AMOLF Institutional Repository
Not a member yet
1351 research outputs found
Sort by
Dynamical regulation in single cells
No full textIn this thesis, we probe single bacterial cells to further understand both the regulation of cell divisions during adverse conditions and the phenomenon of cellular heterogeneity
Polarity sorting drives remodeling of 1 actin-myosin networks
Get PDFCytoskeletal networks of actin filaments and myosin motors drive many dynamic cell processes such as migration and division. A key characteristic of these networks is their contractility. Despite intense experimental and theoretical efforts, it is not yet clear what mechanism favors contraction over expansion in these networks. Recent work points to a dominant role for the nonlinear mechanical response of actin filaments, which can withstand stretching but buckle upon compression. Here we present an alternative mechanism. We study how interactions between actin and myosin-2 at the single filament level translate into contractile activity at the network scale by performing time-lapse imaging on reconstituted quasi-2D-networks mimicking the cell cortex. We observe myosin end-dwelling after it runs processively along actin filaments. We demonstrate how this process leads to the transport and clustering of actin filament ends and the formation of transiently stable bipolar structures. Further we show that this myosin-driven polarity sorting leads to polar actin aster formation. The asters act as contractile nodes that drive contraction in crosslinked networks. Using computer simulations, we show that the contribution of the end-dwelling mechanism increases as the characteristics of the network become more in vivo like, relative to alternative mechanisms requiring nonlinear mechanical response of the filaments (buckling)
Optoacoustics—Advances in high-frequency optomechanics and Brillouin scattering
Get PDFThe fields of cavity optomechanics and Brillouin scattering, linked by common underlying physical mechanisms, involve the interaction of light waves with mechanical vibrations at the micro- and nanoscale. Exciting fundamental research in both classical and quantum regimes as well as opportunities for applications in microwave photonics, frequency conversion, narrow-linewidth lasers, optomechanical sensors, electro-optic transducers, coherent light storage, and Brillouin spectroscopy have stimulated significant interest in the last decade. This special issue brings contributions to fundamental aspects regarding the Brillouin interaction such as novel waveguide structures, novel guiding mechanisms, the interplay between Brillouin and other nonlinear phenomena, and applications in sensing and light storage, as well as an introductory tutorial to the research field. Here, we provide a brief introduction to the topics covered in the iss
Self-Optimized Catalysts: Hot-Electron Driven Photosynthesis of Catalytic Photocathodes
Get PDFPhotogenerated hot electrons from plasmonic nanostructures are very promising for photocatalysis, mostly due to their potential for enhanced chemical selectivity. Here, we present a self-optimized fabrication method of plasmonic photocathodes using hot-electron chemistry, for enhanced photocatalytic efficiencies. Plasmonic Au/TiO2 nanoislands are excited at their surface plasmon resonance to generate hot electrons in an aqueous bath containing a platinum (cocatalyst) precursor. Hot electrons drive the deposition of Pt cocatalyst nanoparticles, without any nanoparticle functionalization and negligible applied bias, close to the hotspots of the plasmonic nanoislands. The presence of TiO2 is crucial for achieving higher chemical reaction rates. The Au/TiO2/Pt photocathodes synthesized using hot-electron chemistry show a photocatalytic activity of up to 2 times higher than that of a control made with random electrodeposited Pt nanoparticles. This light-driven positioning of the cocatalyst close to the same positions where hot electrons are most efficiently generated and transferred represents a novel and simple method for synthesizing complex, self-optimized photocatalytic nanostructures with improved efficiency and selectivity
3D Printed Actuators: Reversibility, Relaxation, and Ratcheting
Get PDFAdditive manufacturing strives to combine any combination of materials into 3D functional structures and devices, ultimately opening up the possibility of 3D printed machines. It remains difficult to actuate such devices, thus limiting the scope of 3D printed machines to passive devices or necessitating the incorporation of external actuators that are manufactured differently. Here, 3D printed hybrid thermoplast/conducter bilayers are explored, which can be actuated by differential heating caused by externally controllable currents flowing through their conducting faces. The functionality of such actuators is uncovered and it is shown that they allow to 3D print, in one pass, simple flexible robotic structures that propel forward under step‐wise applied voltages. Moreover, exploiting the thermoplasticity of the nonconducting plastic parts at elevated temperatures, it is shown that how strong driving leads to irreversible deformations—a form of 4D printing—which also enlarges the range of linear response of the actuators. Finally, it is shown that how to leverage such thermoplastic relaxations to accumulate plastic deformations and obtain very large deformations by alternatively driving both layers of a bilayer; this is called ratcheting. The strategy is scalable and widely applicable, and opens up a new approach to reversible actuation and irreversible 4D printing of arbitrary structures and machines
Response of an actin network in vesicles under electric pulses
Get PDFWe study the role of a biomimetic actin network during the application of electric pulses that induce electroporation or electropermeabilization, using giant unilamellar vesicles (GUVs) as a model system. The actin cortex, a subjacently attached interconnected network of actin filaments, regulates the shape and mechanical properties of the plasma membrane of mammalian cells, and is a major factor influencing the mechanical response of the cell to external physical cues. We demonstrate that the presence of an actin shell inhibits the formation of macropores in the electroporated GUVs. Additionally, experiments on the uptake of dye molecules after electroporation show that the actin network slows down the resealing process of the permeabilized membrane. We further analyze the stability of the actin network inside the GUVs exposed to high electric pulses. We find disruption of the actin layer that is likely due to the electrophoretic forces acting on the actin filaments during the permeabilization of the GUVs. Our findings on the GUVs containing a biomimetic network provide a step towards understanding the discrepancies between the electroporation mechanism of a living cell and its simplified model of the empty GUV
Air-stable and oriented mixed lead halide perovskite (FA/MA) by one-step deposition method using zinc iodide and chloroamine additive
Get PDFWe present a one-step method to produce air-stable, large grain mixed cationic lead perovskite films and powders under ambient condition. The introduction of 2.5 wt% of Zn(II), confirmed by X-Ray Diffraction (XRD), results in stable thin films which show the same absorption and crystal structure after two weeks of storage under ambient conditions. Next to prolonged stability, the introduction of Zn(II) affects photo-physical properties reducing the bulk defect density, enhancing the photoluminescence and extending the charge carrier lifetime. Furthermore, 3-chloropropylamine hydrochloride (3-CPACl) is applied as film-forming agent. The presence of this amine hydrochloride additive results in highly oriented and large crystal domains showing an ulterior improvement of photoluminescence intensity and lifetime. The material can also be prepared as a black precursor powder by a solid-solid reaction under ambient conditions and can be pressed into a perovskite pellet. The prolonged stability and the easy fabrication in air makes this material suitable for large scale, low cost processing for optoelectronic applications
Photophysics of novel optoelectronic materials under hydrostatic pressure
Get PDFIn this thesis, we apply mild hydrostatic pressure on device-scale organic and hybrid semiconductor samples. We focus on organic and inorganic hybrid perovskites and small organic molecular crystals and perform steady-state and time-resolved optical measurements to study the absorption, emission and charge carrier/exciton dynamics in these material systems. We demonstrate the power of hydrostatic pressure for studying the structure-property relationship of organic and hybrid semiconductors. Even mild pressure can significantly change the properties of an organic/hybrid material. The results of this thesis provide insights into design of novel organic/hybrid semiconductors, and suggests potential approaches of improving the performance of (flexible) devices by building-in strain, for example by epitaxial growth of active layers
Cytolinker Gas2L1 regulates axon morphology through microtubule-modulated actin stabilization
Get PDFAbstract
Crosstalk between the actin and microtubule cytoskeletons underlies cellular morphogenesis. Interactions between actin filaments and microtubules are particularly important for establishing the complex polarized morphology of neurons. Here, we characterised the neuronal function of Growth Arrest Specific 2-like 1 (Gas2L1), a protein that can directly bind to actin, microtubules and microtubule plus-end-tracking End Binding proteins. We found that Gas2L1 promotes axon branching, but restricts axon elongation in cultured hippocampal neurons. Using pull-down experiments and in vitro reconstitution assays, in which purified Gas2L1 was combined with actin and dynamic microtubules, we demonstrated that Gas2L1 is autoinhibited. This autoinhibition is relieved by simultaneous binding to actin filaments and microtubules. In neurons, Gas2L1 primarily localizes to the actin cytoskeleton and functions as an actin stabilizer. The ability of Gas2L1 to interact with microtubules directs its actin-stabilizing activity to the axon. We propose that Gas2L1 acts as an actin regulator, the function of which is spatially modulated by microtubules