Search results for "Laboratory"
showing 10 items of 923 documents
Optical-sectioning improvement in two-color excitation scanning microscopy
2004
We present a new beam-shaping technique for two-color excitation fluorescence microscopy. We show that by simply inserting a properly designed shaded-ring filter in the illumination beam of smaller wavelength, it is possible to improve the effective optical sectioning capacity of such microscopes by 23%. Such an improvement is obtained at the expense of only a very small increasing of the overall energy in the point-spread-function sidelobes. The performance of this technique is illustrated by a numerical imaging simulation.
Measuring (biological) materials mechanics with atomic force microscopy. 2. Influence of the loading rate and applied force (colloidal particles)
2020
Atomic force microscopy (AFM) is the most often used tool to study the mechanical properties of eukaryotic cells. Due to their complex assembly, cells show viscoelastic properties. When performing experiments, one has to consider the influence of both loading rate and maximum load on the measured mechanical properties. Here, we employed colloidal particles of various sizes (from 2 to 20 μm diameter) to perform force spectroscopy measurements on endothelial cells at loading rates varying from 0.1 to 50 μm/s, and maximum loads ranging from 1 to 25 nN. We were able to determine the non-linear dependence of cell viscoelastic properties on the loading rate which followed a weak power law. In add…
Laboratory phase‐contrast nanotomography of unstained Bombus terrestris compound eyes
2021
Imaging the visual systems of bumblebees and other pollinating insects may increase understanding of their dependence on specific habitats and how they will be affected by climate change. Current high-resolution imaging methods are either limited to two dimensions (light- and electron microscopy) or have limited access (synchrotron radiation x-ray tomography). For x-ray imaging, heavy metal stains are often used to increase contrast. Here, we present micron-resolution imaging of compound eyes of buff-tailed bumblebees (Bombus terrestris) using a table-top x-ray nanotomography (nano-CT) system. By propagation-based phase-contrast imaging, the use of stains was avoided and the microanatomy co…
Functional assays of oxidative stress using genetically engineered Escherichia coli strains.
2003
Oxidative stress may be induced in bacteria by exogenous biocidal agents and is involved in endogenous metabolism. The oxyR operon is a main sensor of oxidative stress and oxyR-deficient bacteria show enhanced sensitivity to oxidative stress and increased accumulation of intracellular reactive oxygen species (ROS). Flow cytometric functional assays in bacteria are limited by the impaired penetration of vital dyes trough the cell wall. Escherichia coli B WP2 strains possess an altered cell-wall lipopolysaccharide that leads to increased membrane permeability. Flow cytometric analysis of WP2 strains is a convenient alternative for cytometric assays of bacterial function. This unit presents pr…
Estimation of Microbial Viability Using Flow Cytometry.
2020
For microorganisms in particular, viability is a term that is difficult to define and a state consequently difficult to measure. The traditional (and gold standard) usage equates viability and culturability (i.e., the ability to multiply) but the process of determining culturability is often too slow. Flow cytometry provides the opportunity to make rapid and quantitative measurements of dye uptake in large numbers of cells and we can therefore exploit the flow cytometric approach to evaluate so-called viability stains and to develop protocols for more routine assessments of microbial viability. This article provides a commentary and several protocols have been included to ensure that users …
A cytochemical study on the effects of energy deprivation on autophagocytosis in Ehrlich ascites tumor cells
1988
The effect of energy deprivation on autophagocytosis in Ehrlich ascites tumor cells was studied using cytochemical techniques. Autophagocytosis was induced with vinblastine incubation (0.1 mM) and the cellular ATP-level was lowered with 2-deoxy-D-glucose (0.35 mM). Acid phosphatase was used as a marker for lysosomal enzymes and imidazole-buffered osmium tetroxide impregnation in order to study the effects of energy deprivation on the maturation of autophagic vacuole (AV) membranes. Control and vinblastine treated cells maintained their ATP-levels throughout the incubation period tested (120 min). 2-Deoxy-D-glucose alone and with vinblastine decreased the intracellular ATP-level significantl…
Timm-staining intensity is correlated with the density of Timm-positive presynaptic structures in the cerebral cortex of lizards
1987
In cortical areas of the lizard, Podarcis hispanica, Timm staining reveals a distinct pattern of lamination. At the electron-microscope level, virtually all of the reaction product is located in the synaptic vesicles of Timm-positive boutons. Using linear-regression analysis, the area density of Timm-positive bouton profiles as well as the numerical and volume density of stained vesicles were found to be closely correlated with the light-microscopic densitometric values obtained for each Timm-positive cortical zone. We discuss the possibility of estimating stereological electron-microscopic data parameters from densitometric measurements at the light-microscope level.
Histochemical and biochemical investigations concerning the function of larval oenocytes of Tenebrio molitor L. (Coleoptera, Insecta).
1980
Larval oenocytes of Tenebrio molitor were investigated histochemically. In contrast to the lipid droplets of the fat body, they did not stain with Sudan black. A positive reaction for lipoproteins appeared only after destructive oxidation with sodium hypochlorite. These lipoproteins are the remnants of degenerated membranes, as revealed by ultrastructural analysis. Polyphenols could be identified in the exocuticle of exuvia, and in the newly formed procuticle. Endocuticle, epidermis and oenocytes showed no staining reaction. In oenocytes a great amount of lipase is also present which could be detected with several Tweens as substrates. The significance of these lipases remains unclear, sinc…
Towards an understanding of the molecular basis of immune responses in sponges: The marine demospongeGeodia cydonium as a model
1999
The phylogenetic position of the phylum Porifera (sponges) is near the base of the kingdom Metazoa. During the last few years, not only rRNA sequences but, more importantly, cDNA/genes that code for proteins have been isolated and characterized from sponges, in particular from the marine demosponge Geodia cydonium. The analysis of the deduced amino acid sequences of these proteins allowed a molecular biological approach to the question of the monophyly of the Metazoa. Molecules of the extracellular matrix/basal lamina, with the integrin receptor, fibronectin, and galectin as prominent examples, and of cell-surface receptors (tyrosine kinase receptor), elements of sensory systems (crystallin…
Efficiency of QuEChERS approach for determining 52 pesticide residues in honey and honey bees
2016
A comparison between QuEChERS and other pesticide extraction procedures for honey and honey bee matrices is discussed. Honey bee matrix was extracted by solvent based procedure whereas solid phase extraction was the protocol for the honey matrix. The citrate buffered QuEChERS method was used for both matrices. The methods were evaluated regarding cost (equipment and reagents), time, accuracy, precision, sensitivity and versatility. The results proved that the QuEChERS protocol was the most efficient method for the extraction of the selected pesticides in both matrices. QuEChERS is the most economical and less time-consuming procedure.SPE and solvent-based extraction procedures show equivale…