Pump-Probe Microscopic Imaging of Jurassic-Aged Eumelanin

Melanins are biological pigments found throughout the animal kingdom that have many diverse functions. Pump-probe imaging can differentiate the two kinds of melanins found in human skin, eumelanin and pheomelanin, the distributions of which are relevant to the diagnosis of melanoma. The long-term stability of the melanin pump-probe signal is central to using this technology to analyze melanin distributions in archived tissue samples to improve diagnostic procedures. This report shows that most of the pump-probe signal from eumelanin derived from a Jurassic cephalopod is essentially identical to that of eumelanin extracted from its modern counterpart, Sepia officinalis. However, additional classes of eumelanin signals found in the fossil reveal that the pump-probe signature is sensitive to iron content, which could be a valuable tool for pathologists who cannot otherwise know the microscopic distributions of iron in melanins.