Biomedical Engineering Reference
In-Depth Information
the sample are very large and contain moieties with high susceptibility as in the case of
aromatic units.
Fig. 9. The self-assembly of the diphenylalanine-based peptide nanotubes in the presence of
a ferrofluid and their exposure to an external magnetic field resulting in the control over
their horizontal alignment. (a) Schematic representation of the dipeptide monomers self-
assembled in the presence of a ferrofluid solution containing magnetite nanoparticles
approx. 5 nm in diameter. (b) TEM image of a self-assembled peptide tube coated with
magnetic particles. (c) Low-magnification SEM micrograph of the self-assembled magnetic
tubes. (d) Horizontal arrangement of the self-assembled magnetic tubes after their exposure
to a magnetic field, observed by low-magnification SEM. (e) Schematic representation of the
self-assembled magnetic tubes. (f,g) Schematic representations of the magnetic tubes
randomly oriented before exposure to the magnetic field (f) and horizontally aligned upon
exposure to the magnetic field (g). Reprinted by permission from Macmillan Publishers Ltd:
Nature Nanotechnology, (Reches & Gazit, 2006), copyright (2006).
Another contact-free method used for the manipulation of self-assembled nanostructures is
dielectrophoresis. Dielectrophoresis occurs when a polarizable object is exposed to an
inhomogeneous electric field, so that the Coulomb forces induced on the charges on each
half of the dipole differ, causing a net force on the object. The manipulation of self-
assembled peptide nanotubes was reported by our group in 2008. Using micro-patterned
gold electrodes, peptide nanotubes were manipulated by adjusting the amplitude and
frequency of the applied voltage, cf. Figure 10. The electrical characterization of the
immobilized peptide nanotubes was studied, both for single peptide nanotubes and bundles
of them (Castillo et al., 2008).
