Jeroen Cornelissen at Radboud University, Nijmegen, the Netherlands, and colleagues combined the coat protein of a plant virus with polystyrene sulfonate to make highly stable nanoparticles. Coat proteins surround a virus and are thought to have the potential to self-assemble and encapsulate and transport drugs or DNA. The proteins normally form a cage, made up of 90 sub-units, that encapsulates a strand of RNA. This gives a highly defined 28 nanometre virus particle. But by replacing the RNA with a polymer, Cornelissen made smaller particles that are just 16 nanometres across.
A virus coat protein can encapsulate polymer strands to make nanoparticles. (Image: RSC Publishing)
As the size of the protein cage depends on the molecular weight of the polymer, the size of the nanoparticle can be controlled, said Cornelissen. He also plans to work on increasing the number of protein subunits in the cage, to form larger particles.
A further challenge will be to include functional polymers such as chromophoric or electroactive polymers, while maintaining the controlled self-assembly. This might lead on to applications as far afield as drug delivery, electronics, diagnostics and catalysis.