View Larger Version | Magnetic fields and the right fluid can steer particles to self-assemble. Aided by nanosized iron particles, microsized polystyrene beads embedded with iron follow magnetic forces, and beads left nonmagnetic move in other directions. The result is a flower structure, its center a large bubble trapped in the iron nanoparticle broth (left). At right, a scanning electron microscope image shows the beads after the liquid has been evaporated. Credit: Both: Randall Erb, B. Yellen/Duke Univ.; Right: Nature, 2009