In Vivo Confocal Raman Microspectroscopy of the Skin: Noninvasive Determination of Molecular Concentration Profiles

Abstract

Confocal Raman spectroscopy is introduced as a noninvasive in vivo optical method to measure molecular concentration profiles in the skin. It is shown how it can be applied to determine the water concentration in the stratum corneum as a function of distance to the skin surface, with a depth resolution of 5 microm. The resulting in vivo concentration profiles are in qualitative and quantitative agreement with published data, obtained by in vitro X-ray microanalysis of skin samples. Semi-quantitative concentration profiles were determined for the major constituents of natural moisturizing factor (serine, glycine, pyrrolidone-5-carboxylic acid, arginine, ornithine, citrulline, alanine, histidine, urocanic acid) and for the sweat constituents lactate and urea. A detailed description is given of the signal analysis methodology that enables the extraction of this information from the skin Raman spectra. No other noninvasive in vivo method exists that enables an analysis of skin molecular composition as a function of distance to the skin surface with similar detail and spatial resolution. Therefore, it may be expected that in vivo confocal Raman spectroscopy will find many applications in basic and applied dermatologic research.

Feasibility of Spatially Offset Raman Spectroscopy for in Vitro and in Vivo Monitoring Mineralization of Bone Tissue Engineering Scaffolds

“…Although the laser power used here was higher than the safety standard relevant to laser light on the skin (BS EN 60825-1:2007) in order to allow short acquisition times (20 seconds), no damage was observed to the skin layer. This observation is consistent with previous reports of in-vivo confocal Raman micro-spectroscopy of skin 33 , where a laser power of 100mW (730 nm wavelength) was focused to a spot of 1-2 μm (spot diameter in this study was 88 μm). Nevertheless, the feasibility of in-vivo transcutaneous SORS measurements using laser powers capped at the safety limits (10-30 mW) has been demonstrated previously, but at the expense of longer acquisition times (60 seconds) 25 .…”

Raman spectroscopic mapping for the analysis of solar radiation induced skin damage

“…It is a routine technique for fingerprinting and identifying chemicals and acts as a standard method of analytical pharmacy and chemistry 8 . The potential of vibrational spectroscopy for diagnostic applications has been demonstrated, notably in dermal applications [9][10][11] , as well as for in vitro screening of toxicological effects of ionising radiation 12 , nanoparticles 13,14 and the action of chemotherapeutic agents 15 . Raman and infrared (IR) spectroscopy additionally provide detailed information of the molecular structure and composition of the tissue, ultimately promising an analysis of disease origin.…”

Molecular characterization of reconstructed skin model by Raman microspectroscopy: Comparison with excised human skin

“…15 The potential of Raman spectroscopy to discriminate pathologic from healthy skin structures and to classify different types and grades of cutaneous lesions has been demonstrated by several studies. [16][17][18][19][20][21][22][23][24] Other research works studied the molecular composition of the skin, 25,26 followed the effects induced by different types of drugs, 25,27 and established in depth concentration profiles (starting from the surface and going deeper into the skin) of different molecules (water and endogenous molecules). [27][28][29][30][31][32][33][34] The follow-up, in real-time analysis, of the diffusion of the exogenous products through skin layers has also been performed.…”

“…[16][17][18][19][20][21][22][23][24] Other research works studied the molecular composition of the skin, 25,26 followed the effects induced by different types of drugs, 25,27 and established in depth concentration profiles (starting from the surface and going deeper into the skin) of different molecules (water and endogenous molecules). [27][28][29][30][31][32][33][34] The follow-up, in real-time analysis, of the diffusion of the exogenous products through skin layers has also been performed. [35][36][37] To evaluate the potential of the Raman spectroscopy for future investigations on reconstructed skin samples, such as percutaneous absorption studies, toxicological risks investigations, drugs development, cosmetic products safety, and assessment of the effect of environmental aggressions like UV radiations, we have tried for the first time to establish a vibrational identity and a spectral characterization of a synthetic epidermis model, Episkin 1 , reconstructed from a culture of keratinocytes on a type-I collagen matrix.…”