In high school chemistry, we all learned about chemical reactions. But what brings two reacting molecules together? As explained to us by Einstein, it is the random motion of inert molecules driven by the bombardment of solvent molecules. If brought close enough together, by random chance, these molecules may react.
Capturing the motion of single molecules is achieved by a method known as fluorescence correlation spectroscopy (FCS). The catch? It takes many detections of light particles -- photons -- emitted by single molecules to get a clear picture of molecular motion.