One-atom switch overloads fluorescent dyes

The scientists at Rice University needed to replace an atom only to give new powers to biocompatible fluorescent molecules.

Chemical chemistry laboratory of chemist Han Xiao reported in the Journal of the American Chemical Society He developed a single-atom switch to activate and deactivate fluorescent dyes used in biological imaging at will.

This technique will enable high resolution imaging and dynamic tracking of biological processes in cells, tissues and live animals.

Rice has developed a modified probe that can be triggered by a wide range of visible light. The patented process could replace existing photoactivable fluorophores that can only be activated by ultraviolet light or that require the use of toxic chemicals to activate fluorescence, which limits its usefulness.

The researchers took advantage of a phenomenon known as photo-induced electron transfer (PET), already known to attenuate fluorescent signals.

They put fluorophores into thiocarbonyl cages, which were responsible for quenching. With one-step organic synthesis, they replaced an oxygen atom in the cage with a sulfur atom. This allowed them to induce the PET effect to attenuate the fluorescence.

Triggering the complex again with visible light near the preferred absorbance of the fluorescent molecule oxidized the cage in turn. This stunned the sulfur and replaced it with an oxygen atom, restoring the fluorescence.

"It just takes a little chemistry and a step," said Xiao, who joined Rice in 2017 with funding from the Texas Institute of Cancer Research and Prevention (CPRIT) ). "We've shown in the paper that it works the same way for a whole range of fluorescent dyes, basically a reaction solves many problems."

Researchers around the world use fluorescent molecules to tag and track cells or cells inside cells. Enabling labels with visible light of low power rather than ultraviolet is much less damaging to the cells in the study, said Xiao, and makes possible the long live cell exposures required by the 39, super resolution imagery. The super-resolution experiments of Theodore Wensel, Robert A. Welch Chair in Chemistry at Baylor College of Medicine, and his team confirmed their abilities, he said.

"We think it will be a very good probe for live cell imaging," Xiao said. "People are also using a photoactivatable dye to track protein dynamics, to see where, how far and how fast they travel, and our job was to provide a simple, general way to generate that dye."

The researchers found that their technique worked on a wide range of current fluorescent labels and could even be mixed for multicolor imaging of targeted molecules in a single cell.