UC Irvine

Biology provides many sources of inspiration for synthetic and multi-functional nanomaterials. Naturally evolved proteins possess a range of unique functions and self-assembly behavior. Their flexible design, potential for stimuli responsiveness, and the ability for some proteins to undergo electron transport functions as part of metabolic processes make proteins ideal building blocks of bioelectronic interfaces. In biosensor and electrocatalysis applications, bioelectronic materials are designed to interconvert biological signals or processes into electronic signals and vice versa. Some examples of electronically conductive microbial protein materials motivate the use of peptides and proteins for responsive bioelectronic interfaces. In this work, we designed a peptide fiber structure that exhibits stimuli-responsive self-assembly and the capacity to transport electrical current over micrometer long distances. Hierarchically ordered nanofibers of α-helical coiled-coil peptides were assembled using a pH responsive structure ordering motif comprising of two neighboring lysine residues. Cryo-EM structures of these assemblies reveal a novel organization of α-helical peptides in a cross coiled coil arrangement that exhibits electrical conductivity. Both solid-state and solution-based electrochemical characterization show that these fibers are conductive. Single-fiber conductive AFM determined that the solid-state electrical conductivity is on a similar order of magnitude with conductive cytochrome filaments from bacteria. Solution deposited fiber films approximately doubled the electroactive surface area of the electrode, confirming their conductivity in aqueous environments. Furthermore, these fibers can be used as scaffolds for redox enzyme immobilization for electrochemical biosensing. Progress towards immobilized enzymatic devices will be discussed. This work further expands the field of stimuli-responsive and multifunctional nanomaterials by using peptide assemblies as structural supports for future implementation in bioelectronic and bioelectrochemical materials.