David Leigh and colleagues of the University of Manchester in the UK have tied the world’s tightest knot, in the form of an organic molecule. The knot has eight non-alternating crossings in a 192 atom closed loop measuring about 20 nm long, and is made from many benzene rings strung together with octahedral iron(II) ions controlling the relative positions of the three strands at each crossing point. Knots may ultimately prove just as versatile and useful at the nanoscale as at the macroscale, says the team, but a lack of synthetic routes to all but the simplest molecular knots currently prevents systematic investigations of the influence of knotting at the molecular level.