Atomic force microscopy of Bacillus spore surface morphology

Bacillus spore surface morphology was imaged with atomic force microscopy (AFM) to determine if characteristic surface features could be used to distinguish between four closely related species; Bacillus anthracis Sterne strain, Bacillus thuringiensis var. kurstaki, Bacillus cereus strain 569, and Bacillus globigii var. niger. AFM surface height images showed an irregular topography across the curved upper surface of the spores. Phase images showed a superficial grain structure with different levels of phase contrast and significant differences in average surface morphologies among the four species. Although spores of the same species showed similarities, there was significant variability within each species. Overall, AFM revealed that spore surface morphology is rich with information, which can be used to distinguish a sample of about 20 spores from a similar number of spores of closely related species. Statistical analysis of spore morphology from a combination of amplitude and phase images for a small sample allows differentiation between, B. anthracis and its close relatives.     

Atomic force microscopy for transition metals and tip structure effects

We study the influence of tip morphology on the contrast in atomic force microscopy (AFM) for transition metals tips and samples (T/S). For this, we consider a model based on the real space tight binding approach taking into account the electronic structure of the T/S system. Images of an W(001) surface obtained with atomically sharp or blunt tips are considered. The resolution of AFM images, in the attractive force range, is discussed for monatomic (multiatomic) apex(es) tips. Images of clusters deposited on the W(001) surface are also obtained.     

Surface structure of fluorine-graphite intercalation compounds observed by atomic force microscopy

Atomic force microscopy (AFM) has been used to image fluorine-graphite intercalation compounds (C_3.5F; stage 1 + 2, C_3.9F; stage 2, (CF)_n; stage 1). For all samples the atomic resolution is achieved. The AFM image of the C_3.5F compound exhibits a new orthorhombic superlattice structure (a = 0.49 nm, b = 0.42 n, ∠a−b = 90°). In the AFM images of C_3.5F and (CF)_n the protrusions are attributed to fluorine atoms. The AFM image of C_3.9F exhibits a centered hexagonal structure similar to highly oriented pyrolytic graphite (HOPG).     

Atomic force microscopy characterization of the surface wettability of natural fibres

Natural fibres represent a readily available source of ecologically friendly and inexpensive reinforcement in composites with degradable thermoplastics, however chemical treatments of fibres are required to prepare feasible composites. It is desirable to characterize the surface wettability of fibres after chemical treatment as the polarity of cellulose-based fibres influences compatibility with a polymer matrix. Assessment of the surface wettability of natural fibres using conventional methods presents a challenge as the surfaces are morphologically and chemically heterogeneous, rough, and can be strongly wicking. In this work it is shown that under atmospheric conditions the adhesion force between an atomic force microscopy (AFM) tip and the fibre surface can estimate the water contact angle and surface wettability of the fibre. AFM adhesion force measurements are suitable for the more difficult surfaces of natural fibres and in addition allow for correlations between microstructural features and surface wettability characteristics.     

Atomic force microscopy of the mirror cleavage surface of defect TGS crystals

The nanorelief of the mirror cleavage surface of triglycine sulfate crystals with various defect densities has been studied. Typical nanorelief features of both defect and clean (without artificial impurity) crystals are two-dimensional rounded bumps (dips) of equal height (depth) of about half the lattice parameter and sub-micrometer lateral sizes. The density, lateral size, and scatter of such 2D structures are several times larger for defect crystals than for clean ones. The correlation between the crystal defect density and the density and lateral size of 2D structures on the cleavage surface has been revealed. Conclusions are made about the defect origin of the typical nanorelief on the mirror cleavage.     

Metallic reflectance of AsF5-graphite intercalation compounds

Room temperature measurements of the 0.07–2.0 eV optical reflectance of carefully prepared stage 1–4 AsF₅-graphite intercalation compounds have been performed. Stages 1–3 show simple metallic behavior with a well-defined plasma edge. Curve fits to the data give good agreement between dc and optical conductivities for stage 1 and 2. Comparison between stage 2 data for AsF₅ and HNO₃ compounds suggests that the higher conductivity of the former arises from a longer carrier relaxation time rather than from a greater carrier density.     

Atomic scale Kelvin probe force microscopy studies of the surface potential variations on the TiO2(110) surface

From an interplay of simultaneous Kelvin probe force microscopy and noncontact atomic force microscopy we study atomic-scale variations in the electronic surface potential on TiO(2)(110). Both imaging channels reveal an atomic contrast reflected by the geometry and charged state of the alternating rows of Ti and O surface atoms. From a thorough cross-section analysis we add significant trust to the concept of a local contact potential difference, and determine from this the chemical identity of individual surface species and their role in setting up the local surface potential.     

原子力显微镜研究DPPC磷脂多层膜结构与力学性能

应用原子力显微镜(AFM)首先研究了在蔗糖溶液中二棕榈酰磷脂酰胆碱(DPPC)磷脂双层膜的结构,分析了其力学性能;其次,研究了在纯水中、CaCl2溶液中的DPPC磷脂多层膜的结构特性和杨氏模量.实验结果表明,在CaCl2溶液中DPPC多层膜的水层厚度大于在纯水中厚度,在CaCl2溶液中多层膜的杨氏模量变小.     

Synthesis of ZnS nanoparticles on a solid surface: Atomic force microscopy study

In this work, zinc sulfide (ZnS) nanoparticles had been synthesized on DNA network/mica and mica surface, respectively. The synthesis was carried out by first dropping a mixture of zinc acetate and DNA on a mica surface for the formation of the DNA networks or zinc acetate solution on a mica surface, and subsequently transferring the sample into a heated thiourea solution. The Zn²⁺ adsorbed on DNA network/mica or mica surface would react with S²⁻ produced from thiourea and form ZnS nanoparticles on these surfaces. X-ray diffraction and atomic force microscopy (AFM) were used to characterize the ZnS nanoparticles in detail. AFM results showed that ZnS nanoparticles distributed uniformly on the mica surface and deposited preferentially on DNA networks. It was also found that the size and density of ZnS nanoparticles could be effectively controlled by adjusting reaction temperature and the concentration of Zn²⁺ or DNA. The possible growth mechanisms have been discussed in detail.     

Atomic force microscope studies of CuCl island formation on CaF2(111) substrates

We have grown by molecular beam epitaxy (MBE) CuCl thin films at various thicknesses and substrate temperatures on CaF₂(111) substrates. Atomic force microscope (AFM) topographs reveal that islanding is the dominant growth mechanism. Quantitative analysis of the AFM data enabled us to determine the amount of the substrate remaining exposed after the deposition as well as the total amount of CuCl deposited. We calculated the reciprocal-space height correlation function, 〈 | h(q, t) |each of our films and compared them to the predictions of the shadowing growth theory, which enabled us to extract the important kinetic parameter of surface diffusion length for the growth condition of each of the four films.     

Atomic force microscopy probing of cell elasticity

Atomic force microscopy (AFM) has recently provided the great progress in the study of micro- and nanostructures including living cells and cell organelles. Modern AFM techniques allow solving a number of problems of cell biomechanics due to simultaneous evaluation of the local mechanical properties and the topography of the living cells at a high spatial resolution and force sensitivity. Particularly, force spectroscopy is used for mapping mechanical properties of a single cell that provides information on cellular structures including cytoskeleton structure.

This entry is aimed to review the recent AFM applications for the study of dynamics and mechanical properties of intact cells associated with different cell events such as locomotion, differentiation and aging, physiological activation and electromotility, as well as cell pathology. Local mechanical characteristics of different cell types including muscle cells, endothelial and epithelial cells, neurons and glial cells, fibroblasts and osteoblasts, blood cells and sensory cells are analyzed in this paper.     

Atomic force microscopy for the investigation of molecular and cellular behavior

The present review details the methods used for the measurement of cells and their exudates using atomic force microscopy (AFM) and outlines the general conclusions drawn by the mechanical characterization of biological materials through this method. AFM is a material characterization technique that can be operated in liquid conditions, allowing its use for the investigation of the mechanical properties of biological materials in their native environments. AFM has been used for the mechanical investigation of proteins, nucleic acids, biofilms, secretions, membrane bilayers, tissues and bacterial or eukaryotic cells; however, comparison between studies is difficult due to variances between tip sizes and morphologies, sample fixation and immobilization strategies, conditions of measurement and the mechanical parameters used for the quantification of biomaterial response. Although standard protocols for the AFM investigation of biological materials are limited and minor differences in measurement conditions may create large discrepancies, the method is nonetheless highly effective for comparatively evaluating the mechanical integrity of biomaterials and can be used for the real-time acquisition of elasticity data following the introduction of a chemical or mechanical stimulus. While it is currently of limited diagnostic value, the technique is also useful for basic research in cancer biology and the characterization of disease progression and wound healing processes.     

Atomic force microscopy studies on phase transitions and surface morphology transformation of CMTC crystals

Atomic force microscopy (AFM) has been used to investigate the phase transitions and surface morphology transformation of cadmium mercury thiocyanate (CMTC) crystals, which are highly efficient nonlinear optical (NLO) materials for generating blue-violet light by laser frequency doubling. Amorphous aggregates at the crystalline steps become greatly contracted and much more crystalloid after the crystal was kept for one day. Elimination of dangling bonds, which lower the surface free energy at the crystal surface, and structural adjustment inside the crystal are assumed to cause this phase transition. Surface morphology transformations were also observed in CMTC crystals during and after multiple scanning by AFM tips. We have visualized the continuous translation process from two-dimensional nuclei to trigonal microcrystals with almost equal sizes during multiple scanning. In other cases, however, the surface morphology did not change at all during scanning, but became greatly altered hours after scanning. These experimental results suggest that reconstruction is a characteristic growth phenomenon on CMTC crystal surfaces. Reconstruction probably results from the formation of intervening metastable phases that have the potential to arrive at more stable stages; however, multiple scanning of AFM tips greatly affects this translation process. Received: 28 August 2001 / Accepted: 7 November 2001 / Published online: 29 May 2002     

Atomic force microscopy as a suitable technique for surface characterization of activated composite membranes for metal ion facilitated transport

Activated composite membranes (ACM) have been made based on a polysulfone layer over a non-woven support with a dense layer of aromatic polyamide, and deposited on the polysulfone using interfacial polymerisation by a carrier agent – di(2-ethylhexyl) dithiophosphoric acid – added to the membranes at several concentrations. Two polysulfone supports have been used, one of them commercial (PSf-Com) an other made ad hoc by us (PSf-GTS).The membrane structure has been characterised by both atomic force microscopy (AFM) and scanning electron microscopy (SEM). Firstly, the two polysulfonic bases were studied. The results show that structurally both are quite similar. PSf-Com presents a more regular sponge like structure in the bulk with some macrovoids randomly distributed, with an average size of 25 μm.The results obtained demonstrate that after interfacial polymerisation, some structural defects appear with relatively big valleys and peaks. The roughness has been studied versus the AFM scan size, which allowed the evaluation of the corresponding fractal dimensions. This permitted a detailed comparison and detection of the differences and similarities of the surface structure of all the membranes studied.The membranes made on PSf-GTS, whose surface structure seems to yield a better coverage of polyamide, gave good performances in the extraction of certain heavy metals. After extraction the membranes were analysed by EDS to confirm the permanence of the extractant along with some deposits of salt and extracted ions. PACS 68.37.Ps; 68.35.Ct; 82.39.Wj     

Atomic force microscopy investigation of electrochemically produced carbon nanotubes

Carbon nanostructures have been synthesized in NaCl-MgCl₂ and in NaCl-CaCl₂ salt melts and the extracted material was investigated by tapping-mode atomic force microscopy (TM-AFM) and scanning electron microscopy. Some interesting new nanostructures were found and investigated as torus-shaped carbon structures with a ring diameter of 300-400 nm and 10-15 nm height. These tori are closely related to the wrapped SWNT rings described recently. They are probably formed during the electrolysis. A chain-like structure was also revealed.     

Atomic force microscopy investigation of chemically stabilized pericardium tissue

Native and chemically stabilized porcine pericardium tissue was imaged by the contact mode atomic force microscopy (AFM), in air. Chemically stabilized pericardium is used as a tissue-derived biomaterial in various fields of the reconstructive and replacement surgery. Collagen type I is the main component of the fibrous layer of the pericardium tissue. In this study, the surface topography of collagen fibrils in their native state in tissue and after chemical stabilization with different cross-linking reagents: glutaraldehyde (GA), dimethyl suberimidate (DMS) and tannic acid (TA) was investigated. It has been found that chemical stabilization causes considerable changes in the surface topography of collagen fibrils as well as in the spatial organization of the fibrils within the tissue. The observed changes in the D-spacing pattern of the collagen fibril correspond to the formation of intrafibrilar cross-links, whereas formation of interfibrilar cross-links is mainly responsible for the observed tangled spatial arrangement of fibrils and crimp structure of the tissue surface. The crimp structure was distinctly seen for the GA cross-linked tissue. Surface heterogeneity of the cross-linking process was observed for the DMS-stabilized tissue. SDS-PAGE electrophoresis was performed in order to evaluate the stabilization effect of the tissues treated with the cross-linking reagents. It has been found that stabilization with DMS, GA or TA enhances significantly the tissue resistance to SDS/NaCl extraction. The relation between the tissue stability and changes in the topography of the tissue surface was interpreted in terms of different nature of cross-links formed by DMS, GA and TA with collagen.     

Atomic force microscopy observation of peroxynitrite-induced erythrocyte cytoskeleton reorganization

Atomic force microscopy (AFM) was used to study surface layers of fixed intact erythrocytes. Advantages of simultaneous analysis of surface topography and lateral force maps in the investigation of cytoskeleton structure were shown. Fractal analysis was applied to the lateral force maps of erythrocyte surfaces to evaluate the complexity of the cytoskeleton. Peroxynitrite was used as an oxidant to induce changes in the cytoskeleton structure of intact erythrocytes. Peroxynitrite action on whole blood leads to local abnormalities in the erythrocyte cytoskeleton structure, as well as cytoskeleton reorganization in protruded regions of crenated erythrocytes.     

Atomic force microscopy of bamboo-shaped multiwalled carbon nanotube structures

Atomic force microscopy (AFM) was employed for the morphology measurements of bamboo-shaped multiwalled carbon nanotubes (BS-MWNTs) grown by thermal chemical vapor deposition on Fe catalyst deposited SiO₂/Ti substrates. Greater diameters and compartment distances of the bamboo structures were observed for the BS-MWNTs grown at 950 °C than for those grown at 850 °C.     

Atomic force microscopy of cobalt nanoparticles with electro-catalytic properties

A method of controlled potential electrodeposition of the cobalt nanoparticles with sizes from 30 to 400 nm on the surface of highly oriented pyrolytic graphite has been developed. The images of nanoparticles were obtained with an atomic force microscope. A computer program was applied to obtain the size distribution of electrodeposited particles depending on the electrodeposition potential, electrolytic concentration, and deposition time. Using voltammetry it has been established that the cobalt nanoparticles with the diameter of about 50 nm show the maximal catalytic activity during electro-oxidation of ethanol.