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Results for “Microscopy, Scanning Probe”

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PubMed1997

Scanning ion conductance microscopy of living cells.

Currently there is a great interest in using scanning probe microscopy to study living cells. However, in most cases the contact the probe makes with the soft surface of the cell deforms or damages it. Here we report a scanning ion conductance microscope specially developed for imaging living cells. A key feature of the instrument is its scanning algorithm, which maintains the working distance between the probe and the sample such that they do not make direct physical contact with each other. Numerical simulation of the probe/sample interaction, which closely matches the experimental observations, provides the optimum working distance. The microscope scans highly convoluted surface structures without damaging them and reveals the true topography of cell surfaces. The images resemble those produced by scanning electron microscopy, with the significant difference that the cells remain viable and active. The instrument can monitor small-scale dynamics of cell surfaces as well as whole-cell movement.

Animals↗

PubMed2000

Atomic force microscopy captures quantized plastic deformation in gold nanowires.

Scanning probe microscopy has become a powerful tool to detect structural changes in small clusters of atoms. Herein, we use an atomic force microscope to measure the length of gold nanowire structures during extension and compression cycles. We have found that nanowires elongate under force in quantized steps of up to three integer multiples of 1.76 A and that they shorten spontaneously in steps of 1.52 A. Our results can be explained by the sliding of crystal planes within the gold nanowires creating stacking faults that change the local structure from face-centered cubic to hexagonal close packed. Our data also show that there can be up to three simultaneous slip events, in good agreement with the tetrahedral arrangement of slip planes in a gold crystal. These experiments provide direct evidence for the mechanism underlying the plastic deformation of a nanowire. A similar approach can be used to examine the atomic events underlying the plastic failure of other metals and their alloys.

Journal Article↗

PubMed2003

Topological and electron-transfer properties of yeast cytochrome c adsorbed on bare gold electrodes.

The redox metalloprotein yeast cytochrome c was directly self-chemisorbed on "bare" gold electrodes through the free sulfur-containing group Cys102. Topological, spectroscopic, and electron transfer properties of the immobilised molecules were investigated by in situ scanning probe microscopy and cyclic voltammetry. Atomic force and scanning tunnelling microscopy revealed individual protein molecules adsorbed on the gold substrate, with no evidence of aggregates. The adsorbed proteins appear to be firmly bound to gold and display dimensions in good agreement with crystallographic data. Cyclic voltammetric analysis showed that up to 84% of the electrode surface is functionalised with electroactive proteins whose measured redox midpoint potential is in good agreement with the formal potential. Our results clearly indicate that this variant of cytochrome c is adsorbed on bare gold electrodes with preservation of morphological properties and redox functionality.

Computational Biology↗

PubMed1999

Surface topography, corrosion and microhardness of nitrogen-diffusion-hardened titanium alloy.

Mechanical-electrochemical interactions accelerate corrosion in mixed-metal modular hip prostheses. These interactions can be reduced by improving the modular component machining tolerances or by improving the resistance of the components to scratch or fretting damage. Wrought cobalt-alloy (CoCrMo) is known to have better tribological properties compared to the titanium alloy (Ti64). Thus, improving the tribological properties of this mixed-metal interface should center around improving the tribological properties of the Ti64 alloy. This study used scanning probe microscopy (contact, tapping and phase contrast mode), scanning electron microscopy, corrosion testing, and microhardness testing to determine the effect of a nitrogen-diffusion hardening process on the surface morphology, electrochemistry and surface hardness of the Ti64 alloy. The nitrogen-diffusion-hardened titanium alloy samples (N-Ti64) had a more pronounced grain structure, more nodular surface, and significantly (P<0.01) higher mean roughness values than the control-Ti64 samples. The N-Ti64 samples also exhibited at least equivalent corrosion behavior and a definite increase in surface hardness compared to the control Ti64 samples. The equivalent corrosion behavior and improved surface hardness indicate the potential for N-Ti64 samples to resist similar and mixed-metal scratch and fretting damage. The use of N-Ti64 as opposed to control-Ti64 may therefore reduce the occurrence of mechanical-electrochemical degradation in mixed-metal modular total hip prostheses.

Alloys↗

PubMed2003

The application of atomic force microscopy to the study of living vertebrate cells in culture.

Atomic force microscopy (AFM), a relatively new variant of scanning probe microscopy developed for the material sciences, is becoming an increasingly important tool in other disciplines. In this review I describe in nontechnical terms some of the basic aspects of using AFM to study living vertebrate cells. Although AFM has some unusual attributes such as an ability to be used with living cells, AFM also has attributes that make its use in cell biology a real challenge. This review was written to encourage researchers in the biological and biomedical sciences to consider AFM as a potential (and potent) tool for their cell biological research.

Animals↗

PubMed2001

Noncontact electrochemical imaging with combined scanning electrochemical atomic force microscopy.

Combined scanning electrochemical atomic force microscopy (SECM-AFM) is a recently introduced scanned probe microscopy technique where the probe, which consists of a tip electrode and integrated cantilever, is capable of functioning as both a force sensor, for topographical imaging, and an ultramicroelectrode for electrochemical imaging. To extend the capabilities of the technique, two strategies for noncontact amperometric imaging-in conjunction with contact mode topographical imaging-have been developed for the investigation of solid-liquid interfaces. First, SECM-AFM can be used to image an area of the surface of interest, in contact mode, to deduce the topography. The feedback loop of the AFM is then disengaged and the stepper motor employed to retract the tip a specified distance from the sample, to record a current image over the same area, but with the tip held in a fixed x-y plane above the surface. Second, Lift Mode can be employed, where a line scan of topographical AFM data is first acquired in contact mode, and the line is then rescanned to record SECM current data, with the tip maintained at a constant distance from the target interface, effectively following the contours of the surface. Both approaches are exemplified with SECM feedback and substrate generation-tip collection measurements, with a 10-microm-diameter Pt disk UME serving as a model substrate. The approaches described allow electrochemical images, acquired with the tip above the surface, to be closely correlated with the underlying topography, recorded with the tip in intimate contact with the surface.

Journal Article↗

PubMed2001

Examination of line crossings by atomic force microscopy.

Until now, the most widely used methods for the forensic examination of line crossings in documents were optical and electron microscopy. The combination of both techniques allows one in most cases to establish the sequence of lines. The recent development of scanning probe microscopy [1] gives an opportunity to complement or even replace the classical instruments used in this field. Scanning probe microscopes have been designed to study surfaces at high magnification. The aim of this study was to verify if their most popular member, the atomic force microscope (AFM) [2], can be applied to line crossing problems. The results show for the first time that AFM images present the same qualitative information obtained by scanning electron microscope (SEM) images and, consequently, allow the determination of the line crossing sequence under ambient conditions without vacuum and conductive coating of specimens.

Forensic Medicine↗

PubMed2005

Vector near-field calculation of scanning near-field optical microscopy probes using Borgnis potentials as auxiliary functions.

A new boundary integral equation method for solving the near field in three-dimensional vector form in scanning near-field optical microscopy (SNOM) using Borgnis potentials as auxiliary functions is presented. A boundary integral equation of the electromagnetic fields, expressed by Borgnis potentials, is derived based on Green's theorem. The harmonic expansion in rotationally symmetric SNOM probe--sample systems is studied, and the three-dimensional electromagnetic problem is partly simplified into a two-dimensional one. The boundary conditions of Borgnis potentials both on dielectric boundaries and on perfectly conducting boundaries are derived. Relevant algorithms were studied, and a computer program was written. As an example, a SNOM probe-sample system composed of a round metal-covered probe and a sample with a flat surface has been numerically studied, and the computational results are given. This new method can be used efficiently for other electromagnetic field problems with round subwavelength structures.

Algorithms↗

PubMedDate not supplied

Atomic force microscopy of nanometric liposome adsorption and nanoscopic membrane domain formation.

Scanning probe microscopy studies of membrane fusion and nanoscopic structures were performed using hydrated single lipids and lipid mixtures. Extruded vesicles of DMPC and mixtures at various concentrations of DLPC, DPPC and cholesterol were deposited on freshly cleaved mica and studied in a fluid environment by AFM. The nanostructures formed by these extruded liposomes ranged from isolated unilamellar vesicles to flat sheet membranes and were marked influenced by thermodynamic phase behavior. For DMPC membrane, intact bilayers exhibited a phase transition process in agreement with large bilayer patches. In the DLPC, DPPC and cholesterol mixtures, nanoscopic domain diameters ranged from approximately 25 to 48nm with height differences of approximately 1.4nm; all values were lipid composition-dependent. Our data support and extend previous studies of microscopic domains and phase boundaries of the same mixtures in giant unilamellar vesicles determined by confocal light microscopy. Our approach for preparing and utilizing supported membrane structures is potentially relevant to studies of native cell membranes.

Adsorption↗

PubMed2003

DNA height in scanning force microscopy.

The measured height of DNA molecules adsorbed on a mica substrate by scanning probe microscopy is always less than the theoretical diameter. In this paper we show that, when imaged in ambient conditions, the molecules are usually immersed in the salt layer used to adsorb them to the substrate. This layer distorts the measurement of DNA height and is the main source of error but not the only one. We have performed different experiments to study this problem using two scanning force techniques: non-contact tapping mode in air and jumping mode in aqueous solution, where the dehydration phenomena is minimized. Height measurements of DNA in air using tapping mode reveal a height of 0.7+/-0.2nm. This value increases up to 1.5+/-0.2nm when the salt layer, in which the molecules are embedded, is removed. Jumping experiments in water give a value of 1.4+/-0.3nm when the maximum applied force is 300pN and 1.8+/-0.2nm at very low forces, which confirms the removal of the salt layer. Still, in all our experiments, the measured height of the DNA is less than the theoretical value. Our results show that although the salt layer present is important, some sample deformation due to either the loading force of the tip or the interaction with the substrate is also present.

Adsorption↗

PubMed1995

Human dentine as a hydrogel.

The pores (tubules) of human dentine in 0.02-cm planoparallel sections of newly extracted permanent teeth were investigated. By the conventional scanning electron microscopy these pores appear empty, but by the newly developed scanning-probe microscopy the presence of a complex matrix could be established. By measuring the transport of neutral myoglobin by diffusion alone and diffusion+bulk flow, the area of dentine occupied by the matrix was calculated to be 1.9 +/- 0.9% and 2.3 +/- 0.5%, respectively. The hydraulic conductivity was surprisingly small, 1.35 +/- 0.55 x 10(-7) ml/(s.cm2 dentine) at a pressure difference of 0.1 kPa across a 1-cm thick section. This suggests a hydrogel with a relatively dense network, the width of meshes estimated at 2 x 30 nm. In line with this concept, enzymatic degradation of the organic matter increased the hydraulic conductivity 3000 times. By studying the transport of negatively charged myoglobin, the matrix was calculated to carry 18 mEq/l of positive charges. Due to the consequent attraction of small, negative ions and thence of water, the pressure within the matrix would be about 1.33 kPa, a force which will act to immobilize the water in the channels. The concept of a hydrogel in the dentine tubules was also supported by the finding that shielding the charges with bathing media of high ionic strength reduced the hydraulic conductivity.

Adolescent↗

PubMed1975

Scanning electron microscopy and electron probe microanalysis of calcified alpha-elastin coacervates.

The uptake of calcium and phosphorus from a serum calcification medium by coacervated alpha-elastin was studied by electron probe microanalysis and scanning electron microscopy. Calcium and phosphorus were bound by the coacervate in ratios similar to that of hydroxyapatite. A significant difference was observed in the secondary electron image of the coacercules from the serum during calcification of the coacervate.

Animals↗

PubMed2000

Formation of three-dimensional protein-lipid aggregates in monolayer films induced by surfactant protein B.

This study focuses on the structural organization of surfactant protein B (SP-B) containing lipid monolayers. The artificial system is composed of the saturated phospholipids dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) in a molar ratio of 4:1 with 0.2 mol% SP-B. The different "squeeze-out" structures of SP-B were visualized by scanning probe microscopy and compared with structures formed by SP-C. Particularly, the morphology and material properties of mixed monolayers containing 0.2 mol% SP-B in a wide pressure range of 10 to 54 mN/m were investigated revealing that filamentous domain boundaries occur at intermediate surface pressure (15-30 mN/m), while disc-like protrusions prevail at elevated pressure (50-54 mN/m). In contrast, SP-C containing lipid monolayers exhibit large flat protrusions composed of stacked bilayers in the plateau region (app. 52 mN/m) of the pressure-area isotherm. By using different scanning probe techniques (lateral force microscopy, force modulation, phase imaging) it was shown that SP-B is dissolved in the liquid expanded rather than in the liquid condensed phase of the monolayer. Although artificial, the investigation of this system contributes to further understanding of the function of lung surfactant in the alveolus.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1994

Covalent anchoring of proteins onto gold-directed NHS-terminated self-assembled monolayers in aqueous buffers: SFM images of clathrin cages and triskelia.

N-Hydroxysuccinimide-terminated self-assembled monolayers with linear (CH2)10 chains were prepared on ultraflat Au(111) surfaces from dithiobis(succinimidylundecanoate). These monolayers, which are covalently chemisorbed to gold via thiolate bonds, form a highly reactive amino-group specific carpet at the liquid-solid interface. Proteins bind to it covalently in aqueous buffers under mild conditions; this provides a (general) procedure for protein immobilization for scanning probe microscopy. Using this technique, we have obtained what we believe are the first scanning force microscopy images of clathrin cages and of their in situ disassembly, yielding typical triskelia under non-denaturing conditions.

Animals↗

PubMed1993

Analysis of biomedical polymer surfaces: polyurethanes and plasma-deposited thin films.

The surface characterization of biomaterials is important for understanding the biological reactivity of surfaces and for monitoring surface reproducibility and contamination. Electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectrometry (SIMS), contact-angle methods, vibrational spectroscopic methods, and scanning probe microscopies are briefly reviewed. Examples are presented using these methods to characterize RF plasma-deposited surfaces based upon acetone and oxygen for cell culture and Biomer¿ surfaces.

Biocompatible Materials↗

PubMed2003

The birth and evolution of surface science: child of the union of science and technology.

This article is an account of the birth and evolution of surface science as an interdisciplinary research area. Surface science emanated from the confluence of concepts and tools in physics and chemistry with technological innovations that made it possible to determine the structure and properties of surfaces and interfaces and the dynamics of chemical reactions at surfaces. The combination in the 1960s and 1970s of ultra-high-vacuum (i.e., P < 10(-7) Pascal or 10(-9) Torr) technology with the recognition that electrons in the energy range from 50 to 500 eV exhibited inelastic collision mean free paths of the order of a few angstroms fostered an explosion of activity. The results were a reformulation of the theory of electron solid scattering, the nearly universal use of electron spectroscopies for surface characterization, the rise of surface science as an independent interdisciplinary research area, and the emergence of the American Vacuum Society (AVS) as a major international scientific society. The rise of microelectronics in the 1970s and 1980s resulted in huge increases in computational power. These increases enabled more complex experiments and the utilization of density functional theory for the quantitative prediction of surface structure and dynamics. Development of scanning-probe microscopies in the 1990s led to atomic-resolution images of macroscopic surfaces and interfaces as well as videos of atoms moving about on surfaces during growth and diffusion. Scanning probes have since brought solid-liquid interfaces into the realm of atomic-level surface science, expanding its scope to more complex systems, including fragile biological materials and processes.

Journal Article↗

PubMed2002

Chiral recognition in dimerization of adsorbed cysteine observed by scanning tunnelling microscopy.

Stereochemistry plays a central role in controlling molecular recognition and interaction: the chemical and biological properties of molecules depend not only on the nature of their constituent atoms but also on how these atoms are positioned in space. Chiral specificity is consequently fundamental in chemical biology and pharmacology and has accordingly been widely studied. Advances in scanning probe microscopies now make it possible to probe chiral phenomena at surfaces at the molecular level. These methods have been used to determine the chirality of adsorbed molecules, and to provide direct evidence for chiral discrimination in molecular interactions and the spontaneous resolution of adsorbates into extended enantiomerically pure overlayers. Here we report scanning tunnelling microscopy studies of cysteine adsorbed to a (110) gold surface, which show that molecular pairs formed from a racemic mixture of this naturally occurring amino acid are exclusively homochiral, and that their binding to the gold surface is associated with local surface restructuring. Density-functional theory calculations indicate that the chiral specificity of the dimer formation process is driven by the optimization of three bonds on each cysteine molecule. These findings thus provide a clear molecular-level illustration of the well known three-point contact model for chiral recognition in a simple bimolecular system.

Cysteine↗

PubMed2003

Simultaneous in situ total internal reflectance fluorescence/atomic force microscopy studies of DPPC/dPOPC microdomains in supported planar lipid bilayers.

In situ simultaneous total internal reflectance fluorescence and in situ scanning probe microscopy performed on a phase-segregated supported planar lipid bilayer enabled direct in situ real-time correlated topographical and fluorescence images of nanometer-sized gel and fluid-phase lipid domains, presaging future in situ studies of membrane protein assemblies by single molecule imaging.

1,2-Dipalmitoylphosphatidylcholine↗