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Results for “Microscopy, Scanning Probe”

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At least 73 records · Page 4Linked to original sources
PubMed2003

Growth of cationic lipid toward bilayer lipid membrane by solution spreading: scanning probe microscopy study.

The growth of cationic lipid dioctadecyldimethylammonium bromide (DODAB) toward bilayer lipid membrane (BLM) by solution spreading on cleaved mica surface was studied by atomic force microscopy (AFM). Bilayer of DODAB was formed by exposing mica to a solution of DODAB in chloroform and subsequently immersing into potassium chloride solution for film developing. AFM studies showed that at the initial stage of the growth, the adsorbed molecules exhibited the small fractal-like aggregates. These aggregates grew up and expanded laterally into larger patches with time and experienced from monolayer to bilayer, finally a close-packed bilayer film (5.4+/-0.2 nm) was approached. AFM results of the film growth process indicated a growth mechanism of nucleation, growth and coalescence of dense submonolayer, it revealed the direct information about the film morphology and confirmed that solution spreading was an effective technique to prepare a cationic bilayer in a short time.

Aluminum Silicates↗
PubMed1998

Immobilization strategies for biological scanning probe microscopy.

Biological atomic force microscopy (AFM) is now established as a method for studying the structure and function of biomolecular objects at the solid-liquid interface. Major progress in this field is linked to new developments in instrumentation, a better understanding of tip-sample interactions, and improved sample preparation techniques. In this review, the most common strategies for biomolecular immobilization with respect to biological AFM applications are summarized.

Microscopy, Atomic Force↗
PubMed1995

A new DNA nanostructure, the G-wire, imaged by scanning probe microscopy.

G-DNA is a polymorphic family of quadruple helical nucleic acid structures containing guanine tetrad motifs [G-quartets; Williamson, J.R., Raghuraman, M.K. and Cech, T.R. (1989) Cell 59, 871-880; Williamson, J.R. (1993) Proc. Natl. Acad. Sci. USA 90, 3124-3124]. Guanine rich oligonucleotides that are self-complimentary, as found in many telomeric G-strand repeat sequences, form G-DNA in the presence of monovalent and/or divalent metal cations. In this report we use the atomic force microscope (AFM) to explore the structural characteristics of long, linear polymers formed by the telomeric oligonucleotide d(GGGGTTGGGG) in the presence of specific metal cations. In the AFM these polymers, termed G-wires, appear as filaments whose height and length are determined by the metal ions present during the self-assembly process. The highly ordered, controllable self-assembly of G-wires could provide a basis for developing advanced biomaterials.

Base Sequence↗
PubMed1999

Quality assessment of atomic force microscopy probes by scanning electron microscopy: correlation of tip structure with rendered images.

While image quality from instruments such as electron microscopes, light microscopes, and confocal laser scanning microscopes is mostly influenced by the alignment of optical train components, the atomic force microscope differs in that image quality is highly dependent upon a consumable component, the scanning probe. Although many types of scanning probes are commercially available, specific configurations and styles are generally recommended for specific applications. For instance, in our area of interest, tapping mode imaging of biological constituents in fluid, double ended, oxide-sharpened pyramidal silicon nitride probes are most often employed. These cantilevers contain four differently sized probes; thick- and thin-legged 100 microm long and thick- and thin-legged 200 microm long, with only one probe used per cantilever. In a recent investigation [Taatjes et al. (1997) Cell Biol. Int. 21:715-726], we used the scanning electron microscope to modify the oxide-sharpened pyramidal probe by creating an electron beam deposited tip with a higher aspect ratio than unmodified tips. Placing the probes in the scanning electron microscope for modification prompted us to begin to examine the probes for defects both before and after use with the atomic force microscope. The most frequently encountered defect was a mis-centered probe, or a probe hanging off the end of the cantilever. If we had difficulty imaging with a probe, we would examine the probe in the scanning electron microscope to determine if any defects were present, or if the tip had become contaminated during scanning. Moreover, we observed that electron beam deposited tips were blunted by the act of scanning a hard specimen, such as colloidal gold with the atomic force microscope. We also present a mathematical geometric model for deducing the interaction between an electron beam deposited tip and either a spherical or elliptical specimen. Examination of probes in the scanning electron microscope may assist in interpreting images generated by the atomic force microscope.

DNA↗
PubMed2000

Functional tethered lipid bilayers.

Our strategy to provide the structural basis for the build-up of functional tethered membranes focuses on three approaches: the first one is based on the pre-organization of a monomolecular layer of a lipopolymer at the water/air interface which is then transferred to a solid support. Prior to deposition, the substrate is coated with a layer of benzophenone-derivatized silane molecules that allow for a stable covalent attachment by photo-cross-linking of some of the monomer units of the lipopolymer to the support. An alternative concept realizes a layer-by-layer deposition of the various structural elements: (1) the attachment layer with the reactive sites for the chemical stabilization; (2) a polymer 'cushion' prepared by adsorption and simultaneous or subsequent partial covalent binding to the reactive sites; and (3) a lipid monolayer transferred from the water/air interface, that contains a certain amount of lipids with reactive headgroups which, upon binding to the polymer tether, act as anchor lipids stabilizing the whole monolayer/cushion-composite. And finally, we build peptide-supported monolayers by first (self-) assembling amino acid sequences of various lengths via a SH-group near their N-terminus onto Au substances and use then their COO(-)-terminus to chemically attach phosphatidyl-ethanolamine lipids to form a stable monolayer of lipid-peptide conjugates. All the individual preparation steps and the various resulting (multi-) layers are characterized by surface plasmon spectroscopy, X-ray and neutron-reflectometry, contact angle measurements, IR spectroscopy, fluorescence microscopy, scanning probe microscopies, as well as, electrochemical techniques. For all tethering systems, the final membranes' architecture is obtained by fusing lipid vesicles onto the lipid monolayer. Proteins can be incorporated by either fusing vesicles that are loaded with the respective receptors, pores, or ion pumps via a reconstitution procedure, or via a transfer directly from a micellar solution to the pre-formed lipid bilayer at the solid support by a dialysis step. Two structural/dynamical features of tethered membranes which are considered to be of particular functional relevance, i.e. the degree of water uptake and, hence, the degree of swelling of the polymer support, as well as the lateral mobility of the lipid molecules in the membrane, are tested by surface plasmon optics and by measurements of the fluorescence recovery after photobleaching (FRAP), respectively. The results confirm that the presented preparation protocols yield fluid bilayers that mimic certain relevant properties of biological membranes. The functional characterization of tethered membranes, which is briefly summarized, is based on various electrochemical techniques, in particular, impedance spectroscopy, cyclic voltammetry, and chronoamperometric studies. The results obtained for reconstituted H(+)-ATPase from chloroplasts and E. coli and for cytochrome oxidase (with and without cytochrome c) confirm the incorporation of the proteins in an active form, thus, opening opportunities for novel sensor formats or offering a completely new model membrane system.

Biopolymers↗
PubMed2003

Two-dimensional supramolecular self-assembly probed by scanning tunneling microscopy.

Supramolecular chemistry has a very large impact on chemistry of current interest and the use of non-covalent but directional forces is appealing for the construction of 'supramolecular architectures'. The invention of scanning probe microscopy techniques has opened new doorways to study these concepts on surfaces. This review deals with recent progress in the study of two-dimensional supramolecular self-assembly on surfaces probed by scanning tunneling microscopy, with a special emphasis on structure, dynamics and reactivity of hydrogen bonded systems.

Adsorption↗
PubMed2003

Near-field scanning optical microscopy probes: a comparison of pulled and double-etched bent NSOM probes for fluorescence imaging of biological samples.

Bent near-field optical probes for biological applications have been fabricated using a combination of a two-step chemical etching method and focused ion beam milling to create a well-defined aperture. The transmission efficiencies have been evaluated as a function of laser wavelength (lambda) and aperture size (D) for both large and small core fibres. The probe transmission behaviour follows a (D/lambda)3 relationship. The double-etched probes are compared to pulled probes fabricated from highly GeO2-doped dispersion compensating fibre and a standard single-mode optical fibre. The transmission efficiencies of both types of pulled probes are approximately two orders of magnitude lower than double-etched probes with similar aperture sizes. To demonstrate the utility of the various probes, their imaging performance has been evaluated for samples of polymer beads and phase-separated phospholipid monolayers of dipalmitoylphosphatidylcholine or cholesterol/phosphatidylcholine/sphingomyelin mixtures. Both pulled and double-etched probes are suitable for fluorescence imaging of polymer spheres. However, pulled probes are rapidly damaged at the higher input laser intensities required for fluorescence imaging of monolayer samples doped with < 1% of a fluorescent dye-labelled lipid. The images obtained with the double-etched probes show excellent spatial resolution and signal/noise, illustrating the potential of such probes for imaging of biological samples.

Microscopy, Atomic Force↗
PubMed2001

Oxygen consumption of single bovine embryos probed by scanning electrochemical microscopy.

Oxygen consumption of individual bovine embryos was noninvasively quantified by scanning electrochemical microscopy (SECM). A probe microelectrode was used to scan near a single embryo surface in a culture medium to monitor the oxygen reduction current at 37 degrees C, under a water-saturated atmosphere of 5% CO2 and 95% air. The oxygen concentration profiles near the embryos were in good agreement with the theoretical spherical diffusion. When an embryo reached the stage of a morula with a 74-microm radius on day 6 after in vitro fertilization, the oxygen concentration difference (deltaC) between the bulk solution and the morula surface was 6.90 +/- 1.35 microM. The oxygen consumption rate (F) of the single morula was estimated to be (1.40 +/- 0.27) x 10(-14) mol s(-1). After the SECM measurement, the embryo was continuously cultured for another 2 days and grew to the stage of a blastocyst with a 100-microm radius. For the blastocyst, the deltaC values for the inner cell mass side and the trophoblast side were 16.40 +/- 1.83 and 9.14 +/- 1.68 microM, respectively. The oxygen consumption rate of the blastocyst was found to be in the range of (2.50 +/- 0.46) x 10(-14) mol s(-1) < F < (4.49 +/- 0.50) x 10(-14) mol s(-1). We have carried out SECM measurements for 19 embryos, and the results were compared in detail with these from an optical microscopic observation. The deltaC values for the morulae on day 6 after in vitro fertilization were strongly related to the morphological embryo quality. The morulae showing a larger deltaC value developed into blastocysts of a larger size, and the deltaC value after the subsequent 2 days of cultivation was found to be increased.

Animals↗
PubMedDate not supplied

Imaging of DNA by scanning force microscopy.

The scanning probe microscopies applied to the sequencing of DNA is a challenging goal attempted by several groups. But one limitant parameter has been the sample preparation of DNA molecules. Here we report how to hold DNA molecules fixed on mica substrate and we show the three-dimensional configuration of double-stranded DNA obtained with our scanning force microscope. We can image DNA under negative supercoiling, a feature of general importance controlling the activities of DNA. We compared the electron micrographs of a carbon replica of the same DNA specimen with scanning force images which demonstrates well the feasibility and accuracy of our scanning probe measurements.

DNA↗
PubMed1999

Near-field scanning optical microscopy in cell biology.

Near-field optics has produced the highest optical resolution that has ever been achieved. The methods involved lie at the interface of far-field optical microscopy and scanned probe microscopy. This article describes the principles behind near-field scanning optical microscopy (NSOM) and highlights its potential in cell biology.

Humans↗
PubMed2002

Pharmaceutical applications of micro-thermal analysis.

Micro-thermal analysis is a recently introduced thermoanalytical technique that combines the principles of scanning probe microscopy with thermal analysis via replacement of the probe tip with a thermistor. This allows samples to be spatially scanned in terms of both topography and thermal conductivity, whereby placing the probe on a specific region of a sample and heating, it is possible to perform localized thermal analysis experiments on those regions. In this minireview, the principles of the technique are outlined and the current uses within the polymer sciences described. Current pharmaceutical applications are then discussed; these include the identification of components in compressed tablets, the characterization of drug-loaded polylactic acid microspheres, the analysis of tablet coats, and the identification of amorphous and crystalline regions in semicrystalline samples. The current strengths and weaknesses of the technique are outlined, along with a discussion of the future directions in which the approach may be taken.

Crystallization↗
PubMed2001

Biological thermal detection in infrared imaging snakes. 1. Ultramicrostructure of pit receptor organs.

The receptor organs of snakes with "thermal vision" were studied with ultra-high-resolution scanning probe microscopy (SPM) at close to in vivo conditions to elucidate their surface morphology and materials properties critical for prospective biomimetic design of "soft matter"-based infrared (IR) sensors. The surfaces of living tissues were scanned under wet ambient conditions in physiological solution, and the resulting parameters were compared with SPM data obtained for chemically treated (formaldehyde-fixed) tissue in ambient air and TEM studies in high vacuum. We found that the microstructural parameters for the living tissue are similar to ones observed for the formaldehyde-fixed snake tissues. However, previous data obtained from TEM analysis in high vacuum underestimated actual dimensions of surface microstructures. The average spacing of the nanopit array observed within receptor surface areas, which was suggested to play a critical role in selective IR adsorption, was determined to be 520 nm. This value is close to the grating spacing required for efficient reflection of electromagnetic radiation characteristic for sunlight without affecting IR adsorbance.

Animals↗