Soft materials in the nanometere size range are also more difficult to analyse as most of them only reveal their true shape when wet. This means that cryo-electron microscopy, where samples are snap-frozen, is the only feasible technique.
A team of researchers led by Pall Thordarson from UNSW used this approach to show that a perylene-bearing block copolymer can self-assemble into membrane sacs called polymersomes. The researchers showed that these polymersomes spontaneously transition from spheres into unusual faceted polyhedral shapes. They were able to visualise the entire process, uncovering how the shape transformation is driven by the aggregation of perylene as it is confined within a spherical polymersome shell. The team was also able to control the shape transformation process and isolate specific shapes as required.
The particles were also found to be intrinsically fluorescent, an extra feature that could be valuable in tracking them as they are used in a number of different applications. Taking the drug delivery field as an example, the efficiency of nanoparticle uptake into cells has been shown to be highly dependent on the shape of the nanoparticles. These results open opportunities for the use of non-spherical polymersomes for drug delivery, nanoreactor or templating applications.