A critical comparison of some Raman spectroscopic techniques for studies of human stratum corneum.
This study evaluates a variety of techniques and sampling conditions for Raman spectroscopic investigations of human stratum corneum. Using a Fourier-transform Raman system and samples of stratum corneum in vitro, we demonstrated minimal inter- and intracadaver variations in molecular vibrations. We have also shown Raman spectroscopy to be relatively insensitive to the hydration state of human stratum corneum, indicating that the technique should be valuable for monitoring the transdermal delivery of drugs from aqueous solutions. The stability of human stratum corneum to near-infrared laser excitation was verified by spectral collection for approximately 1 hr. We have also compared FT-Raman spectra from human stratum corneum in vitro and in vivo. Of the different types of Raman instruments used in this study (visible-light excitation microprobe, visible-light excitation macroscopic sampling, and Fourier-transform Raman), the FT-Raman system provided good-quality spectra with high sample throughput, but systems using visible-light excitation should provide unique information for use in specialist applications.