Effect of Audible Sounds on the Forces Acting between Charged Surfaces in Water.

We aimed to determine if audible sounds could change the forces acting between charged surfaces in water and their electric double layers (EDLs). This was achieved by using an atomic force microscope to measure force-distance curves between a microsized silica particle attached to a cantilever (probe) and a silicon wafer in water in the absence and presence of sound. Sound decreased the repulsive forces acting between the probe and silicon wafer, where the range and magnitude of the forces decreased with an increase in the sound frequency from 300 to 15000 Hz. The decrease in the force range was explained by a decrease in the EDL thickness. This result was explained by (1) the shrinkage of the EDL by a high-pressure region of the sound wave, where an increased sound frequency caused the number of high-pressure regions that passed between the probe and the substrate to increase and (2) the inability of the EDL to fully re-expand to its original thickness during the time that a low-pressure region of the sound wave was applied. The decrease in the force magnitude with a sound frequency increase was explained by the increased screening of charged surfaces that accompanies a decrease in the EDL thickness. An increase in the force measurement speed caused the sound waves to reduce the repulsive forces less. A faster speed decreased the time to measure a force curve, which reduced the number of high-pressure regions of the sound wave to pass through the water between the probe and the substrate. This reduced the number of times that the EDL was compressed by the sound wave.

Peritoneal natural killer cell chemotaxis is decreased in women with pelvic endometriosis.

PROBLEM: NK cell and macrophage function are decreased in endometriosis, and the disease may involve reduced immune surveillance in the peritoneal cavity. NK cell cytotoxicity and migration ability (chemotaxis) are considered important; the former has been investigated, but the latter has not. METHOD OF STUDY: We compared chemotaxis of immunocompetent cells (NK cells, macrophages, T cells) in peritoneal fluid obtained during laparoscopy in 27 women with and 13 without endometriosis. Peripheral blood NK cells were also obtained by the peripheral blood antibody beads method. Micro-cultured cells were examined by time-lapse photography, and the mean migration speed per cell was calculated as the chemotaxis. We investigated the relationship between chemotaxis and endometriosis. RESULTS: NK cell chemotaxis was significantly lower in the endometriosis group. Macrophages and lymphocytes were not significantly different between the groups. During menstruation, NK cell chemotaxis decreased in both groups. Postmenstrual chemotaxis was increased significantly in women without endometriosis but remained low in women with endometriosis. The Revised-American Society for Reproductive Medicine score was not correlated with chemotaxis; in women with endometriosis, chemotaxis was decreased even at early stages. Peripheral blood NK cells showed no significant differences. CONCLUSIONS: In women with endometriosis, not only cytotoxicity but also chemotaxis by NK cells in peritoneal cavity is significantly decreased, and particularly chemotaxis is decreased throughout the menstrual cycle. Therefore, antigens in retrograde menstrual blood that enters the peritoneal cavity might be left unprocessed. Repetition of this immune process in the peritoneal cavity may lead to the onset and subsequent progression of endometriosis.

A photochemical layer-by-layer solution process for preparing organic semiconducting thin films having the right material at the right place.

The synergistic action of properly integrated semiconducting materials can bring about sophisticated electronic processes and functions. However, it is often a great challenge to achieve optimal performance in organic devices because of the limited control over the distribution of different materials in active layers. Here, we employ a unique photoreaction-based layer-by-layer solution process for preparing ternary organic photovoltaic layers. This process is applicable to a variety of compounds from wide-band-gap small molecules to narrow-band-gap π-extended systems, and enables the preparation of multicomponent organic semiconducting thin films having the right compound at the right place. The resulting ternary photovoltaic devices afford high internal quantum efficiencies, leading to an approximately two times higher power-conversion efficiency as compared to the corresponding binary bulk-heterojunction system. This work opens up new possibilities in designing materials and active layers for solution-processed organic electronic devices.

Mimicking of a Transient Protein Binding in Mammalian Cells Using a Functionalized Magnetic Nanoparticle.

Identification of binding proteins is essential for uncovering biological mechanisms of functional small molecules and proteins, but if the binding is transient it may be quite difficult to find the binding proteins using cell extracts that is commonly used for target identification methods. Usually sticky proteins bind to bait molecule first as long as cell extracts are used. In such cases, it would be very difficult to find transient binding proteins. The best way to circumvent the non-specific bindings might be putting bait molecules into living cells and collects the baits after a certain period of incubation time. In here, we evaluated a new target identification method in living cells with magnetic nanoparticles. For the proof-of-concept, we reproduced a transient interaction between peroxisomal proteins and Pex5p, the peroxisome guiding protein. To that end, carboxyl group-functionalized magnetic nanoparticles were labeled with peroxisomal targeting signal 1 (PTS1) peptide to mimic peroxisomal proteins. The PTS1-labeled magnetic nanoparticles translocated into peroxisomes in the mammalian cells, during which they transiently interacted with Pex5p. These results were confirmed using a fluorescence microscope and "in cell pull-down" experiments. Conclusively, the transient interaction between peroxisomal proteins and Pex5p in cells was reproduced with the PTS1-labeled magnetic nanoparticles in living cells by showing its sequential translocation into peroxisomes and transient interaction with Pex5p in parallel. This result indicates that a magnetic nanoparticle can be a useful tool for analyzing dynamic change of interacting proteins to a functional molecule in living cells depending on circumstances the cells encounter.

Stability of α''-Fe16N2 in hydrogenous atmospheres.

We revealed the inherent instability of α''-Fe16N2 in hydrogenous atmospheres due to the denitrification toward α-Fe by forming NH3 at the particle surface. Coating the particle surface with SiO2 to suppress the formation of NH3 has proven to be a simple yet powerful method to enhance the stability of α''-Fe16N2 in hydrogenous atmospheres.

CaH2-assisted low temperature synthesis of metallic magnetic nanoparticle-loaded multiwalled carbon nanotubes.

We studied synthesis of Ni or Fe nanoparticle-loaded multiwalled carbon nanotubes (MWCNTs) by pyrolyzing metal organic salts with CaH2, a very strong reductant. The use of CaH2 lowered the formation temperature of MWCNTs down to 400 °C without the use of toxic halogen-containing precursors and assistance of plasma.

Quantitative understanding of thermal stability of α''-Fe16N2.

The thermal stability of α''-Fe16N2, which attracts much interest because of its superior magnetic properties featuring a large magnetocrystalline anisotropy (Ku ~ 1 × 10(7) erg cm(-3)) and a large saturation magnetization (Ms ~ 234 emu g(-1)), though unfortunately thermally unstable, has been quantitatively studied.

Carboxylated SiO2-coated α-Fe nanoparticles: towards a versatile platform for biomedical applications.

Carboxylated SiO2-coated α-Fe nanoparticles have been successfully prepared via CaH2-mediated reduction of SiO2-coated Fe3O4 nanoparticles followed by surface carboxylation. These α-Fe-based nanoparticles, which are characterized by ease of coating with additional functional groups, a large magnetization of 154 emu per g-Fe, enhanced corrosion resistivity, excellent aqueous dispersibility, and low cytotoxicity, have potential to be a versatile platform in biomedical applications.

Low temperature solventless synthesis and characterization of Ni and Fe magnetic nanoparticles.

We have successfully implemented a facile, one-pot solventless synthesis procedure starting from acetylacetonate salts and CaH(2) to obtain carbon-coated ferromagnetic metallic Ni and Fe nanoparticles at low temperature. The use of CaH(2) as a reductant drastically reduces reaction temperature down to 140 °C.

Surface and friction forces between grafted polysaccharide layers in the absence and presence of surfactant.

We analyzed the interaction between chemically grafted polysaccharide layers in aqueous solutions. To fabricate such layers, an end-terminated dextran silane coupling agent was synthesized and the polydextran was grafted to oxidized silicon wafers and to silica particles. This resulted in the formation of a 28 nm thick layer (in air) and a grafted amount of 40 mg/m(2) as determined by ellipsometry. The physical properties of the grafted layer were investigated in aqueous solutions by atomic force microscope imaging and colloidal probe force measurements. Surface and friction forces were measured between one bare and one polydextran coated silica surface. A notable feature was a bridging attraction due to affinity between dextran and the silica surface. Surface interactions and friction forces were also investigated between two surfaces coated with grafted polydextran. Repulsive forces were predominant, but nevertheless a high friction force was observed. The repulsive forces were enhanced by addition of sodium dodecyl sulfate (SDS) that associates with the tethered polydextran layers. SDS also decreased the friction force. Our data suggests that energy dissipation due to shear-induced structural changes within the grafted layer is of prime importance for the high friction forces observed, in particular deformation of protrusions in the surface layer.

A straightforward way to form close-packed TiO2 particle monolayers at an air/water interface.

The aim of this study was to analyze if and how monolayers of TiO(2) particles could be directly formed at the air/water interface and if these monolayers could be transferred to a solid surface. TiO(2) particles with diameters of 300 nm, 500 nm, 1 µm, 5 µm, 10 µm, and 20 µm formed stable monolayers at pH 2. At low surface pressures, the particles formed small two-dimensional aggregates. Particles up to a radius of 5 µm displayed close packing at increased surface pressures. Particles of 10 µm radius formed a loose network, which is attributed to the strong adhesion caused by the weight-induced lateral capillary attraction. Every monolayer of particles could be transformed to a solid surface by the Langmuir-Blodgett deposition. At pH 6 or 11, the particles did not form stable monolayers at the air/water interface. They were instead dispersed in the aqueous phase and eventually sank to the bottom of the trough. At pH 11 the monolayer could, however, be stabilized by the addition of salt (0.5 M NaCl). The results are interpreted based on a changed wettability of the particles depending on pH and salt concentration.

Determination of the binding of non-cross-linked and cross-linked gels to living cells by atomic force microscopy.

In this study, we first proposed a method to directly measure the interaction forces between nanoparticle gels and living cells by using the atomic force microscope (AFM). This was achieved by attaching the nanoparticles to a carrier silica probe with epoxy resin and then by directly measuring the interaction force between the probe and the living cells with the AFM. We subsequently used this technique to investigate the ability of triblock copolymer nanoparticle gels to bind to living B16F10 (mouse skin melanoma) cells. We particularly studied how the copolymer composition and structure, and the introduction of chemical cross-linking affected the adhesion magnitude. We found that a gel particle was capable to bind to a living melanoma cell. The binding strength of the particle was determined by the composition of the gel particle, where a composition change appeared to affect the number and type of chemical groups on the surface of the gel that could bind to the cell. The introduction of cross-links into the gel did not decrease the adhesion ability to a cell. Instead, it was seen that the adhesion could be increased, if a cross-linker was chosen that contained chemical groups that could bind with the cell and that preferred a conformation at the surface of the particle.

Large positive magnetoresistive effect in silicon induced by the space-charge effect.

Recent discoveries of large magnetoresistance in non-magnetic semiconductors have gained much attention because the size of the effect is comparable to, or even larger than, that of magnetoresistance in magnetic systems. Conventional magnetoresistance in doped semiconductors is straightforwardly explained as the effect of the Lorentz force on the carrier motion, but the reported unusually large effects imply that the underlying mechanisms have not yet been fully explored. Here we report that a simple device, based on a lightly doped silicon substrate between two metallic contacts, shows a large positive magnetoresistance of more than 1,000 per cent at room temperature (300 K) and 10,000 per cent at 25 K, for magnetic fields between 0 and 3 T. A high electric field is applied to the device, so that conduction is space-charge limited. For substrates with a charge carrier density below approximately 10(13) cm(-3), the magnetoresistance exhibits a linear dependence on the magnetic field between 3 and 9 T. We propose that the observed large magnetoresistance can be explained by quasi-neutrality breaking of the space-charge effect, where insufficient charge is present to compensate the electrons injected into the device. This introduces an electric field inhomogeneity, analogous to the situation in other semiconductors in which a large, non-saturating magnetoresistance was observed. In this regime, the motions of electrons become correlated, and thus become dependent on magnetic field. Although large positive magnetoresistance at room temperature has been achieved in metal-semiconductor hybrid devices, we have now realized it in a simpler structure and in a way different from other known magnetoresistive effects. It could be used to develop new magnetic devices from silicon, which may further advance silicon technology.

Direct and stepwise energy transfer from excitons to plasmons in close-packed metal and semiconductor nanoparticle monolayer films.

We studied the dynamics of photoluminescence (PL) and energy transfer in close-packed monolayer films of CdSe and Au nanoparticles (NPs) assembled using the Langmuir-Blodgett technique. The PL intensity and dynamics depended on the ratio of CdSe to Au NPs in the mixed films. The PL quenching of CdSe NPs occurs through rapid energy transfer from excitons in CdSe NPs to plasmons in Au NPs. The PL decay curves of the mixed NPs monolayers are determined by three decay rates: the direct energy transfer between the nearest-neighbor CdSe and Au NPs (CdSe-->Au), the stepwise energy transfer from CdSe to CdSe to Au NPs (CdSe-->CdSe-->Au), and the radiative recombination in CdSe NPs.

Chemical groups that adhere to the surfaces of living malignant cells.

PURPOSE: We determined the adhesion of particles with phenyl, carboxylic acid (COOH), amine, dialkyl phosphonate, ester, and hydroxyl groups to malignant and nonmalignant cells, in order to better design drug delivery systems (DDS) for malignant cells. METHODS: Living mouse melanoma skin (B16F10) and noncancerous mouse fibroblast (L929) cells, and an Atomic Force Microscope were used to determine the adhesion strengths. RESULTS: The measurement of the particles against B16F10 cells showed that COOH had the highest average maximum adhesion force () and a large standard deviation (std), and phenyl had the lowest and a lower std. The high and std suggested that COOH was binding the strongest to malignant cells, and to groups overexpressed on malignant cells. In the case of L929 cells, of phenyl and COOH were higher and lower, respectively, than those of the B16F10 cells. Additionally, Phenyl and COOH gave a lower std than that for the B16F10 cells. These results suggest that the lower binding of COOH to the nonmalignant cells was due to the lower number of groups that were overexpressed in the malignant cells. CONCLUSIONS: Our results suggest that COOH is the best group for malignant cell targeting DDS systems.

Effect of the physicochemical properties of poly(ethylene glycol) brushes on their binding to cells.

We investigated the effect of the number of oxyethylene groups (polymer molecular weight) and the interchain binding and/or entanglements of methoxy-terminated-poly(ethylene glycol) (m-PEG) brushes on their ability to adsorb to living malignant melanoma B16F10 cells. We used the atomic force microscope colloid probe method to determine the adhering ability of the m-PEG brushes to the cells, as the magnitude of the adhesion force between the m-PEG modified particles and the living cells in a physiological buffer was related to the binding strength of the m-PEGs to the cells. We saw that m-PEG brushes (average molecular weights 330, 1900, and 5000 g/mol), which were chemically attached to silica particles, may bind to living B16F10 cells. The binding of m-PEGs to living B16F10 cells increased as the oxyethylene chain length of the m-PEGs increased, if the m-PEGs had a low degree of entanglements or little inter-m-PEG chain binding. A high degree of entanglements or interchain binding decreased the ability of an m-PEG chain to bind to a living cell. The effect of m-PEG (molecular weight 1900 g/mol) being present at cell surfaces for 24 h was also seen not to induce the death of the cells or affect their growth.

Preparation and characterization of pure and mixed monolayers of poly(ethylene glycol) brushes chemically adsorbed to silica surfaces.

We prepared pure and mixed monolayers of methoxy-terminated poly(ethylene glycol)s (m-PEG's) chemically attached to silica surfaces by using m-PEG silane coupling agents of three different molecular weights. These films were subsequently characterized in water by atomic force microscopy (AFM). Images of pure m-PEG monolayers showed the formation of polymer brushes on silica. Force curves between two modified surfaces suggested that an increase in the number of oxyethylene (OE) groups from 6 (PEG6 surface) to 43 (PEG43 surface) to 113 (PEG113 surface) decreased the flexibility of the m-PEG chains in the m-PEG brushes. Frictional force measurements also showed that the friction increased in the order PEG6 < PEG43

Selenophosphate synthetase genes from lung adenocarcinoma cells: Sps1 for recycling L-selenocysteine and Sps2 for selenite assimilation.

A labile selenium donor compound monoselenophosphate is synthesized from selenide and ATP by selenophosphate synthetase (SPS). In the present study, Sps1 and Sps2 were cloned from a cDNA library prepared from human lung adenocarcinoma cells (NCIH441). The human lung Sps1 has been cloned as an ORF of 1,179 bp, identical in sequence to that of the recently revised human liver Sps1. The in-frame TGA codon of the lung Sps2 was genetically altered to TGT (Cys) to obtain the Sps2Cys gene. Expression of the recombinant plasmids containing Sps1 or Sps2Cys was highly toxic to Escherichia coli host cells grown aerobically. Accordingly, the human lung Sps homologs were characterized by an in vivo complementation assay using a selD mutant strain. An added selenium source and a low salt concentration (0.1-0.25% NaCl) in the medium were required for reproducible and sensitive in vivo complementation. Sps2Cys effectively complemented the selD mutant, and the resulting formate dehydrogenase H activity was as high as that of WT E. coli MC4100. In contrast, only a weak complementation of the selD mutant by the Sps1 gene was observed when cells were grown in selenite media. Better complementation with added l-selenocysteine suggested involvement of a selenocysteine lyase for mobilization of selenium. Based on this apparent substrate specificity of the Sps1 and Sps2 gene products we suggest that the Sps1-encoded enzyme depends on a selenium salvage system that recycles l-selenocysteine, whereas the Sps2 enzyme can function with a selenite assimilation system.