Resolution Atomic Force Microscopy Images Research Articles

Strain energy and lateral friction force distributions of carbon nanotubes manipulated intoshapes by atomic force microscopy

The interplay between local mechanical strain energy and lateral frictional forcesdetermines the shape of carbon nanotubes on substrates. In turn, because of itsnanometer-size diameter, the shape of a carbon nanotube strongly influences its localelectronic, chemical, and mechanical properties. Few, if any, methods exist for resolving thestrain energy and static frictional forces along the length of a deformed nanotubesupported on a substrate. We present a method using nonlinear elastic rod theory in whichwe compute the flexural strain energy and static frictional forces along the length of singlewalled carbon nanotubes (SWCNTs) manipulated into various shapes on a cleanSiO2 substrate. Using only high resolution atomic force microscopy images of curved singlewalled nanotubes, we estimate flexural strain energy distributions on the order ofattojoules per nanometer and the static frictional forces between a SWCNT andSiO2 surface to be aminimum of 230 pN nm−1.

Two-dimensional scaffold layer formations on a solid surface through xanthan polysaccharide: Temperature effect

The influences of temperature on xanthan biopolymer assemblies on a two-dimensional surface have been thoroughly studied. High resolution atomic force microscope images show that the xanthan nanofibrils can be used to build up well-dispersed 2D scaffold layer after 1 day annealing at 35 °C. By increasing annealing temperatures (60 °C, 90 °C) of xanthan solutions, the well-dispersed layers can be produced rapidly (6 h, 0.5 h) with micro-sized pore structures. The xanthan scaffold with pore structures potentially allows accommodating micro-sized cells for tissue engineering.

An Atomic Force Microscopy Study of the Mechanism of Cellulose Biodegradation

Cellulose, a biopolymer consisting of long chains of β (1→4) linked glucose sugars, is used as structural material by plants, bacteria, and some animals, and is the most abundant polymer on earth. Degradation of cellulose to glucose, a sugar easily fermented to ethanol, occurs by the enzymatic hydrolysis of cellulose by cellulase enzymes. The enzymes have a complex structure including carbohydrate binding modules responsible for binding the enzyme to the cellulose and catalytic domains responsible for the biodegradation of cellulose. Atomic force microscopy (AFM) was used to study native cellulose films prepared from a bacterial cellulose source, Acetobacter xylinum, using a novel application of the Langmuir-Blodgett technique. These films allowed high resolution AFM images of single fibers and their microfibril structure to be obtained. Further in situ AFM imaging studies of single cellulose fibers were performed in solution using cellulolytic enzymes. By using genetically modified enzymes with either active or inactive catalytic domains, the catalytic and binding properties of the enzyme-cellulose system can be independently investigated. Studying the modular enzyme action separately will provide insight into the mechanism of cellulose binding and contribute to our understanding of the biodegradation process.

Bacterial Cell Wall Peptidoglycan at Single Molecule Resolution

The major structural component of bacterial cell walls is the peptidoglycan sacculus, which is one of nature's strongest and largest macromolecules that maintains the large internal pressure within the cell while allowing the transport of molecules into and out of the cell and cell growth. The three-dimensional structure of this unique biopolymer is controversial, and two models have been proposed: the planar model, in which the glycan strands lie in the plane of the cell surface, and the scaffold model, in which the glycan strands lie perpendicular to the cell surface. In this study we have used atomic force microscopy (AFM) to investigate the high resolution structure of isolated, intact sacculi of Escherichia coli K12 bacteria. Atomic force microscopy (AFM)-single molecule force spectroscopy was performed on single sacculi exposed to the tAmiB enzyme which cleaves the peptide-glycan bonds. Surprisingly, the measurements revealed individual strands of up to 250 nm in length. This finding combined with high resolution AFM images recorded on hydrated sacculi provide evidence for the validity of the planar model for the peptidoglycan structure in Gram-negative bacteria.

Probe Tips Functionalized with Colloidal Nanocrystal Tetrapods for High‐Resolution Atomic Force Microscopy Imaging

Probe Tips Functionalized with Colloidal Nanocrystal Tetrapods for High‐Resolution Atomic Force Microscopy Imaging

Models of Toxic β-Sheet Channels of Protegrin-1 Suggest a Common Subunit Organization Motif Shared with Toxic Alzheimer β-Amyloid Ion Channels

Antimicrobial peptides (AMPs) induce cytotoxicity by altering membrane permeability. The electrical properties of membrane-associated AMPs as well as their cellular effects have been extensively documented; however their three-dimensional structure is poorly understood. Gaining insight into channel structures is important to the understanding of the protegrin-1 (PG-1) and other AMP cytolytic mechanisms, and to antibiotics design. We studied the β-sheet channels morphology using molecular dynamics simulations. We modeled PG-1 channels as intrinsic barrel-stave and toroidal membrane pores, and simulated them in zwitterionic and anionic lipid bilayers. PG-1 channels consist of eight β-hairpins in a consecutive NCCN (N and C represent the β-hairpin's N- and C-termini) packing organization yielding antiparallel and parallel β-sheet channels. Both channels preserve the toroidal, but not the barrel-stave pores. The two lipid leaflets of the bilayer bend toward each other at the channels’ edges, producing a semitoroidal pore with the outward-pointing hydrophobic residues preventing the polar lipid headgroups from moving to the bilayer center. In all simulated lipid environments, PG-1 channels divide into four or five β-sheet subunits consisting of single or dimeric β-hairpins. The channel morphology with subunit organization is consistent with the four to five subunits observed by NMR in the POPE/POPG bilayer. Remarkably, a β-sheet subunit channel motif is in agreement with Alzheimer ion channels modeled using the universal U-shape β-strand-turn- β-strand structure, as well as with high resolution atomic force microscopy images of β-amyloid channels with four to six subunits. Consistent with the toxic β-amyloid channels that are ion-conducting, the PG-1 channels permeate anions.

Atomic force microscopy reveals binding of mRNA to microtubules mediated by two major mRNP proteins YB-1 and PABP

A significant fraction of mRNAs is known to be associated in the form of mRNPs with microtubules for active transport. However, little is known about the interaction between mRNPs and microtubules and most of previous works were focused on molecular motor:microtubule interactions. Here, we have identified, via high resolution atomic force microscopy imaging, a significant binding of mRNA to microtubules mediated by two major mRNP proteins, YB-1 and PABP. This interaction with microtubules could be of critical importance for active mRNP traffic and for mRNP granule formation. A similar role may be fulfilled by other cationic mRNA partners.

The effect of bulk iron concentration and heterogeneities on the copper activation of sphalerite

Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to study the Cu activation of the (1 1 0) surface of sphalerites with Fe content varying from 0 to 14.79 wt%. Time resolved AFM images show the development of surface oxidation products at high-energy step edges. These small protrusions evolve into larger conglomerates and finally full surface coverage with time. Surface morphology changes show an increase in the number of cleavage steps and the size of precipitates as a function of Fe concentration. Both of these factors contribute to the increased rate of Cu activation of high Fe sphalerite as compared to low Fe sphalerite. XPS analysis of the sphalerites Cu activated for 1 h at pH 5, indicates an increased Cu concentration and the formation of disulphide and polysulphide that correlates with an increase in bulk Fe content.

Immunological identification of fibrinogen in dual-component protein films by AFM imaging

The success of long-term blood-contacting implanted devices is largely dependent upon the interaction of the blood components with the device biomaterial surface. The ability to study these interactions has been hindered by a lack of methods to measure single-molecule interactions in complex multi-protein environments similar to the environment found in vivo. In this paper, we demonstrate the use of atomic force microscopy (AFM) in conjunction with gold nanolabels to detect the protein fibrinogen under aqueous conditions without the topographical clues usually necessary for high resolution visualization. BSA was patterned onto both muscovite mica and plasma-treated polydimethylsiloxane (PDMS) substrates and these test substrates were subsequently backfilled with fibrinogen to yield a featureless protein layer. The fibrinogen in this dual-protein layer was detected using high resolution AFM imaging following infusion of anti-fibrinogen conjugated with nanogold particles. This AFM immuno-detection technique will potentially be applicable to complex multi-component protein films adsorbed on clinically relevant polymers used in medical devices.

On the Horizon From the ORS

On the Horizon From the ORS

Friction-anisotropy dependence in organic self-assembled monolayers

A study in order to understand the origin of the friction at the nanometer scale has been performed. Atomic force microscopy (AFM) has been used to measure the mechanical and frictional properties of self-assembled monolayers of the oligothiophene derivative 4-(5″″-tetradecyl-[2,2′;5′,2″;5″,2‴;5‴,2″″] pentathiophen-5-yl)-butyric acid (C14-5TBA) on mica. The films were prepared by drop casting a dilute THF solution (1 mM) of the oligothiophene on mica. The molecules adsorb on mica through the carboxylic group, and expose the alkyl chain (CH 2) 13CH 3. Instead of complete monolayers, islands were produced to facilitate measurements of the film height. By applying load to the tip a compression of the molecules from an initial height of 4.1 nm to a final height of 2.6 nm was achieved which we attribute to deformation of the alkyl chains. We previously observed that the oligothiophene derivative 4-(5″″-decyl-[2,2′;5′,2″;5″,2‴;5‴,2″″] pentathiophen-5-yl)-butyric acid (C10-5TBA), exhibits strong friction anisotropies showing different domains of friction. The topographic images for both of these films reveals that they form molecularly flat films. However, the longer alkyl chains of the C14-5TBA induces better organization of the molecules as shown by the lattice resolved AFM images obtained. Well-ordered molecular structures were seen with measured unit cell dimensions of 0.65 and 0.46 nm. The ability to resolve the lattice structure of these films allows us to measure friction in different lattice structure domains, and the results show strong friction anisotropy.

Preventing biological activity of Ulocladium sp spores in artifacts using 157-nm laser

High resolution atomic force microscopy images of immobilized Ulocladium sp cultures on silicon wafers reveal the cessation of biological activity after laser illumination at 157 nm. Laser light dissociates the external multilayered proteinaceous membrane of the spores, reducing their thickness to a critical value prior to cell explosion due to the high internal pressure of the nucleus. The population of a monolayer culture was successfully destroyed following illumination with 150 laser pulses at the fluence of 1 mJ/cm2 per pulse. A thin layer of 0.3 nm was removed on the average from the external membrane per pulse, and a thin layer of 45 nm had to be removed from the external membrane before cell explosion. Thus, the use of a 157-nm laser is an effective and controllable method for stopping biological activity of Ulocladium sp spores in artifacts. This finding supports previous results of using 157-nm lasers against foxing in historic paper preservation.

Development of a metal–tip cantilever for noncontact atomic force microscopy

We report on a focused-ion-beam fabrication of a metal–tip cantilever for noncontact atomic force microscopy (AFM) and demonstrate its superior performance by observing atomically resolved AFM images of the Si(111)7×7 surface. Characterization of the tip apex by transmission electron microscope revealed that the tip radius is less than 5nm. Detrimental changes in the resonance frequency and the Q factor of the cantilever due to the attachment of the metal tip are small and do not affect the performance of the AFM imaging. Since the fabrication technique is applicable to any materials, various functional probes can be developed with this method.

Self-organization of phthalocyanines on Al2O3 (1120) in aligned and ordered films

We studied the self-organization process of F16CuPc films (20–30 ML) on stepped Al2O3 (1120) substrates. X-ray diffraction measurements revealed a highly ordered layered structure with the molecules in a nearly upright configuration. The morphology, investigated by atomic force microscopy, consisted of long (several microns) and narrow (20–100 nm) needlelike terraces unidirectionally aligned along one of the main crystallographic directions of the Al2O3 (1120) surface. High resolution atomic force microscopy images revealed in-plane molecular order with the molecular stacking direction parallel to the needlelike terraces. Such anisotropic morphology is the result of a self-organization process of F16CuPc in elongated crystallites driven to a preferential orientation by the interaction with the substrate. Spectroscopic ellipsometry showed that these films exhibit anisotropic optical properties correlated with the molecular arrangement.

Three-dimensional imaging of living and dying neurons with atomic force microscopy.

Atomic Force Microscopy (AFM) has been used to image the morphology of developing neurons and their processes. Additionally, AFM can physically interact with the cell under investigation in numerous ways. Here we use the AFM to both three-dimensionally image the neuron and to inflict a nano/micro-puncture to its membrane. Thus, the same instrument used as a tool to precisely penetrate/cut the membrane at the nanoscale level is employed to image the morphological responses to damage. These first high resolution AFM images of living chick dorsal root ganglion cells and cells of sympathetic ganglion and their growing processes provide confirmation of familiar morphologies. The increased resolution of the AFM revealed these structures to be significantly more complex and variable than anticipated. Moreover we describe novel, dynamic, and unreported architectures, particularly large dorsally projecting ridges, spines, and ribbons of cytoplasm that appear and disappear on the order of minutes. In addition, minute (ca. 100 nm) hair-like extensions of membrane along the walls of nerve processes that also shift in shape and density, appearing and disappearing over periods of minutes were seen. We also provide "real time" images of the death of the neuron cell body after nano/micro scale damage to its membrane. These somas excreted their degraded cytoplasm, revealed as an enlarging pool beneath and around the cell. Conversely, identical injury, even repeated perforations and nanoslices, to the neurite's membrane do not lead to demise of the process. This experimental study not only provides unreported neurobiology and neurotrauma, but also emphasizes the unique versatility of AFM as an instrument that can (1) physically manipulate cells, (2) provide precise quantitative measurements of distance, surface area and volume at the nanoscale if required, (3) derive physiologically significant data such as membrane pressure and compliance, and (4) during the same period of study--provide unexcelled imaging of living samples.

Selective growth of carbon nanotube on scanning probe tips by microwave plasma chemical vapor deposition

We have selectively grown carbon nanotubes on the probe tip of an atomic force microscope by microwave plasma chemical vapor deposition. The catalyst domain was defined on the tip apex of an Si based scanning probe by local electric field induced oxidation of a TiN cap layer, under which the cobalt catalyst layer was predeposited on the probe surface. High resolution atomic force microscopy images of an SiO2 trench pattern are demonstrated using the carbon nanotube tip. The nanotube tip fabrication method is simple and compatible with existing thin film process technology.

Epitaxial growth of quaterthiophene thin films by organic molecular beam deposition

Organic molecular beam deposition (OMBD) in ultra-high vacuum is a valuable technique to carefully control the solid-state structure and properties of molecular thin films. Quaterthiophene (4T) and α, ω-dihexyl-quaterthiophene (DH4T) thin films deposited by OMBD on potassium acid phthalate are investigated by atomic force microscopy (AFM). Direct evidence of epitaxial growth of the thin films is obtained by molecular resolution AFM images. The comparison between 4T and DH4T films reveals the role of chemical substituent groups in modifying the film properties.

K-0720 高分解能AFM・ナノインデンテーション複合装置によるマルテンサイト鋼の強度解析(G03-3 ナノインデンテーション)(G03 材料力学部門一般講演)

We developed a system of combining ultra-micro indentation testing and high resolution atomic force microscopy (AFM). The developed instrument is able to obtain high resolution AFM images by Si tip and conduct indentation tests by a diamond indenter without moving the specimen. The strength of quenched and tempered SCM415 steel was analyzed by the system. The penetration depth under the constant force was dependent on the existence of boundaries and cardides.

Imaging of collagen type III in fluid by atomic force microscopy.

Type III collagen is a component of the basement membrane of endothelial cells, and may play a role in the interaction between hemostatic system proteins and the basement membrane of blood vessels. To begin to investigate these structural interactions, we have imaged type III collagen in solution by atomic force microscopy. A 20 microg/ml solution of type III collagen in bicarbonate buffer (pH 9.5) from calf skin was deposited onto a freshly cleaved mica substrate. Atomic force microscopy images were acquired using a fluid cell and tapping mode with oxide-sharpened silicon nitride probes 2, 3, and 4 hours after deposition of the collagen onto the mica. Two-hour preparations displayed fibrillar networks with well-defined sites of nucleation and lateral growth. At 3 and 4 hour polymerizations, more mature fibrils of increasing lengths, diameters, and complexity were observed. Fibrils appeared to be aligning and twisting (helical formation) to form a mature fibril with a higher mass per unit area. Interestingly, the mature fibrils appeared larger centrally with tapered ends displaying declining slopes. These observations compare favorably with those previously published on collagen type I assembly [Gale et al. (1995) Biophys. J. 68:2124-2128]. High resolution atomic force microscopy images of type III collagen in solution should provide a template for observation of the interactions between basement membrane components and hemostatic system proteins present in cardiovascular disease.

Structure and Growth of Hexyl Azobenzene Thiol SAMs on Au(111)

The structure and growth of functionalized thiol self-assembled monolayers (SAMs) on Au(111) derived from a new compound, 12-(4-((4-hexylphenyl)azo)phenoxy)dodecane-1-thiol (“hexyl azobenzene thiol”), were examined by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), dynamic contact angles, Fourier transform infrared-reflection absorption spectroscopy (FTIR-RAS), and reflection UV−vis absorption spectroscopy. The hexyl azobenzene thiol SAM showed adsorption kinetics comparable to that of alkanethiols. At the initial stage of SAM growth, formation of nanosize domains resulting from the rearrangement of molecules on the surface was confirmed in a similar manner as for alkanethiol SAMs with long alkyl chains. The hexyl azobenzene thiol SAM exhibited a unique molecular ordering due to the intermolecular interaction between tail groups. Molecular resolution AFM images revealed an expanded lattice (nearest neighbor spacings, a = 5.3 ± 0.1 Å, b = 5.6 ± 0.1 Å; angle between the two axes, φ = 85 ± 1°) relative to that of simple azobenzene-terminated SAMs, due to the influence of the hexyl-terminal groups attached to the para-position of the azobenzene moieties. Average molecular tilt and twist angles (α = 14°, β = 42°) were determined by quantitative analysis of C−H stretching mode for FTIR-RAS data. The reflection UV−vis absorption spectra implied that the long axes of the trans-azobenzene moieties were aligned normal to the plane of surface in fully covered SAMs, while those were more tilted (aligned more parallel to the surface plane) in the submonolayers.