Panorama of Conductive Freestanding Biopolymers for Long-Range Charge Transfer: Effect of Chemical Modification and Doping.

The intricate interplay of electron transfer (ET) and proton transfer (PT) across biomaterials extends beyond biology, paving the way for advancements in bioelectronics. These biomaterials, characterized by their biocompatibility, biodegradability, and renewability, offer a promising platform for applications in bioelectronics, biomedical devices, and energy technologies. This review explores the fundamental principles governing PT and ET, including the Grotthuss mechanism, Marcus theory, and relevant quantum mechanical effects. We highlight key advancements in freestanding protein-based biopolymers and their modifications to enhance the conductivity. The discussion begins with an overview of PT and ET theories, followed by synthesis methods for freestanding protein-based biopolymers, emphasizing the role of surface functional groups (oxo-acid and amine), water content, and the incorporation of light-active moieties to improve conductivity in bovine serum albumin (BSA)-based biopolymers. Furthermore, we examine the quantum integration of organic and nanoparticle dopants, such as metal-porphyrins, carbon dots (C-Dots), and C-Dots-based heterostructures within biopolymers, demonstrating their ability to enhance conductivity by establishing synergistic pathways for ionic and electronic charge transport. This analysis provides insights into how structural modifications influence dynamic charge transport, facilitating the development of high-performance bioelectronic devices. By integrating theoretical frameworks with experimental findings, this review illustrates how tuning proton and electron conductance mechanisms can unlock the potential for sustainable, scalable, and multifunctional biomaterials. Ultimately, this work serves as a foundation for interdisciplinary research, bridging materials science, biochemistry, and bioelectronics to enable innovative applications, including biosensors, biomedical devices, energy storage systems, and light-driven transistors.