Plants that emit a glowing light under ultraviolet (UV) light are no longer just a fantasy seen in science fiction TV shows and movies. The roots of a medicinal plant known as Toddalia asiatica or orange climber, have been found to emit an ethereal blue glow. Researchers reporting in the journal ACS Central Science have now uncovered two coumarin molecules that may be the source of this fluorescence.
These natural coumarins possess unique fluorescent qualities, and one of the substances holds the potential of being utilized for medical imaging in the future.
Fluorescent substances take in UV light that’s directed at 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.
Reference: “Natural Coumarin Isomers with Dramatically Different AIE Properties: Mechanism and Application” by Shan-Shan Chen, Haoran Wang, Bo Wu, Qiyao Li, Junyi Gong, Yun-Li Zhao, Yun Zhao, Xia Xiao, Jacky W. Y. Lam, Zheng Zhao, Xiao-Dong Luo and Ben Zhong Tang, 19 April 2023, ACS Central Science.
The study was funded by the High-level Talent Promotion and Training Project of Kunming; Project of Yunnan Characteristic Plant Screening and R&D Service CXO Platform; Science, Technology and Innovation Commission of Shenzhen Municipality; Shenzhen Key Laboratory of Functional Aggregate Materials; the Research Grants Council of Hong Kong; the Innovation and Technology Commission; the Open Fund of Guangdong Provincial Key Laboratory of Luminescence from Molecular Aggregates; and South China University of Technology; and the China Postdoctoral Science Foundation.