Controlled Interactions between Engineered Proteins and Acidic Polymer Electrolytes

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 are especially attractive because they are biocompatible, highly selective, and efficient catalysts at physiological conditions. Challenges associated with enzyme-based electrodes include low current density and short functional lifetimes. An important aspect in creating efficient electrochemical devices is facilitating proton transfer in electrode layers. Often solid polymer electrolytes (ionomers) are utilized in industrial devices such as fuel cells and electrolyzers, but these polymers need to be carefully controlled in bio-electrochemical environments, such that they do not denature enzymes. Protein engineering is emerging as a powerful tool to overcome the challenges in manufacturing enzyme-based electrodes. By taking advantage of the ability to precisely define protein sequences, electrodes can be organized into high performing structures. While many protein engineering tools have been developed for bio-electrodes, no proteins have been specifically designed to help organize ionomer on conductive surfaces. We propose to utilize highly tunable and easily manufactured structural protein sequences found in nature to control the placement of these ionomers, thus potentially enable their use in a multitude of devices. In this talk, we will discuss the protein design, binding and aggregation behavior with ionomer, the effect of ionomer on protein secondary structure, and surface analysis of samples. Specifically, mass change data from a quartz crystal microbalance with dissipation (QCM-D) and hydrodynamic radii data gathered using dynamic light scattering (DLS) show proteins can be modified to bind with ionomer (Nafion®), and this interaction happens in solution as well as when the proteins are immobilized on metal surfaces. Circular dichroism (CD) data shows the secondary structures of the proteins in the presence on ionomer remain unchanged. Surface analysis is performed using x-ray photoelectron spectroscopy (XPS) and an atomic force microscope (AFM) and corroborate the binding analysis results. Since the purpose of these composite materials is to facilitate proton transfer, conductivity through thin films is also characterized. Overall, this work shows for the first time that protein sequences could serve as a promising tool in controlling ionomer architecture. This discovery has broad applications in bio-electrodes, but can also be used to understand the impact of ionomer organization on fuel cell and electrolysis membrane electrode assemblies as well.