A nanoreactor developed at Chalmers University of Technology visualises the activity of individual catalytic nanoparticles. To identify the efficiency of each particle in the catalytic process, the researchers isolated individual gold nanoparticles in separate nanotunnels. They then sent in two kinds of molecules that react with each other on the particles' surfaces. One molecule (fluorescein) is fluorescent and when it meets its partner molecule (borohydride) the light emission stops upon reaction between the two. This makes it possible to track the catalytic process.