A liquid crystal system was used for the fabrication of a highly ordered composite material from genetically engineered M13 bacteriophage and zinc sulfide (ZnS) nanocrystals. The bacteriophage, which formed the basis of the self-ordering system, were selected to have a specific recognition moiety for ZnS crystal surfaces. The bacteriophage were coupled with ZnS solution precursors and spontaneously evolved a self-supporting hybrid film material that was ordered at the nanoscale and at the micrometer scale into approximately 72-micrometer domains, which were continuous over a centimeter length scale. In addition, suspensions were prepared in which the lyotropic liquid crystalline phase behavior of the hybrid material was controlled by solvent concentration and by the use of a magnetic field.

The highly organized structure of M13 bacteriophage was used as an evolved biological template for the nucleation and orientation of semiconductor nanowires. To create this organized template, peptides were selected by using a pIII phage display library for their ability to nucleate ZnS or CdS nanocrystals. The successful peptides were expressed as pVIII fusion proteins into the crystalline capsid of the virus. The engineered viruses were exposed to semiconductor precursor solutions, and the resultant nanocrystals that were templated along the viruses to form nanowires were extensively characterized by using high-resolution analytical electron microscopy and photoluminescence. ZnS nanocrystals were well crystallized on the viral capsid in a hexagonal wurtzite or a cubic zinc blende structure, depending on the peptide expressed on the viral capsid. Electron diffraction patterns showed single-crystal type behavior from a polynanocrystalline area of the nanowire formed, suggesting that the nanocrystals on the virus were preferentially oriented with their [001] perpendicular to the viral surface. Peptides that specifically directed CdS nanocrystal growth were also engineered into the viral capsid to create wurtzite CdS virus-based nanowires. Lastly, heterostructured nucleation was achieved with a dual-peptide virus engineered to express two distinct peptides within the same viral capsid. This work represents a genetically controlled biological synthesis route to a semiconductor nanoscale heterostructure. E xploiting the biologically evolved, self-assembling structures of viral capsids is a possible mechanism in the ordering of technologically important materials. A key characteristic of materials synthesized by natural biological systems is the hierarchical organization of structures on many length scales with controlled size, shape, alignment, and orientation (1-8). There has been much interest in using biological templates in vitro to modulate the growth of inorganic, semiconductor, magnetic, and other technologically important materials (9-14). Our previous work, along with that of others, has shown that biological combinatorial approaches can identify amino acid sequences capable of interacting with a variety of materials (11,15). Here, we present a system that exploits the self-assembling, crystalline structure of the viral coat to nucleate and template II-VI semiconductor nanocrystals into highly oriented quantum dot nanowires. To accomplish this, the pVIII major coat protein was engineered to display evolutionary-selected peptides, enabling directed nanocrystal growth into viral-semiconductor hybrid nanowires that were crystallographically oriented over the micrometer size range.The helical major coat protein, pVIII, of viruses can be engineered to express fusion proteins that readily self-assemble into a highly oriented viral coat structure. A 5-fold axis of rotation relates symmetric points on the coat (16, 17). Peptide sequences engineered into the pVIII protein for use as nanocrystal templates were select...

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