Nanoparticles are tiny stable clusters of atoms or molecules of between one and 100 nanometres. In comparison, the width of a human hair ranges from 80,000 to 100,000 nanometres. At this scale, particles sometimes exhibit unexpected properties, and structured assemblies of nanoparticles can have characteristics which are not found in the natural world. These varied and novel properties are finding applications in new technology domains such as nano-optics, neural computing, nanoscale transistors and cloaking devices. A research group at Nagoya University, led by Professor Miho Tagawa and including Dr Takumi Isogai, graduate students Hayato Sumi and Shoko Kojima, is working at the cutting edge of nanotechnology, finding ways to programme and control the structure of nanoparticle crystals and lattices using DNA mediation. As Tagawa says: ‘programmable self-assembly of matter represents a big challenge in the field of material science and nanotechnology. It will lay the foundations for the creation of highly novel materials and devices, based on the specific properties of nanoparticles.’ The project is funded by a range of Japanese agencies, including government ministries and private foundations. Nanoparticle crystals: Nanoparticle crystallisation is difficult because of the various molecular interactions within and between particles and with the solvent. In 2008, it was discovered that using strands of DNA as surface ligands on nanoparticles would cause nanoparticles to assemble in crystalline structures similar to those exhibited by atoms. The surface strands of DNA interlink through hybridisation and act as a binding agent between the nanoparticles. Varying the lengths and segment types causes the particles to bind in different ways and thus exhibit different properties. Much has been learned about DNA-nanoparticle (DNA-NP). However, many challenges remain. Tagawa elaborates: ‘whereas crystals of DNA-NP superlattice are stable when in a buffer solution, they tend to lose their symmetry when dried and exposed to air.’ The team at Nagoya were determined to find a means of stabilising these structures after dehydration.