Credit: © 2009 Wiley

Nanostructures, such as functionalized nanoparticles, have wide-ranging applications. However, they are generally used in the form of organic or aqueous dispersions, thin films or as bulk powders. Recently, inorganic nanostructures have been reported with liquid-like behaviour. However, proteins, like many nanostructures, have dimensions that exceed the range of their intermolecular forces, which has made formation of liquid proteins difficult to achieve.

Now, Stephen Mann at the University of Bristol and colleagues1 have reported the preparation of a solvent-free liquid protein. They added approximately 240 amino groups to ferritin, a globular protein. When the ferritin cation reacted with an anionic polymer surfactant, an ionic nanomaterial formed. The complex was annealed at 50 °C to produce a viscous red liquid that remained fluid at room temperature. This liquid contained less than 2% water and was composed of discreet nanoparticles, indicating that the protein was structurally intact.

On cooling to 32 °C, the melt underwent a slow ordering transformation from liquid to a liquid-crystalline phase that had a smectic microstructure. The method for preparing solvent-free protein melts is applicable to other related proteins — it is possible to prepare a range of biomimetic ferritins with functional metal cores, so this method could be extended to create a range of biologically derived nanostructures.