Controlling ions and electrons in aqueous solution: an alternative point of view of the charge-transport behavior of eumelanin-inspired material

The possibility of current injection and transport in eumelanin films, humans' most common natural pigment, has fascinated physicists and materials scientists since the early’ 60s. Nowadays, it is accepted that ionic transport is dominant in wet environments. The present study evaluates the charge transport in eumelanin-inspired films immersed in pure water and ionic aqueous solutions. Both current vs. voltage and voltage-dependent impedance/dielectric spectroscopy measurements are reported. The data confirm that the electrical response in pure water is dominated by ionic/protonic conduction, similar to standard eumelanin. Contrariwise, the protonic contribution is suppressed by faster electronic transport in an ionic aqueous solution. Considering these observations, an electrochemically doped mechanism is evoked to explain the charge transport of this class of material. The results yield new opportunities for tuning eumelanin-inspired materials' protonic and electronic conductivity and advancing towards in vivo implantable eumelanin-based (bio)devices.