Evaluation of Skin Penetration of Fluorescent Dissolved Formulations Using Confocal Laser Scanning Microscopy

November 2025 in “ Pharmaceutics ”

Yoshihiro Oaku, Toyoyasu Kuwae, Takeshi Misono, Taku Ogura, Akinari Abe

confocal laser scanning microscopy skin penetration fluorescent dyes lipophilicity Rhodamine B Rhodamine 123 Fluorescein Sodium Nile Red transdermal route follicular route

TLDR Moderately lipophilic dyes penetrate skin deeply, while highly hydrophobic or lipophilic dyes stay on the surface.

The study used confocal laser scanning microscopy (CLSM) to evaluate the skin penetration of four fluorescent dyes with varying lipophilicities on excised human abdominal skin. Rhodamine B and Rhodamine 123, which are moderately lipophilic, penetrated deeply through transdermal and follicular routes, while highly hydrophobic Nile Red remained superficial. Fluorescein Sodium showed minimal intensity increase over time. The study concluded that CLSM is a non-destructive, semi-quantitative tool for early-stage screening of transdermal penetration behaviors, highlighting the influence of lipophilicity on penetration depth and pathways.

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