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  • Chen, Yun, 1966, et al. (författare)
  • Characterization of VCAM-1-Binding Peptide-Functionalized Quantum Dots for Molecular Imaging of Inflamed Endothelium
  • 2013
  • Ingår i: Plos One. - 1932-6203. ; 8:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Inflammation-induced activation of endothelium constitutes one of the earliest changes during atherogenesis. New imaging techniques that allow detecting activated endothelial cells can improve the identification of persons at high cardiovascular risk in early stages. Quantum dots (QDs) have attractive optical properties such as bright fluorescence and high photostability, and have been increasingly studied and developed for bio-imaging and bio-targeting applications. We report here the development of vascular cell adhesion molecule-1 binding peptide (VCAM-1 binding peptide) functionalized QDs (VQDs) from amino QDs. It was found that the QD fluorescence signal in tumor necrosis factor alpha (TNF-alpha) treated endothelial cells in vitro was significantly higher when these cells were labeled with VQDs than amino QDs. The VQD labeling of TNF-alpha-treated endothelial cells was VCAM-1 specific since pre-incubation with recombinant VCAM-1 blocked cells' uptake of VQDs. Our ex vivo and in vivo experiments showed that in the inflamed endothelium, QD fluorescence signal from VQDs was also much stronger than that of amino QDs. Moreover, we observed that the QD fluorescence peak was significantly blue-shifted after VQDs interacted with aortic endothelial cells in vivo and in vitro. A similar blue-shift was observed after VQDs were incubated with recombinant VCAM-1 in tube. We anticipate that the specific interaction between VQDs and VCAM-1 and the blue-shift of the QD fluorescence peak can be very useful for VCAM-1 detection in vivo.
  • Fontana, J. M., et al. (författare)
  • Transport and release of colloidal 3-mercaptopropionic acid-coated CdSe-CdS/ZnS core-multishell quantum dots in human umbilical vein endothelial cells
  • 2017
  • Ingår i: International Journal of Nanomedicine. - : Dove Medical Press Ltd. - 1178-2013 .- 1176-9114. ; 12, s. 8615-8629
  • Tidskriftsartikel (refereegranskat)abstract
    • Colloidal semiconductor quantum dots (QDs) have been extensively researched and developed for biomedical applications, including drug delivery and biosensing assays. Hence, it is pivotal to understand their behavior in terms of intracellular transport and toxicological effects. In this study, we focused on 3-mercaptopropionic acid-coated CdSe-CdS/ZnS core-multishell quantum dots (3MPA-QDs) converted from the as-grown octadecylamine-coated quantum dots (ODA-QDs) and their direct and dynamic interactions with human umbilical vein endothelial cells (HUVECs). Live cell imaging using confocal fluorescence microscopy showed that 3MPAQDs first attached to and subsequently aggregated on HUVEC plasma membrane similar to 25 min after QD deposition. The aggregated QDs started being internalized at similar to 2 h and reached their highest internalization degree at similar to 24 h. They were released from HUVECs after similar to 48 h. During the 48 h period, the HUVECs responded normally to external stimulations, grew, proliferated and wound healed without any perceptible apoptosis. Furthermore, 1) 3MPA-QDs were internalized in newly formed LysoTracker-stained early endosomes; 2) adenosine 5'-triphosphateinduced [Ca2+](i) modulation caused a transient decrease in the fluorescence of 3MPA-QDs that were attached to the plasma membrane but a transient increase in the internalized 3MPA-QDs; and 3) fluorescence signal modulations of co-stained LysoTracker and QDs induced by the lysosomotropic agent Gly-Phe-beta-naphthylamide were spatially co-localized and temporally synchronized. Our findings suggest that 3MPA-QDs converted from ODA-QDs are a potential nontoxic fluorescent probe for future use in clinical applications. Moreover, the photophysical strategy and techniques reported in this work are easily applicable to study of direct interactions between other nanoparticles and live cells; contributing to awareness and implementation of the safe applications of nanoparticles.
  • Li, Li, et al. (författare)
  • Reversible Modification of CdSe-CdS/ZnS Quantum Dot Fluorescence by Surrounding Ca2+ Ions
  • 2014
  • Ingår i: ; 118:19, s. 10424-10433
  • Tidskriftsartikel (refereegranskat)abstract
    • It has been known for a long time that the fluorescence intensity of colloidal quantum dots (QDs) becomes modified when free ions are added to the QD solution. The consequences of removing free ions from the QD solution, however, have not been closely investigated. In this work we studied fluorescence from 3-mercaptopropionic acid (3-MPA) coated CdSe-CdS/ZnS core-multishell QDs when free Ca2+ ions were added to and subsequently removed from the QD solution. It was found that QD fluorescence intensity was reduced when Ca2+ ions were added to the QD solution, while the wavelength of the QD fluorescence peak remained unchanged. QD fluorescence recovered when the concentration of free Ca2+ ions in the QD solution was reduced by adding Ca2+ chelator (ethylene glycol tetraacetic acid, EGTA). It was further observed that the time of single QD fluorescence at on-state and QD fluorescence lifetimes were also reduced after adding Ca2+ and then recovered when EGTA was added. Theoretical study shows that a free Ca2+ ion can attach stably to the system of [QD + surface ligand], attract the photoexcited electron, and repel the photoexcited hole inside the QD core, leading to the reduction of the radiative recombination between the electron and hole, thereafter decreasing the QD fluorescence intensity, on-state time, and fluorescence lifetimes, as observed experimentally. To the best of our knowledge, this is a first study to show that the changes of QD optical properties are reversible under the influence of Ca2+ ions. We further estimated the equilibrium association constant pK(a) of our QDs with Ca2+, which is much larger than QDs with Mg2+, Na+, and K+, indicating the feasibility of developing a QD-based Ca2+ sensor.
  • Shambetova, N., et al. (författare)
  • Acid Dissociation of 3-Mercaptopropionic Acid Coated CdSe-CdS/Cd0.5Zn0.5S/ZnS Core-Multishell Quantum Dot and Strong Ionic Interaction with Ca2+ Ion
  • 2016
  • Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:6, s. 3519-3529
  • Tidskriftsartikel (refereegranskat)abstract
    • By devising careful electrophoresis, it was shown that at pH below 7.0, the electrophoretic mobility of 3-mercaptopropionic acid (3MPA) coated CdSe-ZnS core-shell quantum dots (denoted as QD-3MPA) was very small. At pH above 7.0, QD-3MPA migrated toward the anode, implying acid dissociation, and the degree of which was proportional to the pH value. QD-3MPA's electrophoretic mobility was impaired after adding sufficient Ca2+ ions to the QD solution and revived when a similar amount of Ca2+ chelators (ethylene glycol tetraacetic acid, EGTA) was added. This demonstrated that acid dissociation and its pH dependence of 3MPA on the QD surface are critical factors in understanding the electric and optical properties of QDs. The acid dissociated QD-3MPA interacted strongly with Ca2+, forming a charge neutral QD-3MPA Ca2+ complex in the absence of EGTA. First-principles study confirmed the observed experimental evidence. The strong ionic interaction between acid dissociated QD-3MPA and Ca2+ is critical for developing reliable QD-based biosensing assays. Moreover, the strategy and techniques reported in this work are easily applicable to other fluorescent biomarkers and therefore can be important for advancing in vivo and in vitro imaging, sensing, and labeling.
  • Abrahamsson, S., et al. (författare)
  • Multifocus structured illumination microscopy for fast volumetric super-resolution imaging
  • 2017
  • Ingår i: Biomedical Optics Express. - : OSA - The Optical Society. - 2156-7085 .- 2156-7085. ; 8:9, s. 4135-4140
  • Tidskriftsartikel (refereegranskat)abstract
    • We here report for the first time the synergistic implementation of structured illumination microscopy (SIM) and multifocus microscopy (MFM). This imaging modality is designed to alleviate the problem of insufficient volumetric acquisition speed in superresolution biological imaging. SIM is a wide-field super-resolution technique that allows imaging with visible light beyond the classical diffraction limit. Employing multifocus diffractive optics we obtain simultaneous wide-field 3D imaging capability in the SIM acquisition sequence, improving volumetric acquisition speed by an order of magnitude. Imaging performance is demonstrated on biological specimens.
  • Agostinho, Ana, et al. (författare)
  • High density of REC8 constrains sister chromatid axes and prevents illegitimate synaptonemal complex formation
  • 2016
  • Ingår i: ; 17:6, s. 901-913
  • Tidskriftsartikel (refereegranskat)abstract
    • During meiosis, cohesin complexes mediate sister chromatid cohesion (SCC), synaptonemal complex (SC) assembly and synapsis. Here, using super-resolution microscopy, we imaged sister chromatid axes in mouse meiocytes that have normal or reduced levels of cohesin complexes, assessing the relationship between localization of cohesin complexes, SCC and SC formation. We show that REC8 foci are separated from each other by a distance smaller than 15% of the total chromosome axis length in wild-type meiocytes. Reduced levels of cohesin complexes result in a local separation of sister chromatid axial elements (LSAEs), as well as illegitimate SC formation at these sites. REC8 but not RAD21 or RAD21L cohesin complexes flank sites of LSAEs, whereas RAD21 and RAD21L appear predominantly along the separated sister-chromatid axes. Based on these observations and a quantitative distribution analysis of REC8 along sister chromatid axes, we propose that the high density of randomly distributed REC8 cohesin complexes promotes SCC and prevents illegitimate SC formation.
  • Agostinho, A., et al. (författare)
  • Sexual dimorphism in the width of the mouse synaptonemal complex
  • 2018
  • Ingår i: ; 131:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Sexual dimorphism has been used to describe morphological differences between the sexes, but can be extended to any biologically related process that varies between males and females. The synaptonemal complex (SC) is a tripartite structure that connects homologous chromosomes in meiosis. Here, aided by superresolution microscopy techniques, we show that the SC is subject to sexual dimorphism, in mouse germ cells. We have identified a significantly narrower SC in oocytes and have established that this difference does not arise from a different organization of the lateral elements nor from a different isoform of transverse filament protein SYCP1. Instead, we provide evidence for the existence of a narrower central element and a different integration site for the C-termini of SYCP1, in females. In addition to these female-specific features, we speculate that post-translation modifications affecting the SYCP1 coiled-coil region could render a more compact conformation, thus contributing to the narrower SC observed in females.
  • Aizman, O., et al. (författare)
  • Ouabain, a steroid hormone that signals with slow calcium oscillations
  • 2001
  • Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - 0027-8424 .- 1091-6490. ; 98:23, s. 13420-13424
  • Tidskriftsartikel (refereegranskat)abstract
    • The plant-derived steroid, digoxin, a specific inhibitor of Na,K-ATPase, has been used for centuries in the treatment of heart disease. Recent studies demonstrate the presence of a digoxin analog, ouabain, in mammalian tissue, but its biological role has not been elucidated. Here, we show in renal epithelial cells that ouabain, in doses causing only partial Na,K-ATPase inhibition, acts as a biological inducer of regular, low-frequency intracellular calcium ([Ca2+](i)) oscillations that elicit activation of the transcription factor, NF-KB. Partial inhibition of Na,K-ATPase using low extracellular K+ and depolarization of cells did not have these effects. Incubation of cells in Ca2+-free media, inhibition of voltage-gated calcium channels, inositol triphosphate receptor antagonism, and redistribution of actin to a thick layer adjacent to the plasma membrane abolished [Ca2+](i) oscillations, indicating that they were caused by a concerted action of inositol triphosphate receptors and capacitative calcium entry via plasma membrane channels. Blockade of ouabain-induced [C-a2+](i) oscillations prevented activation of NF-kappaB. The results demonstrate a new mechanism for steroid signaling via plasma membrane receptors and underline a novel role for the steroid hormone, ouabain, as a physiological inducer of [Ca2+](i) oscillations involved in transcriptional regulation in mammalian cells.
  • Akpe, Victor, et al. (författare)
  • Photophysical and photochemical parameters of octakis (benzylthio) phthalocyaninato zinc, aluminium and tin : Red shift index concept in solvent effect on the ground state absorption of zinc phthalocyanine derivatives
  • 2010
  • Ingår i: Journal of Molecular Structure. - 0022-2860 .- 1872-8014. ; 984:1-3, s. 1-14
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper addresses the synthesis of octa-substituted benzylthio metallophthalocyanines (OBTMPcs) that contain the central metal ions of Zn2+, Al3+ and Sn4+. The ground state absorption of ZnPc(SR)(8) (OBTZnPc) along with the ZnPc derivatives, well documented in literature were used to study a new concept called the red shift index (RsI). The concept is based on the empirical values of RsI of the different complexes in solvent media. Unequivocally, parameters used in this paper show strong correlations that are consistent with the results obtained. For instance, 12,1 of the complexes tend to increase as the refractive index, n(D), and solvent donor, DN, of solvent increases. Photodegradation (photobleaching) quantum yield, phi(d) measurements of these compounds show that they are highly photostable, phi(d) (0.03-0.33 x 10(-5)). The triplet quantum yield, phi(T) (0.40-0.53) and the triplet lifetime, tau(T) (610-810 mu s) are within the typical range for metallophthalocyanines in DMSO. The photosensitisation efficiency. S-Delta, is relatively high for all the molecules (0.74-0.90). (C) 2010 Elsevier B.V. All rights reserved.
  • Akpe, Victor, et al. (författare)
  • Red-Shift Index Concept in Solvent Effects of Chromophore-Substituted Metallophthalocyanines : A Look at the Empirical Relationship of the Macroscopic Properties of the Solute-Solvent Interactions
  • 2015
  • Ingår i: ; 44:2, s. 307-326
  • Tidskriftsartikel (refereegranskat)abstract
    • Solvent effects on the UV/vis spectra of metallopthalocyanines (MPcs) have been interpreted using the red-shift index concept (R (s) I). The concept connects empirically, direct, experimental, easily accessible optical spectral data, which are explained by considering the differential behavior of the solute-solvent interactions at the ground state and excited state using the spectral values of MPcs along with the derived concept, called the associated solvation energy (ASE). R (s) I is formulated from three fundamental parameters, which are: ground state electronic absorption spectrum, polarization red-shift and a scaling factor of MPc (N (dye)) in the respective solvents. The R (s) I is a reflection of the index value of the chromophore substituent of MPc in the solvent; thus, the concept can be used as a solvatochromic parameter to study a wide range of supramolecular and heterocyclic compounds that can be modified at their periphery or 'handles'. Particularly, in this study, the concept has been used to rank MPc candidates by using the statistical mean performance of the solvatochromic parameters, which are red shift index, polarizability efficiency and ASE. We hereby review the solvent effects on the UV/vis spectra of substituted and unsubstituted MPcs.
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