CPOS Seminar: "Protein-based biopolymers as a platform for enabling long-range electron and proton transport"

Abstract: Our study is concerning the use of proteins for the making of large-scale free-standing biopolymers followed by investigating their ability to support charge transport. One of our inspirations for the choice of proteins as the medium for charge transport is the natural role of proteins in mediating charges. The field of protein-based conductive (bio-)polymers has only recently emerged, whereas to date, most of the protein-based conductive materials are a result of synthetic biology (protein expression). Our approach is based on identifying waste proteins that are available in bulk quantities from raw materials and using them preferably in a green polymerization to create conductive biopolymers, a methodology that can be considered more sustainable. The protein that we have used the most in our studies is the bovine serum albumin (BSA) protein, which is a waste product of the extensive bovine industry. We show that we can form large-scale highly-elastic, free-standing, and insoluble polymers on the macroscale. Due to the water uptake of our protein-based polymers and the presence of oxo-amino-acids, our new protein-based polymers show excellent ionic conductivity in the order of 5 mS/cm, which we ascribed to protonic transport. Using various post-polymerization modifications (PPM) as well as physical modifications is allowing us to explore the important factors and mechanism of the protonic transport, where we show the important amino acids participating in the process and the important role of the protein:water interface in dictating the transport efficiency. While switching to electronic transport, we have two methodologies of enabling such transport across the BSA structures. The first one is based on the ability of BSA to strongly bind a variety of small molecules. We use such ability to bind electron mediating groups into the protein matrix in a process we refer to as molecular doping. This process is allowing us to discuss the role of biological (or non-biological) electron mediators in long-range electron transfer across proteins. The second methodology is PPM, where we can chemically decorate with common conjugated mono-/oligo-/poly-mers used in the conductive polymers field. In this way, we are creating a chimeric system with mixed conductivity: protonic transport through the protein matrix and electronic transport through the conjugated system. From an application point of view, our new protein-based biopolymers have several attractive properties; they are environmentally friendly, they possess inherent biodegradability and biocompatibility, they have good mechanical properties, and their formation obeys most principles of green chemistry. Moreover, due to the low price tag of our chosen proteins and the simple formation process, the cost of the biopolymers can reach as low as 1 USD for 100cm² of the final polymer. Currently, our main targeted application for our new family of polymers is for biological interfaces, and we show their use in biosensing applications, while other lines of applications include the use of our biopolymers for biomedical and energy applications.