Imaging the distribution of sodium dodecyl sulfate in skin by confocal Raman and infrared microspectroscopy

To image SDS distribution across different skin regions, to compare the permeability difference between porcine and human skin, and to evaluate the interaction between SDS and skin.

Full thickness porcine and human skin was treated with acyl chain perdeuterated SDS (SDS-d(25)) at room temperature and at 34 °C for 3, 24 and 40 h. SDS distribution in skin was monitored by confocal Raman and IR microspectroscopic imaging. Permeation profiles of SDS-d(25) in skin were derived from the band intensities of the CD(2) stretching vibrations. The interaction between SDS and skin was monitored through the CH(2) and CD(2) stretching frequencies and the Amide I and II spectral region.

SDS-d(25) penetrates both porcine and human skin in a time and temperature-dependent manner, with slightly higher permeability through the stratum corneum (SC) in porcine skin. When SDS permeates into the SC, its chains are more ordered compared to SDS micelles. The secondary structure of keratin in the SC is not affected by SDS-d(25).

The spatial distribution of SDS-d(25) in skin was obtained for the first time. Infrared microscopic imaging provides unique opportunities to measure concentration profiles of exogenous materials in skin and offers insights to interaction between permeants and skin.