BIOMEDICAL AND BIOMEDICINE APPLICATIONS OF CNTs - Bio-Inspired and Nanoscale Integrated Computing - page 503

combines a functionalized SWCNT probe with specifically probing single proteins
labeled for single-molecule fluorescence studies. In addition, researchers can
electrically couple the SWCNT probe to the protein in order to induce conforma-
tional changes within the protein that can be detected by AFM and fluorescence
measurements.
18.6. ISSUES IN THE BIOLOGICAL APPLICATIONS
18.6.1. Challenges
In a very short duration, CNTs appear to be the frontrunner that has the potential
to dominate the biomedical research. However, challenges remain that need
to be addressed before the full potential of CNTs for biomedical applications
can be realized. For example, there is a lack of detailed understanding of the
growth mechanism of CNTs. First, an efficient growth approach to structurally
perfect nanotubes at large scales is currently not available. Second, it is difficult to
grow defect-free nanotubes continuously to macroscopic lengths. Third, control
over nanotubes' growth on surfaces is required in order to obtain large-scale
ordered nanowire structures. Fourth, controlling the chirality of SWNTs by
any existing growth method is very difficult. Also, the above-mentioned limita-
tions result in high cost of production for pure and uncontaminated nanotubes
with uniform characteristics. In short, the optimization of production parameters
and the control on the growth of nanotubes is to be mastered. In addition to the
challenges at the fabrication level, the low dimensional geometry results in
structural instability, which is an important issue for the mechanical application
of CNTs, as larger strains are prone to buckling, kink forming, and collapse.
Besides, the toxicology of CNTs is not well understood. Dagani [90] compiled a
report on the adverse effects of potential drug-carrying nanoparticles at the
blood-brain barrier from the national meeting of the American Chemical Society.
On the basis of their experiments, researchers suggested that CNTs possess health
risks. They reasoned that humans can potentially be exposed to CNTs by
inhalation because unprocessed CNTs are lightweight and, therefore, can become
airborne. If CNTs reach the lung, they can agglomerate and fill the air passages,
which may lead to suffocation. This warrants an in-depth study about the
toxicology of CNTs to come up with a final conclusion with respect to their
acceptance by the human immune system. Finally, the time from proof of concept
in the laboratory of the CNT-based devices to the commercial marketplace should
be reduced as the competition from other novel materials and technologies
continue to emerge.
18.6.2. Toxicity
18.6.2.1. Occupational Exposure: Unmodified CNTs. To date, most stu-
dies regarding carbon nanotube toxicity have focused on potential hazards