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  • 1.
    Faxälv, Lars
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Diagnostics, Department of Clinical Chemistry.
    Hume, Jasmin
    Chalmers.
    Kasemo, Bengt
    Chalmers.
    Svedhem, Sofia
    Chalmers.
    Imaging of blood plasma coagulation at supported lipid membranes2011In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 364, no 2, p. 582-587Article in journal (Refereed)
    Abstract [en]

    The blood coagulation system relies on lipid membrane constituents to act as regulators of the coagulation process upon vascular trauma, and in particular the 2D configuration of the lipid membranes is known to efficiently catalyze enzymatic activity of blood coagulation factors. This work demonstrates a new application of a recently developed methodology to study blood coagulation at lipid membrane interfaces with the use of imaging technology. Lipid membranes with varied net charges were formed on silica supports by systematically using different combinations of lipids where neutral phosphocholine (PC) lipids were mixed with phospholipids having either positively charged ethylphosphocholine (EPC), or negatively charged phosphatidylserine (PS) headgroups. Coagulation imaging demonstrated that negatively charged SiO(2) and membrane surfaces exposing PS (obtained from liposomes containing 30% of PS) had coagulation times which were significantly shorter than those for plain PC membranes and EPC exposing membrane surfaces (obtained from liposomes containing 30% of EPC). Coagulation times decreased non-linearly with increasing negative surface charge for lipid membranes. A threshold value for shorter coagulation times was observed below a PS content of similar to 6%. We conclude that the lipid membranes on solid support studied with the imaging setup as presented in this study offers a flexible and non-expensive solution for coagulation studies at biological membranes. It will be interesting to extend the present study towards examining coagulation on more complex lipid-based model systems. (C) 2011 Elsevier Inc. All rights reserved.

  • 2.
    Faxälv, Lars
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre for Laboratory Medicine, Department of Clinical Chemistry.
    Hume, Jasmin
    Deptartment of Applied Physics, Chalmers University of Technology,.
    Lindahl, Tomas L.
    Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre for Laboratory Medicine, Department of Clinical Chemistry.
    Kasemo, Bengt
    Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden.
    Svedhem, Sofia
    Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden.
    Activation of blood coagulation at charged supported lipid membranesManuscript (preprint) (Other academic)
    Abstract [en]

    The purpose of this work was to investigate the relationship between surface charge of phospholipid membranes and coagulation. Also, we wanted to demonstrate that coagulation at phospholipid membranes could successfully be studied in the method for imaging of coagulation.

    Analytical procedure: Supported phospholipid membranes were formed from palmitoyl-oleoyl-glycero-3-ethylphosphocholine (POEPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and 1- palmitoyl-2-oleoyl-sn-glycero-3-[phospho-L-serine] (POPS) on silicon substrates. The surface charge of the phospholipid membranes was controlled by using different compositions of POPS (negative net charge), POPC (weak negative net charge) and POEPC (positive net charge). Imaging of coagulation experiments were performed on all phospholipid membrane coated surfaces as well as the clean silicon substrate. The experiments were performed in platelet-free plasma (PFP) diluted 50:50 with phosphate-buffered saline (PBS).

    Results: Comparing the negatively charged SiO2 surface with the negatively charged POPS (30%)/POPC(70%) we found an interesting difference. Although both surfaces activated coagulation rapidly, the POPS surface facilitated a faster propagation of coagulation from the surface than the SiO2 surface. It was also found that in order for the phospholipid membranes to exert procoagulant properties, the POPS content in the membrane had to exceed ~6 %. It was also found that positively charged phospholipid membranes did not induce activation of coagulation.

    Conclusions: The work in this paper demonstrated that the coagulation process at phospholipid membranes can be studied in a straightforward manner using the imaging of coagulation setup. Furthermore, we speculate that the negatively charged phospholipid membranes but not the SiO2 surface can support the binding of coagulation factor complexes, thus facilitating a faster propagation of coagulation. The fact that the POPS content must exceed ~ 6% to fully exert procoagulant properties was also a very interesting result, especially since platelets, when activated, become procoagulant by increasing their negatively charged phosphatidylserine exposure from ~0 % to maximally ~10 %.

  • 3.
    Hook, Fredrik
    et al.
    Lund University, Sweden; Chalmers, Sweden.
    Stengel, Gudrun
    Division of Solid State Physics, Lund University, Lund, SE-22100, Sweden .
    Dahlin, Andreas B.
    Lund University, Sweden; Chalmers, Sweden.
    Gunnarsson, Anders
    Division of Solid State Physics, Lund University, Lund, SE-22100, Sweden .
    Jonsson, Magnus P.
    Division of Solid State Physics, Lund University, Lund, SE-22100, Sweden .
    Jonsson, Peter
    Division of Solid State Physics, Lund University, Lund, SE-22100, Sweden .
    Reimhult, Erik
    Department of Applied Physics, Chalmers University of Technology, Göteborg, SE-41296, Sweden .
    Simonsson, Lisa
    Division of Solid State Physics, Lund University, Lund, SE-22100, Sweden .
    Svedhem, Sofia
    Department of Applied Physics, Chalmers University of Technology, Göteborg, SE-41296, Sweden .
    Supported lipid bilayers, tethered lipid vesicles, and vesicle fusion investigated using gravimetric, plasmonic, and microscopy techniques2008In: Biointerphases, ISSN 1934-8630, E-ISSN 1559-4106, Vol. 3, no 2, p. FA108-FA116Article in journal (Refereed)
    Abstract [en]

    This article summarizes our most recent contributions to the rapidly growing field of supported lipid assemblies with emphasis on current studies addressing both fundamental and applied aspects of supported lipid bilayer (SLB) and tethered lipid vesicles (TLVs) to be utilized in sensing applications. The new insights obtained from combining the quartz crystal microbalance with dissipation monitoring technique with surface plasmon resonance are described, and we also present recent studies in which nanoplasmonic sensing has been used in studies of SLBs and TLVs. To gain full control over the spatial arrangement of TLVs in both two and three dimensions, we have developed a method for site-selective and sequence-specific sorting of DNA-tagged vesicles to surfaces modified with complementary DNA. The combination of this method with nanoplasmonic sensing formats is covered as well as the possibility of using DNA-modified vesicles for the detection of unlabeled DNA targets on the single-molecule level. Finally, a new method for membrane fusion induced by hybridization of vesicle-anchored DNA is demonstrated, including new results on content mixing obtained with vesicle populations encapsulating short, complementary DNA strands.

  • 4.
    Svedhem, Sofia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Enander, Karin
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Karlsson, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Sjöbom, Hans
    Biacore AB, Uppsala, Sweden.
    Liedberg, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Löfås, Stefan
    Biacore AB, Uppsala, Sweden.
    Mårtensson, Lars-Göran
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Sjöstrand, Sven-Erik
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Svensson, Stefan
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Carlsson, Uno
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Lundström, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Subtle differences in dissociation rates of interactions between destabilized human carbonic anhydrase II mutants and immobilized benzenesulfonamide inhibitors probed by a surface plasmon resonance biosensor2001In: Analytical Biochemistry, ISSN 0003-2697, E-ISSN 1096-0309, Vol. 296, no 2, p. 188-196Article in journal (Refereed)
    Abstract [en]

    The development of commercial biosensors based on surface plasmon resonance has made possible careful characterization of biomolecular interactions. Here, a set of destabilized human carbonic anhydrase II (HCA II) mutants was investigated with respect to their interaction kinetics with two different immobilized benzenesulfonamide inhibitors. Point mutations were located distantly from the active site, and the destabilization energies were up to 23 kJ/mol. The dissociation rate of wild-type HCA II, as determined from the binding to the inhibitor with higher affinity, was 0.019 s−1. For the mutants, dissociation rates were faster (0.022–0.025 s−1), and a correlation between faster dissociation and a high degree of destabilization was observed. We interpreted these results in terms of increased dynamics of the tertiary structures of the mutants. This interpretation was supported by entropy determinations, showing that the entropy of the native structure significantly increased upon destabilization of the protein molecule. Our findings demonstrate the applicability of modern biosensor technology in the study of subtle details in molecular interaction mechanisms, such as the long-range effect of point mutations on interaction kinetics.

  • 5.
    Valiokas, Ramunas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Östblom, Mattias
    Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics. Linköping University, The Institute of Technology.
    Svedhem, Sofia
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Svensson, Stefan C. T.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Liedberg, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics.
    Temperature-driven phase transitions in oligo(ethylene glycol)-terminated self-assembled monolayers2000In: The Journal of Physical Chemistry B, ISSN 1520-6106, Vol. 104, no 32, p. 7565-7569Article in journal (Other academic)
    Abstract [en]

    This letter explores the phase behavior of oligo(ethylene glycol) self-assembled monolayers using temperature-programmed infrared reflection absorption spectroscopy. The monolayers are formed by self-assembly of hexa(ethylene glycol) (EG(6)) and tetra(ethylene glycol) (EG(4))-terminated and amide group containing alkanethiols on polycrystalline gold. The ethylene glycol portions of the two monolayers are known to exist in two different conformations at room temperature: EG(6) in helical and EG(4) in all-trans (zigzag). The helical phase of the EG(6) gradually diminishes upon increasing the temperature and a pronounced conformational transition occurs around 60 degrees C, leading to a rapidly increasing population of all-trans conformers along the EG(6) chain. The EG(4) SAM exhibits a much simpler phase behavior. The oligomer conformation is marginally affected upon increasing the temperature to 75 degrees C, displaying the dominating all-trans phase, which possibly coexists with a small fraction of gauche-rich (disordered) regions. The reported conformational changes are reversible upon returning to 20 degrees C after stepwise heating to 70 degrees C.

  • 6.
    Van De Keere, Isabel
    et al.
    Vrije University Brussels.
    Svedhem, Sofia
    Chalmers.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Vereecken, Jean
    Vrije University Brussels.
    Kasemo, Bengt
    Chalmers.
    Hubin, Annick
    Vrije University Brussels.
    In Situ Control of the Oxide Layer on Thermally Evaporated Titanium and Lysozyme Adsorption by Means of Electrochemical Quartz with Dissipation2009In: ACS APPLIED MATERIALS and INTERFACES, ISSN 1944-8244, Vol. 1, no 2, p. 301-310Article in journal (Refereed)
    Abstract [en]

    Electrochemical (EC) quartz crystal microbalance with dissipation monitoring (ECQCM-D) is a new and powerful technique for the in situ study of adsorption phenomena. e.g., as a function of the potential of the substrate. When titanium Ti) is employed as the substrate, its oxidation behavior needs to be taken into account. Ti is always covered with a native oxide layer that can grow by, e.g., thermal oxidation or under anodic polarization. For biomolecular adsorption studies on oxidized Ti under applied potential, a stable oxide layer is desired in order to be able to distinguish the adsorption studies on oxidized Ti under applied potenital, a stable oxide layer is desired in order to be able to distinguish the adsorption phenomena and the oxide growth. Therefore, the oxidation of thermally evaporated Ti films was investigated in phosphate buffered saline by means of ECOCM-d, using a specially designed EC flow cell Upon stepping the potential applied to Ti up to 2.6 V vs standard hydrogen electrode (SHE), a fast increase of the mass was observed initially for each potential step evolving slowly to an asymptotic mass change after several hours. The oxide layer thickness increased as a quasi-linear function of the oxidation potential for potential up to 1.8 V vs SHE. The composition of the oxide layer was analyzed by X-ray photoelectron spectroscopy (XPS) it was mainly composed of TiO2 with a small percentage of suboxides (TiO and Ti2O3) primarily at the inner metal/oxide interface. The amount composed of TiO2, with a small percentage of suboxides TiO and Ti2O3 decreased with increasing oxidation potential. For each oxidation potential the calculated thickness obtained from ECQCM-D correlated well with the thickness obtained by XPS depth profiling. A procedure to prepare Ti samples with a stable oxide layer was successfully established for investigations on the influence of an electric field on the adsorption of biomolecules. As such, the effect of an applied potential on the adsorption behavior of lysozyme on oxidized Ti was investigated. It was observed that the adsorption of lysozyme on oxidized Ti was not influnced by the applied potential.

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