OVERVIEW ON THE MAJOR RESEARCH ACTIVITIES ON CARBON NANOTUBES BEING DONE IN AMERICA, EUROPE AND ASIA - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 251

The last research focus deals with the fabrication and characterisation
of ordered nanomaterial architectures, a speciic research program involving
the development of new synthetic procedures to obtain well-deined CNT
or graphene architectures on surfaces for future device applications. To that
purpose, the group combines inorganic synthesis of mesoporous catalytic
materials and chemical vapour deposition with microfabrication techniques,
followed by electrical and electromechanical measurements of individual
structures, in order to understand the properties of quasi-1D solids and
explore their applications in future miniaturised devices. Therefore, the main
objective is to realise nanoscale transistors through the fabrication of ordered
substrates and semiconducting nanowires.
9.2.2.1 Funconalisaon of CNTs for biomedical applicaons
An important aspect concerning CNTs is that the raw material needs to undergo
an extensive surface functionalisation in order to become suitable tool for
biomedical applications. Functionalisation of the tubes not only enhances
water solubility and CNTs' biocompatibility, but it has also demonstrated
to inluence biological systems both in vitro (e.g., in the mechanism of
cellular uptake) and in vivo (in terms of binding with blood proteins, tissue
accumulation and CNT elimination). 43-45
There are two major types of functionalisation protocols for CNTs, namely
covalent reactions and non-covalent coating by amphiphilic molecules onto
nanotubes. It is important to note that, although both are extremely useful,
they are not interchangeable: covalent chemical reactions have been shown
to be useful in drug and gene delivery, 46,47 where solubility in aqueous
media and stability of the complexes between CNTs and bioactive molecules
represent crucial aspects. However, through this procedure, the properties of
CNTs are modiied when the nanotube sidewall is functionalised, dramatically
decreasing the Raman scattering and NIR luorescence signals of SWCNTs,
thus rendering this functionalisation not ideal for sensing and imaging
applications. 48 Conversely, the structure and optical properties of the tubes
are preserved when they are non-covalently functionalised, although the
stability can be hampered by such weaker interactions. The research group
has therefore developed a few protocols (summarised in a recent review) 49
that help maintain both chemical stability and bio-conjugation with drugs
and molecules: an important example is represented by the incorporation
of poly(ethylene glycol) (PEG) on the nanotube sidewalls, which has led to
a remarkable follow-up on “supramolecular chemistry” with nanotubes. 50
This strategy has shown extremely high degrees of π-stacking of aromatic
molecules, including some luorescent dyes and even drug molecules (e.g.,
doxorubicin), which are commonly associated with eficacy but also unwanted