University of Oregon chemists have created a new class of fluorescent dyes that function in water and emit colors based solely on the diameter of circular nanotubes made of carbon and hydrogen. The six-member team is now exploring their potential use in biological imaging.

The synthesized organic molecules, called nanohoops, which initially were not water soluble, were manipulated with a chemical side chain to allow them to pass through cell membranes and maintain their colors within live cells.

For years, scientists involved in biological research and medical diagnostics have relied on chemical compounds called fluorophores, which have flat structures and emit different colors upon light excitation, to label specific biological molecules. The potential for circular structures to provide new fluorescent properties is far less explored.

Nanohoops, which are short circular slices of carbon nanotubes, could allow for the use of multiple fluorescent colors, triggered by a single excitation, to simultaneously track multiple activities in live cells, said Ramesh Jasti, a professor in the UO's Department of Chemistry and Biochemistry and member of the Materials Science Institute.

"The fluorescence of the nanohoops is modulated differently than most common fluorophores, which suggests that there are unique opportunities for using these nanohoop dyes in sensing applications," said Michael Pluth, also a professor in the UO's Department of Chemistry and Biochemistry. "These dyes retain their fluorescence at a broad range of pH values, making them functional and stable fluorophores across a wide range of acidic and basic conditions."

"We have seen nothing like these nanohoops in the world of dye chemistry before," said Bruce P. Branchaud, professor emeritus of chemistry and biochemistry at the UO and distinguished scientist in the Cancer Early Detection Advanced Research Center of OHSU's Knight Cancer Institute.

"All other dyes have been flat, whereas these nanohoops are non-planar circles," he said. "Their unique structures provide unique properties that we intend to develop and exploit for significant new contributions to chemical biology, biotechnology, biomedical sciences, and medicine."