Biological Applications of Dynamic Force Spectroscopy - Dynamic Force Spectroscopy and Biomolecular Recognition - page 232

(a) (b)

Linker

Label

Ligand

DNA

Receptor

FIGURE 6.12 (See color insert.) Sketch of the experimental setup used for a force-based
biosensor. A DNA strand is bound to the top plate through a linker. Both a fluorescent label
and the ligand molecule are bound to DNA. The receptor molecules are immobilized on the
bottom plate. (a) The top and the bottom plates approached each other to promote a biorecog-
nition process between the partners. (b) During the retraction, one of the two DNA strands
is expected to remain attached to the bottom plate, with a concomitant deposition of the fluo-
rophore label upon the interaction between the ligand and the receptor overcomes that between
the DNA strands. (Adapted from Blank, K. et al. 2003. Proc. Nat. Acad. Sci. USA , 100:11356-
11360.)

oligomers were picked up from a depot area by means of a complementary DNA
strand bound to an AFM tip. These units have been then transferred to and deposited
on a target area to create basic geometric structures assembled from units with dif-
ferent functions. This process can be followed by monitoring the force curves; the
spatial precision of the AFM coupled to the selectivity of the DNA biorecognition
process among strands having been exploited for the bottom-up assembly of the
biomolecular structures.
Miyachi et al. have exploited the biorecognition capability of DFS to screen-
ing DNA aptamers through a SELEX-based strategy (Miyachi et al., 2010). Single
strands of DNA have been immobilized on the cantilever through the avidin-biotin
pair while the target molecule, thrombin, has been anchored onto a gold substrate.
During the approach of the tip to the substrate, a biorecognition between the aptamers
and thrombin is promoted. Upon the retraction, if the binding force between the
aptamer and the target molecule is higher than that between avidin and biotin, the
latter interaction breaks and the DNA aptamer is deposited on the substrate; such
a approach-retraction cycle being repeated to allow a further selection of DNA