Materials displaying 'self-erasing' colour images have been created by chemists in the US, who have studied how certain nanoparticles can assemble and disassemble themselves under different wavelengths of light.The materials, which are printed with ultraviolet (UV) light and erased with visible light, could one day be used for self-expiring bus tickets or for carrying secret messages.'Self-erasing papers are important for time-sensitive materials and secure communications,' said study leader Bartosz Grzybowski of Northwestern University in Evanston, Illinois. 'On the fundamental level, what we describe is also a very different way of looking at the concept of information storage. We're not using traditional coloured inks per se,...