Eumelanin from water-treated cuttlefish ink: Complex chemistry, optical absorption and electrical response under illumination

We studied the biopigment Sepia eumelanin obtained from cuttlefish (Sepia) ink after a minimal water-based treatment, for low-environmental impact organic electronics. We characterised the complex chemistry of Sepia eumelanin, which includes organic and inorganic fractions, by neutron activation analysis and X-ray energy dispersive spectroscopy. Afterwards, we studied the structure of binder-free drop-cast films; the organic fraction present after water treatment could explain the good filmability of the material. Absorptance featured a plateau-like behaviour, possibly originating from the convolution of the contribution of the organic molecular components in the material; the extinction confirmed the light scattering properties of Sepia eumelanin granules. The electrical (current–voltage and electrochemical impedance spectroscopy) measurements revealed that transport is predominantly electronic. Under simulated solar light, we observed that heat has a major contribution to the current increase. This work opens a novel perspective on the valorization of materials synthesised in living environments for electronic technologies and devices.