**2.7 Fluorescence microscopy**

The level of dye penetration into fibers was visualised by fluorescence microscopy on polyamide transversal cuts. The fibers were embedded into an epoxy resin and transversal cuts of the fibers with 15 mm were prepared using a microtome (Microtome Leitz). Fibers' cross sections were analyzed by a fluorescence microscope LEICA DM 5000B at 40x magnification.
