Genetically Encoding Stimulated Raman-Scattering Probes for Cell Imaging Using Infrared Fluorescent Proteins.

Stimulated Raman scattering (SRS) microscopy offers great potential to surpass fluorescent-based approaches, owing to the sharp line width of Raman vibrations amenable to supermultiplex cell imaging, but currently lacks one crucial component: genetically encodable tags equivalent to fluorescent proteins. Here, we show that infrared fluorescent proteins (IRFPs) can be used as genetically encoded SRS probes and benefit from the electronic preresonant SRS enhancement effect with near-infrared exciting pulses, comparable to synthetic dyes reported in the literature. SRS imaging of the nucleus in mammalian cells is demonstrated where a histone protein is fused to an IRFP. This work opens the route toward Raman-based cell imaging using genetically encoded probes, motivating efforts in solving the challenges of photostability and creating a vibrational palette.