DATA: THE NEW CORPORATE RESOURCE - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 16

spectroscopy. They found that the supernatant was richer in small-diameter
(0.91 and 0.82 nm) semiconducting CNTs as shown by the presence of only
two radial breathing mode (RBM) bands at 258 and 284 cm -1 as opposed to
the increased intensity of bands below 240 cm -1 , typical of large-diameter
conducting CNTs, observed in the precipitate. Similar results were previously
obtained by Takahashi et al . 49 Furthermore, the chitosan derivative TMC
has shown size segregation capacity; in fact, SWCNTs suspended in TMC
solutions presented a Raman spectrum with a reduction in lower-frequency
RBM bands (<220 cm -1 ) corresponding to larger-diameter tubes. These data
were also veriied by AFM studies. 57
The complexation of CNTs with chitosan produces composites that
present the mechanical strength, electrical conductivity and thermal
stability of nanotubes, combined with the biocompatibility and pH
sensitivity of the polysaccharide. These properties are promising for several
nanotechnology and biotechnology applications. 66 One application that
has attracted considerable attention is the use of CNT-chitosan complexes
in the construction of biosensors. 61,67 Recent literature reports their use
in the preparation of amperometric sensors, such as oxygen peroxide
biosensors, 68 sulite sensors, 69 immunosensors for α -fetoprotein, 70 glucose
oxidase sensors 71 and biosensors for the detection of deep DNA damage, 72
to mention only a few. CNT-chitosan complexes have also shown enhanced
DNA condensation properties compared with chitosan alone; this could
be useful in the development of gene delivery systems. 73 Furthermore, the
metal-binding properties of chitosan, combined with absorption properties
of CNTs, give the scope for further investigation into environmentally friendly
nanocomposites. 62
Unmodiied CNTs are very hydrophobic; they readily aggregate and
therefore ind it dificult to interface with biological materials. Various
systems have been investigated to stabilise CNT suspensions in water yielding
unbundled, individual CNTs to increase biocompatibility. However, more
efforts are needed to achieve stable suspensions with high concentrations of
individual CNTs, which could be further used as biomaterials in the ield of
pharmaceutical nanotechnology.

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2. Foldvari, M., and Bagonluri, M. (2008) Carbon nanotubes as functional excipients

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