Dissertation Defense: Marc Nabhan, Chemical and Biomolecular Engineering
DISSERTATION DEFENSE
Marc A. Nabhan, Chemical and Biomolecular Engineering
*under the direction of Kane Jennings
“Interfacing Proteins with Conducting Polymers for the Fabrication of Biohybrid and Biomolecular-based Electronics”
12.04.23 | 2:30PM CST | 048 Engineering Science Building (ESB)
The overarching theme of the work presented herein is the combination of proteins with conducting polymers for the investigation of biohybrid and biomolecular-based electronics. While this topic is broad and encompasses many potential avenues of application, this doctoral research focuses on the interfacial properties and applications of proteins and conducting polymers through the themes of green renewable energy and biosensing. In exploring novel approaches for solar energy conversion, Photosystem I (PSI), an intrinsically photoactive multi-subunit protein that is found in higher order photosynthetic organisms, is highlighted. PSI is a promising candidate for renewable biohybrid energy applications due to its abundance in nature and its high quantum yield. To utilize PSI’s light-responsive properties and to overcome its innate electrically insulating nature, the protein can be paired with a biologically compatible conducting polymer that carries charge at appropriate energy levels, allowing excited PSI electrons to travel within a composite network upon light excitation.
This dissertation offers insight into the combination of PSI with two intrinsically conducting polymers (ICPs). First, PSI is mixed with the ICP poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) to deposit well-mixed thin films via spin coating from aqueous solution, enabling uniform, reproducible, and rapid film formation in which the composition and thickness of composite films can be readily tuned up to a few hundred nanometers. The combination of the protein and ICP yields increased photocurrents and turnover numbers when compared to single-component films of the protein or ICP alone to reveal a synergistic combination of film components. Second, we chemically oxidize a methoxy aniline (para-anisidine) to synthesize poly(p-anisidine) (PPA) and interface this polymer with PSI for the fabrication of PSI-PPA composite films by drop casting. Combining PPA with PSI yields composite films that exhibit photocurrent densities on the order of several μA/cm2 when tested with appropriate mediators in a 3-electrode setup. The composite films also display increased photocurrent output when compared to single-component films of the protein or PPA alone to reveal a synergistic combination of the film components. Tuning film thickness and PSI loading within the PSI-PPA films yields optimal photocurrents for the described system.
For biosensing applications in bacteria or virus detection, we functionalize gold surfaces with antibodies via photo- and electrochemical approaches by combining the polymer polyaniline (PAni) with Staphylococcal Protein A Fluorescein antibody mimic, in the presence of a light-active benzophenone derivative. Effective mechanisms of detecting bacteria or viruses, i.e., SARS-CoV-2, have shown inadequate aptness to identify a virus rapidly and accurately, especially in early stages of infection, and at low pathogen concentrations. In this work, we fabricate photoactive films that could selectively bind an antibody protein to the surface. The functionalized surfaces are shown to be transferrable to micron-scale substrates for potential applications in microcantilever-based biosensing. The protein, Staphylococcal Protein A Fluorescein is tagged with a green fluorescent protein (GFTag) and is used as an antibody mimic to test the light reactivity and efficiency of poly(aniline-4-aminobenzophenone) films in selective protein binding. Cyclic voltammetry confirms the synthesis of conductive poly(aniline- 4-aminobenzophenone) films with improved binding to the GFTag protein under UV-light exposure.