Shell-crosslinked nanoparticles with a remarkable rosette shape have been formed using a simple and elegant technique. 

Karen Wooley from the University of Washington, US, used a radical polymerisation reaction between maleic anhydride and styrene to form block copolymers. The particles they made had an unexpected and unusual rosette structure. 

Initially the reaction formed micellar structures; crosslinking followed to produce shell-crosslinked nanostructures. The synthesis is a simple one pot reaction, without any need for separate additions of the reagents. This labour saving technique is cheaper and more efficient than any method used for preparing similar structures to date. 

The impetus of this work came from a need to simplify the production of these versatile and well studied crosslinked structures. The ordered rosette pattern was seen using tunnelling electron microscopy. Wooley thinks the pattern arises from the internal arrangement of the polystyrene core. This structural complexity could have huge potential for areas as diverse as nanoreactors and drug delivery. 

Wooley said these remarkable nanoparticles might 'open the door to a greater degree of control over the way nanoparticles aggregate into larger assemblies than has hitherto been possible'. 

In future, Wooley hopes her group's work will establish how the rosettes form. She also wants to investigate the effects that higher-order structure can have on the properties of the nanoparticles. Sophia Anderton