Melanin Chemistry Revealed by Excited State Dynamics and the Resulting Biological Implications

2219 FFSCDermatopathologists need more reliable tools for analyzing biopsies of potential melanomas. The chemical and physical properties of melanin provide insight into melanoma biochemistry. Two-color, near-infrared pump-probe microscopy of unstained, human pathology slides reveals differences in the type of melanins and their distributions in malignant and non-cancerous lesions. Because the pump-probe response of melanin is resilient to aging, this tool could prove useful in retrospective studies to correlate melanin characteristics with patient outcome, thus eliminating the pathologist¿s uncertainty from the development of this classification method.Pump-probe spectroscopy of a variety of melanin preparations including those with varying amounts of metal ions and toxins, and those that have been photo-damaged or chemically oxidized, shows that the pump-probe response is sensitive to slight chemical and physical differences, rather than just melanin type as previously hypothesized. When sampling the response at several pump wavelengths, the specificity of this technique is derived from the absorption spectra of the underlying chromophores. Therefore, hyperspectral pump-probe microscopy of melanin could serve as an indicator of the chemical environment in a variety of biological contexts. For example, the melanin chemistry of macrophages suggests that these cells oxidize, homogenize, and compact melanin granules; whereas melanocytes produce heterogeneous melanins.