As a means for sensing proteins and other molecular tasks, researchers have managed to link nanoparticles to DNA. Now investigators at the University of Dortmund in Germany have figured out how to unlink them under normal physiological conditions, potentially offering a controllable way to construct complicated nanostructures or devices that interact with the body. The researchers synthesized batches of two different single DNA strands, then attached each strand to its own 20-nanometer- wide gold particle. A longer third strand of DNA binds to both shorter sequences, linking the gold particles together. The trick is that the third strand has an extra region that hangs loose. In the December 3 Angewandte Chemie International Edition, they describe how they separated the gold particles by introducing a fourth strand that binds to the third strand's loose end and unzips it from the gold particles; reconnection simply meant introducing the naked third strand again.