No abstract

CitationTowards drug quantification in human skin with confocal Raman microscopy. AbstractUnderstanding the penetration behavior of drugs into human skin is a prerequisite for the rational development and evaluation of effective dermal drug delivery.The general procedure for the acquisition of quantitative drug penetration profiles in human skin is performed by sequential segmentation and extraction. Unfortunately, this technique is destructive, laborious and lacks spatial resolution. Confocal Raman microscopy bares the potential of a chemically selective, label free and nondestructive analysis. However, the acquisition of quantitative drug depth profiles within skin by Raman microscopy is impeded by imponderable signal attenuation inside the tissue.In this study, we present a chemical semi-solid matrix system simulating the optical properties of human skin. This system serves as a skin surrogate for investigation of Raman signal attenuation under controlled conditions. Caffeine was homogeneously incorporated within the skin surrogate and Raman intensity depth profiles were acquired. A mathematical algorithm describing the Raman signal attenuation within the surrogate was derived from these profiles. Human skin samples were incubated with caffeine and Raman intensity depth profiles were similarly acquired. The surrogate algorithm was successfully applied to correct the drug profiles in human skin for signal attenuation. For the first time, a mathematical algorithm was established which allows correction of Raman signal attenuation in human skin, thus facilitating reliable drug quantification in human skin by confocal Raman spectroscopy.Keywords: confocal Raman microscopy, human skin, quantitative depth profiling, dermal drug delivery, skin surrogate, Raman signal attenuation 3

No abstract

No abstract

The opportunity of label-free and non-destructive detection of substances inside human skin by confocal Raman microscopy represents a novel approach for investigating drug penetration and permeation. Several studies already introduced confocal Raman microscopy for depth profiling in skin; however, the reported results show high deviations. Thus, analysis of the spectral variability of human skin itself is a necessary prerequisite for systematic quantitative investigations of drug penetration and permeation by confocal Raman microscopy.In our work, we acquired Raman depth profiles from excised human skin samples after abdominal plastic surgery and investigated the absolute intensity fluctuation of four major skin derived Raman peaks. The results prove the expected high variability in spectral intensity, but we could not detect dissimilarities between different skin donors. A detailed analysis of the major endogenous skin components revealed differences in spatial distribution which consequently affects their individual applicability as reference peaks for relative depth profiling. Furthermore, we discovered an increase in signal variability in deeper stratum corneum layers, which has to be considered in future substance depth profiling investigations. In addition, we discovered an exponential decay of the Raman signal for all major skin components accounting for signal attenuation inside biological tissue. Based on this mathematical description, quantitative follow-up of substances in human skin can be realized. All in all, the results of this study elucidate the necessity of substantial understanding of endogenous spectral characteristics inside human skin as essential prerequisite for rational depth profiling of substances in human skin.