Infrared spectroscopic investigation of in vivo and ex vivo human nails

Mid (700-4000 cm^-1) and near (4000-10000 cm^-1) infrared spectra of viable and clipped human finger nails are presented. Mid-infrared depth profiles acquired by physically etching the nail plate and those acquired nondestructively using photoacoustic spectroscopy (PAS) are compared. The dorsal, intermediate, and ventral layers of the nail plate could be discerned spectroscopically. Near infrared (NIR) attenuated total reflectance (ATR), NIR-PAS and NIR diffuse reflectance spectra of the nail plate are compared. At high energies (> 7000 cm^-1), ATR lacks sensitivity while the diffuse reflectance spectra contain significant contributions from deep within the finger. At lower energies (< 7000 cm^-1) ATR can be used to probe the near surface of the nail while diffuse reflectance and PA spectra contain only minor contributions from the nail bed and primarily represent the deeper portion of the nail. The low energy near infrared region appears to be the most valuable region for viable nail plate diagnostic spectroscopy. This region is discussed in considerable detail.