Scientists from the University of Warwick, UK and the University of Sydney, Australia, have created Janus protein nanotubes – nanotubes with two distinct faces. The Janus nanotubes have a tubular structure formed by the stacking of cyclic peptides resulting in a molecular channel with an internal diameter of 1 nanometer, big enough to allow ions and small molecules to pass through. Each cyclic peptides has two distinct polymer attachments that give rise to a two-faced shell for the nanotubes. In the solid state, these materials could act as molecular sieves for separating mixtures of fluids. In solution, they form bilayers that could be exploited in drug delivery.