Multiphoton polarization imaging of the stratum corneum and the dermis in ex-vivo human skin

In this work, we demonstrate the application of multiphoton polarization imaging in resolving the structures in surface stratum corneum and dermal layers of ex-vivo human skin. By varying the excitation and emission polarizations, we characterized the structural features in both Laurdan labeled stratum corneum and dermal fibers. The results presented here have important consequences in bioimaging applications of the skin. Both the mechanics of transdermal drug delivery across the skin and physiological significance of the structural changes of the dermis can be monitored. Our results show that the transition dipoles of Laurdan molecules are preferentially oriented normal to the membrane surface. Furthermore, polarization imaging shows that fibrous structures in the dermis generate emission aligned strongly along the excitation polarization. This work shows that multiphoton polarization imaging can be a powerful method in identifying structural orientations in the skin and other biological structures.