Bio-sourced Eumelanin Pigments: Charge Transport Properties and Beyond

Green electronics recently opened new research avenues to use bio-sourced, biocompatible materials to limit the environmental footprint of electronics^1-3. Within bio-sourced carbon-based materials, eumelanin, a black-brown conjugated biopigment, emerged as an excellent candidate for green electronics.
Eumelanin features fascinating properties (e.g. broadband optical absorption^4,5, metal-ion chelation⁶, mixed ionic/electronic conductivity^7–9) and biocompatibility^1,10. Its conjugated sp² backbone suggests that it would be a naturally occurring semiconductor. The amorphous semiconductor model (ASM) for eumelanin, proposed in the 70s after the observation of an electrical resistive switching of wet melanin pellets¹¹ , has been recently questioned by proposing mixed electronic/protonic and proton membrane models^8,9,12.
Herein, we report for the first time the electrical resistive switching response of dry eumelanin pellets, as opposed to previous studies indicating dry eumelanin as an insulating material^11,13 . Wet pellets show a reversible and reproducible resistive switching, in agreement with McGinness et al¹¹. These findings rather suggest that dry pellets would be predominant electronic conductors.