Modular Metalloprotein Nanowires With Semiconductor‐Scale Conductivity and Tunable Redox Behavior

The creation of structured protein assemblies with tailorable electronic conductivity and electrochemical behaviors would be transformative for diverse applications, including bioelectronic interfaces, redox‐active biosensors, and energy conversion systems. However, engineered protein nanowires have often exhibited conductivities orders of magnitude below those of natural bacterial nanowires or inorganic semiconductor nanowires, limiting their practical use. Here, we describe the protein design and modular assembly of conductive metalloprotein nanowires through the alignment of cytochrome c3, rubredoxin, or azurin metalloproteins on a filamentous protein scaffold. The assembled micrometer‐length nanowires exhibited distinct and metalloprotein‐specific redox potentials and conductive properties, with conductive AFM measurements of single nanowires revealing intrinsic average conductivities of up to 1.75 S cm −1 depending on the metalloprotein type. These conductivities are within an approximate order of magnitude of the most conductive cytochrome‐based bacterial nanowires, and comparable to moderately doped silicon nanowires, while also enabling tuning of redox potential by metalloprotein choice. The redox behavior of the nanowires is set by the choice of metalloprotein, whereas their conductivity is governed by the spacing of redox centers imposed by the scaffold, establishing a programmable approach to protein‐based electronic conductors and building blocks for biomolecular electronic devices.