A team of scientists at Rice University (Houston, TX) has developed a single-atom switch to turn fluorescent dyes used in bioimaging on and off at will. The technique will enable high-resolution imaging and dynamic tracking of biological processes in living cells, tissues, and animals.
The research team, led by chemist Han Xiao, developed a minimally modified probe that can be triggered by a broad range of visible light. The patented process could replace existing photoactivatable fluorophores that may only be activated with ultraviolet (UV) light or require toxic chemicals to turn on the fluorescence—characteristics that limit their usefulness.
The researchers took advantage of a phenomenon known as photo-induced electron transfer (PET), which was already known to quench fluorescent signals. They put fluorophores in cages of thiocarbonyl, the moeity responsible for quenching. With one-step organic synthesis, they replaced an oxygen atom in the cage with one of sulfur. That enabled them to induce the PET effect to quench fluorescence. Triggering the complex again with visible light near the fluorescent molecule's preferred absorbance oxidized the cage in turn, knocking out the sulfur and replacing it with an oxygen atom to restore fluorescence.
Researchers worldwide use fluorescent molecules to tag and track cells or elements within cells. Activating the tags with low-powered visible light rather than UV is much less damaging to the cells being studied, Xiao says, and makes the long exposures of living cells required by superresolution imaging possible. Superresolution experiments by Theodore Wensel, the Robert A. Welch Chair in Chemistry at Baylor College of Medicine, and his team confirmed their abilities, he says.
"We feel this will be a really good probe for living-cell imaging," Xiao says. "People also use photoactivatable dye to track the dynamics of proteins, to see where and how far and how fast they travel. Our work was to provide a simple, general way to generate this dye."
The researchers found their technique worked on a wide range of common fluorescent tags and could even be mixed for multicolor imaging of targeted molecules in a single cell.
Full details of the work appear in the Journal of the American Chemical Society.