Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Biological Resolution”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 649 records · Page 36Linked to original sources
PubMed2007

Miniature near-infrared dual-axes confocal microscope utilizing a two-dimensional microelectromechanical systems scanner.

The first, to our knowledge, miniature dual-axes confocal microscope has been developed, with an outer diameter of 10 mm, for subsurface imaging of biological tissues with 5-7 microm resolution. Depth-resolved en face images are obtained at 30 frames per second, with a field of view of 800 x 100 microm, by employing a two-dimensional scanning microelectromechanical systems mirror. Reflectance and fluorescence images are obtained with a laser source at 785 nm, demonstrating the ability to perform real-time optical biopsy.

Computer Systems↗
PubMed2004

AFM as a high-resolution imaging tool and a molecular bond force probe.

This focused review summarizes certain aspects of recent developments in the use of atomic force microscope in high-resolution imaging of membrane-bound biological macromolecules and in molecular force probing of the interaction between biological conjugates. We point out the pros and cons in these approaches and critically analyze details involved in experiments.

Adsorption↗
PubMed2005

Variable incidence angle fluorescence interference contrast microscopy for z-imaging single objects.

Surface-generated structured illumination microscopies interrogate the position of fluorescently labeled objects near surfaces with nanometer resolution along the z axis. However, these techniques are either experimentally cumbersome or applicable to a limited set of experimental systems. We present a new type of surface-generated structured illumination fluorescence microscopy, variable incidence angle fluorescence interference contrast microscopy (VIA-FLIC), in which the fluorescent sample is assembled above a reflective Si surface and the incidence angle of excitation light is varied by placing annular photomasks with different radii in the aperture diaphragm plane of the microscope. The variation in incidence angle alters the interference pattern of excitation light, and hence the intensity of detected fluorescence. Quantitative VIA-FLIC is tested by using a set of fluorophore-containing supported membranes separated from the Si surface by SiO2 layers of variable thicknesses. The resulting fluorescence intensity versus incidence angle curves depends on the separation from the Si surface and when fit with an appropriate model yield precise SiO2 thicknesses that are accurate with respect to the known SiO2 thicknesses. Since only a simple modification to a standard epifluorescence microscope is required, VIA-FLIC offers a versatile method to produce z-reconstructions with high resolution for a wide range of biological systems.

Algorithms↗
PubMed1992

Investigation of living cells in the nanometer regime with the scanning force microscope.

Membrane structures of different types of cells are imaged in the nanometer regime by scanning force microscopy (SFM). The images are compared to those obtained with a scanning electron microscope (SEM). The SFM imaging can be done on the outer cell membrane under conditions that keep the cells alive in aqueous solutions. This opens up the possibility of observing the kinematics of the structures that determine the interaction of a cell with its environment. Therefore, STM observations, together with information obtained with the electron microscope, open up new ways of studying the development of biological structures. With the currently possible resolution, the SFM gives access to processes such as antibody binding or endo- and exocytosis, including processes correlated to the infection of cells by viruses.

Animals↗
PubMed1980

Specimen damage considerations in biological microprobe analysis.

In many biological materials radiation damage limits the resolution of the microanalytical measurement. To provide some perspective regarding the relative merits of different experimental arrangements, the dose to the specimen may be calculated using a simple model. While electron and proton probe X-ray microanalysis are found to involve heavy doses to the specimen, X-ray fluorescence, performed with a polarized, monochromatic X-ray probe, is the least destructive for the analysis of medium to heavy elements. For light elements (Z less than or equal to 20), electron energy loss spectroscopy or X-ray absorption microanalysis involve the lowest dose in most applications. Other advantages and limitations of the various techniques are also summarized.

Electron Probe Microanalysis↗
PubMed1995

Designing of peptides with immuno-modulatory properties using protein A as a probe.

A series of reports from our laboratory have described the multifarious properties of protein A of Staphylococcus aureus Cowan I, apart from its IgG binding affinity. Original reports regarding its anti-tumor, anti-toxic, anti-carcinogenic and immunomodulatory properties published earlier by the authors have implicated some uniqueness of this bacterial protein. It was conceived that such diversified properties must lie in its specific peptide sequences, rendering it to act and behave as a multipotent "Biological Response Modifier" (BRM). The high resolution X-ray structure of protein A-Fc complex has been delineated earlier, and has been the foundation of many protein engineering studies. This structure along with the amino acid sequence data of its four repetitive domains provided us the basis for designing an octapeptide. This octapeptide was synthesized by solid phase peptide synthesis considering it as the probable site through which PA binds IgG. This octapeptide (NH2-Gln-Asn-Ala-Phe-Tyr-Glu-Ile-Leu-COOH) is present in the first helical segment of B-domain of protein A, and also is a part of domain D, A and C. This octapeptide has been shown to bind IgG by the immunoblotting technique. The binding affinity of the octapeptide appears to be significantly higher than that of intact protein A, as was revealed by calculation of Ka (association constant) and Kd (dissociation constant) values. This octapeptide might serve as a good immunoadsorbant for IgG and/or immune complexes.

Adjuvants, Immunologic↗
PubMed2001

Construction of low-resolution x-ray crystallographic electron density maps of the ribosome.

Advances in X-ray crystallography now allow biological macromolecules of almost any size to be imaged at atomic resolution. Here, I outline the strategy that allowed for the solution of the 70S ribosome structure to 7.8-A resolution. The most important factors involve the effective use of synchrotron radiation and the application of existing crystallographic software to very large structures.

Algorithms↗
PubMed1992

Image blurring by thermal diffusion in the observation of hydrated biomolecules with soft X-ray microscopy.

A simple model is presented for the estimation of image blurring in X-ray microscopy of biological specimens in a hydrated environment. The model is essentially based on thermal diffusion of an object to be imaged. The degree of image blurring by diffusion depends on the following situations of the object. The object is free from, is tightly fixed to, or is partially connected to the surrounding structures. The proper imaging time required to achieve a given resolution in X-ray microscopy of biological structures was estimated with the present method. The results suggest that imaging time shorter than 3 msec (free) to 1.4 sec (tightly fixed) is required for the observation of a cell (30 microns in diameter) at the resolution of 100 nm. The model is also applicable to a fragmented object caused by imaging X-rays.

Cell Nucleus↗
PubMedDate not supplied

Correlative high-resolution morphologic analysis of the three-dimensional organization of human chromosomes.

A correlative morphologic analysis was carried out on isolated metaphase chromosomes by means of field emission in-lens scanning electron microscopy (FEISEM) and atomic force microscopy (AFM). Whereas FEISEM provides ultra-high resolution power and allows the surface analysis of biological structures free of any conductive coating, the AFM allows imaging of biological specimens in ambient as well as in physiologic conditions. The analysis of the same samples was made possible by the use of electrical conductive and light transparent ITO glass as specimen holder. Further preparation of the specimen specific for the instrumentation was not required. Both techniques show a high correlation of the respective morphologic information, improving their reciprocal biological significance. In particular, the biological coat represents a barrier for surface morphologic analysis of chromosome spreads and it is sensitive to protease treatment. The chemical removal of this layer permits high-resolution imaging of the chromatid fibers but at the same time alters the chromosomal dimension after rehydration. The high-resolution level, necessary to obtain a precise physical mapping of the genome that the new instruments such as FEISEM and AFM could offer, requires homogeneously cleaned samples with a high grade of reproducibility. A correlative microscopical approach that utilizes completely different physical probes provides complementary useful information for the understanding of the biological, chemical, and physical characteristics of the samples and can be applied to optimize the chromosome preparations for further improvement of the knowledge about spatial genome organization.

Chromosomes, Human↗
PubMed1983

[Effect of the photometric resolution on the precision of microphotometric measurements].

From investigations on microautoradiographs of suitable biological structures, it is concluded, that for the determination of photometric quantities without loss of accuracy a photometric resolution of n = 10 intervals of optical density is sufficient. A low photometric resolution allows to represent the local distribution of substances more clear and the expense of analysis is reduced.

Animals↗
PubMed2005

On the nature of the species problem and the four meanings of 'species'.

Present-day thought on the notion of species is troubled by a mistaken understanding of the nature of the issue: while the species problem is commonly understood as concerning the epistemology and ontology of one single scientific concept, I argue that in fact there are multiple distinct concepts at stake. An approach to the species problem is presented that interprets the term 'species' as the placeholder for four distinct scientific concepts, each having its own role in biological theory, and an explanation is given of the concepts involved. To illustrate how these concepts are commonly conflated, two widely accepted ideas on species are criticized: species individualism and species pluralism. I argue that by failing to distinguish between the four concepts and their particular roles in contemporary biological theory, these ideas stand in the way of a final resolution of the species problem.

Biological Evolution↗
PubMed1994

Atomic force microscopy produces faithful high-resolution images of protein surfaces in an aqueous environment.

The atomic force microscope has the potential to monitor structural changes of a biological system in its native environment. To correlate them with the biological function at a molecular level, high lateral and vertical resolution are required. Here we demonstrate that the atomic force microscope is capable of imaging the surface of the hexagonally packed intermediate layer of Deinococcus radiodurans in buffer solution with a lateral resolution of 1 nm and a vertical resolution of 0.1 nm. On average, these topographs differ from those determined by electron microscopy by <0.5 nm.

Journal Article↗
PubMed1997

Interstitial pH and pO2 gradients in solid tumors in vivo: high-resolution measurements reveal a lack of correlation.

The partial pressure of oxygen (pO2) and pH play critical roles in tumor biology and therapy. We report here the first combined, high-resolution (< or = 10 microns) measurements of interstitial pH and pO2 profiles between adjacent vessels in a human tumor xenograft, using fluorescence ratio imaging and phosphorescence quenching microscopy. We found (1) heterogeneity in shapes of pH and pO2 profiles; (2) a discordant relation between local pH profiles and corresponding pO2 profiles, yet a strong correlation between mean pH and pO2 profiles; (3) no correlation between perivascular pH/pO2 and nearest vessel blood flow; and (4) well-perfused tumor vessels that were hypoxic and, consequently, large hypoxic areas in the surrounding interstitium. Such multiparameter measurements of the in vivo microenvironment provide unique insights into biological processes in tumors and their response to treatment.

Adenocarcinoma↗
PubMed1977

Some ultrastructural aspects of biological apatite dissolution and possible role of dislocations.

High resolution electron microscope techniques now make it possible to study the mineralization of calcified tissues at the crystal structure level. Dislocations play an important part in the course of crystal maturation and modifications. At least two origins of dislocations are known. The first is due to phenomena related to the incorporation of fluoride ions into the lattice. The second is due to mechanical stresses occurring between crystals during their maturation. Dislocations are the starting-points of acid dissolution which proceeds along dislocation-lines, sometimes inducing a splitting of the crystals. In the present study, dislocations have been visualized, either isolated in the crystal core and perhaps the two-dimensional surface representation of a screw-shaped dislocation, or forming nets of dislocations producing a spiral staircase on the sides faces of the crystals. There is evidence of a maturation cycle of the crystals, which may grow, split, coalesce or dissolve; liberated elements and small crystal fragments may allow development of near-by crystals. This remodelling explains the existence of a standard size as well as the perfect fitting of the crystals. These morphological data involve physico-chemical properties of biological apatites.

Acid Etching, Dental↗
PubMed2004

Biomimetic actuators: where technology and cell biology merge.

The structural and functional analysis of biological macromolecules has reached a level of resolution that allows mechanistic interpretations of molecular action, giving rise to the view of enzymes as molecular machines. This machine analogy is not merely metaphorical, as bio-analogous molecular machines actually are being used as motors in the fields of nanotechnology and robotics. As the borderline between molecular cell biology and technology blurs, developments in the engineering and material sciences become increasingly instructive sources of models and concepts for biologists. In this review, we provide a--necessarily selective--summary of recent progress in the usage of biological and biomimetic materials as actuators in artificial environments, focussing on motors built from DNA, classical cellular motor systems (tubulin/kinesin, actin/myosin), the rotary motor F1F0-ATPase and protein-based 'smart' materials.

Actins↗
PubMed1975

High resolution scanning electron microscopy at the subcellular level.

Recently developed scanning electron microscopes provide sufficient resolution to allow useful observation of subcellular biological objects. Preparation methods for such objects need not be limited to the traditional coating and mounting procedures. Many methods developed for transmission electron microscopy are immediately adaptable to scanning electron microscopy. We show that a number of techniques are available to the microscopist which yield adequate contrast and high resolution. As examples we show skeletal muscle myofibrils dispersed to reveal thick filaments, uncoated on a thin carbon film; a tropomyosin tactoid, negatively stained with uranyl acetate; oncornavirus, conventionally coated; and T4 bacteriophage on an aluminium substrate.

Animals↗
PubMed1984

Picosecond spectroscopy: applications in biochemistry. Part I: Techniques.

A number of sources of picosecond optical pulses and the means by which they may be used to investigate fast molecular processes have been described. In addition, it should be pointed out that most of these techniques can be extended to take advantage of other properties of the laser pulses; in particular, the polarization is of use in measuring time-dependent antisotropy. The state of the art is now the generation of 30fs pulses; it seems likely that this is all the time resolution that one is likely to need for investigating biological and other molecular processes as at such short times the uncertainty principle leads to a considerable loss of spectral resolution.

Argon↗
PubMed1985

Working at higher magnifications in scanning electron microscopy with secondary and backscattered electrons on metal coated biological specimens and imaging macromolecular cell membrane structures.

Membrane structures of macromolecular dimensions were imaged with high resolution secondary electron type I (SE-I) signal contrasts on metal coated biological specimens. The quality of the surface information was strongly dependent on the signal used for microscopy and on the properties of metal films, i.e., thickness, continuity, structure and decoration effects. Films of 10 nm thickness produced so much type II electrons that identical images were obtained with the conventional SE-II and BSE-II signals. In such images, the type I SE signal was so low that only very weak contrasts were recognizable. If the films--continuous or discontinuous--were composed of large metal aggregates (gold and platinum) a strong micro-roughness contrast was produced by the type II signal. At high magnifications (100,000 x) this background signal greatly reduced the S/N ratio of the SE-I signal. A similar effect was previously shown to be produced by the type III background signal. The type II background signal minimized when continuous films of small aggregates (tantalum and chromium) were applied. SE-I contrast dominated in the image if the film thickness was limited to 1 nm. Additionally, it was found that gold and platinum decorated membrane surface structures, less than 20 nm in size, and did not reveal all the topographic information available (size, shape, orientation spacing of small surface features) but merely displayed center-to-center distances. These decoration effects were avoided and extensive topographic information was obtained through surface coating with Ta or Cr.

Animals↗