| 1. |
- Björk, Per, et al.
(författare)
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Oligothiophene Assemblies Defined by DNA Interaction : From Single Chains to Disordered Clusters
- 2009
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Ingår i: SMALL. - : Wiley. - 1613-6810 .- 1613-6829. ; 5:1, s. 96-103
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Tidskriftsartikel (refereegranskat)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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| 2. |
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| 3. |
- Herland, Anna, et al.
(författare)
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Decoration of amyloid fibrils with luminescent conjugated polymers
- 2008
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 18:1, s. 126-132
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Tidskriftsartikel (refereegranskat)abstract
- In this work we report the coating of a biological template with a polar, but uncharged, luminescent conjugated polymer, soluble in organic solvents but not in water, to produce a nanowire. Amyloid fibrils from bovine insulin were decorated with an alternating polyfluorene derivative. Decorated fibrils were partially aligned on hydrophobic surfaces as separate and bundled fibrils, by means of molecular combing. The single molecule spectroscopy technique utilizing excitation by rotating linearly polarized light and fluorescence detection through a rotating polarizer showed a high degree of anisotropy of the polymer chains on the individual fibrils. The high degree of polarization indicated highly oriented polymer chains with the preferential orientation of the polymer backbone along the fibrils. The anisotropy ratios are comparable with those of well-oriented polymer chains in films. © The Royal Society of Chemistry.
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| 4. |
- Huang, Weiming, et al.
(författare)
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Assessment and benchmarking of spatially enabled RDF stores for the next generation of spatial data infrastructure
- 2019
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Ingår i: ISPRS International Journal of Geo-Information. - : MDPI AG. - 2220-9964. ; 8:7
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Tidskriftsartikel (refereegranskat)abstract
- Geospatial information is indispensable for various real-world applications and is thus a prominent part of today’s data science landscape. Geospatial data is primarily maintained and disseminated through spatial data infrastructures (SDIs). However, current SDIs are facing challenges in terms of data integration and semantic heterogeneity because of their partially siloed data organization. In this context, linked data provides a promising means to unravel these challenges, and it is seen as one of the key factors moving SDIs toward the next generation. In this study, we investigate the technical environment of the support for geospatial linked data by assessing and benchmarking some popular and well-known spatially enabled RDF stores (RDF4J, GeoSPARQL-Jena, Virtuoso, Stardog, and GraphDB), with a focus on GeoSPARQL compliance and query performance. The tests were performed in two different scenarios. In the first scenario, geospatial data forms a part of a large-scale data infrastructure and is integrated with other types of data. In this scenario, we used ICOS Carbon Portal’s metadata—a real-world Earth Science linked data infrastructure. In the second scenario, we benchmarked the RDF stores in a dedicated SDI environment that contains purely geospatial data, and we used geospatial datasets with both crowd-sourced and authoritative data (the same test data used in a previous benchmark study, the Geographica benchmark). The assessment and benchmarking results demonstrate that the GeoSPARQL compliance of the RDF stores has encouragingly advanced in the last several years. The query performances are generally acceptable, and spatial indexing is imperative when handling a large number of geospatial objects. Nevertheless, query correctness remains a challenge for cross-database interoperability. In conclusion, the results indicate that the spatial capacity of the RDF stores has become increasingly mature, which could benefit the development of future SDIs.
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| 5. |
- Lin, Hongzhen, et al.
(författare)
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Fate of Excitations in Conjugated Polymers : Single-Molecule Spectroscopy Reveals Nonemissive "Dark" Regions in MEH-PPV Individual Chains
- 2009
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 9:12, s. 4456-4461
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Tidskriftsartikel (refereegranskat)abstract
- Single chains of the conjugated polymer MEH-PPV (poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene)) were studied with wide-field fluorescence microscopy (dispersion in inert polymer matrices) and with fluorescence correlation spectroscopy (chloroform solution). The fluorescence yield of individual molecules in matrices was found to be 1-2 orders of magnitude lower than that in solution and it decreased substantially with increasing chain length. It suggests that isolation of MEH-PPV molecules in polymer matrices creates favorable conditions for photogeneration of nonemissive primary excited states.
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| 6. |
- Lin, Hongzhen, et al.
(författare)
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Fluorescence blinking, exciton dynamics, and energy transfer domains in single conjugated polymer chains.
- 2008
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 130:22, s. 7042-7051
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Tidskriftsartikel (refereegranskat)abstract
- In order to understand exciton migration and fluorescence intensity fluctuation mechanisms in conjugated polymer single molecules, we studied fluorescence decay dynamics at "on" and "off" fluorescence intensity levels with 20 ps time resolution using MEH-PPV [poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] dispersed in PMMA. Two types of intensity fluctuations were distinguished for single chains of conjugated polymers. Abrupt intensity fluctuations (blinking) were found to be always accompanied by corresponding changes in fluorescence lifetime. On the contrary, during "smooth" intensity fluctuations no lifetime change was observed. Time-resolved data in combination with data on fluorescence emission and excitation anisotropy lead to a picture where a single polymer molecule is seen as consisting of several energy transfer domains. Exciton migration is efficient within a domain and not efficient between domains. Each domain can have several emitting low-energy sites over which the exciton continuously migrates until it decays. Emission of individual domains is often highly polarized. Fluorescence from a domain can be strongly quenched by Forster energy transfer to a quencher (hole polaron) if the domain overlaps with the quenching sphere.
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| 7. |
- Lin, Hongzhen, et al.
(författare)
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Single chain versus single aggregate spectroscopy of conjugated polymers. Where is the border?
- 2010
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Ingår i: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 12, s. 11770-11777
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Tidskriftsartikel (refereegranskat)abstract
- Single chains of conjugated polymers e.g. MEH-PPV (poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) have become interesting objects for single molecule spectroscopy (SMS) studies. However, most of the experiments so far were performed without full awareness of the isolation status of the polymer chains in host matrices. We used steady-state and time-resolved fluorescence methods and 2D polarization single molecule imaging technique to unravel the isolation/aggregation status of MEH-PPV in spin-coated films prepared at different conditions. It turned out that a sample showing isolated bright spots in fluorescence images could be obtained in a very broad concentration range of MEH-PPV when toluene was used as a solvent and PMMA as a matrix. If the MEH-PPV concentration was not sufficiently low, a substantial fraction of the fluorescence spots should be assigned to individual nano-aggregates rather than truly isolated chains of the polymer. Contrary to single aggregates, truly isolated MEH-PPV chains showed blue-shifted emission spectra, mono-exponential fluorescence decay dynamics with relatively long lifetimes (0.4-1.2 ns), and high polarization anisotropy. We argue that insufficient control of the concentration in the published SMS studies of MEH-PPV resulted in incorrect assigning of some spectroscopic properties of single aggregates to isolated MEH-PPV chains. We believe this to be the main origin of discrepancies among the published data in this field.
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| 8. |
- Mirzov, Oleg, et al.
(författare)
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Direct exciton quenching in single molecules of MEH-PPV at 77 K
- 2004
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 386:4-6, s. 286-290
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescence blinking behaviour was observed for single molecules of the conjugated polymer poly[2-methoxy,5-(2'-ethylhexyloxy)-p-phenylene-vinylene] (MEH-PPV) at 77 and 300 K. No strict qualitative dependence on temperature was observed, despite of the expected suppression of exciton migration at the low temperature. We assume MEH-PPV molecules to form dense nanoparticles with a characteristic size of about 10 nm at the largest. In such small nanoparticles exciton can be efficiently quenched by a photogenerated quencher due to Forster transfer just after a few hops over the polymer nanoparticle. Thus, long-distance exciton migration is not necessary to have strong fluorescence intensity fluctuations. (C) 2004 Elsevier B.V. All rights reserved.
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| 9. |
- Mirzov, Oleg, et al.
(författare)
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Fluorescence blinking in MEH-PPV single molecules at low temperature
- 2005
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 112:1-4, s. 353-356
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescence intensity transients of single molecules of the conjugated polymer poly[2-methoxy,5-(2-ethylhexyloxy)-p-phenylene-vinylene] (MEH-PPV) were studied at 15 K. Fluorescence blinking behavior was observed despite the expected low-temperature suppression of energy migration in such disordered molecular systems. Presence of the fluorescence blinking effect at 15K indicates that the single molecules possess a collapsed conformation with characteristic size of not more than several nanometers, which corresponds to only a few exciton hops over a polymer chain. (c) 2004 Elsevier B.V. All rights reserved.
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| 10. |
- Mirzov, Oleg, et al.
(författare)
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Large spectral diffusion of conjugated polymer single molecule fluorescence at low temperature
- 2005
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 408:4-6, s. 317-321
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Tidskriftsartikel (refereegranskat)abstract
- The conductive polymer poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4- phenylene vinylene) (MEH-PPV) was investigated by means of single molecule spectroscopy at 15 K. MEH-PPV single chains were deposited onto a surface from a toluene solution and covered with a polymer cap layer spin-coated from an aqueous solution for protection from air. The MEH-PPV molecules exhibited large fluorescence spectral diffusion with the range reaching 1000 cm(-1). We concluded that conformational changes, affecting dispersive interactions and conjugation length, is the most probable mechanism of the observed effect. It is the matrix-free environment that allows the MEH-PPV chains to undergo sufficiently large conformational changes even at low temperature. (c) 2005 Elsevier B.V. All rights reserved.
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