Spectrofluorescence of skin and hair

There are numerous chromophores present throughout the strata of human skin, which present many challenges and opportunities to probe molecular events. Fluorescence spectroscopy is principally employed to identify important biochemical components of the skin including endogenous tryptophan, tyrosine, pepsin-digestible collagen cross-links, collagenase-digestible collagen cross-links, NADH, etc. Over the last 15 years, many advances in instrument technology have been introduced allowing for much faster data acquisition with spectrofluorometers. As a result, a series of spectrofluorescence emission scans can be generated for a range of excitation wavelengths, or vice versa (excitation scans for a range of emission wavelengths), quickly to generate excitation-emission matrices. In this work, we constructed an endogenous fingerprint of fluorescent compounds present in skin, hair and nail tissues by employing a range of excitation wavelengths from 270 to 450 nm with a resolution of 2 nm. As a result, we generated surface plots of fluorescence emission as a function of excitation and emission wavelengths. From these data, we identified the predominant fluorescent chromophores in each tissue. We examined several sources of skin including in vivo human and ex vivo pig, sheep, goat and cow skin. We also analysed various types of mature hair characterized by the degree of melanin content. These analyses provided us with a fundamental understanding of the effects of melanin distribution in hair fibres and aided with the identification of fluorophores present in hair.