Inorganic carbon nanomaterials, also called carbon nanodots, exhibit a strong photoluminescence with unusual properties and, thus, have been the focus of intense research. Nonetheless, the origin of ...their photoluminescence is still unclear and the subject of scientific debates. Here, we present a single particle comprehensive study of carbon nanodot photoluminescence, which combines emission and lifetime spectroscopy, defocused emission dipole imaging, azimuthally polarized excitation dipole scanning, nanocavity-based quantum yield measurements, high resolution transmission electron microscopy, and atomic force microscopy. We find that photoluminescent carbon nanodots behave as electric dipoles, both in absorption and emission, and that their emission originates from the recombination of photogenerated charges on defect centers involving a strong coupling between the electronic transition and collective vibrations of the lattice structure.
The measurement of the elastic properties of cells is widely used as an indicator for cellular changes during differentiation, upon drug treatment, or resulting from the interaction with the ...supporting matrix. Elasticity is routinely quantified by indenting the cell with a probe of an AFM while applying nano-Newton forces. Because the resulting deformations are in the micrometer range, the measurements will be affected by the finite thickness of the cell, viscous effects and even cell damage induced by the experiment itself. Here, we have analyzed the response of single 3T3 fibroblasts that were indented with a micrometer-sized bead attached to an AFM cantilever at forces from 30-600 pN, resulting in indentations ranging from 0.2 to 1.2 micrometer. To investigate the cellular response at lower forces up to 10 pN, we developed an optical trap to indent the cell in vertical direction, normal to the plane of the coverslip. Deformations of up to two hundred nanometers achieved at forces of up to 30 pN showed a reversible, thus truly elastic response that was independent on the rate of deformation. We found that at such small deformations, the elastic modulus of 100 Pa is largely determined by the presence of the actin cortex. At higher indentations, viscous effects led to an increase of the apparent elastic modulus. This viscous contribution that followed a weak power law, increased at larger cell indentations. Both AFM and optical trapping indentation experiments give consistent results for the cell elasticity. Optical trapping has the benefit of a lower force noise, which allows a more accurate determination of the absolute indentation. The combination of both techniques allows the investigation of single cells at small and large indentations and enables the separation of their viscous and elastic components.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Organic hole-transporting materials are intensively investigated as thin-layer electro-optical devices, including organic light-emitting diodes, solar cells, organic field-effect transistors and ...photo-refractive holographic materials. In this review, we discuss synthetic routes and optical (UV–vis, PL, CV) and electrical (
I–
V, EL, hole drift mobility) properties of polymers with triphenylamine (TPA) units in the main chain or as pendant groups, such as poly(vinylene)s, poly(amide)s, poly(imide)s, poly(azomethine)s, poly(arylate)s, poly(urethane)s and poly(ester)s. The introduction of vinyl, acetylene, ester, imide, amide or azomethine moieties in TPA leads to new functional materials based on their synergistic effects. The introduction of bulky triphenylamine in macromolecules tends to suppress intermolecular aggregation, reduce the crystallisation propensity and improve the hole-transporting ability of the materials.
Rapid conduction of nerve impulses requires coating of axons by myelin. To function as an electrical insulator, myelin is generated as a tightly packed, lipid-rich multilayered membrane sheath. ...Knowledge about the mechanisms that govern myelin membrane biogenesis is required to understand myelin disassembly as it occurs in diseases such as multiple sclerosis. Here, we show that myelin basic protein drives myelin biogenesis using weak forces arising from its inherent capacity to phase separate. The association of myelin basic protein molecules to the inner leaflet of the membrane bilayer induces a phase transition into a cohesive mesh-like protein network. The formation of this protein network shares features with amyloid fibril formation. The process is driven by phenylalanine-mediated hydrophobic and amyloid-like interactions that provide the molecular basis for protein extrusion and myelin membrane zippering. These findings uncover a physicochemical mechanism of how a cytosolic protein regulates the morphology of a complex membrane architecture. These results provide a key mechanism in myelin membrane biogenesis with implications for disabling demyelinating diseases of the central nervous system.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Viruses package their genome in a robust protein coat to protect it during transmission between cells and organisms. In a reaction termed uncoating, the virus is progressively weakened during entry ...into cells. At the end of the uncoating process the genome separates, becomes transcriptionally active, and initiates the production of progeny. Here, we triggered the disruption of single human adenovirus capsids with atomic force microscopy and followed genome exposure by single-molecule fluorescence microscopy. This method allowed the comparison of immature (noninfectious) and mature (infectious) adenovirus particles. We observed two condensation states of the fluorescently labeled genome, a feature of the virus that may be related to infectivity. Beyond tracking the unpacking of virus genomes, this approach may find application in testing the cargo release of bioinspired delivery vehicles.
Success in super-resolution imaging relies on a proper choice of fluorescent probes. Here, we suggest novel easily produced and biocompatible nanoparticlescarbon nanodotsfor super-resolution ...optical fluctuation bioimaging (SOFI). The particles revealed an intrinsic dual-color fluorescence, which corresponds to two subpopulations of particles of different electric charges. The neutral nanoparticles localize to cellular nuclei suggesting their potential use as an inexpensive, easily produced nucleus-specific label. The single particle study revealed that the carbon nanodots possess a unique hybrid combination of fluorescence properties exhibiting characteristics of both dye molecules and semiconductor nanocrystals. The results suggest that charge trapping and redistribution on the surface of the particles triggers their transitions between emissive and dark states. These findings open up new possibilities for the utilization of carbon nanodots in the various super-resolution microscopy methods based on stochastic optical switching.
B cells are central to the pathogenesis of multiple autoimmune diseases, through antigen presentation, cytokine secretion, and the production of autoantibodies. During development and ...differentiation, B cells undergo drastic changes in their physiology. It is emerging that these are accompanied by equally significant shifts in metabolic phenotype, which may themselves also drive and enforce the functional properties of the cell. The dysfunction of B cells during autoimmunity is characterised by the breaching of tolerogenic checkpoints, and there is developing evidence that the metabolic state of B cells may contribute to this. Determining the metabolic phenotype of B cells in autoimmunity is an area of active study, and is important because intervention by metabolism-altering therapeutic approaches may represent an attractive treatment target.
The integration of children’s literature, specifically mathematical story picture books, in mathematics education has demonstrated significant benefits. Nevertheless, its actual implementation ...largely hinges on teachers’ beliefs. This exploratory mixed-methods study examines the beliefs of 78 teachers regarding the integration of children’s literature into mathematics teaching and learning, with a focus on identifying its barriers and enablers. Data were collected through an open-ended survey and semi-structured interviews and analyzed using thematic analysis framed by the concept of belief indication. The study identifies 15 barriers (across five themes) and 16 enablers (across six themes) that, teachers believe, affect their decisions to integrate children’s literature into mathematics teaching and learning. This paper contextualizes the findings within the Theory of Planned Behavior (TPB), a framework from social psychology, to provide actionable recommendations and compare findings from studies conducted in Asian and Western countries. Ultimately, this research offers a broader understanding of teachers’ behaviors and their receptiveness to educational reforms, such as the integration of children’s literature, across diverse cultural and international settings.
During CNS development, oligodendrocytes wrap their plasma membrane around axons to generate multilamellar myelin sheaths. To drive growth at the leading edge of myelin at the interface with the ...axon, mechanical forces are necessary, but the underlying mechanisms are not known. Using an interdisciplinary approach that combines morphological, genetic, and biophysical analyses, we identified a key role for actin filament network turnover in myelin growth. At the onset of myelin biogenesis, F-actin is redistributed to the leading edge, where its polymerization-based forces push out non-adhesive and motile protrusions. F-actin disassembly converts protrusions into sheets by reducing surface tension and in turn inducing membrane spreading and adhesion. We identified the actin depolymerizing factor ADF/cofilin1, which mediates high F-actin turnover rates, as an essential factor in this process. We propose that F-actin turnover is the driving force in myelin wrapping by regulating repetitive cycles of leading edge protrusion and spreading.
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•F-actin is redistributed to the leading edge of the myelin sheath during growth•Oligodendrocytes exhibit an adhesion-independent mode of leading edge protrusion•F-actin depolymerization reduces tension and triggers myelin sheet growth•ADF/cofilin1 activity drives myelin wrapping by maintaining high F-actin turnover
Oligodendrocytes wrap their plasma membrane around axons to generate multilamellar myelin sheaths, but the molecular machinery that drives growth has not been identified. Nawaz and Sánchez et al. show that F-actin turnover is the driving force in myelin wrapping by regulating repetitive cycles of leading edge protrusion and spreading.
Upon endocytosis in its cellular host, influenza A virus transits via early to late endosomes. To efficiently release its genome, the composite viral shell must undergo significant structural ...rearrangement, but the exact sequence of events leading to viral uncoating remains largely speculative. In addition, no change in viral structure has ever been identified at the level of early endosomes, raising a question about their role. We performed AFM indentation on single viruses in conjunction with cellular assays under conditions that mimicked gradual acidification from early to late endosomes. We found that the release of the influenza genome requires sequential exposure to the pH of both early and late endosomes, with each step corresponding to changes in the virus mechanical response. Step 1 (pH 7.5–6) involves a modification of both hemagglutinin and the viral lumen and is reversible, whereas Step 2 (pH <6.0) involves M1 dissociation and major hemagglutinin conformational changes and is irreversible. Bypassing the early-endosomal pH step or blocking the envelope proton channel M2 precludes proper genome release and efficient infection, illustrating the importance of viral lumen acidification during the early endosomal residence for influenza virus infection.
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