1,720,965 research outputs found
Quantitative characterization of biological systems at singlemolecule level by atomic force microscopy
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Adhesive-free colloidal probes for nanoscale force measurements : production and characterization
Full text linkWe describe novel approaches for the production and characterization of epoxy- and adhesive-free colloidal probes for atomic force microscopy (AFM). Borosilicate glass microspheres are strongly attached to commercial AFM cantilevers exploiting the capillary adhesion force due to the formation of a water meniscus, and then a thermal annealing of the sphere-cantilever system at a temperature slightly below the softening point of borosilicate glass. Controlling the wettability of the surfaces involved turned out to be a crucial element for the control of surface adhesion and for the implementation of a completely adhesive-free production method of colloidal probes. Moreover, we present a statistical characterization protocol of the probe dimensions and roughness based on the AFM inverse imaging of colloidal probes on spiked gratings. We have assessed the influence of defects of the grating on the characterization of the probe, and discussed the accuracy of our characterization technique in comparison to the methods based on scanning electron or optical microscopy, or on the manual analysis of AFM inverse images
Quantitative investigation by atomic force microscopy of supported phospholipid layers and nanostructures on cholesterol-functionalized glass surfaces
No full textUnderstanding the interaction mechanisms of phospholipids with surfaces is crucial for the exploitation of lipid bilayers as models of the cell membrane as well as templates for biosensors. Moreover, controlling and manipulating lipid nanoparticles for the investigation of their properties by means of single-particle sensitive surface techniques require the ability to tailor the chemical properties of surfaces to achieve a stable and sparse binding of lipid particles, while keeping them from aggregating, or denaturing. Here we present a quantitative morphological and structural investigation by atomic force microscopy of supported phospholipid layers and nanostructures on cholesterol-functionalized glass surfaces, in comparison with other surfaces with different interfacial properties. We show that the functionalization of glass coverslips with cholesterol groups is a viable route for the production of optically transparent, scanning probe microscopy-compatible clean substrates for the effective immobilization of both extended single lipid bilayers and lipid nanoparticles
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Investigation of the structural properties and oligomerization state of the complex enzyme glutamate synthase by atomic force microscopy
No full textInteraction of bacterial cells with cluster-assembled nanostructured titania surfaces : an atomic force microscopy study
No full textThe nanoscale interaction of bacterial cells with solid surfaces is a key issue in biomedicine because it constitutes the first pathogenic event in the complex series of biofilm development on prosthetic devices. We report on an Atomic Force Microscopy study of the interaction of Escherichia coli and Pseudomonas aeruginosa bacterial cells with nanostructured titania thin films with controlled and reproducible nanometer-scale morphology, produced by assembling Ti clusters from the gas phase in a Supersonic Cluster Beam Deposition apparatus. The results demonstrate that bacterial adhesion and biofilm formation are significantly influenced by a pure physical stimulus, that is, the nanoscale variation of surface topography. The increase of nanoscale film roughness promotes bacterial adhesion with respect to flat substrates; remarkably, Pseudomonas aeruginosa cells lose their flagella on nanostructured TiO2 thin films upon adhesion, as opposed to same bacteria onto reference smooth glass substrates. Further, we have observed increased cell biovolume and other biofilm properties on nanostructured substrates in comparison with smooth glasses. These findings suggest that the design of innovative biomaterials with a suitable patterning of biomaterials surfaces can be an effective approach to control the adhesion of microorganisms to in vivo implant surfaces with active biological functionalities
Nanoscale roughness affects the activity of enzymes adsorbed on cluster-assembled titania films
No full textIn this study, we investigated how the adsorption properties governed by the nanometer-scale surface morphology of cluster-assembled titanium oxide films influence the catalytic activity of immobilized serine-protease trypsin. We developed an activity assay for the parallel detection of physisorbed enzyme activity and mass density of the adsorbed proteins in microarray format. The method combines a microarray-based technique and advanced quantitative confocal microscopy approaches based on fluorescent labeling of enzymes and covalent labeling of active sites of surface-bound enzymes. The observed diminishing trypsin binding affinity with increasing roughness, as opposed to the steep rise in its saturation uptake, was interpreted as heterogeneous nucleation-driven adsorption of trypsin at the rough nanoporous titania surface. The increase in relative activity of adsorbed trypsin is proportional to the fractional saturation of titania surfaces, expressed as percentage of saturation uptake. In turn, the specific activity, that is, the ratio of active proteins to the absolute number of adsorbed proteins, drops with growing saturation uptake and surface roughness, witnessing a reduction in the accessibility of enzyme active sites. Both geometrical constraints of titania nanopores and the clusterwise adsorption of trypsin were identified as the key factors underpinning the steric hindrance of the immobilized enzyme. These findings are relevant for the optimization of rough nanoporous surfaces as carriers of immobilized enzymes. The proposed activity assay is particularly advantageous in the screening of candidate materials for enzyme immobilization
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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