Visible Light Activated Polymerization of Conjugated Molecules : Mechanism and Applications

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. 2024-09-26 The thesis was first published online. 2024-10-17 A revised PDF was published online that reflects the printed version. Before this date the first PDF has been downloaded 50 times.</p

Method Matters : Exploring Alkoxysulfonate-Functionalized Poly(3,4-ethylenedioxythiophene) and Its Unintentional Self-Aggregating Copolymer toward Injectable Bioelectronics

Injectable bioelectronics could become an alternative or a complement to traditional drug treatments. To this end, a new self-doped p- type conducting PEDOT-S copolymer (A5) was synthesized. This copolymer formed highly water-dispersed nanoparticles and aggregated into a mixed ion-electron conducting hydrogel when injected into a tissue model. First, we synthetically repeated most of the published methods for PEDOT-S at the lab scale. Surprisingly, analysis using high-resolution matrix-assisted laser desorption ionization-mass spectroscopy showed that almost all the methods generated PEDOT-S derivatives with the same polymer lengths (i.e., oligomers, seven to eight monomers in average); thus, the polymer length cannot account for the differences in the conductivities reported earlier. The main difference, however, was that some methods generated an unintentional copolymer P(EDOT-S/EDOT-OH) that is more prone to aggregate and display higher conductivities in general than the PEDOT-S homopolymer. Based on this, we synthesized the PEDOT-S derivative A5, that displayed the highest film conductivity (33 S cm(-1)) among all PEDOT-S derivatives synthesized. Injecting A5 nanoparticles into the agarose gel cast with a physiological buffer generated a stable and highly conductive hydrogel (1-5 S cm(-1)), where no conductive structures were seen in agarose with the other PEDOT-S derivatives. Furthermore, the ion-treated A5 hydrogel remained stable and maintained initial conductivities for 7 months (the longest period tested) in pure water, and A5 mixed with Fe3O4 nanoparticles generated a magnetoconductive relay device in water. Thus, we have successfully synthesized a water-processable, syringe-injectable, and self-doped PEDOT-S polymer capable of forming a conductive hydrogel in tissue mimics, thereby paving a way for future applications within in vivo electronics.Funding Agencies|Swedish Research Council [2018-05258, 2018-06197]; Swedish Foundation for Strategic Research (e-NeuroPharmacology) [RMX18-0083]; European Research Council (ERC) project [e-NeuroPharma 834677]</p

Influence of Molecular Weight on the Organic Electrochemical Transistor Performance of Ladder-Type Conjugated Polymers

Organic electrochemical transistors (OECTs) hold promise for developing a variety of high-performance (bio-)electronic devices/circuits. While OECTs based on p-type semiconductors have achieved tremendous progress in recent years, n-type OECTs still suffer from low performance, hampering the development of power-efficient electronics. Here, it is demonstrated that fine-tuning the molecular weight of the rigid, ladder-type n-type polymer poly(benzimidazobenzophenanthroline) (BBL) by only one order of magnitude (from 4.9 to 51 kDa) enables the development of n-type OECTs with record-high geometry-normalized transconductance (g(m,norm) approximate to 11 S cm(-1)) and electron mobility x volumetric capacitance (mu C* approximate to 26 F cm(-1) V-1 s(-1)), fast temporal response (0.38 ms), and low threshold voltage (0.15 V). This enhancement in OECT performance is ascribed to a more efficient intermolecular charge transport in high-molecular-weight BBL than in the low-molecular-weight counterpart. OECT-based complementary inverters are also demonstrated with record-high voltage gains of up to 100 V V-1 and ultralow power consumption down to 0.32 nW, depending on the supply voltage. These devices are among the best sub-1 V complementary inverters reported to date. These findings demonstrate the importance of molecular weight in optimizing the OECT performance of rigid organic mixed ionic-electronic conductors and open for a new generation of power-efficient organic (bio-)electronic devices.Funding Agencies|Knut and Alice Wallenberg foundationKnut &amp; Alice Wallenberg Foundation; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2016-03979, 2020-03243]; AForsk [18-313, 19-310]; Olle Engkvists Stiftelse [204-0256]; VINNOVAVinnova [2020-05223]; European Commission through the Marie Sklodowska-Curie project HORATES [GA-955837]; FET-OPEN project MITICS [GA-964677]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat-LiU 2009-00971]; National Research Foundation of KoreaNational Research Foundation of Korea [NRF-2019R1A2C2085290, 2019R1A6A1A11044070]; National Science FoundationNational Science Foundation (NSF) [DMR-2003518]</p

Metabolite-induced in vivo fabrication of substrate-free organic bioelectronics

Interfacing electronics with neural tissue is crucial for understanding complex biological functions, but conventional bioelectronics consist of rigid electrodes fundamentally incompatible with living systems. The difference between static solid-state electronics and dynamic biological matter makes seamless integration of the two challenging. To address this incompatibility, we developed a method to dynamically create soft substrate-free conducting materials within the biological environment. We demonstrate in vivo electrode formation in zebrafish and leech models, using endogenous metabolites to trigger enzymatic polymerization of organic precursors within an injectable gel, thereby forming conducting polymer gels with long-range conductivity. This approach can be used to target specific biological substructures and is suitable for nerve stimulation, paving the way for fully integrated, in vivo-fabricated electronics within the nervous system