Biomedical Engineering Reference
In-Depth Information
The open-end functionalization of CNT probes allows the tips to have as few as one
active molecular site localized in a relatively controlled orientation, which leads to
subnanometer resolution in chemical contrast and binding site recognition even for single-
molecule measurements (Figure 12.24) [181]. These functionalized CNT tips can be used
to study ligand-receptor binding/unbinding with control of orientation, and to map the
position of ligand-receptor binding site in proteins and on cell surfaces with nanometer or
better resolution. Figure 12.24 also shows force spectra of the interaction between tips
linked with biotin and immobilized streptavidin and a mica substrate. Force-displace-
ment measurements show well-defined binding force quanta of ca. 200 pN per
biotin-steptavidin pair [193].
10 nm
F
b
Z
displacement
(a)
(b)
(c)
FIGURE 12.24
Nanotube AFM tips for single-molecule force spectroscopy and mapping: (a) Schematic illustration of the exper-
iment, where the lower gray rectangle corresponds to a mica substrate, the green blocks correspond to strepta-
vidin molecules, and the dark blue inverted triangle is biotin covalently linked to a carbon nanotube (heavy black
vertical line). (b) Representative force-displacement curve recorded with a biotin-modified MWNT tip in pH 7.0
solution. The binding force, 200 pN, is consistent with unbinding of a single biotin ligand from streptavidin. (c)
Model of an SWNT tip that has been modified with biotin and is interacting with a streptavidin molecule. (From
Hafner, J. H., Cheung, C., Woolly, A. T., Lieber, C. M. (2001). Structural and Functional Imaging With Carbon
Nanotube AFM Probes.
Prog. Biophys. Mol. Biol.,
77, 73-110.)
