Viral-based Janus Particles for Nanomotor Assembly

Viral nanoparticles are monodisperse, self-assembled biomaterials. Their structure and chemistry, including exact shape and site-specific functional groups, is genetically encoded and known with atomic scale precision, establishing a benchmark unrivaled by synthetic nanoparticles. Importantly, the biodiversity of viruses is vast, including an array of geometries and surface chemistries. Of specific interest, here, are viruses with asymmetric capsid proteins, like the M13 bacteriophage, that can serve as programmable bio-derived Janus particles. The M13 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. Each of these proteins can be modified to create a low-symmetry template with peptide affinity for two different materials. In addition, using simple chemical exposure, this filamentous template can undergo a shape transformation to form 150 nm rods or 50 nm spheres, while maintaining site-specific affinity. The capacity for extreme modification of morphology combined with the asymmetric placement of the p3 and p8 on the viral surface make the M13 bacteriophage a potentially powerful scaffold for Janus particle assembly. In this work, the asymmetric Janus-like structure and functionality of the M13 bacteriophage capsid was used to create nanoswimmers. A cysteine-rich peptide fusion was inserted into the minor coat protein (p3) at the virus tip and Pt nanoparticles were attached via metal-thiol bonding. Using a brief chloroform treatment, the shape of the hybrid organic-inorganic Janus materials was transformed from filament to spheroid. The size and morphology of the resulting nanomaterials were characterized. The viral-based Janus particles were fluorescently tagged and exposed to low concentrations of H₂O₂ to fuel self-propulsion. Using confocal fluorescence microscopy, the nanomotor trajectory was explored, diffusion coefficients were measured, and particle motion was correlated to size and shape.