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- Asplund, Maria, 1978-
(author)
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Conjugated Polymers for Neural Interfaces : Prospects, possibilities and future challenges
- 2009
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Doctoral thesis (other academic/artistic)abstract
- Within the field of neuroprosthetics the possibility to use implanted electrodes for communication with the nervous system is explored. Much effort is put into the material aspects of the electrode implant to increase charge injection capacity, suppress foreign body response and build micro sized electrode arrays allowing close contact with neurons. Conducting polymers, in particular poly(3,4-ethylene dioxythiophene) (PEDOT), have been suggested as materials highly interesting for such neural communication electrodes. The possibility to tailor the material both mechanically and biochemically to suit specific applications, is a substantial benefit with polymers when compared to metals. PEDOT also have hybrid charge transfer properties, including both electronic and ionic conduction, which allow for highly efficient charge injection. Part of this thesis describes a method of tailoring PEDOT through exchanging the counter ion used in electropolymerisation process. Commonly used surfactants can thereby be excluded and instead, different biomolecules can be incorporated into the polymer. The electrochemical characteristics of the polymer film depend on the ion. PEDOT electropolymerised with heparin was here determined to have the most advantageous properties. In vitro methods were applied to confirm non-cytotoxicity of the formed PEDOT:biomolecular composites. In addition, biocompatibility was affirmed for PEDOT:heparin by evaluation of inflammatory response and neuron density when implanted in rodent cortex. One advantage with PEDOT often stated, is its high stability compared to other conducting polymers. A battery of tests simulating the biological environment was therefore applied to investigate this stability, and especially the influence of the incorporated heparin. These tests showed that there was a decline in the electroactivity of PEDOT over time. This also applied in phosphate buffered saline at body temperature and in the absence of other stressors. The time course of degradation also differed depending on whether the counter ion was the surfactant polystyrene sulphonate or heparin, with a slightly better stability for the former. One possibility with PEDOT, often overlooked for biological applications, is the use of its semi conducting properties in order to include logic functions in the implant. This thesis presents the concept of using PEDOT electrochemical transistors to construct textile electrode arrays with in-built multiplexing. Using the electrolyte mediated interaction between adjacent PEDOT coated fibres to switch the polymer coat between conducting and non conducting states, then transistor function can be included in the conducting textile. Analogue circuit simulations based on experimentally found transistor characteristics proved the feasibility of these textile arrays. Developments of better polymer coatings, electrolytes and encapsulation techniques for this technology, were also identified to be essential steps in order to make these devices truly useful. In summary, this work shows the potential of PEDOT to improve neural interfaces in several ways. Some weaknesses of the polymer and the polymer electronics are presented and this, together with the epidemiological data, should point in the direction for future studies within this field.
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| 3. |
- Björk, Per, 1978-
(author)
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Biological Sensing and DNA Templated Electronics Using Conjugated Polymers
- 2007
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Doctoral thesis (other academic/artistic)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.
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| 4. |
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| 5. |
- Nemec, Hynek, et al.
(author)
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Sub-Picosecond Time-Dependent Mobility in Low-Band-Gap Polyphenylene:Fullerene Blend Probed by Terahertz Spectroscopy
- 2008
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In: Conference on Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science. CLEO/QELS 2008. - : IEEE. - 1092-8081. - 9781557528599 ; , s. 3108-3109
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Conference paper (peer-reviewed)abstract
- Time-resolved terahertz spectroscopy is used to investigate photoinduced dynamics of charge carriers in a polymer heterojunction. We directly observe instantaneous generation of highly mobile charge carriers followed by a rapid drop in their mobility. (C) 2008 Optical Society of America
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| 6. |
- Svanstrom, C. M. B., et al.
(author)
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Device Performance of APFO-3/PCBM Solar Cells with Controlled Morphology
- 2009
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In: Advanced Materials. - Weinheim : Wiley. - 0935-9648 .- 1521-4095. ; 21:43, s. 4398-
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Journal article (peer-reviewed)abstract
- Polymer/fullerene solar cells with three different device structures: A) diffuse bilayer, B) spontaneously formed multilayer and C) vertically homogeneous thin films, are fabricated. The photocurrent/voltage performance is compared and it is found that the self-stratified structure (B) yields the highest energy conversion efficiency.
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| 7. |
- Andersson, Viktor, et al.
(author)
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Comparative study of organic thin film tandem solar cells in alternative geometries
- 2008
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 104:12, s. 124508-
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Journal article (peer-reviewed)abstract
- Optical modeling of one folded tandem solar cell and four types of stacked tandem solar cells has been performed using the finite element method and the transfer matrix method for the folded cell and the stacked cells, respectively. The results are analyzed by comparing upper limits for short circuit currents and power conversion efficiencies. In the case of serial connected tandems all of the five cell types may be compared, and we find that the folded cells are comparable to stacked tandem cells in terms of currents and power conversion efficiencies.
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| 8. |
- Asplund, Maria, 1978-, et al.
(author)
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Composite biomolecule/PEDOT materials for neural electrodes
- 2008
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In: Biointerphases. - NY : American Institute of Physics. - 1559-4106 .- 1934-8630. ; 3:3, s. 83-93
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Journal article (peer-reviewed)abstract
- Electrodes intended for neural communication must be designed to meet boththe electrochemical and biological requirements essential for long term functionality. Metallic electrode materials have been found inadequate to meet theserequirements and therefore conducting polymers for neural electrodes have emergedas a field of interest. One clear advantage with polymerelectrodes is the possibility to tailor the material to haveoptimal biomechanical and chemical properties for certain applications. To identifyand evaluate new materials for neural communication electrodes, three chargedbiomolecules, fibrinogen, hyaluronic acid (HA), and heparin are used ascounterions in the electrochemical polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT). The resultingmaterial is evaluated electrochemically and the amount of exposed biomoleculeon the surface is quantified. PEDOT:biomolecule surfaces are also studiedwith static contact angle measurements as well as scanning electronmicroscopy and compared to surfaces of PEDOT electrochemically deposited withsurfactant counterion polystyrene sulphonate (PSS). Electrochemical measurements show that PEDOT:heparinand PEDOT:HA, both have the electrochemical properties required for neuralelectrodes, and PEDOT:heparin also compares well to PEDOT:PSS. PEDOT:fibrinogen isfound less suitable as neural electrode material.
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| 9. |
- Björk, Per, et al.
(author)
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Oligothiophene Assemblies Defined by DNA Interaction : From Single Chains to Disordered Clusters
- 2009
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In: SMALL. - : Wiley. - 1613-6810 .- 1613-6829. ; 5:1, s. 96-103
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Journal article (peer-reviewed)abstract
- The organization of conjugated polyelectrolytes (CPEs) interacting with biomolecules sets conditions for the biodetection of biological processes and identity, through the use of optical emission from the CPE. Herein, a well-defined CPE and its binding to DNA is studied. By using dynamic light scattering and circular dichroism spectroscopy, it is shown that the CPE forms a multimolecule ensemble in aqueous solution that is more than doubled it? size when interacting with a small DNA chain, while single chains are evident in ethanol. The related changes in the fluorescence spectra upon polymer aggregation are assigned to oscillator strength redistribution between vibronic transitions in weakly coupled H-aggregates. An enhanced single-molecule spectroscopy technique that allows full control of excitation and emission light polarization is applied to combed and decorated;,DNA chains. It is found that the organization of combed CPE-lambda DNA complexes (when dry on the surface) allows considerable variation of CPE distances and direction relative to the DNA chain. By analysis of the polarization data. energy transfer between the polymer chains in individual complexes is confirmed and their sizes estimated.
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| 10. |
- Björk, Per, et al.
(author)
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Single molecular imaging and spectroscopy of conjugated polyelectrolytes decorated on stretched aligned DNA
- 2005
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 5:10, s. 1948-1953
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Journal article (peer-reviewed)abstract
- DNA is the prototype template for building nanoelectronic devices by self-assembly. The electronic functions are made possible by coordinating electronic polymer chains to DNA. This paper demonstrates two methods for fabrication of aligned and ordered DNA nanowires complexed with conjugated polyelectrolytes (CPEs). The complex can be formed either in solution prior to stretching or after stretching of the bare DNA on a surface. Molecular combing was used to stretch the complexes on surface energy patterned surfaces, and PMMA for the bare DNA. Single molecular spectroscopy, in fluorescence, and microscopy, in atomic force microscopy, give evidence for coordination of the short CPE chains to the aligned DNA.
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