2, University of California, Riverside, Riverside, California, United States
Viruses are widely known biological macromolecules with self-assembly and molecular recognition capabilities. Genetic modification of viruses to include high affinity peptide fusions allows templating of a variety of materials, and formation of hierarchical nanoarchitectures. Despite the success of biotemplate employment, there is a significant disadvantage: the geometry of the scaffold cannot be drastically changed. A different virus with the required architecture must be individually engineered. The desire to develop a viral scaffold with geometry tuning capability, while preserving its material binding properties has led us to study M13 bacteriophage transformation. The M13 bacteriophage is a high aspect ratio, 880 nm long and 6.5 nm diameter filamentous virus. It contains approximately 2700 copies of p8 major coat protein along its length and 5 copies of p3 minor coat protein at the proximal end of the filament. An extensive collection of peptides with affinity for an array of materials has been developed for and is compatible with this biotemplate. Moreover, the M13 can contract from nanowire to rod and spheroidal structures upon exposure to nonpolar media. This is a considerable advantage, since it enables low-cost manufacturing of variable nanoarchitectures under mild conditions. In this work, genetically-modified bacteriophage with Au- and ZnS-binding peptides displayed on the p8 and p3 sites, respectively, have been transformed via chloroform treatment into 250 nm long and 15 nm diameter rod structures, known as intermediate- or i-forms. Circular dichroism and UV-vis absorption spectroscopy were employed to study the structural changes which accompanied the morphological modification. I-form peptide fusion functionality was compared with that of the filamentous and spheroidal geometries through templated Au and ZnS synthesis. Size, growth rate and crystallinity of the resulting Au and ZnS nanostructures were investigated by transmission electron microscopy and electron diffraction techniques. Optical absorbance and photoluminescence were measured and correlated to viral scaffold architecture. This research shows that fine-tuning of the virus geometry allows assembly of inorganic materials with desired morphological and optical properties.