Nanoparticles that self-assemble into complex optical structures sounds like an early ingredient in a future Robot Uprising recipe, but the science team at University of California, Berkeley thinks they'll be useful for nicely tame things. The self-assembly of the nanoparticle silver crystals can be controlled to produce different nano "devices" and it's a a neat way of putting together nanotech that is more typically produced top-down by lithography. The devices can be as diverse as colour-changing paint, optical computer elements, and ultrasensitive chemical sensors.
Most interesting, perhaps, is the possibility of using the nanoparticles to construct metamaterials. In this guise they may find use as "invisibility cloaks"... which are currently nearly impossible to manufacture, and that's where the self-assembly part comes in.
The octahedral silver nanoparticles are produced in solution, and are relatively large scale, which lends them potentially better optical properties than competing nanoparticle inventions. [TechnologyReview]