VNPs as Templates for Materials Synthesis - Viral Nanoparticles: Tools for Materials Science and Biomedicine - page 155

. BIoteMPlAtIng uSIng genetICAlly engIneered M1
PhAgeS

In the above-described systems, the natural surface properties of VNPs
are exploited for metal deposition. The research team led by Belcher
(Massachusetts Institute of Technology, MIT; Cambridge, MA, USA) has
brought the biotemplating approach to the next level by making use of
phage library screening techniques (recall Chapter 2 — Section 2.3.3).
The approach uses phage display screening and selection to identify peptide
sequences that bind and nucleate specific inorganic materials. These
peptides can be genetically engineered to the pIII or pVIII protein and hence
be displayed at one end of the phage, or along the virus body. A variety of
peptides specific for binding different materials have been identified and
utilized on the M13 scaffold (see Table 6.1).
The specificity of the interaction of these peptide sequences with the
inorganic counterpart is not fully understood. However, the beauty of the
selection process in the phage display system is that it simply allows the
discovery of peptides that bind to a desired material, without requiring
that the precise mechanism of binding is understood. The peptides are
highly selective, and the effective binding motif is rather small; peptides
selected are typically from 7-mer libraries (i.e., peptides consisting of
seven amino acids).
In a first approach, peptides that bind the crystalline semi-conductors
such as GaAs, InP, and Si were selected (Whaley ., 2000). Figure 6.10

demonstrates the selectivity and specificity of the system, and shows
the interaction of a GaAs-specific M13 phage with a semi-conductor
heterostructure consisting of GaAs and SiO

et al

. The phage is exclusively bound

2

to the GaAs surface.
The peptides can be engineered into the pIII protein and thus be
displayed on the M13 end structure. When the appropriate metal precursors
are added to induce the nucleation and crystal growth, a crystal is formed
selectively at the end structure of the phage (Fig. 6.11a) (Lee ., 2002).

Alternatively, the peptides can be fused with the major coat protein pVIII.
When the metal precursor are added to such a phage, nucleation and
crystal growth occurs throughout the virus body and highly oriented
nanowires are synthesized (Fig. 6.11b) (Mao

et al

et al ., 2003).