Tracking heavy water incorporated confocal Raman spectroscopy for evaluating the effects of PEGylated emulsifiers on skin barrier.

The class of PEGylated emulsifiers finds broad application in the pharmaceutical and cosmetic industry. We target on one of the categories of polyethylene glycol (PEG) alkyl ethers with different lipophilic and hydrophilic chain length and aim to examine their effects on the skin comprehensively. In this study, we employed confocal Raman spectroscopy (CRS) for skin depth profiling and imaging. A unique probe of heavy water (D2 O) was incorporated, which can be tracked percutaneously and simultaneously monitor the effects caused by emulsifiers. According to the results, most of the PEGylated emulsifiers caused changes in skin lipid content/organization and induced the alteration in relative water content/hydrogen bonding structure. The results obtained from the depth profiling analysis provided the possibility to estimate the least penetration depth of emulsifiers. Among them, PEG-20 ethers displayed the most penetration ability. Meanwhile, it is interesting to find that the treatment of emulsifiers also affected the spatial distribution of D2 O whose differences were in line with the molecular skin variations. In particular, the isotopic H/D substitution in the skin was highlighted in detail. This result supports the possibility to use D2 O as an excellent and cost-effective probe to evaluate the skin barrier function. This article is protected by copyright. All rights reserved.