Sometimes, for technical reasons, it is extremely challenging, if not impossible, to visualize active penetration in biological tissues using vibrational spectroscopy, especially when the actives are peptides or oils. In these specific cases, the use of fluorescence probe can offer a suitable alternative to visualize the penetration of these components using fluorescence microscopy. TRI Princeton have experience in labelling skin actives and visualizing penetration using a fluorescence microscope. Fluorescence microscopy is ideal for actives that are difficult to visualize directly with spectroscopy imaging, such as peptides and proteins. TRI also has access to a confocal fluorescence microscope for higher quality imaging.