Protonic conductivity in metalloprotein nanowires

The development and processing of materials for devices that meaningfully translate signals between biology and electronics is a major challenge in materials science. Protonics-based devices are analogous to electronic devices but use protons as charge carriers instead of electrons. These devices show promise for interfacing with biological systems that commonly employ protons to perform work and transmit information. Proton-conductive materials (PCMs), the media through which protons are transported in protonic devices, are a key target for development because PCMs dominate the performance of these devices. We investigate protonic devices with a bundle of electrically conductive metalloprotein nanowires (MPNs) and palladium hydride (PdHx) protodes, the proton-injecting contact, to analyze how proton transport depends on the chemical groups in proteins. Current-voltage (I-V) measurements of the protonic devices under hydrogen atmospheres show that the MPN bundles exhibit high protonic conductivity, enhancing the device conductivity by a factor of 4-5 when compared to an environment without hydrogen. First-principles-based molecular dynamics simulations suggest that the high concentration of carboxylic acid groups in the protein nanowires contributes to their protonic conductivity.