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Theses

2012 10 23
Roger Gabrielsson 2012

Electroactive Conjugated Polyelectrolytes Based on EDOT From Synthesis to Organic Electronics
Linköping University, ISBN: 978-91-7519-812-5, (2012)
Full text: N/A

Abstract
Conjugated polyelectrolytes (CP) show interesting electrical and optical properties for organic electronics as well as for life science applications. Their possibilities of supramolecular assembly with nanowire like misfolded proteins, amyloids, as well as synthetic polypeptides or DNA forming conducting nano composites is highly interesting as being a truly bottom up approach for fabrication of OLEDs, photovoltaic’s as well as logic devices.A special class of CPs is that of electroactive cojugated polymers (ECPs), which, due to their structure, will exhibits a unique combination of properties, including the following; electrically conducting, ability to store an electric charge and ability to exchange ions. The positive or negative excess charge can be introduced into the conjugated polymer by means of chemical or electrochemical oxidation/reduction (a process called doping) following the polymerization reaction. In order to preserve overall electroneutrality of the polymer during introduction of excess charge, ionexhange processes occurs between the polymer phase and the surrounding electrolyte solution. This charge/discharge process can be utilized for application such as; pseudo super capacitors (energy storage through oxidation/reduction processes), electro mechanical actuators (convert electrical energy to mechanical energy) and sensors (converts a chemical signal to electrical conductivity).

In this thesis we describes the synthetic challenges with ECPs for applications vide supra. These mostly relates to solubility, ionic functionalization, conductivity and macromolecular properties such as size and shape of the ECPs. The key requirement in the synthesis of ECPs is that the conjugated nature of the monomer is conserved in the synthesis process and that insertion of excess charge (doping) can be obtained. This limits both the choice of monomer and the choice of polymerization process. Monomers of great complexity have been synthesized with this careful goal in mind. Furthermore, the development of novel monomers must also target the appropriate functionality for polymerization. As such, most ECP monomers are electron-rich molecules with pendant groups containing pyrroles, thiophenes, or 3,4-ethylenedioxythiophenes. These three well known ECP monomers are excellent additions to conjugated systems as they typically enable electrochemical polymerization and direct the polymerizations toward linear polymers with good stability towards doping.

The first topic of this thesis we demonstrate how we can obtain water soluble ECPs with good electrical conductivity by controlling the polymerization techniques and proper ionic functionalization of the monomer. We also show how these polymers can be incorporated by self-assembly with biomolecular templates, such as, DNA and amyloid fibrils, thus generating novel electrically conductive nanowires.

The second topics of this thesis demonstrate how hydrogels of ECPs can be used as bioand charge storage materials, were we demonstrate electronically controlled cell release for biology applications. Both applications are based on ECPs ability to ionexhange processes during electrochemical redox reactions. As well as ions, solvent and other neutral molecules may enter the film during charge/discharge processes. This cause a swelling or shrinking of the ECP films and the expansion and contraction of the polymer network in conjugation with the sorption/desorption of solvent molecules and ions can be described in terms of mechanical work.

In the first case we were able to synthesize a water soluble ECP with high amphiphilic character. The polymer was immobilized onto a flexible electrode, suitable for cell growth and subjected to a cell growth media. When the desired cell layer was formed we applied a potential to the flexible electrode. This resulted in that the mechanical work of the immobilized ECP during the applied potential overcame the week adhesive forces to the flexible electrode, which resulted in super swelling and disintegration of the ICP and the cell layer could be harvested.

In the second case the possibilities of using synthetically modified ECPs as a dopant during electropolymerization of another ECP monomer to obtain a polymer integrated network with high charge density and good charge transport properties. We demonstrate how this polymer network can be used as porous electrodes suitable for supercapacitors.

2012 10 11
Maria Bolin 2011

Conjugated Polymer Surface Switches for Active Cell Control
Linköping University, ISBN: 978-91-7393-063-5, (2011)
Full text: FULLTEXT01.pdf

Abstract
Conjugated polymers have been found useful in a wide range of applications such as sensors, electrochemical transistors, solar cells, and printed electronics due to their mechanical, optical and electronic properties. An amazing research field has grown during the last three decades since the discovery of conducting polymers in 1976. Since the materials can be made from solutions, different processing methods such as spin coating and vapor phase polymerization can be used to coat a huge variety of substrates. The choice of method depends mainly on monomer solubility and kind of substrate to be coated. During the synthesis the polymers can be chemically modified to tailor their functionalities. Due to this variability in materials and the processability, electronics can be achieved on unconventional substrates such as flexible plastic foils and cell culturing dishes. As a contrast to inorganic, usually metallic materials, conducting polymers are built up from organic compounds in a molecular structure with soft mechanical properties that have shown to be a benefit in combination with biology, ranging from interactions with cells to interactions with advanced biological species such as tissues. This combination of research fields and the possible applications are merged within the field of organic bioelectronics.

The primary purpose of this thesis is to give a background to organic electronics in general and how electrochemical devices can be processed and developed for biological applications in particular. An organic electronic surface switch is introduced to control cell adhesion and proliferation as well as an electrochemical transistor to spatially tune the cell adhesion along an electrochemical gradient. To mimic a more natural cell environment a three dimensional fiber substrate was used to design an electronically active matrix to promote nerve cell adhesion and communication. By combining standard microfabrication techniques and conjugated polymers desired patterns of electroactive polymer were created to enable active regulation of cell populations and their extracellular environment at high spatial resolution. Finally, a brief look into future challenges will also be presented.

2012 10 11
Karl Svennersten 2011

Regulation of eukaryotic cell physiology using organic bioelectronics
Karolinska Institutet , ISBN: 978-91-7457-285-8, (2011)

2012 10 11
Shirin Ilkhanizadeh 2010

Microenvironmental control and molecular detection of neural stem cell state and fate
Karolinska Institutet, ISBN: 978-91-7409-946-1, (2010)

2012 10 11
Maria Asplund 2009

Conjugated Polymers For Neural Interfaces : Prospects, Possibilities And Future Challenges
KTH Royal Institute of Technology, ISBN: 978-91-7415-213-5, (2009)

2012 10 11
Andreas Åslund 2009

Designing thiophene-based fluorescent probes for the study of neurodegenerative protein aggregation diseases: From test tube to in vivo experiments
Linköping University, ISBN: 978-91-7393-496-1, (2009)
Full text: FULLTEXT01.pdf

Abstract
Protein aggregation is an event related to numerous neurodegenerative diseases, such as Alzhemier’s disease and prion diseases. However little is known as to how and why the aggregates form and furthermore, the toxic specie may not be the mature fibril but an on route or off route specie towards mature aggregates. During this project molecular probes were synthesized that may shed some light to these questions. The probes are thiophene based and the technique used for detection was mainly fluorescence. It was shown that the previously established thiophene based in vitro staining technique is valid ex vivo and in vivo. This would not have been possible without the synthesis of a variety of functionalized polymeric thiophene based probes; their in vitro and ex vivo staining properties were taken into consideration when the design of the small oligomeric probes were decided upon. These probes were shown to spectrally distinguish different types of amyloid, pass the bloodbrain barrier within minutes and specifically and selectively stain protein aggregates in the brains of mice.

2012 10 11
Per Björk 2007

Biological Sensing and DNA Templated Electronics using Conjugated Polymers
Linköping University, ISBN: 978-91-85895-17-5, (2007)
Full text: FULLTEXT01.pdf

Abstract
Conjugated polymers have been found useful in a wide range of applications such as solar cells, sensor elements and printed electronics, due to their optical and electronic properties. Functionalization with charged side chains has enabled water solubility, resulting in an enhanced interaction with biomolecules. This thesis focus on the emerging research fields, where these conjugated polyelectrolytes (CPEs) are combined with biomolecules for biological sensing and DNA nanowire assembling.

CPEs have shown large potential in biomolecular detection where the optical read out is due to the geometrical alternation in the backbone and aggregation state. This thesis focused on transferring the biomolecular detection to a surface of CPEs. The characterization of the CPE layer show that a hydrogel can be formed, and how the layer can undergo geometrical changes upon external stimulus such as pH change. A selective sensor surface can be created by imprinting ssDNA or an antibody in the CPE layer. The discrimination for complementary DNA hybridization and specific antibody interaction can be monitored by surface plasmon resonance or quartz crystal microbalance. We have also taken the step out from the controlled test tube experiments to the complex environment of the cell showing the potential for staining of compartments and structures in live and fixed cell. Depending on the conditions and CPE used, cell nuclei, acidic vesicles and cytoskeleton structure can be visualized. Furthermore, the live staining shows no sign of toxic effect on cultured fibroblasts.

CPEs can also be a valuable element when assembling electronics in the true nano regime. I have used DNA as building template due to its attractive size features, with a width of around 2 nm and a length scale in the µm regime, and the inbuilt base-paring recognition elements. This thesis shows how DNA can be decorated with CPEs and stretched on surfaces into a model for aligned semiconducting nanowire geometries. Not only making the template structures is of importance, but also how to place them on the correct surface position, i.e. on electrodes. Strategies for positioning DNA nanowires using transfer printing and surface energy patterning methods have therefore been developed in the thesis. The stretched DNA decorated with CPE also offers a way to further study the molecular binding interaction between the two molecules. Single molecular spectroscopy in combination with polarization has given information of the variation of the CPE binding along a DNA chain.

2012 10 11
Anna Herland 2007

Conjugated Polymers, Amyloid Detection and Assembly of Biomolecular Nanowires
Linköping University, ISBN: 978-91-85831-42-5, (2007)
Full text: FULLTEXT01.pdf

Abstract
The research field of conjugated polymers has grown due to the optical and electronic properties of the material, useful in applications such as solar cells and printed electronics, but also in biosensors and for interactions with biomolecules. In this thesis conjugated polymers have been used in two related topics; to detect conformational changes in proteins and to assemble the polymers with biomolecules into nanowires.

Within biosensing, conjugated polymers have been used for detection of a wide range of biological events, such as DNA hybridization or enzymatic activity, utilizing both electronic and optical changes in the polymer. Here the focus has been to use the polymers as optical probes to discriminate between native and misfolded protein, as well as to follow the misfolding processes in vitro. The understanding and detection of protein misfolding, for example amyloid fibril formation, is a topic of growing importance. The misfolding process is strongly associated with several devastating diseases such as Alzheimer’s disease, Parkinson’s disease and Bovine Spongiform Encephalopathy (BSE). We have developed detection schemes for discrimination between proteins in the native or amyloid fibril state based on luminescent polythiophene derivatives. Through a synthesis strategy based on polymerization of trimer blocks rather than of monomers, polythiophene derivatives with higher optical signal specificity for amyloid-like fibrils were obtained.

Self-assembly of nanowires containing conjugated polymers is a route to generate structures of unique opto-electrical characteristics without the need for tedious topdown processes. Biomolecules can have nanowire geometries of extraordinary aspect ratio and functionalities. The DNA molecule is the most well known and exploited of these. In this thesis work the more stable amyloid fibril has been used as a template to organize conjugated polymers. Luminescent, semi-conducting, conjugated polymers have been incorporated in and assembled onto amyloid fibrils. Using luminescence quenching we have demonstrated that the conjugated material can retain the electro-activity after the incorporation process. Furthermore, the amyloid fibril/conjugated polymer hybrid structures can be organized on surfaces by the means of molecular combing and soft lithography.

In the process of generating self-assembled biomolecular nanowires functionalized with conjugated polymers, we have shown a new synthesis strategy for a water-soluble highly conducting polythiophene derivative. This material, PEDOT-S, has shown affinity for amyloid fibrils, but can also be very useful in conventional opto-electronic polymer-based devices.

2012 10 11
Joakim Isaksson 2007

Organic Bioelectronics: Electrochemical Devices using Conjugated Polymers
Linköping University, ISBN: 978-91-85831-03-6, (2007)
Full text: FULLTEXT01.pdf

Abstract
Since the Nobel Prize awarded discovery that some polymers or “plastics” can be made electronically conducting, the scientific field of organic electronics has arisen. The use of conducting polymers in electronic devices is appealing, because the materials can be processed from a liquid phase, much like ordinary non-conducting plastics. This gives the opportunity to utilize printing technologies and manufacture electronics roll-to-roll on flexible substrates, ultimately at very low costs. Even more intriguing are the possibilities to achieve completely novel functionalities in combination with the inherent compatibility of these materials with biological species. Therefore, organic electronics can be merged with biology and medicine to create organic bioelectronics, i.e. organic electronic devices that interact with biological samples directly or are used for biological applications.

This thesis aims at giving a background to the field of organic bioelectronics and focuses on how electrochemical devices may be utilized. An organic electronic wettability switch that can be used for lab-on-a-chip applications and control of cell growth as well as an electrochemical ion pump for cell communication and drug delivery are introduced. Furthermore, the underlying electrochemical structures that are the basis for the above mentioned devices, electrochemical display pixels etc. are discussed in detail. In summary, the work contributes to the understanding of electrochemical polymer electronics and, by presenting new bioelectronic inventions, builds a foundation for future projects and discoveries.

2012 10 11
Peter Kjäll 2007

Studies of Cell Signaling using Bacterial Toxins and Organic Electronic Devices
Karolinska Institutet, ISBN: 978-91-7357-364-1, (2007)