Cell-Permeant Large Stokes Shift Dyes for Transfection-Free Multicolor Nanoscopy

We designed cell-permeant red-emitting fluorescent dye labels with >140 nm Stokes shifts based on 9-iminoanthrone, 9-imino-10-silaxanthone, and 9-imino-10-germaxanthone fluorophores. The corresponding probes selectively targeting mitochondria, lysosomes, and F-actin demonstrate low toxicity and enable stimulated emission depletion (STED) nanoscopy in neurons, human fibroblasts, U2OS, and HeLa cells. In combination with known small Stokes shift dyes, our probes allow live-cell three-color STED nanoscopy of endogenous targets on popular setups with 775 rim STED wavelength.