Swapping 1 atom lets visible light trigger fluorescent dyes


Replacing just one atom gives new powers to biocompatible fluorescent molecules, say researchers.

The Rice University lab of chemist Han Xiao reports in the Journal of the American Chemical Society that it has developed a single-atom switch to turn fluorescent dyes used in biological imaging 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 team developed a minimally modified probe that a broad range of visible light can trigger. The patented process could replace existing photoactivatable fluorophores that may only be activated with ultraviolet 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. That knocked out the sulfur and replaced it with an oxygen atom, restoring fluorescence.

“All it takes to make these is a little chemistry and one step,” says Xiao, assistant professor of chemistry, biosciences, and bioengineering. “We demonstrated in the paper that it works the same for a range of fluorescent dyes. Basically, one reaction solves a lot of problems.”

Researchers worldwide use fluorescent molecules to tag and track cells or elements within cells. Activating the tags with low-powered visible light rather than ultraviolet is much less damaging to the cells being studied, Xiao says, and makes the long exposures of living cells required by super-resolution imaging possible. Super-resolution experiments by Theodore Wensel, 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.

Additional collaborators are from Rice, Baylor, and the Center for Translational Cancer Research at Texas A&M University. CPRIT, the Robert A. Welch Foundation, a Hamill Innovation Award, a John S. Dunn Foundation Collaborative Research Award, and the National Institutes of Health supported the research.

Source: Rice University



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