High-resolution optical imaging of single molecules has been achieved in living cells through the design of a small fluorescent organic molecule that outperforms commonly used fluorescent proteins.

Organic fluorophores generally emit much more light than fluorescent proteins. William Moerner of Stanford University in California and his colleagues have devised a system in which a commercial enzyme is fused to the protein of interest. The 'fluorogen' then binds to the enzyme and is activated by light, enabling high-resolution imaging by the controlled activation of single molecules.

Credit: AM. CHEM. SOC.

The authors were able to image protein microtubules in mammalian cells (pictured), as well as other protein structures in living bacteria, with a resolution beyond the limit of optical diffraction.

J. Am. Chem. Soc. doi:10.1021/ja1044192 (2010)