SPECTROSCOPIC AND MICROSCOPIC CHARACTERISTICS OF HUMAN SKIN AUTOFLUORESCENCE EMISSION

To improve the understanding of human skin autofluorescence emission, the spectroscopic and microscopic characteristics of skin autofluoresc ence were studied using a combined fluorescence and reflectance spectr oanalyzer and a fiber optic microspectrophotometer. The autofluorescen ce spectra of in vivo human skin were measured over a wide excitation wavelength range (350-470 nm). The excitation-emission matrices of in vivo skin were obtained. An excitation-emission maximum pair (380 nm, 470 nm) was identified. It was revealed that the most probable energy of skin autofluorescence emission photons increases monotonically and near linearly with increasing excitation photon energy. It was demonst rated that the diffuse reflectance, R, can be used as a first order ap proximation of the fluorescence distortion factor f to correct the mea sured in vivo autofluorescence spectra for the effect of tissue reabso rption and scattering. The microscopic in vitro autofluorescence prope rties of excised skin tissue sections were examined using 442 nm He-Cd laser light excitation as an example. It was demonstrated that the fl uorophore distribution inside the skin tissue is not uniform and the s hapes of the autofluorescence spectra of different anatomical skin lay ers vary. The result of this study confirms that the major skin fluoro phores are located in the dermis and provides an excellent foundation for Monte Carlo modeling of in vivo autofluorescence measurements.