Attenuated total reflection-fourier transform infrared spectroscopy as a possible method to investigate biophysical parameters of stratum corneum in vivo

We investigated the use of attenuated total reflection-Fourier transform in frared spectroscopy as a method to study differences in the molecular compo nents of human stratum corneum in vivo. These variations as a function of t he anatomic site and of the depth into its layered structure are important to understand the biology and physiology of the tissue. In this preliminary study we have investigated spectroscopic changes in 18 healthy individuals . Total reflection-Fourier transform infrared spectroscopy represents a pot entially powerful tool to study biophysical properties of surfaces. We obse rved that, in vivo, biophysical parameters of the stratum corneum (such as hydration, lipid composition, and conformation of the aliphatic chains) are indeed dependent on the anatomic site. As in total reflection-Fourier tran sform infrared spectroscopy experiments the penetration depth of the evanes cent field into the stratum corneum is comparable with the thickness of a l ayer of corneocytes, this technique can be used to follow the distribution of lipids, water, and proteins as a function of depth into the tissue. We f ound that, in vivo, these molecular components are non-uniformly distribute d, in agreement with the presence of water and lipid reservoirs as observed with ex vivo ultrastructural investigations. Composition and conformationa l order of lipids are also a function of depth into the stratum corneum. Fi nally we compared the in vivo superficial hydration measured using the infr ared absorption of the OH stretch of water, with the hydration measured usi ng the Skicon hygrometer. Our results indicate that total reflection-Fourie r transform infrared spectroscopy might be useful to measure important chem ical and biophysical parameters of stratum corneum in vivo.