Yadong Yin and colleagues at the University of California, Riverside, have discovered that a simple magnet can be used to change the color of nanoparticles of iron oxide in aqueous suspension. The discovery could lead to a new class of low-power electronic displays. It also has the potential to be exploited in rewritable electronic paper and e-ink products. Yin explains that, "The key was to design the structure of superparamagnetic iron oxide nanoparticles through chemical synthesis so that they self-assemble into three-dimensionally ordered colloidal crystals in a magnetic field." Unlike certain other designer nanoparticle materials, such as coated gold particles, iron oxide is cheap, non-toxic and anything but rare.