Multiple fluorescence 2PE imaging. 2PE multiple fluorescence image from a 16 μm cryostat section of mouse intestine stained with a combination of fluorescent stains (F-24631, Molecular Probes). Alexa Fluor 350 wheat germ agglutinin, a blue-fluorescent lectin, was used to stain the mucus of goblet cells. The filamentous actin prevalent in the brush border was stained with red-fluorescent Alexa Flu or 568 phalloidin. Finally, the nuclei were stained with SYTOX ® Green nucleic acid stain. Imaging has been performed at 780 nm, 100 x 1.4 NA Leica objective, using a Chameleon XR ultrafast Ti-Sapphire laser (Coherent Inc., USA) coupled at LAMBS-MicroScoBio with a Spectral Confocal Laser Scanning Microscope, Leica SP2-AOBS.