(17d) Short Elastin-like Peptides Engineered to Control Ionomer on Metal Surfaces for Electrode Manufacturing Applications

Bio-electrochemical technologies have an important and growing role in healthcare, with applications in sensing and diagnostics, as well as the potential to be used as implantable power sources and be integrated with automated drug delivery systems. Enzymatic bio-electrodes already play an important part in the medical community, since the enzymes are biocompatible, highly selective and efficient catalytic at physiological conditions. However, challenges exist with enzyme-based electrodes, including short functional life, low current density, and lack of control of components (e.g. metals, enzymes). One important electrode component that is challenging to control is the highly-charged, ion-conductive polymer called ionomer, which facilitates efficient ionic transport, but has the potential to denature enzymes. Some of the same challenges in ionomer control exist in traditional metal-based electrodes as well, having an impact in other fields such as renewable energy and fuel cells.

Protein engineering is emerging as a powerful tool to overcome these issues and control the organization of components in electrodes. By taking advantage of the ability to precisely define protein sequences, electrodes can be organized into complex and high performing structures, increasing the efficiency, current density and functional lifetime. While proteins have been engineered to control enzyme orientation, tether mediators, or provide supportive hydrogel environments, no proteins or peptides have been engineered to control ionomers, which facilitate ion conduction in industrial devices such as fuel cells or electrolyzers.

In this talk, we will present a peptide system which is designed to control ionomer on metal surfaces. Specifically, an amino acid sequence derived from elastin serves as the basis for peptide design, because elastin is highly tunable and easy to manufacture. The short engineered elastin-like peptides consist of a CVPGXG motif where ‘X’ is a guest residue, and cysteine is used to bind to a model gold surface. Neutral and charged guest residues are used to control ionomer binding. A few different methods are employed to confirm and characterize binding behavior. Mass loading data are obtained from a quartz crystal microbalance with dissipation (QCM-D) and hydrodynamic radii data are obtained from dynamic light scattering (DLS). These data show that an electrostatic interaction between peptides and ionomer can be engineered to take place in solution as well as when immobilized on metals. The secondary structures of the peptides in the presence of ionomer is analyzed using circular dichroism (CD) in solution, and Fourier-transform infrared spectroscopy (FTIR) on metal surfaces. X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM) are used for surface analysis of the thin films. Notably, the peptide films facilitate a thin phase-separated ionomer layer on the metal surface. Overall, this work shows for the first time that short elastin-like peptides could serve as a promising tool in controlling electrode architecture and ionomer thin-film properties on metal surfaces.