Penetration Depth of Propylene Glycol, Sodium Fluorescein and Nile Red into the Skin Using Non-Invasive Two-Photon Excited FLIM.

The stratum corneum () forms a strong barrier against topical drug delivery. Therefore, understanding the penetration depth and pathways into the is important for the efficiency of drug delivery and cosmetic safety. In this study, TPT-FLIM (two-photon tomography combined with fluorescence lifetime imaging) was applied as a non-invasive optical method for the visualization of skin structure and components to study penetration depths of exemplary substances, like hydrophilic propylene glycol (), sodium fluorescein () and lipophilic Nile red () into porcine ear skin ex vivo.