Angew. Chem. Int. Edn doi:10.1002/anie.200905827 (2010)


Molecules tumbling out of solution onto surfaces often self-assemble into ordered nanometre-scale patterns. For the first time, one such delicate assembly has been repeatedly switched back and forth between two designs.

Paolo Samorì at the University of Strasbourg in France, Gian Piero Spada at the University of Bologna in Italy and their colleagues used a scanning tunnelling microscope to watch a modified form of guanine, dissolved in a tiny amount of solvent, form ribbons on a graphite surface (pictured above, left). After the authors added potassium ions, the guanine clustered in a quartet pattern (right). Adding another chemical, a cryptand, reverted the surface structure to the original ribbon-like pattern. The designs could be switched reversibly for hours.