Single-Molecule Mechanics of DNA - DNA Nanotechnology: From Structure to Function - page 106

Fig. 6.22 Schematic
of the DNA-CNT force
measurements (Reprinted
with permission from Ref.
[ 59 ]. Copyright 2011
American Chemical Society)

recently, Manohar et al. observed a sequence-dependent desorption force from a
single crystal of graphite [ 57 ]. A desorption force of 85 pN is observed for
poly(dT) and 61 pN for poly(dC), which both were substantially independent
of salt concentration and the rate of detachment. The average binding energy per
monomer can then be calculated to be 11.5 and 8.3 k B T in the cases of thymine
and cytosine nucleotides. The result that adhesion force of T is larger than that of C
is in agreement with previous reports [ 58 ].

6.5.3 Friction Between Single Molecule of ssDNA

and Solid Materials

6.5.3.1 Friction Between Single Molecule of ssDNA and Flat Substrates

Kuehner et al. designed a special experiment to study the single-molecule friction
behavior of 1.4 kb ssDNA from different kinds of solid substrates [ 56 ]. They found
that the friction coefficient of the ssDNA is virtually infinite on gold coating surface.
However, a very low friction force (0.1 pN) was observed between ssDNA and
Mg 2C /mica surface. These results indicate that ssDNA have very different motilities
on different surfaces, though similar binding energies were measured.