Bifunctional M13 Bacteriophage Nanospheroids for the Synthesis of Hybrid Noncentrosymmetric Nanoparticles

Noncentrosymmetric nanostructures are composed of two different materials displayed on spatially distinct surface regions. These nontrivial building blocks facilitate self-assembly of hierarchical nanostructures with increased complexity and support cooperative material behaviors. The arrangement of M13 bacteriophage structural proteins within its capsid creates a promising monodisperse and readily modifiable template for these low-symmetry nanomaterials. Here, a 9-mer ZnS-binding peptide was inserted into the p3 minor coat protein (capsid tip) of an M13 bacteriophage with Au-binding motif fused to its p8 major coat protein (capsid body). Multiple vortex/rest cycles with chloroform were used to convert this bifunctional, Au/ZnS (p8/p3)-binding phage from filament to spheroid. The shape transformation was studied with transmission electron microscopy, circular dichroism spectroscopy, and fluorescence spectroscopy. The effects of the p3 peptide fusion and conversion temperature were evaluated. Compared to the Au-binding phage without a p3 peptide fusion, the insertion of the ZnS-binding motif increased spheroid size, molar ellipticity loss, and intrinsic fluorescence quenching. Reduced temperature (0 °C) within early transformation cycles diminished spheroid polydispersity and increased agglomeration resistance. In addition, Au/ZnS-binding spheroids retained peptide motif affinity and relative placement of the p3 and p8. Site-specific synthesis of ZnS and Au on the p3 and p8, respectively, produced noncentrosymmetric hybrid metal/semiconductor nanostructures. This work highlights the effect of a p3 mutation on filament to spheroid transformation as well as the importance of temperature in producing a robust scaffold for inorganic material synthesis. Finally, the manufactured bifunctional M13 spheroids were used for the biodirected synthesis of noncentrosymmetric nanoparticle assemblies demonstrating the potential for heterojunction formation.