Laser-scanning confocal fluorescence microscopy images in 3D TECs, combining CE LS-ECM and human MDA-MB-231 cells that were incubated with free Dox and AMS-6-Dox nanoparticles for 24 h. Intrinsic Dox fluorescence was detected in the red channel (Dox), while DAPI fluorescence (blue channel, DAPI) was used for contrasting of cell nuclei. Control bright field (BF) images were acquired to visualize the tissue structures, and merged images highlight the colocalization of Dox and DAPI signals. Note the absence of preserved cell nuclei in the depth of TEC treated with AMS-6-Dox nanoparticles (the bottom row), in comparison with TECs treated with free Dox (upper row). Dox concentration, 10 μg/mL. Scale bars, 20 μm (upper row) and 10 μm (bottom row). The illumination conditions were kept constant for every imaging channel.