon wafers using this technique, resulting in line widths as low as 70 nm. Using
such systems based on AFM technology, it would be possible to design assay chips
with a much higher density of components for screening, and with a parallel readout
using multicantilever systems may be developed into new high-throughput screen-
ing tools.
7
Outlook
The simple design and invariance to the operating environment allow AFM to be
integrated with other techniques for simultaneous structure-function correlation
studies. The integration of the AFM and fl uorescence microscope is one such excit-
ing development. Other combinations, specifi cally a combined near-fi eld differential
scanning optical microscope with AFM, near-fi eld optical imaging, electrophysio-
logical recordings, and the AFM-based NMR imaging, provide promising avenues
