| 1. |
- Castelain, Mickaël, et al.
(författare)
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Fast uncoiling kinetics of F1C pili expressed by uropathogenic Escherichia coli are revealed on a single pilus level using force-measuring optical tweezers
- 2011
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Ingår i: European Biophysics Journal. - : Springer Science and Business Media LLC. - 0175-7571 .- 1432-1017. ; 40:3, s. 305-316
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Tidskriftsartikel (refereegranskat)abstract
- Uropathogenic Escherichia coli (UPEC) expressvarious kinds of organelles, so-called pili or fimbriae, thatmediate adhesion to host tissue in the urinary tract throughspecific receptor-adhesin interactions. The biomechanicalproperties of these pili have been considered important forthe ability of bacteria to withstand shear forces from rinsingurine flows. Force-measuring optical tweezers have beenused to characterize individual organelles of F1C typeexpressed by UPEC bacteria with respect to such properties.Qualitatively, the force-versus-elongation response wasfound to be similar to that of other types of helix-like piliexpressed by UPEC, i.e., type 1, P, and S, with force-inducedelongation in three regions, one of which represents theimportant uncoiling mechanism of the helix-like quaternarystructure. Quantitatively, the steady-state uncoiling forcewas assessed as 26.4 ±1.4 pN, which is similar to those ofother pili (which range from 21 pN for SI to 30 pN for type 1).The corner velocity for dynamic response (1,400 nm/s) wasfound to be larger than those of the other pili (400–700 nm/sfor S and P pili, and 6 nm/s for type 1). The kinetics werefound to be faster, with a thermal opening rate of 17 Hz, afew times higher than S and P pili, and three orders ofmagnitude higher than type 1. These data suggest that F1Cpili are, like P and S pili, evolutionarily selected to primarilywithstand the conditions expressed in the upper urinary tract.
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| 2. |
- Konkoli, Zoran, 1966
(författare)
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Safe uses of Hill's model: an exact comparison with the Adair model
- 2011
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Ingår i: Theoretical Biology and Medical Modelling. - : Springer Science and Business Media LLC. - 1742-4682. ; 8:10
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Tidskriftsartikel (refereegranskat)abstract
- Background: The Hill function and related Hill's model are used frequently to study processes in the living cell. There are very few studies that focus on investigating in which situations the model can be safely used. It is investigated whether it is possible to use Hill's model to describe fluctuations in particle numbers of a more complicated reaction system. Quantitative statements are made regarding when such approach is possible. Results: The particle number distribution functions for Hill's and Adair's models were compared by solving the respective master equations. Adair's model was used as a representative of a more complicated reaction model. Three similarity measurers were introduced to compare the distributions in a quantitative way. Both time dependent and the equilibrium properties of the similarity measures were studied.Conclusions: Hill's model can be safely used to investigate noise characteristics of strongly cooperative Adair's model. For a given reaction in the reaction chain, the dissociation constant of the reaction that follows should be much smaller that the dissociation constant of the chosen reaction. However, such statement needs to be used with caution. The quantitative analysis showed that boundaries of the regions in the parameter space where the models behave in the same way, exhibit a rather rich structure.
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| 3. |
- Rydell, Gustaf E, et al.
(författare)
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QCM-D studies of human norovirus VLPs binding to glycosphingolipids in supported lipid bilayers reveal strain-specific characteristics. : QCM-D studies of norovirus and glycosphingolipid interactions
- 2009
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Ingår i: Glycobiology. - : Oxford University Press (OUP). - 1460-2423 .- 0959-6658. ; 19:11, s. 1176-84
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Tidskriftsartikel (refereegranskat)abstract
- Susceptibility to norovirus infection has been linked to secretor status. Norovirus virus-like particles (VLPs; 0- 20 microg/mL) from the Norwalk (GI.1) and Dijon (GII.4) strains were assayed for binding to H type 1 and Lewis a pentaglycosylceramides, incorporated in laterally fluid supported lipid bilayers. Binding kinetics was monitored in real time in 40 microL stationary reaction chambers, using quartz crystal microbalance with dissipation (QCM-D) monitoring. Both strains displayed binding only to H type 1 and not to Lewis a glycosphingolipids, typical for epithelial cells of susceptible and resistant individuals, respectively. This binding specificity was confirmed by VLPs binding to the two glycosphingolipids chromatographed on TLC-plates. Experiments using bilayers with mixtures of H type 1 and Lewis a, with the total glycosphingolipid concentration constant at 10 wt%, showed that binding was only dependent on H type 1 concentrations and identical to experiments without additional Lewis a. Both strains showed a threshold concentration of H type 1 below which no binding was observable. The threshold was one order of magnitude higher for the Dijon strain (2 wt% versus 0.25 wt%) demonstrating that the interaction with a significantly larger number of glycosphingolipids was needed for the binding of the Dijon strain. The difference in threshold glycosphingolipid concentrations for the two strains suggests a lower affinity for the glycosphingolipid for the Dijon compared to the Norwalk strain. We propose that VLPs initially bind only a few glycosphingolipids but the binding is subsequently strengthened by lateral diffusion of additional glycosphingolipids moving into the interaction area.
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| 4. |
- Rydell, Gustaf E, et al.
(författare)
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QCM-D studies of human norovirus VLPs binding to glycosphingolipids in supported lipid bilayers reveal strain-specific characteristics.
- 2009
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Ingår i: Glycobiology. - : Oxford University Press (OUP). - 1460-2423 .- 0959-6658. ; 19:11, s. 1176-84
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Tidskriftsartikel (refereegranskat)abstract
- Susceptibility to norovirus infection has been linked to secretor status. Norovirus virus-like particles (VLPs; 0- 20 microg/mL) from the Norwalk (GI.1) and Dijon (GII.4) strains were assayed for binding to H type 1 and Lewis a pentaglycosylceramides, incorporated in laterally fluid supported lipid bilayers. Binding kinetics was monitored in real time in 40 microL stationary reaction chambers, using quartz crystal microbalance with dissipation (QCM-D) monitoring. Both strains displayed binding only to H type 1 and not to Lewis a glycosphingolipids, typical for epithelial cells of susceptible and resistant individuals, respectively. This binding specificity was confirmed by VLPs binding to the two glycosphingolipids chromatographed on TLC-plates. Experiments using bilayers with mixtures of H type 1 and Lewis a, with the total glycosphingolipid concentration constant at 10 wt%, showed that binding was only dependent on H type 1 concentrations and identical to experiments without additional Lewis a. Both strains showed a threshold concentration of H type 1 below which no binding was observable. The threshold was one order of magnitude higher for the Dijon strain (2 wt% versus 0.25 wt%) demonstrating that the interaction with a significantly larger number of glycosphingolipids was needed for the binding of the Dijon strain. The difference in threshold glycosphingolipid concentrations for the two strains suggests a lower affinity for the glycosphingolipid for the Dijon compared to the Norwalk strain. We propose that VLPs initially bind only a few glycosphingolipids but the binding is subsequently strengthened by lateral diffusion of additional glycosphingolipids moving into the interaction area.
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| 5. |
- Sawant, Rajath, et al.
(författare)
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Lens aberration correction using large scale metasurfaces
- 2020
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Ingår i: Optics InfoBase Conference Papers. - 2162-2701.
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Konferensbidrag (refereegranskat)abstract
- Hybrid refractive-metasurface devices, with nondispersive refraction in the visible, have been experimentally demonstrated. Here, relying on Pancharatnam Berry phase gradient metasurfaces, we propose a centimeter scale metasurface for correction of chromatic and spherical aberration of a lens.
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| 6. |
- Bandyopadhyay, Sulalit, et al.
(författare)
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Synthesis and in vitro cellular interactions of superparamagnetic iron nanoparticles with a crystalline gold shell
- 2014
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 316, s. 171-178
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Tidskriftsartikel (refereegranskat)abstract
- Fe@Au core-shell nanoparticles (NPs) exhibit multiple functionalities enabling their effective use in applications such as medical imaging and drug delivery. In this work, a novel synthetic method was developed and optimized for the synthesis of highly stable, monodisperse Fe@Au NPs of average diameter similar to 24 nm exhibiting magneto-plasmonic characteristics. Fe@Au NPs were characterized by a wide range of experimental techniques, including scanning (transmission) electron microscopy (S(T)EM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS) and UV-vis spectroscopy. The formed particles comprise an amorphous iron core with a crystalline Au shell of tunable thickness, and retain the superparamagnetic properties at room temperature after formation of a crystalline Au shell. After surface modification, PEGylated Fe@Au NPs were used for in vitro studies on olfactory ensheathing cells (OECs) and human neural stem cells (hNSCs). No adverse effects of the Fe@Au particles were observed post-labeling, both cell types retaining normal morphology, viability, proliferation, and motility. It can be concluded that no appreciable toxic effects on both cell types, coupled with multifunctionality and chemical stability make them ideal candidates for therapeutic as well as diagnostic applications.
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| 7. |
- Isaksson, Simon, 1988, et al.
(författare)
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Protein-Containing Lipid Bilayers Intercalated with Size-Matched Mesoporous Silica Thin Films
- 2017
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 17:1, s. 476-485
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Tidskriftsartikel (refereegranskat)abstract
- Proteins are key components in a multitude of biological processes, of which the functions carried out by transmembrane (membrane-spanning) proteins are especially demanding for investigations. This is because this class of protein needs to be incorporated into a lipid bilayer representing its native environment, and in addition, many experimental conditions also require a solid support for stabilization and analytical purposes. The solid support substrate may, however, limit the protein functionality due to protein material interactions and a lack of physical space. We have in this work tailored the pore size and pore ordering of a mesoporous silica thin film to match the native cell-membrane arrangement of the transmembrane protein human aquaporin 4 (hAQP4). Using neutron reflectivity (NR), we provide evidence of how substrate pores host the bulky water-soluble domain of hAQP4, which is shown to extend 7.2 nm into the pores of the substrate. Complementary surface analytical tools, including quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescence microscopy, revealed successful protein-containing supported lipid bilayer (pSLB) formation on mesoporous silica substrates, whereas pSLB formation was hampered on nonporous silica. Additionally, electron microscopy (TEM and SEM), light scattering (DLS and stopped-flow), and small-angle X-ray scattering (SAXS) were employed to provide a comprehensive characterization of this novel hybrid organic-inorganic interface, the tailoring of which is likely to be generally applicable to improve the function and stability of a broad range of membrane proteins containing water-soluble domains.
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| 8. |
- Ruffieux, Silvia, 1990
(författare)
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High-temperature superconducting magnetometers for on-scalp MEG
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the growing field of on-scalp magnetoencephalography (MEG), brain activity is studied by non-invasively mapping the magnetic fields generated by neuronal currents with sensors that are flexibly placed in close proximity to the subject's head. This thesis focuses on high-temperature superconducting magnetometers made from YBa2Cu3Ox-7 (YBCO), which enables a reduction in the sensor-to-room temperature standoff distance from roughly 2 cm (for conventional MEG systems) down to 1 mm. Because of the higher neuromagnetic signal magnitudes available to on-scalp sensors, simulations predict that even a relatively low-sensitivity (higher noise) full-head on-scalp MEG system can extract more information about brain activity than conventional systems. In the first part of this thesis, the development of high critical temperature (high-Tc) superconducting quantum interference device (SQUID) magnetometers for a 7-channel on-scalp MEG system is described. The sensors are single layer magnetometers with a directly coupled pickup loop made on 10 mm × 10 mm substrates using bicrystal grain boundary Josephson junctions. We found that the kinetic inductance strongly varies with film quality and temperature. Determination of all SQUID parameters by combining measurements and inductance simulations led to excellent agreement between experimental results and theoretical predictions. This allowed us to perform an in-depth magnetometer optimization. The best magnetometers achieve a magnetic field noise level of 44 fT/√Hz at 78 K. Fabricated test SQUIDs provide evidence that noise levels below 30 fT/√Hz are possible for high quality junctions with fairly low critical currents and in combination with the optimized pickup loop design. Different feedback methods for operation in a densely-packed on-scalp MEG system were also investigated. Direct injection of current into the SQUID loop was identified as the best on-chip feedback method with feedback flux crosstalk below 0.5%. By reducing the operation temperature, the noise level can be further reduced, however, the effective area also decreases because of the decreasing kinetic inductance contribution. We present a method that allows for one-time sensor calibration independent of temperature. In the second part, the design, operation, and performance of the constructed 7-channel on-scalp MEG system based on the fabricated magnetometers is presented. With a dense (2 mm edge-to-edge) hexagonal head-aligned array, the system achieves a small sensor-to-head standoff distance of 1-3 mm and dense spatial sampling. The magnetic field noise levels are 50-130 fT/√Hz and the sensor-to-sensor feedback flux crosstalk is below 0.6%. MEG measurements with the system demonstrate the feasibility of the approach and indicate that our on-scalp MEG system allows retrieval of information unavailable to conventional MEG. In the third part, two alternative magnetometer types are studied for the next generation system. The first alternative is magnetometers based on Dayem bridge junctions instead of bicrystal grain boundary junctions. With a magnetometer based on the novel grooved Dayem bridge junctions, a magnetic field noise level of 63 fT/√Hz could be achieved, which shows that Dayem bridge junctions are starting to become a viable option for single layer magnetometers. The second alternative are high-Tc SQUID magnetometers with an inductively coupled flux transformer. The best device with bicrystal grain boundary junctions reaches a magnetic field noise level below 11 fT/√Hz and outperforms the best single layer device for frequencies above 20 Hz. In the last part, the potential of kinetic inductance magnetometers (KIMs) is investigated. We demonstrate the first high-Tc KIMs, which can be operated in fields of 9-28 µT and achieve a noise level of 4 pT/√Hz at 10 kHz.
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| 9. |
- Sepehri, Sobhan, 1986, et al.
(författare)
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Characterization of Binding of Magnetic Nanoparticles to Rolling Circle Amplification Products by Turn-On Magnetic Assay
- 2019
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Ingår i: Biosensors-Basel. - : MDPI AG. ; 9:3
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Tidskriftsartikel (refereegranskat)abstract
- The specific binding of oligonucleotide-tagged 100 nm magnetic nanoparticles (MNPs) to rolling circle products (RCPs) is investigated using our newly developed differential homogenous magnetic assay (DHMA). The DHMA measures ac magnetic susceptibility from a test and a control samples simultaneously and eliminates magnetic background signal. Therefore, the DHMA can reveal details of binding kinetics of magnetic nanoparticles at very low concentrations of RCPs. From the analysis of the imaginary part of the DHMA signal, we find that smaller MNPs in the particle ensemble bind first to the RCPs. When the RCP concentration increases, we observe the formation of agglomerates, which leads to lower number of MNPs per RCP at higher concentrations of RCPs. The results thus indicate that a full frequency range of ac susceptibility observation is necessary to detect low concentrations of target RCPs and a long amplification time is not required as it does not significantly increase the number of MNPs per RCP. The findings are critical for understanding the underlying microscopic binding process for improving the assay performance. They furthermore suggest DHMA is a powerful technique for dynamically characterizing the binding interactions between MNPs and biomolecules in fluid volumes.
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| 10. |
- von Malottki, S, et al.
(författare)
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Enhanced skyrmion stability due to exchange frustration
- 2017
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Skyrmions are localized, topologically non-trivial spin structures which have raised high hopes for future spintronic applications. A key issue is skyrmion stability with respect to annihilation into the ferromagnetic state. Energy barriers for this collapse have been calculated taking only nearest neighbor exchange interactions into account. Here, we demonstrate that exchange frustration can greatly enhance skyrmion stability. We focus on the prototypical film system Pd/Fe/Ir(111) and use an atomistic spin model parametrized from first-principles calculations. We show that energy barriers and critical fields of skyrmion collapse as well as skyrmion lifetimes are drastically enhanced due to frustrated exchange and that antiskyrmions are metastable. In contrast an effective nearest-neighbor exchange model can only account for equilibrium properties of skyrmions such as their magnetic field dependent profile or the zero temperature phase diagram. Our work shows that frustration of long range exchange interactions – a typical feature in itinerant electron magnets – is a route towards enhanced skyrmion stability even in systems with a ferromagnetic ground state.
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