Non-invasive depth profile imaging of the stratum corneum using confocal Raman microscopy: First insights into the method

The stratum corneum is a strong barrier that must be overcome to achieve successful transdermal delivery of a pharmaceutical agent. Many strategies have been developed to enhance the permeation through this barrier. Traditionally, drug penetration through the stratum corneum is evaluated by employing tape-stripping protocols and measuring the content of the analyte. Although effective, this method cannot provide a detailed information regarding the penetration pathways. To address this issue various microscopic techniques have been employed. Raman microscopy offers the advantage of label free imaging and provides spectral information regarding the chemical integrity of the drug as well as the tissue. In this paper we present a relatively simple method to obtain XZ-Raman profiles of human stratum corneum using confocal Raman microscopy on intact full thickness skin biopsies. The spectral datasets were analysed using a spectral unmixing algorithm. The spectral information obtained, highlights the different components of the tissue and the presence of drug. We present Raman images of untreated skin and diffusion patterns for deuterated water and beta-carotene after Franz-cell diffusion experiment.