Fluorescent blue coumarins in a folk-medicine plant could help us see inside cells

Fluorescent substances take in UV light that's directed on them and release vibrantly colored visible light. And some glow even more brightly when they are close together, a phenomenon seen in compounds called aggregation-induced emission luminogens (AIEgens). They are key components in some optical devices, cellular imaging techniques and environmental sensors. However, these molecules are usually made in a lab, and many are toxic. Some plants already have this ability, so, Ben Zhong Tang, Zheng Zhao, Xiao-Dong Luo and colleagues turned to nature to find naturally occurring and safer AIEgens.

The researchers dried orange climber roots, crushed them into a powder, and then isolated and identified coumarin compounds with aggregation-induced emission properties: 5-methoxyseselin (5-MOS) and 6-methoxyseselin (6-MOS). When dissolved in an organic solvent, 5-MOS exhibited a blue-green glow and 6-MOS had a slightly dimmer blue glow. In addition, both AIEgens had low cytotoxicity and good biocompatibility. Then in a final series of experiments, the team found that mitochondria could be clearly identified in live cells stained with 5-MOS without any additional processing, making cell imaging easier and faster than with most current methods. The newly reported compound is a natural, plant-derived option that could advance bioimaging, the researchers say.