13 July 2007 Uncovering of melanin fluorescence in human skin tissue
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Due to its extremely low fluorescence quantum yield, in the conventionally (one-photon) excited autofluorescence of skin tissue, melanin fluorescence is masked by several other endogenous and possibly also exogenous fluorophores (e.g. NADH, FAD, Porphyrins). A first step to enhance the melanin contribution had been realized by two-photon fs-pulse excitation in the red/near IR, based on the fact that melanin can be excited by stepwise two-photon absorption, whereas all other fluorophores in this spectral region allow only simultaneous two-photon excitation. Now, the next and decisive step has been realized: Using an extremely sensitive detection system, for the first time twophoton fluorescence of skin tissue excited with pulses in the ns-range could be measured. The motivation for this step was based on the fact that the population density of the fluorescent level resulting from a stepwise excitation has a different dependence of the pulse duration than that from a simultaneous excitation (&Dgr;t2 vs. &Dgr;t). Due to this strong discrimination between the fluorophores, practically pure melanin fluorescence can be obtained. Examples for in-vivo, ex-vivo as well as paraffin embedded skin tissue will be shown. The content of information with respect to early diagnosis of skin deseases will be discussed.
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Matthias Scholz, Matthias Scholz, Goran Stankovic, Goran Stankovic, Gunter Seewald, Gunter Seewald, Dieter Leupold, Dieter Leupold, } "Uncovering of melanin fluorescence in human skin tissue", Proc. SPIE 6633, Biophotonics 2007: Optics in Life Science, 663321 (13 July 2007); doi: 10.1117/12.728272; https://doi.org/10.1117/12.728272

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