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Quantitative Scattering of Melanin Solutions

Jennifer Riesz ^*, Joel Gilmore  and Paul Meredith ^*

^* Soft Condensed Matter Physics Group, Condensed Matter Theory Group, Physics Department, University of Queensland, St. Lucia, Brisbane, Australia, QLD 4072

Correspondence: Address reprint requests to J. Riesz, Tel.: 61-7-3365-3406; Fax: 61-7-3365-1242; E-mail address: riesz{at}physics.uq.edu.au.

The optical scattering coefficient of a dilute, well-solubilized eumelanin solution has been accurately measured as a function of incident wavelength, and found to contribute <6% of the total optical attenuation between 210 and 325 nm. At longer wavelengths (325–800 nm), the scattering was less than the minimum sensitivity of our instrument. This indicates that ultraviolet and visible optical density spectra can be interpreted as true absorption with a high degree of confidence. The scattering coefficient versus wavelength was found to be consistent with Rayleigh theory for a particle radius of 38 ± 1 nm. Our results shed important light on the role of melanins as photoprotectants.