The stepwise two-photon excited melanin fluorescence is a unique diagnostic tool for the detection of malignant transformation in melanocytes.

Malignant transformation of melanocytes is associated with changes in melanogenesis. Therefore, fluorescence of melanin may be an informative indicator of this process. But the conventionally excited autofluorescence of melanin in skin tissue is ultra-weak and its main part in the visible spectral region is hidden by the much stronger fluorescence from other endogenous fluorophores.