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At least 235 records · Page 13Linked to original sources
PubMed2005

Chemically functionalized carbon nanotubes.

Since their discovery, carbon nanotubes have attracted the attention of many a scientist around the world. This extraordinary interest stems from their outstanding structural, mechanical, and electronic properties. In fact, apart from being the best and most easily available one-dimensional (1D) model system, carbon nanotubes show strong application potential in electronics, scanning probe microscopy, chemical and biological sensing, reinforced composite materials, and in many more areas. While some of the proposed applications remain still a far-off dream, others are close to technical realization. Recent advances in the development of reliable methods for the chemical functionalization of the nanotubes provide an additional impetus towards extending the scope of their application spectrum. In particular, covalent modification schemes allow persistent alteration of the electronic properties of the tubes, as well as to chemically tailor their surface properties, whereby new functions can be implemented that cannot otherwise be acquired by pristine nanotubes.

Carbon↗
PubMed1995

Clusterin (apoJ) alters the aggregation of amyloid beta-peptide (A beta 1-42) and forms slowly sedimenting A beta complexes that cause oxidative stress.

Clusterin (apoJ), a multifunctional apolipoprotein made by cells in the brain and many other locations, is associated with aggregated amyloid beta-peptide (A beta) in senile and diffuse plaques of Alzheimer's disease (AD). We observed that purified human serum clusterin partially blocked the aggregation of synthetic A beta 1-42, as shown by centrifugal assays (14,000g x 10 min) and by atomic force (scanning probe) microscopy. Slowly sedimenting A beta complexes were formed in the presence of clusterin, which included aggregates > 200 kDa that resist dissociation by low concentrations of SDS. Clusterin enhanced the oxidative stress caused by A beta, as assayed by oxidative stress in PC12 cells with MTT, which is widely used to estimate neurotoxicity. These indications of enhanced neurotoxicity by the MTT assay were observed in the highly aggregated rapidly sedimenting fraction, but also in more slowly sedimenting "soluble" forms. This novel activity of slowly sedimenting A beta may enhance the neurotoxicity of A beta deposits in AD brains, because soluble complexes have a potential for diffusing to damage distal neurons.

Alzheimer Disease↗
PubMed2002

Direct measurement of the laplace pressure in a very thin liquid film.

Meniscus force plays an important part in magnetic storage devices, scanning probe microscopy, and micromachines, because the meniscus force increases steeply as the clearance between solid surfaces decreases down to submicrometers. Recently increased experimental and analytical studies on the subject have been published from the point of view of mechanical engineering. Meniscus force is generated by the Laplace pressure within the thin liquid film. Investigating the Laplace pressure is a direct way to clarify the generation mechanism of meniscus force. However, no appropriate measuring method of the Laplace pressure is available for a very thin liquid film confined by solid surfaces. This paper proposes a simple method of direct measurement of the Laplace pressure for the cases. The principle of the measurement method is described. Measurement is conducted using the measuring device. Experimental results on the Laplace pressure show good agreement with the theoretical predictions.

Journal Article↗
PubMed2004

Determination of diffusion coefficient in gel and in aqueous solutions using scanning electrochemical microscopy.

Diffusion coefficient of different species in different media is an important property needed in scientific research and practice. A method taking advantage on the special capability of scanning electrochemical microscopy (SECM) is described for the easy and accurate measurement of diffusion coefficient. The method is based on detecting the concentration-time transients with appropriate electrochemical microsensor positioned at the close vicinity of a miniature dose-source device. At a given time (ti), a small dose of the investigated species is introduced. The Deltatmax=(tcmax-ti) value and the distance (d=x+Deltaxn) between the source and the detector microelectrode are used for the calculation of D. While the original set distance (x) cannot be accurately measured in the micrometer scale, the tip travel distance (Deltaxn) of the microscope is well defined. Collecting a few Deltatmax-(x+Deltaxn) data pairs, a reliable value of the diffusion coefficient can be obtained. The procedure is simple, and no exact knowledge of the introduced dose is needed. Two ways of sample dose delivery were used: on the one hand, coulometric generation with current-controlled electric pulse using micro-disc electrode, and on the other one, pressure ejection of a nano-droplet from a glass micropipette. Diffusion coefficient of I2, H2O2, [Ru(NH3)6]Cl3 and K3[Fe(CN)6] were measured in solution and in agarose gel phases of different composition. The effect of polyelectrolyte ion exchangers on the diffusion of the investigated species was checked.

Diffusion↗
PubMed2005

Computational methods to produce enhanced images out of given SNOM raw data.

We propose to produce enhanced images out of given raw data read out by SNOM through (i) improved image formation from the raw data; (ii) wavelet de-noising of the image; and (iii) resolution enhancement by deconvolution. Our methods of improvement are based on refined models for the reduction of noise present in SNOM images and on a linear model for the imaging process. They are successfully demonstrated on (magneto-)optical SNOM images of suitable test samples, but yet they are applicable to other scanning probe microscopy techniques.

Journal Article↗
PubMed1999

Nanoscale design of snake skin for reptation locomotions via friction anisotropy.

Multi-mode scanning probe microscopy is employed to investigate the nanostructure of dermal samples from three types of snakes. Sophisticated friction modifying nanostructures are described. These include an ordered microfibrillar array that can function to achieve mission adaptable friction characteristics. Significant reduction of adhesive forces in the contact areas caused by the 'double-ridge' nanoscale microfibrillar geometry provides ideal conditions for sliding in forward direction with minimum adhesive forces and friction. Low surface adhesion in these local contact points may reduce local wear and skin contamination by environmental debris. The highly asymmetric, 'pawl-like' profile of the microfibrillar ends with radius of curvature 20-40 nm induces friction anisotropy in forward backward motions and serves as an effective stopper for backward motion preserving low friction for forward motion. The system of continuous micropores penetrating through the snake skin may serve as a delivery system for lubrication/anti-adhesive lipid mixture that provides for boundary lubrication of snake skins.

Actin Cytoskeleton↗
PubMed2001

Surface characterization of porous, biocompatible protein polymer thin films.

Genetically engineered protein polymer coatings are intended to improve the performance of implantable neural prosthetic devices. To facilitate device integration with tissue, three-dimensionally structured protein polymer films were deposited on the devices using electrostatic atomization and gas-evolution foaming. Periodic features and the length-scale dependence of the surface roughness were identified in topographic data collected using scanning probe microscopy. Using the power spectral density of surface data, the influence of process parameters on the surface roughness of protein polymer thin films was examined. Details of surface topography are known to influence biological behavior, and the method presented was capable of quantifying the evolution of surface features at biologically relevant length scales. This study provides a means for the quantitative exploration of the effects of topography on the performance of these devices and on biocompatibility in general.

Biocompatible Materials↗
PubMed2000

Chemical etching of optical fibre tips--experiment and model.

The formation of chemically etched fibre tips for use in optical scanning probe microscopy is addressed. For tips formed at a cleaved fibre end in the bulk of a buffered HF acid solution the morphological features (tip height, cone angle) are found to depend strongly on the temperature and etchant composition. The tip formation process is analysed and explained in terms of a simple model in which the only pertinent physical parameters are the fibre core diameter and etch rates of the fibre core and cladding. The etch rates are determined in separate experiments as a function of temperature (in the range 24-50 degrees C) for etchant solutions of de-ionised water: 50% HF acid: 40% NH4F in the volume ratio 1:1:X for X = 2, 4 and 6, and used in the model to yield a correct description of the experimental tip cone angles. The model is successfully extended to the intriguing case of negative tip formation which initiates in a normal, positive tip structure. By contrast, tip formation in the meniscus region of a bare fibre/etchant/organic solvent system is found to be independent of etchant composition and temperature.

Journal Article↗
PubMed2001

Imaging tip formation in single-mode optical fibres.

The formation of probe tips is a crucial step in all forms of scanning probe microscopy (SPM). In this work single-mode optical fibres are chemically etched in a variable temperature bath of etchant solution (HF acid buffered with ammonium fluoride) to produce tips for optical SPM. Tip evolution is monitored by prematurely truncating the etching process and imaging the tip end-structure using atomic force microscopy (AFM). In the case of a visible regime single-mode fibre the AFM images show a remarkable ring structure in the central cladding region and a tip structure in the core with a central depression; this serves to demonstrate the efficacy of chemical etching for converting compositional variation to three-dimensional topography. In the case of a standard, single-mode optical communications fibre the (projected) tip cone angle is assessed from AFM images in the early stages of tip formation. Values of the cone angle thus determined, for different etch conditions, are compared to those predicted by a model in which the independently determined core and cladding etch rates, and core diameter are the sole determinants of the final tip geometry. The model was devised in the context of etching multi-mode fibres and is shown to be valid here for single-mode fibres within the range of experimental accuracy and etch conditions examined.

Journal Article↗
PubMedDate not supplied

Highly ordered thin films prepared with octabutoxy copper phthalocyanine complexes.

Langmuir-Blodgett (LB) films of copper (II) 1,4,8,11,15,18,22,25-octabutoxyphthalocyanine, nCuPc(OBu)(8), (non-peripheral substitution) and copper (II) 2,3,9,10,16,17,23,24-octabutoxyphthalocyanine, pCuPc(OBu)(8), (peripheral substitution), were fabricated and characterized by optical spectroscopy and scanning probe microscopy. The LB films were transferred onto hydrophilic substrates by vertical dipping. Although they posses relatively short polar substituents both compounds form smooth, uniform, dense, and highly stable LB monolayers composed of linear arrays of cofacial oligomers. The long range discotic assemblies of LB and spun cast films of pCuPc(OBu)(8) and nCuPc(OBu)(8) posses physical and chemical properties favorable for molecular electronic device application.

Journal Article↗
PubMedDate not supplied

Quantum size aspects of the piezoresistive effect in ultra thin piezoresistors.

Proximal probe sensors with an ability to detect extremely small forces (10(-15)-10(-18)N) play significant role in scanning probe microscopy applications. The detection of extremely low forces, require producing micromachined cantilevers with as small as possible spring constants, which is considered by the optimization of the sensor design. In the last year many papers describing the fabrication process of producing ultrathin cantilevers (below 100nm) with integrated piezoresistors for deflection read-out have been published. In the case of such cantilevers the required thickness of piezoresistors is in the range of 50nm. From a quantum mechanical point of view, an electrical carrier transport confinement in direction perpendicular to the cantilever surface can be expected and in this manner we have to consider the quantum size effect. The goal of the project described in this paper is to calculate and determine the piezoresistive coefficients in p type Si thin (under 50nm) piezoresistors taking into account the quantum size effect and to compare them with the corresponding coefficients for bulk material. The calculation of the band structure will use the mathematical apparatus of an exact analytical diagonalization six-band k.p model, modified with the envelope function approximation. The behaviour of the thin piezoresistors employed as integrated deflection read-out will be also discussed. Moreover, critical issues in the realization of piezoresistors formed by MOS transistor channel will be presented.

Journal Article↗
PubMed1997

Factors affecting protein interaction at sorbent interfaces.

Interactions between surfaces and macromolecules are the fundamentals in separation and detection of diverse solutes. In this very brief review the central aspects of protein-surface interactions are discussed with the intention of identifying the important factors influencing such processes and placing them in relation to the established knowledge in this field. Some perspectives of new techniques related to scanning probe microscopy for studying interactions at the nanometer level are also discussed.

Adsorption↗
PubMed2004

Properties of nanobelts and nanotubes measured by in situ TEM.

Characterizing the physical properties of individual nanostructures is challenging because of the difficulty in manipulating the objects of sizes from nanometers to micrometers. Most nanomeasurements have been carried using scanning probe microscopy. In this article, we demonstrate that transmission electron microscopy can be a powerful tool for quantitative measurements of the mechanical and electrical properties of a single nanostructure. Dual-mode resonance of an oxide nanobelt has been observed, and its bending modulus has been measured. An in situ technique was demonstrated for measuring the work function at the tip of a carbon nanotube. The ballistic quantum conductance of a multiwalled carbon nanotube was observed at room temperature using the setup in TEM. It is concluded that in situ measurement by directly linking structure with property is a future direction of electron microscopy.

Electric Conductivity↗
PubMed1998

Nanomanipulation Experiments Exploring Frictional and Mechanical Properties of Carbon Nanotubes.

: In many cases in experimental science, the instrument interface becomes a limiting factor in the efficacy of carrying out unusual experiments or prevents the complete understanding of the acquired data. We have developed an advanced interface for scanning probe microscopy (SPM) that allows intuitive rendering of data sets and natural instrument control, all in real time. The interface, called the nanoManipulator, combines a high-performance graphics engine for real-time data rendering with a haptic interface that places the human operator directly into the feedback loop that controls surface manipulations. Using a hand-held stylus, the operator moves the stylus laterally, directing the movement of the SPM tip across the sample. The haptic interface enables the user to "feel" the surface by forcing the stylus to move up and down in response to the surface topography. In this way the user understands the immediate location of the tip on the sample and can quickly and precisely maneuver nanometer-scale objects. We have applied this interface to studies of the mechanical properties of nanotubes and to substrate-nanotube interactions. The mechanical properties of carbon nanotubes have been demonstrated to be extraordinary. They have an elastic modulus rivaling that of the stiffest material known, diamond, while maintaining a remarkable resistance to fracture. We have used atomic-force microscopy (AFM) to manipulate the nanotubes through a series of configuration that reveal buckling behavior and high-strain resilience. Nanotubes also serve as test objects for nanometer-scale contact mechanics. We have found that nanotubes will roll under certain conditions. This has been determined through changes in the images and through the acquisition of lateral force during manipulation. The lateral force data show periodic stick-slip behavior with a periodicity matching the perimeter of the nanotube.

Journal Article↗
PubMedDate not supplied

Hepatocyte adhesion on a poly[N-p-vinylbenzyl-4-O-beta-D-galactopyranosyl-D-glucoamide]-coated poly(L-lactic acid) surface.

A surface of poly(l-lactic acid) (PLLA) was modified by coating with poly[N-p-vinylbenzyl-4-O-beta-d-galactopyranosyl-d-glucoamide] (PVLA), which was employed to improve the hepatocyte adhesion owing to its amphiphilic property and the presence of a hepatocyte recognition motif. We characterized the surface properties through water contact angle, electron spectroscopy for chemical analysis (ESCA), and scanning probe microscopy (SPM). The effect of PVLA coating on the efficiency of hepatocyte adhesion was evaluated by protein assay and optical microscopy. The surface morphology was under the influence of the concentration of PVLA coating solution and it played a critical role in hepatocyte adhesion. It was confirmed that galactose moieties in PVLA, which can bind to the asialoglycoprotein receptor (ASGPR) on hepatocytes, have a more dominant effect on hepatocyte adhesion than enhanced hydrophilicity. We suggest that the PVLA-PLLA system will be a useful method to improve hepatocyte cell seeding and adhesion onto scaffold matrices.

Animals↗
PubMed2005

Nano-welding by scanning probe microscope.

A novel method, nano-welding, analogous to spot welding at the nanoscale level using scanning probe microscopy (SPM) is presented. Using SPM oxidation of the underlying silicon, single-walled carbon nanotubes (SWNTs) have been immobilized to the surface at point sites along their lengths by the nano-welding. It is shown that this nano-welding process nearly has no structural damage to the SWNTs. This immobilization makes the SPM manipulation of SWNTs controllable and desirable, which is helpful for the construction of SWNT-based nanodevices.

Journal Article↗
PubMed1999

Facile Convergent Route to Molecular Caltrops.

The convergent syntheses of molecular caltrops are described starting from tetraethyl orthosilicate and using organolithium additions and Pd/Cu-catalyzed coupling methods. The caltrop core is based on a tetrahedral silicon atom, and there are three legs each bearing sulfur-tipped feet for adhesion to metallic surfaces. The forth prong (arm) is non-sulfur-bearing for projection upward from the surface. Rigid phenyleneethynylene segments are used for the legs and arms. These organosilicon caltrops may have utility as scanning probe microscopy tips.

Journal Article↗
PubMed2005

Computational study of the structure, dynamics, and photophysical properties of conjugated polymers and oligomers under nanoscale confinement.

Computational simulations were used to investigate the dynamics and resulting structures of several para-phenylenevinylene (PPV) based polymers and oligomers (PPV, 2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylenevinylene --> MEH-PPV and 2,5,2',5'-tetrahexyloxy-7,8'-dicyano-p-phenylenevinylene --> CN-PPV). The results show how the morphology and structure are controlled to a large extent by the nature of the solute-solvent interactions in the initial solution-phase preparation. Secondary structural organization is induced by using the solution-phase structures to generate solvent-free single molecule nanoparticles. Isolation of these single molecule nanostructures from microdroplets of dilute solution results in the formation of electrostatically oriented nanostructures at a glass surface. Our structural modeling suggests that these oriented nanostructures consist of folded PPV conjugated segments with folds occurring at tetrahedral defects (sp3 C-C bonds) within the polymer chain. This picture is supported by detailed experimental fluorescence and scanning probe microscopy studies. We also present results from a fully quantum theoretical treatment of these systems which support the general conclusion of structure-mediated photophysical properties.

Journal Article↗