Charge gradient microscopy.
Ontology highlight
ABSTRACT:
SUBMITTER: Hong S
PROVIDER: S-EPMC4020115 | biostudies-other | 2014 May
REPOSITORIES: biostudies-other
Similar Datasets
Project description:A charge gradient microscopy (CGM) probe was used to collect surface screening charges on poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] thin films. These charges are naturally formed on unscreened ferroelectric domains in ambient condition. The CGM data were used to map the local electric current originating from the collected surface charges on the poled ferroelectric domains in the P(VDF-TrFE) thin films. Both the direction and amount of the collected current were controlled by changing the polarity and area of the poled domains. The endurance of charge collection by rubbing the CGM tip on the polymer film was limited to 20 scan cycles, after which the current reduced to almost zero. This degradation was attributed to the increase of the chemical bonding strength between the external screening charges and the polarization charges. Once this degradation mechanism is mitigated, the CGM technique can be applied to efficient energy harvesting devices using polymer ferroelectrics.
| S-EPMC4853730 | biostudies-literature
Project description:The charging and dissolution of mineral surfaces in contact with flowing liquids are ubiquitous in nature, as most minerals in water spontaneously acquire charge and dissolve. Mineral dissolution has been studied extensively under equilibrium conditions, even though non-equilibrium phenomena are pervasive and substantially affect the mineral-water interface. Here we demonstrate using interface-specific spectroscopy that liquid flow along a calcium fluoride surface creates a reversible spatial charge gradient, with decreasing surface charge downstream of the flow. The surface charge gradient can be quantitatively accounted for by a reaction-diffusion-advection model, which reveals that the charge gradient results from a delicate interplay between diffusion, advection, dissolution, and desorption/adsorption. The underlying mechanism is expected to be valid for a wide variety of systems, including groundwater flows in nature and microfluidic systems.
| S-EPMC8253779 | biostudies-literature
Project description:We present a phase derivative microscopy technique referred to as gradient field microscopy (GFM), which provides the first-order derivatives of the phase associated with an optical field passing through a transparent specimen. GFM utilizes spatial light modulation at the Fourier plane of a bright field microscope to optically obtain the derivatives of the phase and increase the contrast of the final image. The controllable spatial modulation pattern allows us to obtain both one component of the field gradient (derivative along one direction) and the gradient intensity, which offers some advantages over the regular differential interference contrast (DIC) microscopy. Most importantly, unlike DIC, GFM does not use polarizing optics and, thus, it is applicable to birefringent samples. We demonstrate these features of GFM with studies of static and dynamic biological cells (HeLa cells and red blood cells). We show that GFM is capable of qualitatively providing information about cell membrane fluctuations. Specifically, we captured the disappearance of the bending mode of fluctuations in osmotically swollen red blood cells.
| S-EPMC3482907 | biostudies-other
Project description:Anthrax lethal toxin is used as a model system to study protein translocation. The toxin is composed of a translocase channel, called protective antigen (PA), and an enzyme, called lethal factor (LF). A proton gradient (?pH) can drive LF unfolding and translocation through PA channels; however, the mechanism of ?pH-mediated force generation, substrate unfolding, and establishment of directionality are poorly understood. One recent hypothesis suggests that the ?pH may act through changes in the protonation state of residues in the substrate. Here we report the charge requirements of LF's amino-terminal binding domain (LF(N)) using planar lipid bilayer electrophysiology. We found that acidic residues are required in LF(N) to utilize a proton gradient for translocation. Constructs lacking negative charges in the unstructured presequence of LF(N) translocate independently of the ?pH driving force. Acidic residues markedly increase the rate of ?pH-driven translocation, and the presequence is optimized in its natural acidic residue content for efficient ?pH-driven unfolding and translocation. We discuss a ?pH-driven charge state Brownian ratchet mechanism for translocation, where glutamic and aspartic acid residues in the substrate are the "molecular teeth" of the ratchet. Our Brownian ratchet model includes a mechanism for unfolding and a novel role for positive charges, which we propose chaperone negative charges through the PA channel during ?pH translocation.
| S-EPMC3123086 | biostudies-literature
Project description:Wave fields with orbital angular momentum (OAM) have been widely investigated in metasurfaces. By engineering acoustic metasurfaces with phase gradient elements, phase twisting is commonly used to obtain acoustic OAM. However, it has limited ability to manipulate sound vortices, and a more powerful mechanism for sound vortex manipulation is strongly desired. Here, we propose the diffraction mechanism to manipulate sound vortices in a cylindrical waveguide with phase gradient metagratings (PGMs). A sound vortex diffraction law is theoretically revealed based on the generalized conservation principle of topological charge. This diffraction law can explain and predict the complicated diffraction phenomena of sound vortices, as confirmed by numerical simulations. To exemplify our findings, we designed and experimentally verified a PGM based on Helmholtz resonators that support asymmetric transmission of sound vortices. Our work provides previously unidentified opportunities for manipulating sound vortices, which can advance more versatile design for OAM-based devices.
| S-EPMC7852395 | biostudies-literature
Project description:Exosomes are nanometer-sized lipid vesicles present in liquid biopsies and used as biomarkers for several diseases including cancer, Alzheimer's, and central nervous system diseases. Purification and subsequent size and surface characterization are essential to exosome-based diagnostics. Sample purification is, however, time consuming and potentially damaging, and no current method gives the size and zeta potential from a single measurement. Here, we concentrate exosomes from a dilute solution and measure their size and zeta potential in a one-step measurement with a salt gradient in a capillary channel. The salt gradient causes oppositely directed particle and fluid transport that trap particles. Within minutes, the particle concentration increases more than two orders of magnitude. A fit to the spatial distribution of a single or an ensemble of exosomes returns both their size and surface charge. Our method is applicable for other types of nanoparticles. The capillary is fabricated in a low-cost polymer device.
| S-EPMC7214416 | biostudies-literature
Project description: Not available
| S-EPMC8613208 | biostudies-literature
Project description:To improve the performance of Li-ion batteries (LIBs), it is essential to understand the behaviour of Li ions during charge-discharge cycling. However, the analytical techniques for observing the Li ions are limited. Here, we present the complementary use of scanning transmission electron microscopy and atom probe tomography at identical locations to demonstrate that the evolution of the local Li composition and the corresponding structural changes at the atomic scale cause the capacity degradation of Li(Ni0.80Co0.15Mn0.05)O2 (NCM), an LIB cathode. Using these two techniques, we show that a Li concentration gradient evolves during cycling, and the depth of the gradient expands proportionally with the number of cycles. We further suggest that the capacity to accommodate Li ions is determined by the degree of structural disordering. Our findings provide direct evidence of the behaviour of Li ions during cycling and thus the origin of the capacity decay in LIBs.
| S-EPMC8217543 | biostudies-literature
Project description:Multiple scattering limits the contrast in optical imaging of thick specimens. Here, we present gradient light interference microscopy (GLIM) to extract three-dimensional information from both thin and thick unlabeled specimens. GLIM exploits a special case of low-coherence interferometry to extract phase information from the specimen, which in turn can be used to measure cell mass, volume, surface area, and their evolutions in time. Because it combines multiple intensity images that correspond to controlled phase shifts between two interfering waves, gradient light interference microscopy is capable of suppressing the incoherent background due to multiple scattering. GLIM can potentially become a valuable tool for in vitro fertilization, where contrast agents and fluorophores may impact the viability of the embryo. Since GLIM is implemented as an add-on module to an existing inverted microscope, we anticipate that it will be adopted rapidly by the biological community.Challenges in biological imaging include labeling, photobleaching and phototoxicity, as well as light scattering. Here, Nguyen et al. develop a quantitative phase method that uses low-coherence interferometry for label-free 3D imaging in scattering tissue.
| S-EPMC5547102 | biostudies-literature
Project description:Phase-contrast techniques, such as differential interference contrast microscopy, are widely used to obtain morphological images of unstained biological samples. The transillumination geometry required for these techniques restricts their application to thin samples. We introduce oblique back-illumination microscopy, a method of collecting en face phase-gradient images of thick scattering samples, enabling near-video-rate in vivo phase imaging with a miniaturized probe suitable for endoscopy.
| S-EPMC8407656 | biostudies-literature