What is the difference between linear chains and rings composed of the same material? The molecular building blocks are identical, but from a mathematical point of view, the two structures have distinct topologies, ring and linear chain. This difference is readily recognizable on a macroscopic scale, as, for example, a golden ring and a gold bar, but represents a tricky task on the microscopic scale. The physicists Lisa Weiss and Christos Likos of the University of Vienna and Arash Nikoubashman of the Johannes-Gutenberg University of Mainz investigated strategies to separate nano- and microparticles of distinct topology. Their results are published in the high-impact journal ACS Macro Letters.