In vivo Raman Microspectroscopy: Intra- and Intersubject Variability of Stratum Corneum Spectral Markers

Abstract

Background: In vivo Raman spectroscopy is a powerful tool for real-time analysis and in situ evaluation of tissues such as the skin. The efficiency of this technique has been widely demonstrated as a label-free method for in vivo evaluation of the skin. The aim of this study is to gather information about inter- and intra-individual variations in the spectral descriptors of water content and structure, organization of the lipid barrier and structure of proteins in the stratum corneum (SC). Methods: In vivo SC measurements were performed on 17 female volunteers aged 20-30 years (phototypes I and II). For intra-individual variability, spectral collection was performed on 5 successive days per volunteer. Shapiro-Wilk and Cochran tests were applied to check the normality and the homoscedasticity of variances. ANOVA was then applied to evaluate intra- and intergroup variability. Results: ANOVA was performed on the spectral descriptors of water content and structure, organization of the lipid barrier and secondary structure of proteins in the SC. No significant intra- and interday variability was observed for all volunteers. Despite the low value of the total relative standard deviation, a highly significant variation was observed between volunteers. Conclusion: Interindividual variability for Raman measurements is significant for a set of volunteers with normal nondiseased SC and close phototypes. This variability should be taken into consideration as a threshold for significant variance when working in vivo.

In vivo confocal Raman microscopic determination of depth profiles of the stratum corneum lipid organization influenced by application of various oils

“…Slight inter-individual variations of the Raman spectral features were recently reported by Quatela et al [69] which is confirmed in the present study. In order to improve readability of Fig.…”

Depth-dependent autofluorescence photobleaching using 325, 473, 633, and 785 nm of porcine ear skin ex vivo

“…For a detailed analysis of the total fluorescence, a wavelength-dependent light throughput of the detecting optics, as well as the detector sensitivity, would have to be taken into account. 58 Because of scattering, absorption, and anisotropy propagation, the total intensity of the spectra decreases with increasing depth in the skin (data not shown). The Raman/fluorescence ratio clearly increases during the photobleaching process, which is in accordance with previously published data.…”

“…Further investigations are necessary to compensate the depth-and wavelength-dependent irradiation and autofluorescence intensities. One approach could be the fluorescence normalization based on the keratin contribution of the recorded Raman spectra, 58 as the keratin distribution within the SC is considered to be homogenous. 41,56 However, for deeper skin layers, the normalization is a very complicated task due to the inhomogeneous distribution of the fluorophors.…”

Confocal Raman Spectroscopy as a tool to measure the prevention of skin penetration by a specifically designed topical medical device

“…The detection level of the investigated product with respect to its Raman spectra was determined by performing dilution assessments in dilutions of 1:10, 1:100, and 1:1000 in octyl dodecanol. This was necessary to also compensate for the restriction and limits of intra‐ and inter‐subject variability of stratum corneum spectral markers . Furthermore, the noise signal of the fitment model at Baseline was also deducted.…”

“…This was necessary to also compensate for the restriction and limits of intra-and inter-subject variability of stratum corneum spectral markers. 26 Furthermore, the noise signal of the fitment model at Baseline was also deducted.…”