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Document Server@UHasselt (58.393 recursos)

Repository of the University of Hasselt containing publications in the fields of statistics, computer science, information strategies and material from the Institute for behavioural sciences.

Physics - Bio-Physics

Mostrando recursos 1 - 20 de 33

  1. Molecular engineering of chromophores for combined second-harmonic and two-photon fluorescence in cellular imaging

    De Meulenaere, Evelien; Chen, Wei-Qiang; Van Cleuvenbergen, Stijn; Zheng, Mei-Ling; Psilodimitrakopoulos, Sotiris; Paesen, Rik; Taymans, Jean-Marc; Ameloot, Marcel; Vanderleyden, Jos; Loza-Alvarez, Pablo; Duan, Xuan-Ming; Clays, Koen
    A series of chromophores with enhanced second-and third-order nonlinear optical properties were engineered for use in combined second-harmonic and two-photon fluorescence microscopy. Electronaccepting moieties imparted nonlinear optical properties to the chromophores. The electron-rich carbazole core served as a template towards one-or two-dimensional chromophores. More efficient acceptor groups (pyridinium, benzazolium, benzothiazolium) on the carbazole donor core resulted in improved second-and third-order nonlinear optical properties. A selection of these chromophores was tested in a cellular environment with a multimodal multiphoton microscope. The structural differences of the chromophores resulted in high selectivity for mitochondria or the nucleus in two-photon fluorescence and ranging from...

  2. Ensemble and single particle fluorimetric techniques in concerted action to study the diffusion and aggregation of the glycine receptor alpha 3 isoforms in the cell plasma membrane

    NOTELAERS, Kristof; SMISDOM, Nick; Rocha, Susana; JANSSEN, Daniel; Meier, Jochen C.; RIGO, Jean-Michel; Hofkens, Johan; AMELOOT, Marcel
    The spatio-temporal membrane behavior of glycine receptors (GlyRs) is known to be of influence on receptor homeostasis and functionality. In this work, an elaborate fluorimetric strategy was applied to study the GlyR alpha 3K and L isoforms. Previously established differential clustering, desensitization and synaptic localization of these isoforms imply that membrane behavior is crucial in determining GlyR alpha 3 physiology. Therefore diffusion and aggregation of homomeric alpha 3 isoform-containing GlyRs were studied in HEK 293 cells. A unique combination of multiple diffraction-limited ensemble average methods and subdiffraction single particle techniques was used in order to achieve an integrated view of...

  3. Distributing the Optical Near-Field for Efficient Field-Enhancements in Nanostructures

    Valev, V. K.; DE CLERCQ, Ben; Biris, C. G.; Zheng, X.; Vandendriessche, S.; Hojeij, M.; Denkova, D.; Jeyaram, Y.; Panoiu, N. C.; Ekinci, Y.; Silhanek, A. V.; Volskiy, V.; Vandenbosch, G. A. E.; AMELOOT, Marcel; Moshchalkov, V. V.; Verbiest, T.
    Circularly polarized light imparts a sense of rotation on the electron density in ring-shaped gold nanostructures. As a consequence, the near-field enhancement becomes homogeneous on the surface of the nanostructures, thereby increasing the opportunity for interaction with molecules. This type of nanostructured samples can find a broad range of applications in chemical processes where the interaction between molecules and local field enhancements play an important role.

  4. Plasmon-Enhanced Sub-Wavelength Laser Ablation: Plasmonic Nanojets

    Valev, Ventsislav K.; Denkova, Denitza; Zheng, Xuezhi; Kuznetsov, Arseniy I.; Reinhardt, Carsten; Chichkov, Boris N.; Tsutsumanova, Gichka; Osley, Edward J.; Petkov, Veselin; De Clercq, Ben; Silhanek, Alejandro V.; Jeyaram, Yogesh; Volskiy, Vladimir; Warburton, Paul A.; Vandenbosch, Guy A. E.; Russev, Stoyan; Aktsipetrov, Oleg A.; Ameloot, Marcel; Moshchalkov, Victor V.; Verbiest, Thierry

  5. Volumetric Method of Moments and Conceptual Multilevel Building Blocks for Nanotopologies

    Zheng, X.; Valev, V. K.; Verellen, N.; Jeyaram, Y.; Silhanek, A. V.; Metlushko, V.; AMELOOT, Marcel; Vandenbosch, G. A. E.; Moshchalkov, V. V.
    On the basis of the relationship between charge dimensionality and singular field behavior, it is proven that in a volumetric description of a volume current carrying topology, half rooftops of different binary hierarchical level are allowed without introducing numerical difficulties. This opens the possibility to use a very efficient multilevel hierarchical meshing scheme in a volumetric method-of-moments (V-MoM) algorithm. The new meshing scheme is validated by numerical calculations and experiments. It paves the way toward a much more efficient use of MoM in the description of arbitrarily shaped nanostructures at infrared and optical frequencies.

  6. Liver X receptors regulate cholesterol homeostasis in oligodendrocytes

    NELISSEN, Katherine; Mulder, Monique; SMETS, Ilse; TIMMERMANS, Silke; SMEETS, Karen; AMELOOT, Marcel; Hendriks, Jerome J. A.
    Cholesterol synthesis and transport in oligodendrocytes are essential for optimal myelination and remyelination in pathological conditions such as multiple sclerosis. However, little is known about cholesterol homeostasis in the myelin-forming oligodendrocytes. Liver X receptors (LXRs) are nuclear oxysterol receptors that regulate genes involved in cholesterol homeostasis and may therefore play an important role in de- and remyelination. We investigated whether LXRs regulate cholesterol homeostasis in oligodendrocytes. mRNA expression of genes encoding LXR-alpha and LXR-beta and their target genes (ABCA1, ABCG1, ABCG4, apoE, and LDLR) was detected in oligodendrocytes derived from both neonatal and adult rats using quantitative real-time PCR. The...

  7. Heat-Transfer Resistance at Solid???Liquid Interfaces: A Tool for the Detection of Single-Nucleotide Polymorphisms in DNA

    van Grinsven, Bart; Vanden Bon, Natalie; Grieten, Lars; Murib, Mohammed; Jimenez Monroy, Kathia L.; Janssens, Stoffel D.; Haenen, Ken; Sch??ning, Michael J.; Vermeeren, Veronique; Ameloot, Marcel; Michiels, Luc; Thoelen, Ronald; De Ceuninck, Ward; Wagner, Patrick; Strauven, Hannelore
    In this article, we report on the heat-transfer resistance at interfaces as a novel, denaturation-based method to detect single-nucleotide polymorphisms in DNA. We observed that a molecular brush of double-stranded DNA grafted onto synthetic diamond surfaces does not notably affect the heat-transfer resistance at the solid-to-liquid interface. In contrast to this, molecular brushes of single-stranded DNA cause, surprisingly, a substantially higher heat-transfer resistance and behave like a thermally insulating layer. This effect can be utilized to identify ds-DNA melting temperatures via the switching from low- to high heat-transfer resistance. The melting temperatures identified with this method for different DNA duplexes...

  8. The role of chiral local field enhancements below the resolution limit of Second Harmonic Generation microscopy

    Valev, V.K.; Clercq, B.D.; Zheng, X.; Denkova, D.; Osley, E.J.; Vandendriessche, S.; Silhanek, A.V.; Volskiy, V.; Warburton, P.A.; Vandenbosch, G.A.E.; Ameloot, M.; Moshchalkov, V.V.; Verbiest, T.
    While it has been demonstrated that, above its resolution limit, Second Harmonic Generation (SHG) microscopy can map chiral local field enhancements, below that limit, structural defects were found to play a major role. Here we show that, even below the resolution limit, the contributions from chiral local field enhancements to the SHG signal can dominate over those by structural defects. We report highly homogeneous SHG micrographs of star-shaped gold nanostructures, where the SHG circular dichroism effect is clearly visible from virtually every single nanostructure. Most likely, size and geometry determine the dominant contributions to the SHG signal in nanostructured systems.

  9. Plasmon-Enhanced Sub-Wavelenght Laser Ablation: Plasmonic Nanojets

    Valev, Ventsislav K.; Denkova, Denitza; Zheng, Xuezhi; Kuznetsov, Arseniy I.; Reinhardt, Carsten; Chichkov, Boris N.; Tsutsumanova, Gischka; Osley, Edward J.; Petkov, Veselin; De Clercq, Ben; Silhanek, Alejandro V.; Yogesh, Jeyaram; Volskiy, Vladimir; Warburton, Paul A.; Vandenbosch, Guy A.E.; Russev, Stoyan; Aktsipetrov, Oleg A.; Ameloot, Marcel; Moshchalkov, Victor V.; Verbiest, Thierry
    In response to the incident light's electric field, the electron density oscillates in the plasmonic hotspots producing an electric current. Associated Ohmic losses raise the temperature of the material within the plasmonic hotspot above the melting point. A nanojet and nanosphere ejection can then be observed precisely from the plasmonic hotspots.

  10. Molecular engineering of chromophores for combined second-harmonic and two-photon fluorescence in cellular imaging

    De Meulenaere, Evelien; Chen, Wei-Qiang; Van Cleuvenbergen, Stijn; Zheng, Mei-Ling; Psilodimitrakopoulos, Sotiris; Paesen, Rik; Taymans, Jean-Marc; Ameloot, Marcel; Vanderleyden, Jos; Loza-Alvarez, Pablo; Duan, Xuan-Ming; Clays, Koen
    A series of chromophores with enhanced second- and third-order nonlinear optical properties were engineered for use in combined second-harmonic and two-photon fluorescence microscopy. Electronaccepting moieties imparted nonlinear optical properties to the chromophores. The electron-rich carbazole core served as a template towards one- or two-dimensional chromophores. More efficient acceptor groups (pyridinium, benzazolium, benzothiazolium) on the carbazole donor core resulted in improved second- and third-order nonlinear optical properties. A selection of these chromophores was tested in a cellular environment with a multimodal multiphoton microscope. The structural differences of the chromophores resulted in high selectivity for mitochondria or the nucleus in two-photon fluorescence and ranging from no signal to high selectivity...

  11. The origin of second harmonic generation hotspots in chiral optical metamaterials [Invited]

    Valev, V. K.; Zheng, X.; Biris, C. G.; Silhanek, A. V.; Volskiy, V.; DE CLERCQ, Ben; Aktsipetrov, Oleg A.; AMELOOT, Marcel; Panoiu, N. C.; Vandenbosch, G. A. E.; Moshchalkov, V. V.
    Novel ways to detect the handedness in chiral optical metamaterials by means of the second harmonic generation (SHG) process have recently been proposed. However, the precise origin of the SHG emission has yet to be unambiguously established. In this paper, we present computational simulations of both the electric currents and the electromagnetic fields in chiral planar metamaterials, at the fundamental frequency (FF), and discuss the implications of our results on the characteristics of experimentally measured SHG. In particular, we show that the results of our numerical simulations are in good agreement with the experimental mapping of SHG sources. Thus, the...

  12. Real-time study of protein adsorption on thin nanocrystalline diamond

    Grieten, Lars; Janssens, S.D.; Ethirajan, Anitha; Vanden Bon, Natalie; Ameloot, Marcel; Michiels, Luc; Haenen, Ken; Wagner, Patrick
    The study of protein adsorption on solid surfaces is interesting for theoretical and practical bio-analytical sensing applications. In this work we combine electrochemical impedance spectroscopy, enzyme linked immunosorbent assay, and fluorescence microscopy with thin boron doped nanocrystalline diamond films to address and study the adsorption behavior of globular proteins (antibodies) on hydrophobic and hydrophilic diamond surfaces. A powerful combination of time resolved impedance spectroscopy and data modeling with equivalent circuits allow a detailed insight in the protein behavior at an interface. It is found that hydrogenated diamond is greatly favorable for impedimetric read-out but causes slight conformational loss of the...

  13. Rapid assessment of the stability of DNA duplexes by impedimetric real-time monitoring of chemically induced denaturation

    Van Grinsven, Bart; Vanden Bon, Natalie; Grieten, Lars; Murib, Mohammed Sharif; Janssens, S.D.; Haenen, Ken; Schneider, E.; Ingebrandt, S.; Schöning, M.J.; Vermeeren, Veronique; Ameloot, Marcel; Michiels, Luc; Thoelen, Ronald; De Ceuninck, Ward; Wagner, Patrick
    In this article, we report on the electronic monitoring of DNA denaturation by NaOH using electrochemical impedance spectroscopy in combination with fluorescence imaging as a reference technique. The probe DNA consisting of a 36-mer fragment was covalently immobilized on nanocrystalline-diamond electrodes and hybridized with different types of 29-mer target DNA (complementary, single-nucleotide defects at two different positions, and a non-complementary random sequence). The mathematical separation of the impedimetric signals into the time constant for NaOH exposure and the intrinsic denaturation-time constants gives clear evidence that the denaturation times reflect the intrinsic stability of the DNA duplexes. The intrinsic time constants...

  14. Hotspot Decorations Map Plasmonic Patterns with the Resolution of Scanning Probe Techniques

    Valev, V. K.; Silhanek, A. V.; Jeyaram, Y.; Denkova, D.; DE CLERCQ, Ben; Petkov, V.; Zheng, X.; Volskiy, V.; Gillijns, W.; Vandenbosch, G. A. E.; Aktsipetrov, Oleg A.; AMELOOT, Marcel; Moshchalkov, V. V.; Verbiest, T.
    In high definition mapping of the plasmonic patterns on the surfaces of nanostructures, the diffraction limit of light remains an important obstacle. Here we demonstrate that this diffraction limit can be completely circumvented. We show that upon illuminating nanostructures made of nickel and palladium, the resulting surface-plasmon pattern is imprinted on the structures themselves; the hotspots (regions of local field enhancement) are decorated with overgrowths, allowing for their subsequent imaging with scanning-probe techniques. The resulting resolution of plasmon pattern imaging is correspondingly improved.

  15. Fluorescence recovery after photobleaching on the confocal laser-scanning microscope: generalized model without restriction on the size of the photobleached disk

    SMISDOM, Nick; Braeckmans, Kevin; Deschout, Hendrik; VAN DE VEN, Martin; RIGO, Jean-Michel; De Smedt, Stefaan C.; AMELOOT, Marcel
    Fluorescence recovery after photobleaching (FRAP) carried out on a confocal laser-scanning microscope (CLSM) performs well for photobleached disks that are large compared to the resolution of the bleaching beam. For smaller disks approaching this resolution, current FRAP models providing a closed-form solution do not allow one to extract the diffusion coefficient accurately. The new generalized disk model we present addresses this shortcoming by bringing into account the bleaching resolution and the total confocal imaging resolution. A closed-form solution is obtained under the assumption of linear photobleaching. Furthermore, simultaneous analysis of FRAP data collected at various disk sizes allows for the...

  16. Linearly polarized second harmonic generation microscopy reveals chirality (vol 18, pg 8286, 2010)

    Valev, V. K.; Silhanek, A. V.; SMISDOM, Nick; DE CLERCQ, Ben; Gillijns, W.; Aktsipetrov, Oleg A.; AMELOOT, Marcel; Moshchalkov, V. V.; Verbiest, T.
    An erratum is presented to clarify both the direction of light polarization in our experiments and the unit cell geometry of the samples. Additionally, the spectral dependence of the second harmonic generation response in the G-shaped nanostructures made of gold is corrected. These changes do not affect our previous conclusions. (C) 2011 Optical Society of America

  17. Rapid assessment of the stability of DNA duplexes by impedimetric real-time monitoring of chemically induced denaturation

    VAN GRINSVEN, Bart; VANDEN BON, Natalie; GRIETEN, Lars; MURIB, Mohammed; JANSSENS, Stoffel; HAENEN, Ken; Schneider, E.; Ingebrandt, S.; Schoening, M. J.; VERMEEREN, Veronique; AMELOOT, Marcel; MICHIELS, Luc; THOELEN, Ronald; DE CEUNINCK, Ward; WAGNER, Patrick
    In this article, we report on the electronic monitoring of DNA denaturation by NaOH using electrochemical impedance spectroscopy in combination with fluorescence imaging as a reference technique. The probe DNA consisting of a 36-mer fragment was covalently immobilized on nanocrystalline-diamond electrodes and hybridized with different types of 29-mer target DNA (complementary, single-nucleotide defects at two different positions, and a non-complementary random sequence). The mathematical separation of the impedimetric signals into the time constant for NaOH exposure and the intrinsic denaturation-time constants gives clear evidence that the denaturation times reflect the intrinsic stability of the DNA duplexes. The intrinsic time constants...

  18. Plasmons Reveal the Direction of Magnetization in Nickel Nanostructures

    Valev, Ventsislav K.; Silhanek, Alejandro V.; Gillijns, Werner; Jeyaram, Yogesh; Paddubrouskaya, Hanna; Volodin, Alexander; Biris, Claudiu G.; Panoiu, Nicolae C.; DE CLERCQ, Ben; AMELOOT, Marcel; Aktsipetrov, Oleg A.; Moshchalkov, Victor V.; Verbiest, Thierry
    We have applied the surface sensitive nonlinear optical technique of magnetization induced second harmonic generation. (MSHG) to plasmonic, magnetic nanostructures made of Ni. We show that surface plasmon contributions to the MSHG signal can reveal the direction of the magnetization. Both the plasmonic and the magnetic nonlinear optical responses can be tuned; our results indicate novel ways to combine nanophotonics, nanoelectronics, and nanomagnetics and suggest the possibility for large magneto-chiral effects in metamaterials.

  19. Liver X receptors regulate cholesterol homeostasis in oligodendrocytes

    NELISSEN, Katherine; Mulder, Monique; SMETS, Ilse; AMELOOT, Marcel; HENDRIKS, Jerome

  20. Simvastatin Interferes With Process Outgrowth and Branching of Oligodendrocytes

    SMOLDERS, Inge; SMETS, Ilse; Maier, Olaf; Van de Ven, Martin; STEELS, Paul; AMELOOT, Marcel
    Statins have attracted interest as a treatment option for multiple sclerosis (MS) because of their pleiotropic antiinflammatory and immunomodulatory effects. However, contradictory results have been described when they are applied to oligodendrocytes (OLGs), the cell type predominantly affected in MS. In this study we focus on the in vitro effect of statins on process outgrowth in OLN-93 cells, a well-characterized OLG-derived cell line, and primary cultures of neonatal rat OLGs. Application of the lipophilic simvastatin, as low as 0.1-1 mu M, disturbs process formation of both cell types, leading to less ramified cells. We show that both protein isoprenylation and...

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