BiophysicalLOVE writes: "Scientists working with colloids — micro- and nanoscale particles suspended in a liquid — as components of self-assembling systems have found that imparting directions and specificity to the bonds they are aiming to create has been particularly tricky. To overcome this they originally attached single-stranded DNA molecules to particles, so that they interact only with other particles bearing complementary DNA. But imparting directional bonding interactions to colloidal particles has remained more of a challenge. Here scientists take the concept of DNA-mediated interactions a step further with their report of micrometre-sized particles that have symmetrically arranged, 'sticky' patches of DNA on their surfaces. The patches force the particles to interact only along certain vectors, mimicking the connectivity of atoms in molecules. Here is a major advance on earlier attempts to generate directional interactions between particles, allowing a great increase in the sophistication of structures that can be built 'bottom up' from smaller components."