A newly discovered class of fluorescent dyes could be useful in the next wave of biological imaging technology.

Chemists from the University of Oregon (UO) have developed the new fluorescent dyes that function in water and emit colors based on the diameter of circular nanotubes comprised of carbon and hydrogen.

The researchers focused on synthesized organic molecules called nanohoops—short, circular slices of carbon nanotubes—that allow for the use of multiple fluorescent colors, triggered by a single excitation, to simultaneously track multiple activities in live cells.

While the nanohoops were not initially water soluble, the scientists were able to manipulate them with a chemical side chain that allowed them to pass through cell membranes and maintain their colors within live cells.

Scientists have often relied on chemical compounds called fluorophores that have flat structures and emit different colors upon light excitation, for biological research and medical diagnostics.

“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,” co-author Michael Pluth, a professor in the UO’s Department of Chemistry and Biochemistry, said in a statement. “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.”

The nanohoops have a precise atomic composition and after a chemical sidechain was designed, they became soluble and passed freely through cellular membranes.

“Circular structures like these nanohoops dissolve in aqueous media better than flat structures,” Ramesh Jasti, a professor in the UO’s Department of Chemistry and Biochemistry and member of the Materials Science Institute, said in a statement. “We figured this out by just doing it. It wasn’t part of the plan.

“We just wanted to make carbon nanostructures in an ultrapure way,” he added. “The bright emissions from the different sizes they produced just happened. It is a nanoscale phenomenon.”

The toxicity levels of the nanohoops are also similar to what is traditionally used in fluorescent dyes.

The researchers will next attempt to explain where the nanohoops were going inside of the cells. They also want to see whether the nanohoops can be guided to particular sites inside of cells after finding that an additional sidechain containing folic acid led the nanohoops to cancer cells.

“That success told us that these nanohoops can be trafficked to different types of cells or even to intracellular compartments,” Jasti said. “This also suggested their possible use in medical diagnostics or even drug delivery, because our nanohoops can easily carry little compartments that will go to specific locations.”

The study was published in ACS Central Science.