Alkyne-tag Raman imaging for visualization of small molecules

Raman microscopy has been used for visualizing molecular distribution and dynamics in a living cell [1, 2]. Recently, we have proposed to use alkyne as a tag for Raman imaging of small molecule incorporated into biological samples [3]. Alkyne shows a characteristic peak at Raman silent region (~2050-2300cm) and is free from interference with Raman signal of endogenous biomolecules. Furthermore, since the size of alkyne-tag is much smaller compared with fluorescent labels, it rarely changes the property of tagged molecules, such as biological activity and localization in a cell. As a proof of concept, Raman observation of alkyne-tagged cell proliferation probe, EdU, in a living cell was examined and successfully visualized the localization of EdU at the nucleus. In this research, we investigated relationships between tag-structures and Raman scattering properties, such as scattering efficiency and Raman shift to provide a guideline to design appropriate alkyne-tagged small molecule and to extend the potential of alkyne-tag Raman imaging [4]. In particular, the information of structure dependence on Raman shift allows us to design alkyne tags that show Raman shift at different wavenumbers to simultaneously obtain the image of small molecules with multiple alkyne tags in a live cell. According to the guideline, we have synthesized conjugated diynes-tagged coenzyme Q (CoQ), which shows the Raman peak at 2248 cm. Raman imaging of live cell treated with a CoQ analogue and EdU visualized the different distributions constructed at each different Raman shift (Figure), proving the ability of alkyne-tag Raman imaging for multi-molecules working in a live cell.