Biomedical Engineering Reference
In-Depth Information
Figure 11.24
FE-SEM images of the imprinted (a, b) and control (c, d) electrospun
nanoi bermats with dif erent concentration of monomers used during their synthesis
[Co-opted from reference 54 with permission].
structure is formed with each carbon atom having four nearest neighbors
arranged in a tetrahedron, graphite is formed as a 2-D sheet of carbon
atoms arranged in a hexagonal array. In this case, each carbon atom has
three nearest neighbors. 'Rolling' sheets of graphite into cylinders forms
carbon nanotubes. h e properties of nanotubes depend on atomic arrange-
ment (how the sheets of graphite are 'rolled'), the diameter and length
of the tubes, and the morphology, or nano structure [55].
h e two main
types of CNTs are single-walled CNTs (SWCNTs) and multi-walled car-
bon nanotubes (MWCNTs). SWCNTs are sp
2
-hybridized carbon in a
hexagonal honeycomb structure that is rolled into hollow tube morphol-
ogy. MWCNTs are multiple concentric tubes encircling one another [56].
SWCNTs can be classii ed as either semi-conducting or metallic allotropes,
depending on the chirality. h e distinction of semiconducting or metallic
is important for their use in dif erent sensors but the physical separation
of allotropes has proven to be one of the more dii cult challenges to over-
come. In MWCNTs, a single metallic layer results in the entire nanotube
displaying metallic behavior. Due to cheap and easier synthesis procedure,
MWCNTs are more widely used as compared to SWCNTs.
MWCNTs were employed as medium for electron transfer and the
electro-catalyst to enhance the sensitivity of the electrochemical detec-
tion in electrochemical sensor. h e poor solubility of carbon nanotubes
in organic solvents restricts them to be used as drug delivery agents into
living systems in drug therapy. Hence many modii cation approaches like
