The electrical properties of eumelanin, a ubiquitous natural pigment, have fascinated scientists since the late 1960s. For several decades, the hydrationdependent electrical properties of eumelanin have mainly been interpreted within the amorphous semiconductor model. Recent works undermined this paradigm. Here we study protonic and electronic charge carrier transport in hydrated eumelanin in thin film form. Thin films are ideal candidates for these studies since they are readily accessible to chemical and morphological characterization and potentially amenable to device applications. Current−voltage (I-V) measurements, transient current measurements with proton-transparent electrodes, and electrochemical impedance spectroscopy (EIS) measurements are reported and correlated with the results of the chemical characterization of the films, performed by X-ray photoelectron spectroscopy. We show that the electrical response of hydrated eumelanin films is dominated by ionic conduction (10 −4 −10 −3 S cm −1 ), largely attributable to protons, and electrochemical processes. To propose an explanation for the electrical response of hydrated eumelanin films as observed by EIS and I-V, we considered the interplay of proton migration, redox processes, and electronic transport. These new insights improve the current understanding of the charge carrier transport properties of eumelanin opening the possibility to assess the potential of eumelanin for organic bioelectronic applications, e.g. protonic devices and implantable electrodes, and to advance the knowledge on the functions of eumelanin in biological systems.

The use of high surface area, low cost, activated carbon gate electrodes enables low voltage (sub-1 V) operation in ionic liquid-gated organic transistors and renders unnecessary the presence of an external reference electrode to monitor the channel potential.

We report the proof-of-concept of the TransCap, a monolithically integrated device that exhibits the storage properties of a supercapacitor and the low-voltage operation of an electrolyte-gated transistor.

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