Material Synthesis for applications in Bioelectronic Devices

The field of bioelectronics is currently being augmented by the emergence of new applications, enabled by rapid progress in the performance of organic semiconducting materials which serve as the active layer in a range of devices including sensors and electrochemical transistors. Organic materials can be tailored to exhibit biocompatible interfaces and possess similar mechanical properties such as Youngs modulus, conformability and ductility. The facile integration of organic materials broadens the scope of applications as well as the lifetime of devices. Molecular design and synthesis can facilitate molecular functionality within the semiconducting polymer structure, designed to exhibit specific physical properties such as tensile strength, hydration and permeability, combined with electrical properties such as conductivity and capacitance. One exemplary device employed in organic bioelectronics has been the organic electrochemical transistor (OECT), which is able to amplify and transduce biological signals and therefore act as a sensor to both cations and metabolites. We propose to improve the current performance of PEDOT based devices by the design and synthesis of a series of semiconducting polymers with the following criteria. They will be be intrinsically semiconducting, but can be doped at voltages within the electrochemical window for water, ensuring hole injection from the transistor electrode, and not water oxidation. This requires an electron rich conjugated aromatic polymer backbone, with an ionization potential less than approximately 5.0 eV. Thiophene, and thienothiophene copolymers generally meet this requirement. Additionally, the polymers should have a high charge carrier mobility. This requires relatively coplanar polymer backbone with close intermolecular interactions and ordering. Key to these technologies is the high-quality interface between tissue and electronics. Organic electronic materials share a similar chemical "nature" with biological molecules, can be engineered on various forms, including hydrogels that have Young's moduli similar to soft tissues and are ionically conducting. Furthermore, the structure of organics can be tuned through synthetic chemistry, and their biological properties can be controlled using a variety of functionalization strategies. Finally, organics electronic materials can be integrated with a variety of mechanical supports giving rise to devices with form factors (conformable, stretchable, fibrous, 3D porous) that enable integration with biological systems.