Near-infrared STED nanoscopy with an engineered bacterial phytochrome

The near infrared (NIR) optical window between the cutoff for hemoglobin absorption at 650 nm and the onset of increased water absorption at 900 nm is an attractive, yet largely unexplored, spectral regime for diffraction-unlimited super-resolution fluorescence microscopy (nanoscopy). We developed the NIR fluorescent protein SNIFP, a bright and photostable bacteriophytochrome, and demonstrate its use as a fusion tag in live-cell microscopy and STED nanoscopy. We further demonstrate dual color red-confocal/NIR-STED imaging by co-expressing SNIFP with a conventional red fluorescent protein. Super-resolution microscopy using wavelengths in the near infrared (NIR) optical window is particularly appealing for live cell and tissue imaging, yet largely unexplored. Here the authors present NIR-STED nanoscopy of living mammalian cells using the new bacteriophytochrome-based fluorescent protein SNIFP.