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234 Biomimetics: Biologically Inspired Technologies

Figure 8.5 (See color insert following page 302) The bacterial ribosome. 30S ribosome (left panel) and 50S
ribosome (right panel). The ribosome is one of the most sophisticated molecular machines nature has ever self-
assembled. It has more than 50 different kinds of proteins and 3 different size and functional RNAs, all through weak
interactions to form the remarkable assembly line. (Source: http://www.molgen.mpg.de/~ag_ribo/ag_franceschi/.)

These weak interactions promote the assembly of molecules into units of well-defined and stable
hierarchical macroscopic structures. Although each of the bonds or interaction is rather weak, the
collective interactions can result in very stable structures and materials. The key elements in
molecular self-assembly are chemical complementarity and structural compatibility. Like hands
and gloves, both the size or shape and the correct orientation, that is chirality, are important in order
to have a complementary and compatible fitting (Schnur, 1993).
The key engineering principle for molecular self-assembly is to artfully design the molecular
building blocks that are able to undergo spontaneously stepwise fine-tuned interactions and
assemblies through the formations of numerous noncovalent week chemical bonds.

8.5 SELF-ASSEMBLING SYSTEMS — MODELS TO STUDY MOLECULAR
ANTENNA FOR PROGRAMMED ASSEMBLY, SURFACE ENGINEERING,
AND FABRICATION OF NANOSCAFFOLD TO NANOBIOTECHNOLOGY

8.5.1 Fabricating Nanowires using Bioscaffolds

In the computing industry, the fabrication of nanowires and nanofeatures using the ‘‘top-down’’
approach increasingly faces tremendous challenges. Thus, the possibility of molecular fabrication
of conducting nanowires using DNA (Braun et al., 1998; Keren et al., 2003) peptides and protein
scaffolds is of particular interest to electronics industry. One can readily envision that nanotubes,
nanofibers, actin filaments, yeast prion nanofibers made from self-assembling peptides and proteins
may serve as templates for metallization (Djalali et al., 2002; Scheibel et al., 2003; Reches and
Gazit, 2003; Mao et al., 2003). Once the organic scaffold is removed, a pure conducting wire is left-
behind and immobilized on a surface. There is great interest in developing various methods for
attaching conducting metal nanocrystals to DNA, peptides, and proteins for such a purpose.
Furthermore, the coupled DNA, peptides and proteins may not only respond to electronic
signals but may also be used as antennae for a wide range of applications including to study
detailed molecular interactions and fabricate miniature devices (Hamad-Schifferli et al., 2002;
Sung et al., 2004).
8.5.2 Molecular Ink and Nanometer Coatings on Surfaces

Molecular assembly can be targeted to alter the chemical and physical properties of a material’s
surface (Whitesides et al., 1991; Mrksich and Whitesides, 1996; Whitesides and Grzybowski,
2002). Surface coatings instantly alter a material’s texture, color, compatibility with, and respon-
siveness to the environment. Conventional coating technology is typically accomplished through