Biomedical Engineering Reference
In-Depth Information
beta sheets of aminoacids stack together in aggregates to form long insoluble fibrils. The
insolubility of the structures can be harmful in the body and, for instance, Alzheimer's
disease is caused by such an aggregation of the amyloid beta 42 protein fragments.
However, in biosensor applications the insolubility of the self-assembled nanofibers is
highly desirable since it will insure the long-term stability of the sensor.
2.2 Nanotubes
Overall, the shape of nanotubes is very similar to that of the nanofibers discussed above; the
difference being that the nanotubes are hollow. Nanotubes can therefore be used in much of
the same applications as nanofibers and can furthermore be employed in implementations
where the cavity inside the structures is loaded with drugs or for reducing metal ions to
form nanowires of metal covered with a peptide shell for easy functionalization purposes
(Reches & Gazit, 2003).
Nanotubes can be obtained from a large variety of monomers such as cyclic peptides, as
demonstrated in (Ghadiri et al., 1993) and (Tarek et al., 2003), linear peptide fragments such
as phenylene ethynylene oligomers (Kim et al., 2010, Slotta et al., 2008) and disc-shaped
motifs. Another structure that shares the tubular configuration is that of the rosette
nanotubes formed from a heteroaromatic bicyclic base (Fenniri et al., 2002). Figure 1 offers
illustrations of these different formation processes.
Fig. 1. Examples of self-assembly processes that can give nanotube structures: coiled peptide
fragment similar to the alpha helices in proteins, supramolecular assembly of tubular
structures to form larger tubes, stacking of cyclic peptide motifs, and an arrangement of
disc-shaped motifs in larger nanotubes. Reprinted from (Bong et al., 2001).
2.3 Nanoparticles
The field of nanoparticles is somewhat diverse and covers the small well-defined structures
formed by different monomers. Such structures range from nanospheres with a hollow core
to various solid structures. The hollow particles have received much attention as possible
drug delivery candidates and their non-hollow counterparts as biological variants of
nanobeads.
2.4 Nanotapes
Peptide nanotapes are formed from the stacking of peptide beta sheets as described in
(Fishwick et al., 2003). The formed tape structure often interacts to form double layers with
