Bioelectronics, a field that bridges biology and electronics, has a rich history dating back to the 18th century. The inception of bioelectronics is generally attributed to Luigi Galvani, who in the late 1700s discovered that frog legs twitch as if alive when struck by electrical current. Consequently, this was the idea leading to what is known as animal electricity, which is considered the precursor to modern bioelectronics. Furthermore, in the mid-1800s, the electrical phenomena of exposed cerebral hemispheres in rabbits and monkeys were discovered by Richard Caton leading to the advancement in the 20th century bringing us closer to what we refer as bioelectronics nowadays, with the development of medical devices to aid with cardiological or hearing disorders such as the pacemaker and cochlear implants. What is more, a big milestone in the field of bioelectronics was the invention of the transistor in the middle of the 20th century opening countless new possibilities for biocompatible devices and electronic miniaturization. Nowadays bioelectronics have been evolving into a broad and diverse field with applications ranging from medical imaging to even genetic modification. The focus is on areas like bioelectronic medicine, neural interfaces and biosensors as well as the development and testing of new biocompatible materials. The field is growing every day driven by advancements in both organic electronics and biology. As our understanding is expanding more about the properties of biological cells and tissues, the potential ideas and applications will also continue to grow.   

Currently, the state of the art is Neuralink with the aim of creating a brain-computer interface that could potentially restore autonomy to those with medical needs that could not be met with the current advancements in technology. A device containing a chip and several electrode arrays of more than 1,000 super thin, flexible conductors that a surgical robot carefully implants into the cerebral cortex was utilized. Implantable devices designed to make controlling a computer or mobile device at will come closer to reality, with the biggest success being that these devices were successfully implanted in a human for the first time ever.   

Organic electronics is a field with focus on the synthesis, characterization, design, and application of polymers that exhibit desirable electronic properties such as high conductivity and processability. Organic electronic materials are constructed from organic polymers unlike their inorganic semiconductor counter parts. Benefits of organic electronics include their (potential) lower cost compared to traditional inorganic electronics as well as increased material flexibility. What is more, organic electronics are a better fit for the growing field of green environmentally friendly chemistry. However, the implementation of organic electronic materials can be challenging, especially considering their inferior thermal stability and diverse fabrication issues. Organic electrochemical transistors (OECTs) are transistor devices where the channel betwixt the source and drain is comprised by an organic semiconductor. The electrical current produced is governed by the interchange of ions between the device channel and the electrolyte solution (usually phosphate buffered saline for our experiments). The operation of OECTs is governed by potential changes between the organic semiconductor channel and the gate electrode (usually AgCl or Pt) leading to modulation of the charge density and thus conductivity. For this reason, OECTs are great for applications like bioelectronics and biosensors due to the excellent modulation properties they exhibit  

This thesis focuses on the development of a new wave of conducting polymers by selective visible-light-activated polymerization of advanced processable functional materials for possible applications in neural interfaces, biosensors, photocatalysis, conductive inks, and energy storage. Chemical and morphological effects of micro-structured processable materials are of utmost importance. Bioelectronic technologies were developed to enable new discoveries like soft electrodes that can be grown inside living tissue utilizing processes taking place inside the brain. Several new strategies were developed for the polymerization of these materials that were also electrically characterized afterwards. These strategies include the photoinduced polymerization of EEE-COONa (EDOT-EDOT-EDOT moieties with a carboxylic acid side chain) as well as EEE-S (EDOT-EDOT-EDOT moieties with a sulfonate side chain). What is more, these materials can be successfully processed and utilized in applications like photopatterning, where photolithography masks are used as the desired patterning shape with high fidelity structures as a result with micrometer resolution. Photopatterning can also be implemented in vivo with the use of photocatalytic dyes like SiR-COOH which extends the polymerization capabilities to longer wavelengths (650 nm) on zebrafish brains and tails, essentially creating conductive tattoos on living organisms.   

One other important part of this thesis is the mechanistic studies of the photoinduced polymerization, to gain further insight on how this new technology can be refined and implemented in new applications. Our findings suggest that oxygen plays an integral role in the polymerization reaction since hydrogen peroxide production has been observed after the illumination of the monomer/polymer solutions. Furthermore, a study on the stability of enzymatically crafted OECTs containing materials such as ETE-COONa (EDOT-Thiophene-EDOT moieties with a carboxylic acid side group), ETE-S (EDOT-Thiophene-EDOT moieties with a sulfonate side group), and EEE-COONa was conducted to improve adhesion and long-term usage. Sulfo-NHS click chemistry was implemented to improve the adhesion to modified epoxy group silane (GOPS) to create a stronger covalent bond between the organic molecules and the surface of the interface.