Is it possible to measure the forces of the links that bind macromolecules like DNA together? Fèlix Ritort, head of research at BIOSMALL (Laboratory for Biomolecular Physics and Small Systems) at the University of Barcelona, insists that it is. He explains how, with the aid of large optical tweezers, it is possible to separate the synthetic pearls attached to the ends of a DNA chain and measure the force exerted to separate each link. The aim? To decipher DNA sequences from the forces required to separate the two chains.