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In a different approach, M13 constructs expressing a gold-binding peptide
as pVIII fusion and a streptavidin-binding peptide as pIII fusion were used as
building blocks. The gold-binding peptide facilitated metallization, whereas
the streptavidin-binding peptide allowed self-organization. Up to three
phages could be linked to a single streptavidin (streptavidin is a tetrameric
protein), and a tripod-like structure was created (see Fig. 6.12) (Huang
et al
.,
2005).
7.3 2D THIN-FILM ASSEMBLIES
Rod-shaped particles have the intrinsic property to form crystalline liquid
film assemblies. A liquid crystal is a liquid, in which the molecules (here
VNPs) are regularly arrayed in either one or two dimensions. Viral liquid
crystals consisting of aligned TMV and M13 particles have been fabricated.
Ordering of the VNPs occurs typically in the
nematic
or
smectic
phase;
however, ordering into other phases has also been observed. In a
nematic
crystal, the VNPs have long-range orientational order, but do not show
any positional order. The VNPs all point in one direction but there is no
side-to-side alignment. In contrast, in the
phase, the VNPs are
aligned orientational and also ordered in well-defined layers. One further
differentiates a
smectic
smectic A
versus
a
smectic C
phase. In the
smectic A
phase,
the molecules or VNPs are oriented along the main axis; in a
smectic C
phase,
the particles are tilted from the main axis (Fig. 7.5).
Figure 7.5
Liquid crystalline phases: nematic (a), smectic A (b), and smectic C (c).
Long-range ordered liquid crystalline films of M13 particles have been
assembled and studied. When using genetically engineered VNPs that
display peptides for biotemplating, metalized films for potential application
in electronics can be prepared. When such assemblies are dried, self-
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