Virus-templated iridium oxide–gold hybrid nanowires for electrochromic application

Abstract

A highly porous electrode comprised of biologically templated iridium oxide–gold (IrO₂–Au) hybrid nanowires is introduced for electrochromic applications. A filamentous M13 virus is genetically engineered to display IrO₂-binding peptides on the viral surface and used as a template for the self-assembly of IrO₂ nanoclusters into a nanowire. The open porous morphology of the prepared nanowire film facilitates ion transport. Subsequently, the redox kinetics of the IrO₂ nanowires seems to be limited by the electric resistance of the nanowire film. To increase the electron mobility in the nanowires, gold nanoparticles are chemically linked to the virus prior to the IrO₂ mineralization, forming a gold nanostring structure along the long axis of the virus. The resulting IrO₂–Au hybrid nanowires exhibit a switching time of 35 ms for coloration and 25 ms for bleaching with a transmission change of about 30.5% at 425 nm. These values represent almost an order of magnitude faster switching responses than those of an IrO₂ nanowire film having the similar optical contrast. This work shows that genetically engineered viruses can serve as versatile templates to co-assemble multiple functional molecules, enabling control of the electrochemical properties of nanomaterials.