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At least 289 records · Page 16Linked to original sources
PubMed1997

Subpiconewton intermolecular force microscopy.

We refined scanning probe force microscopy to improve the sensitivity of force detection and control of probe position. Force sensitivity was increased by incorporating a cantilever with very low stiffness, 0.1 pN/ nm, which is over 1000-fold more flexible than is typically used in conventional atomic force microscopy. Thermal bending motions of the cantilever were reduced to less than 1 nm by exerting feed-back positioning with laser radiation pressure. The system was tested by measuring electrostatic repulsive forces or hydrophobic attractive forces in aqueous solutions. Subpiconewton intermolecular forces were resolved at controlled gaps in the nanometer range between the probe and a material surface. These levels of force and position sensitivity meet the requirements needed for future investigations of intermolecular forces between biological macromolecules such as proteins, lipids and DNA.

Eyeglasses↗
PubMed2005

Characterization of batch-microfabricated scanning electrochemical-atomic force microscopy probes.

A procedure for the batch microfabrication of scanning electrochemical-atomic force microscopy (SECM-AFM) probes is described. The process yields sharp AFM tips, incorporating a triangular-shaped electrode (base width 1 microm, height 0.65 microm) at the apex. Microfabrication was typically carried out on (1)/(4) 3-in. wafers, yielding 60 probes in each run. The measured spring constant of the probes was in the range 1-1.5 N m(-1). To date, processing has been carried out twice successfully, with an estimated success rate for the fabrication process in excess of 80%, based on field emission-scanning electron microscopy imaging of all probes and current-voltage measurements on a random selection of approximately 30 probes. Steady-state voltammetric measurements for the reduction of Ru(NH(3))(6)(3+) in aqueous solution indicate that the electrode response is well-defined, reproducible, and quantitative, based on a comparison of the experimental diffusion-limited current with finite element simulations of the corresponding mass transport (diffusion) problem. Topographical imaging of a sputtered Au film with the SECM-AFM probes demonstrates lateral resolution comparable to that of conventional Si(3)N(4) AFM probes. Combined electrochemical-topographical imaging studies have been carried out on two model substrates: a 10-microm-diameter disk ultramicroelectrode (UME) and an array of 1-microm-diameter UMEs, spaced 12.5 microm apart (center to center). In both cases, an SECM-AFM probe was first employed to image the topography of the substrates. The tip was then moved back a defined distance from the surface and use to detect Ru(NH(3))(6)(2+) produced at the substrate, biased at a potential to reduce Ru(NH(3))(6)(3+), present in bulk solution, at a diffusion-controlled rate (substrate generation-tip collection mode). These studies establish the success of the batch process for the mass microfabrication of SECM-AFM tips.

Journal Article↗
PubMed2002

Spin-polarized scanning tunneling microscopy with antiferromagnetic probe tips.

We have performed low temperature spin-polarized scanning tunneling microscopy (SP-STM) of two monolayers Fe on W(110) using tungsten tips coated with different magnetic materials. We observe stripe domains with a magnetic period of 50 +/- 5 nm. Employing Cr as a coating material we recorded SP-STM images with an antiferromagnetic probe tip. The advantage of its vanishing dipole field is most apparent in external magnetic fields. This new approach resolves the problem of the disturbing influence of a ferromagnetic tip in the investigation of soft magnetic materials and superparamagnetic particles.

Journal Article↗
PubMed2002

Fabrication and characterization of probes for combined scanning electrochemical/optical microscopy experiments.

A technique that combines scanning electrochemical microscopy (SECM) and optical microscopy (OM) was implemented with a new probe tip. The tip for scanning electrochemicaVoptical microscopy (SECM/OM) was constructed by insulating a typical gold-coated near-field scanning optical microscopy tip using electrophoretic anodic paint. Once fabricated, the tip was characterized by steady-state cyclic voltammetry, as well as optical and electrochemical approach experiments. This tip generated a stable steady-state current and well-defined SECM approach curves for both conductive and insulating substrates. Durable tips whose geometry was a ring with < 1 microm as outer ring radius could be consistently fabricated. Simultaneous electrochemical and optical images of an interdigitated array electrode were obtained with a resolution on the micrometer scale, demonstrating good performance of the tip as both an optical and an electrochemical probe for imaging microstructures. The SECM feedback current measurements were successfully employed to determine tip-substrate distances for imaging.

Journal Article↗
PubMed1997

Mechanical and morphological properties of living 3T6 cells probed via scanning force microscopy.

Scanning Force Microscopy (SFM) is utilized to study living confluent 3T6 cells. Images based on mechanical contrast are obtained and related morphological details, mostly regarding the cell cytoskeleton, are analyzed. Moreover, numerical estimates of the local mechanical properties of the living cells are given, by extensive use of the "force-vs.-distance" operation mode. On the basis of the results obtained, the potentialities of SFM as an optimal new technique available for probing the cell cytoskeleton of unstained living cells, and assessing related models, are shortly discussed.

Actins↗
PubMed1990

Usefulness of MC-540 fluorescent dye as probe versus scanning electron microscopy for assessing membrane changes.

The effect of primaquine enantiomers on cell membranes of glucose-6-phosphate (G-6PD)-deficient erythrocytes was studied in vitro. Staining with merocyanine (Mc-540) showed that exposure to primaquine enantiomers produces significant fluorescence in G-6PD-deficient erythrocytes, indicating marked drug-induced alterations in membrane fluidity. Scanning electron microscopy (SEM) studies confirmed that primaquine enantiomers altered membrane morphology (by producing stomatocytes) in both normal and G-6PD-deficient cells. The concentration-dependent effect, however, was more pronounced with MC-540, a lipophylic dye, than with SEM (an expensive technique).

Erythrocyte Membrane↗
PubMed1995

Scanning electron microscopy-electron probe microanalysis study of the interface between apatite and wollastonite-containing glass-ceramic and rabbit tibia under load-bearing conditions after long-term implantation.

Glass-ceramic implants containing oxy- and fluoroapatite [Ca10(PO4)6(O, F2)] and beta-wollastonite (CaSiO3) were studied under load-bearing conditions in a segmental replacement model in the tibia of the rabbit. A 16-mm segment of the middle of the tibial shaft was resected at a point distal to the junction of the tibia and the fibula. The defect was replaced by a 15 mm-long hollow, cylindrical implant that was fixed by intramedullary nailing using Kirschner wire. The implants were 9 mm in diameter and 15 mm long bearing a central hole 3.05 mm in dianeter. The rabbits used were killed 6 months, 1 year, 18 months, and 2 years after implantation. The interface between the bone and the glass-ceramic was investigated by scanning electron microscopy-electron-probe microanalysis (SEM-EPMA). None of the glass-ceramic implants broke, and the glass-ceramic had bonded directly to the bone tissue without any intervening soft tissue. A calcium-phosphorus layer (Ca-P layer) was observed at the glass-ceramic/bone interface. This layer was 30-100 microns thick at 6 months after implantation, 60-110 microns thick at 1 year after implantation, 80-200 microns thick at 18 months, and 120-350 microns thick at 2 years. At the lateral surface of the glass-ceramic uncovered by the bone, the calcium-phosphorus layer was 50-80 microns thick at 6 months after implantation, 250-450 microns thick at 1 year, 300 approximately 400 microns thick at 18 months, and 300 microns thick at 2 years. The thickness of the calcium-phosphorus layer increased moderately after long-term implantation. However, it was difficult to estimate the rate of increase in the thickness of calcium-phosphorus layer.

Animals↗
PubMed2004

Scanning electrochemical microscopy: theory and characterization of electrodes of finite conical geometry.

Finite conical electrodes, which are of particular interest as probes for imaging of surfaces using scanning electrochemical microscopy (SECM), in kinetic studies and in probing thin films were investigated. Theoretical SECM tip current-distance feedback (approach) curves for a finite conical electrode were calculated by numerical (finite element) analysis and compared to an earlier approximate model. The SECM curves obtained depended on the ratio of the base radius of the cone to the height of the cone and on the thickness of the insulating sheath. A new approach to fabricating conical tips of Pt in glass is described. These were used to obtain approach curves over both electrically conducting and insulating substrates. Comparison of experimental and simulated SECM approach curves provided a sensitive method of evaluating the size and shape of finite conical electrodes.

Electrochemistry↗
PubMed1995

In Situ Localization of Azospirillum brasilense in the Rhizosphere of Wheat with Fluorescently Labeled, rRNA-Targeted Oligonucleotide Probes and Scanning Confocal Laser Microscopy.

The colonization of wheat roots by Azospirillum brasilense was used as a model system to evaluate the utility of whole-cell hybridization with fluorescently labeled, rRNA-targeted oligonucleotide probes for the in situ monitoring of rhizosphere microbial communities. Root samples of agar- or soil-grown 10- and 30-day-old wheat seedlings inoculated with different strains of A. brasilense were hybridized with a species-specific probe for A. brasilense, a probe hybridizing to alpha subclass proteobacteria, and a probe specific for the domain Bacteria to identify and localize the target bacteria. After hybridization, about 10 to 25% of the rhizosphere bacteria as visualized with 4(prm1),6-diamidino-2-phenylindole (DAPI) gave sufficient fluorescence signals to be detected with rRNA-targeted probes. Scanning confocal laser microscopy was used to overcome disturbing effects arising from autofluorescence of the object or narrow depth of focus in thick specimens. This technique also allowed high-resolution analysis of the spatial distribution of bacteria in the rhizosphere. Occurrence of cells of A. brasilense Sp7 and Wa3 was restricted to the rhizosphere soil, mainly to the root hair zone. C-forms of A. brasilense were demonstrated to be physiologically active forms in the rhizosphere. Strain Sp245 also was found repeatedly at high density in the interior of root hair cells. In general, the combination of fluorescently labeled oligonucleotide probes and scanning confocal laser microscopy provided a very suitable strategy for detailed studies of rhizosphere microbial ecology.

Journal Article↗
PubMed1994

In situ analysis of microbial consortia in activated sludge using fluorescently labelled, rRNA-targeted oligonucleotide probes and confocal scanning laser microscopy.

Activated sludge flocs are complex consortia of various micro-organisms. The community structures of samples taken from municipal sewage treatment plants were characterized using fluorescently labelled, 16S and 23S rRNA-targeted oligonucleotide probes in combination with confocal scanning laser microscopy (CSLM). In comparison with conventional epifluorescence microscopy, CSLM considerably improved the capability to visualize directly the spatial distribution of defined bacterial populations inside the sludge flocs. Analyses could be performed at high resolution undisturbed by problems such as autofluorescence or limited spatial resolution in thick samples. In addition, CSLM was used to analyse some structural properties of paraformaldehyde-fixed activated sludge flocs, such as floc size and homogeneity. Typical floc sizes were found to be in the range between 5 and 50 microns. Whereas most of the flocs were completely colonized by bacteria, there were also examples of flocs containing gas bubbles or particles in the interior.

Bacteria↗
PubMed2005

Electrostatic field and partial Fermi level pinning at the pentacene-SiO(2) interface.

Monolayer islands of pentacene deposited on silicon substrates with thermally grown oxides were studied by electric force microscopy (EFM) and scanning Kelvin probe microscopy (SKPM) in ultrahigh vacuum (UHV) after prior 10 min exposure to atmospheric ambient. On 25-nm-thick oxides, the pentacene islands are 0.5 V higher in electrostatic potential than the silicon dioxide background because of intrinsic contact potential differences. On 2-nm-thin oxides, tunneling across the oxides allows Fermi level equilibration with pentacene associated states. The surface potential difference depends on the doping of the underlying Si substrates. The Fermi level movement at the pentacene SiO(2) interface was restricted and estimated to lie between 0.3 and 0.6 eV above the pentacene valence band maximum. It is proposed that hole traps in the pentacene or at the pentacene-oxide interface are responsible for the observations.

Journal Article↗
PubMed2005

Numerical simulation of scanning electrochemical microscopy experiments with frame-shaped integrated atomic force microscopy--SECM probes using the boundary element method.

Integrated submicroelectrodes for combined AFM-SECM measurements are characterized with numerical simulations using the boundary element method. SECM approach curves and SECM images are calculated and analyzed for a model substrate containing pronounced topographical and electrochemical features. The theoretically calculated image has been compared to the experimental data and shows excellent quantitative agreement. Hence, the applicability of integrated AFM-SECM electrodes for combined electrochemical and topographical imaging and a profound theoretical description including quantification of the obtained results are demonstrated.

Electrochemistry↗
PubMed1998

Doxorubicin distribution in multicellular prostate cancer spheroids evaluated by confocal laser scanning microscopy and the "optical probe technique".

Multicell-mediated drug resistance is a major impediment for the effectiveness of chemotherapeutic approaches and has been shown to be a feature of many solid tumors. We used confocal laser scanning microscopy to evaluate the depth distribution of the fluorescent cytostatic drug doxorubicin (Dox) in two size classes of multicellular cancer spheroids (MCS) (psi150+/-50 microm and 350+/-50 microm). MCS (psi150+/-50 microm) solely consist of proliferating cells, whereas in MCS (psi350+/-50 microm) peripheral proliferating cell layers are followed in the depth of the tissue by drug resistant quiescent cell areas. A technique was developed which allows noninvasively to trace fluorescence distributions down to a depth of approximately 180 microm in living MCS. This was achieved by confocal radial recordings of the mean Dox fluorescence in 600 microm2 regions of interest (ROI), equidistantly spaced (10 microm) from the center of MCS towards their periphery. The resulting fluorescence intensity profiles were subsequently corrected for absorbtion and light scattering in the depth of the tissue by a convenient algorithm. A 10 min incubation of MCS (psi150+/-50 microm) with Dox (10 microM) led to a peripheral accumulation, after 2 h Dox was homogeneously distributed within the whole MCS. In contrast, after Dox treatment of MCS (psi350+/-50 microm) for 2 h, the drug was accumulated within the peripheral proliferating cell rim of 78+/-8 microm, whereas deeper, quiescent cell layers remained unstained. When MCS were incubated with verapamil, cyclosporin A, orthovanadate, and quinidine, which are known to reverse P-glycoprotein (Pgp)-mediated multidrug resistance (MDR), Dox accumulated also in deeper cell layers. Genistein and indometacin which reverse multidrug resistance mediated by the multidrug resistance-associated protein (MRP) were without effects. The optical probe technique proved to be well suited to study MDR in a living three dimensional tissue context.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

In situ identification of Legionellaceae using 16S rRNA-targeted oligonucleotide probes and confocal laser scanning microscopy.

Bacteria of the family Legionellaceae form a monophyletic group within the gamma-subclass of Proteobacteria. Based on comparative sequence analysis we constructed two oligonucleotide probes complementary to regions of 16S rRNA characteristic for Legionellaceae. Probe specificities were tested by whole-cell or dot-blot hybridization against 14 serogroups of Legionella pneumophila, 22 different Legionella spp. and 72 non-legionellae reference strains. Using optimized conditions both probes hybridized to all tested strains of L. pneumophila. Probes LEG226 and LEG705 hybridized to 71% and 90% of the Legionella species tested, respectively. With the exception of Methylomonas alba none of the non-target strains showed complete sequence homology within the target molecule. In a preliminary evaluation the results of classical techniques employing selective media, immunofluorescence and the probe assay were in good accordance for routine environmental and clinical isolates. L. pneumophila suspended in drinking water at approximately 10(3)-10(4) c.f.u. ml-1 could be rapidly detected by a combination of membrane filtration on polycarbonate filters and whole-cell hybridization. Even after incubation for 1 year a proportion of the released cells was still detectable. In situ hybridization also facilitated visualization of Legionella spp, cells in model biofilms. A combination of in situ hybridization and confocal laser scanning microscopy (CLSM) was used to analyse the three-dimensional arrangement of L. pneumophila within cells of the ciliated protozoan Tetrahymena pyriformis. Whole-cell probing with 16S rRNA-targeted oligonucleotides could, in the future, complement established techniques like immunofluorescence and PCR in ecological and epidemiological studies of Legionellaceae.

Animals↗