BIOMEDICAL AND BIOMEDICINE APPLICATIONS OF CNTs - Bio-Inspired and Nanoscale Integrated Computing - page 488

interactions have also been performed through nonspecific protein binding and
ionic interactions, which have coupled CNTs to crown ether.
18.2.2.2. Sidewall Functionalization. Sidewall functionalization methods
can introduce higher concentrations of covalently attached functional groups onto
the surface of CNTs with the trade off of significant perturbation in the electronic
structure. Indeed, the loss of van Hove singularities as observed in the absorption
spectrum has been used to probe the degree of sidewall modification.
Halogenation of CNTs has been achieved through the incorporation of a high
density of fluorine, chlorine, and bromide atoms on tube surfaces. In particular,
fluorination of CNTs is achieved through gas-phase reactions and offers a
nondestructive means of high-density sidewall functionalization. The degree of
fluorination can be controlled and in any case, the electronic properties of the
CNT are significantly altered. Fluorination has been shown to be reversible,
therefore somewhat restoring the electronic properties of the tubes. Fluorination
also offers a means of introducing a wide variety of additional functional groups
on the CNT surface. Chlorination and bromination of CNTs has also been
demonstrated. Hydrogenation, nitration, radical addition, nucleophilic addition,
electrophilic addition, diazotization, ozmylation, and ozonolysis also offer a
variety of modification routes that result in a wide range of functionality. In
particular, treatment with ozone in the presence of various reagents provides a
means of controlling the proportions of the type of oxygenated groups introduced
onto CNTs. Furthermore, CNTs oxidized with this method were coordinated with
metal ions that acted as precursors for the formation of quantum dots on the CNT
surface. Cycloaddition reactions of various types and have been employed in
introducing a variety of functionality for biomedical applications of CNTs.
18.3. POTENTIAL APPLICATIONS OF CARBON NANOTUBES
IN BIOLOGY AND MEDICINE
The unique and diverse properties of CNTs, in addition to the wide range of
functionality afforded by chemical modification, allow for many exciting applica-
tions. Due to their nanometer dimensions, CNTs have the potential to interact at
the cellular and molecular level.
In the last few years, several studies have been proposed that indicate
potential applications of CNTs. However, this section attempts to report the
existing and future applications of CNTs in the biomedical industry exclusively.
The following sections detail the areas in biomedical engineering where CNTs can
be potentially applied.
18.3.1. Diagnostic Tools and Devices
18.3.1.1. Radiation Oncology. The traditional method of generating
X-rays comprises of a metallic filament (cathode) that acts as a source of electrons