Attenuated total reflection protein layer

There is substantial history regarding the application of conventional vibrational spectroscopy methods to study the intact surface of skin, the extracted stratum corneum and the ceramide-cholesterol-fatty acid mixtures that constitute the primary lipid components of the barrier. The complexity of the barrier and the multiple phases formed by the interactions of the barrier components have begun to reveal the role of each of these substances in barrier structure and stability. The use of bulk phase IR to monitor lipid phase behavior and protein secondary structures in the epidermis, as well as in stratum corneum models, is also well established 24-28 In addition, in vivo and ex vivo attenuated total reflectance (ATR) techniques have examined the outer layers of skin to probe hydration levels, drug delivery and percutaneous absorption at a macroscopic level.29-32 Both mid-IR and near-IR spectroscopy have been used to differentiate pathological skin samples.33,34 The above studies, and many others too numerous to mention, lend confidence to the fact that the extension to IR imaging will produce useful results. 

The complexity of the FT-IR spectra collected in the Attenuated Total Reflectance (ATR) mode which can include contributions from (a) the adsorbed protein layer or (b) the soluble proteins in the liquid layer adjacent to the ATR surface but within the "depth of penetration" of the evanescent field of the IR beam (this so-called "bulk" effect is especially significant when near-physiological protein concentrations are studied) ... 

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