| 1. |
- Akhtar, Sultan, et al.
(författare)
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Real-Space Transmission Electron Microscopy Investigations of Attachment of Functionalized Magnetic Nanoparticles to DNA-Coils Acting as a Biosensor
- 2010
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 114:41, s. 13255-13262
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Tidskriftsartikel (refereegranskat)abstract
- The present work provides the first real-space analysis of nanobead-DNA coil interactions. Immobilization of oligonucleotide-functionalized magnetic nanobeads in rolling circle amplified DNA-coils was studied by complex magnetization measurements and transmission electron microscopy (TEM), and a statistical analysis of the number of beads hybridized to the DNA-coils was performed. The average number of beads per DNAcoil using the results from both methods was found to be around 6 and slightly above 2 for samples with 40 and 130 nm beads, respectively. The TEM analysis supported an earlier hypothesis that 40 nm beads are preferably immobilized in the interior of DNA-coils whereas 130 nm beads, to a larger extent, are immobilized closer to the exterior of the coils. The methodology demonstrated in the present work should open up new possibilities for characterization of interactions of a large variety of functionalized nanoparticles with macromolecules, useful for gaining more fundamental understanding of such interactions as well as for optimizing a number of biosensor applications.
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| 2. |
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| 3. |
- Akhtar, Sultan
(författare)
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Transmission Electron Microscopy of Graphene and Hydrated Biomaterial Nanostructures : Novel Techniques and Analysis
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transmission Electron Microscopy (TEM) on light element materials and soft matters is problematic due to electron irradiation damage and low contrast. In this doctoral thesis techniques were developed to address some of those issues and successfully characterize these materials at high resolution. These techniques were demonstrated on graphene flakes, DNA/magnetic beads and a number of water containing biomaterials. The details of these studies are given below.A TEM based method was presented for thickness characterization of graphene flakes. For the thickness characterization, the dynamical theory of electron diffraction is used to obtain an analytical expression for the intensity of the transmitted electron beam as a function of thickness. From JEMS simulations (experiments) the absorption constant λ in a low symmetry orientation was found to be ~ 208 nm (225 ± 9 nm). When compared to standard techniques for thickness determination of graphene/graphite, the method has the advantage of being relatively simple, fast and requiring only the acquisition of bright-field (BF) images. Using the proposed method, it is possible to measure the thickness change due to one monolayer of graphene if the flake has uniform thickness over a larger area.A real-space TEM study on magnetic bead-DNA coil interaction was conducted and a statistical analysis of the number of beads attached to the DNA-coils was performed. The average number of beads per DNA coil was calculated around 6 and slightly above 2 for samples with 40 nm and 130 nm beads, respectively. These results are in good agreement with magnetic measurements. In addition, the TEM analysis supported an earlier hypothesis that 40 nm beads are preferably attached interior of the DNA-coils while 130 nm beads closer to the exterior of the coils.A focused ion-beam in-situ lift-out technique for hydrated biological specimens was developed for cryo-TEM. The technique was demonstrated on frozen Aspergillus niger spores which were frozen with liquid nitrogen to preserve their cellular structures. A thin lamella was prepared, lifted out and welded to a TEM grid. Once the lamella was thinned to electron transparency, the grid was cryogenically transferred to the TEM using a cryo-transfer bath. The structure of the cells was revealed by BF imaging. Also, a series of energy filtered images was acquired and C, N and Mn elemental maps were produced. Furthermore, 3 Å lattice fringes of the underlying Al support were successfully resolved by high resolution imaging, confirming that the technique has the potential to extract structural information down to the atomic scale. The experimental protocol is ready now to be employed on a large variety of samples e.g. soft/hard matter interfaces.
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| 4. |
- Akhtar, Sultan, et al.
(författare)
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Visualization of functionalization of nano-particles and graphene in the TEM
- 2010
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Ingår i: Advanced Materials Workshop 2010.
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Konferensbidrag (refereegranskat)abstract
- Recently, the activity on functionalized nano-objects has strongly increased. Yet, there are, to our knowledge no techniques available that visualize the attachment of molecules to nano-entities such as nanoparticles and graphene. In this work, we show a methodology to analyse the attachment of molecules to nanoparticles and graphene. The difficulty of such transmission electron microscopy (TEM) characterization consists in the high beam sensitivity of these nanoobjects. We employed a high resolution- as well as diffraction contrast-imaging methods to characterize graphene. First, we have developed a method to measure the thickness of free-standing graphene-like layers. The refinement of these imaging techniques enabled the imaging of functionalized C60 (fullerene) on top of a few-layer graphene flake by TEM. We also developed a methodology to visualize the attachment of functionalized gold and magnetic nanoparticles (different sizes) to nonstained and unlabeled single strand DNA-coils. This technique can be used to understand the interaction of a large variety of functionalized nanoparticles with their solution environment and/or macromolecular structures for their large applications.
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| 5. |
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| 6. |
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| 7. |
- Rubino, Stefano, et al.
(författare)
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A site-specific focused-ion-beam lift-out method for cryo Transmission Electron Microscopy
- 2012
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Ingår i: Journal of Structural Biology. - : Elsevier BV. - 1047-8477 .- 1095-8657. ; 180:3, s. 572-576
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Tidskriftsartikel (refereegranskat)abstract
- The focused-ion-beam (FIB) is the method of choice for site-specific sample preparation for Transmission Electron Microscopy (TEM) in material sciences. A lamella can be physically lifted out from a specific region of a bulk specimen with submicrometer precision and thinned to electron transparency for high-resolution imaging in the TEM. The possibility to use this tool in life sciences applications has been limited by the lack of lift-out capabilities at the cryogenic temperatures often needed for biological samples. Conventional cryo-TEM sample preparation is mostly based on ultramicrotomy, a procedure that is not site-specific and known to produce artifacts. Here we demonstrate how a cooled nanomanipulator and a custom-built transfer station can be used to achieve cryo-preparation of TEM samples with the FIB, enabling high-resolution investigation of frozen-hydrated specimens in the TEM.
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| 8. |
- Strömberg, Mattias, et al.
(författare)
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Immobilization of oligonucleotide-functionalized magnetic nanobeads in DNA-coils studied by electron microscopy and atomic force microscopy
- 2011
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Ingår i: MRS Online Proceedings Library. - : Springer Science and Business Media LLC.
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Konferensbidrag (refereegranskat)abstract
- Immobilization of oligonucleotide-functionalized magnetic nanobeads by hybridization in DNA-coils formed by rolling circle amplification has been investigated using transmission electron microscopy (TEM) and atomic force microscopy (AFM). The TEM results supported earlier made observations that small beads with low oligonucleotide surface coverage preferably immobilize in the interior of the DNA-coils and do not tend to link several DNA-coils together whereas large beads with high surface coverage to a larger extent connect several DNA-coils together to clusters of several DNA-coils with beads. AFM provided direct visualization of the DNA-coils as thread-like objects. DNA-coils with immobilized beads appeared as a collection of beads with thread-like features in their near vicinity.
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| 9. |
- Talyzin, Alexandr, 1969-, et al.
(författare)
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Coronene Fusion by Heat Treatment : Road to Nanographenes
- 2011
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Ingår i: The Journal of Physical Chemistry C. - Washington : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:27, s. 13207-13214
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Tidskriftsartikel (refereegranskat)abstract
- The reactions of coronene dehydrogenation and fusion upon heat treatment in the temperature range of 500-700 degrees C were studied using XRD, TEM, Raman, IR, and NEXAFS spectroscopy. The formation of a coronene dimer (dicoronylene) was observed at temperatures 530-550 degrees C; dicoronylene can easily be separated using sublimation with a temperature gradient. An insoluble and not sublimable black precipitate was found to form at higher temperatures. Analysis of the data shows that dimerization of coronene is followed at 550-600 degrees C by oligomerization into larger molecules. Above 600 degrees C amorphization of the material and formation of graphitic nanoparticles was observed. Coronene fusion by annealing is proposed as a road to synthesis of larger polycyclic aromatic hydrocarbons and nanographenes.
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| 10. |
- Wessman, Per, et al.
(författare)
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Impact of matrix properties on survival of freeze-dried bacteria
- 2011
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Ingår i: Journal of the Science of Food and Agriculture. - : Wiley. - 0022-5142 .- 1097-0010. ; 91:14, s. 2518-2528
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Tidskriftsartikel (refereegranskat)abstract
- Background: Disaccharides are in general first choice as formulation compounds when freezedrying microorganisms. Although polysaccharides and other biopolymers are considered too large to stabilize and interact with cell components in the same beneficial way as disaccharides, polymers have been reported to support cell survival. In the present study we compare the efficiency of sucrose, the polymers Ficoll, hydroxyethylcellulose, hydroxypropylmethylcellulose and polyvinylalcohol to support survival of three bacterial strains during freeze-drying. The initial osmotic conditions were adjusted to be similar for all formulations. Formulation characterization was used to interpret the impact that different compound properties had on cell survival. Results: Despite differences in molecular size, both sucrose and the sucrose based polymer Ficoll supported cell survival after freeze-drying equally well. All formulations became amorphous upon dehydration. Scanning electron microscopy and X-ray diffraction data showed that the discerned differences in structure of the dry formulations had little impact on the survival rates. The capability of the polymers to support cell survival correlated with the surface activity of the polymers in a similar way for all investigated bacterial strains. Conclusion: Polymer-based formulations can support cell survival as effectively as disaccharides if formulation properties of importance for maintaining cell viability are identified and controlled.
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