Biomedical Engineering Reference
In-Depth Information
The chromatographic elution showed that in case of metallic CNTs, the
linear charge density was reduced from that of the DNA alone, and it was
responsible for early fractions enriched in smaller-diameter and metallic
tubes, as demonstrated by a more pronounced absorption in the metallic M 11
(400-600 nm) band, and weaker absorption in the semiconductor E 11 band
(900-1,600 nm); instead, for semiconducting tubes, since the polarisability
of the nanotubes was lower and more inluenced by the diameter of the
tubes, the separation resulted in late fractions enriched in larger-diameter
and semiconducting tubes. Therefore, ion exchange chromatography (IEC)
enabled the separation of CNTs with different electronic properties by coating
DNA sequences with speciic length.
To conirm the obtained results, an elution model was associated with these
experiments 15 in order to elucidate the most signiicant factors contributing
to the separation of CNT-DNA hybrids. The advantage of such investigation is
that the elution model semiquantitatively captured the available experimental
observations made by Zheng et al. 16 and it predicted that the IEC separations
are very sensitive to SWCNTs' radius, a t , in addition to the CNTs' dielectric
constant (Fig. 5.3). In fact it conirmed that metallic hybrids are expected
to elute before semiconducting hybrids of the same radius size. Since in the
simulation studies the binding distance between the DNA and SWCNTs, a h - a t ,
was kept constant, the helix angle increased with SWCNT radius. Therefore,
higher salt concentrations were generally required to elute larger diameter
hybrids when the DNA intercharge segment bond angle was held constant.
Figure 5.3 Salt concentration at hybrid elution as a function of the SWCNT radius for
metallic, t = 5000 (solid line), and semiconducting, t = 4 (dashed line), SWCNTs.
Reproduced from Lustig et al. 15 with permission.
 
Search WWH ::




Custom Search