A new device for checking surface contamination based upon electrical measurement

Surface treatments, such as plating, painting, marking or assembling with adhesives, require reliable surface cleanliness. Industrial workshops cannot use sophisticated techniques, and there is a need for fast and reliable tests. Very simple drop or marker tests exist, but they provide only go — no go information. Measurements of electrical surface potential decay have been found to be convenient, and a commercial device for metal surfaces is now available, based upon this principle. Positive electrical charges are deposited upon the metal through corona discharge, and the resulting surface potential is measured by an electrostatic probe; its decay is followed over 5–10s. Usually, the relationship between the logarithm of the potential and the decay time is linear; a microcomputer calculates the two parameters of this law, which are related to the nature and thickness of the contaminating layer. Flatness of the surface is not required, making it possible to control parts with various geometries. It is easy to compare the contamination of a surface with a standard, and to decide whether the surface can be considered sufficiently clean. The device is rather small, inexpensive and very simple to operate; it is designed for quality control in industry. Developments for plastic parts are under progress, and valuable results have already been obtained, e.g. for ageing of epoxy parts.     

Monitoring surfactant-induced hemolysis by surface tension measurement

Surface tension measurements were employed to monitor the erythrocyte hemolysis process induced by surfactants. Two types of surfactants were used: the cationic surfactant DTAB and the anionic surfactant SDS. During DTAB-induced hemolysis, the changes in surface tension clearly demonstrate three stages. The first stage is characterized by surface tension increase, which is explained by surfactant removal from the suspending solution, due to adsorption onto cell membranes. In the second stage, surface tension remains constant, implying that equilibrium is attained between the membrane-bound surfactant and the surfactant in solution. The third stage is characterized by surface tension decrease that begins simultaneously with measurable cell-interior release, and lasts until hemolysis is completed. With SDS-induced hemolysis, the same three stages are observed at a low concentration; however, fluctuational increase in surface tension is obtained for higher concentrations. The latter is explained by additional adsorption of surfactant to solubilized membrane fragments.     

Rapid evaluation of nickel binding properties of His-tagged lactate dehydrogenases using surface plasmon resonance

The use of surface plasmon resonance (SPR), for the comparison of metal binding properties of polyhistidine tags, was evaluated. Six different tags containing various number of histidines, either none (tags n and t), three (tags H3A3 and HA2HA2H) or six (tags H6 and His6), were genetically fused to the N-terminal of lactate dehydrogenase (LDH). The binding ability of these constructs to nickel ions, immobilised with nitrilotriacetic acid (NTA), was tested both by conventional immobilised metal ion affinity chromatography (IMAC) and SPR. The relative binding strengths of the tags to nickel were identical using both methods (n approximately t < HA2HA2H < H3A3 < His6 < H6), confirming the value of the SPR technique for investigating metal-protein interactions. Protein modelling has also proved to be useful in supporting the experimental results.     

Energetic properties of nio surface examined by heat-of-adsorption measurement

Heat of adsorption and isotherm of water vapor on NiO samples were measured simultaneously at 301 K to examine the energetic properties of the surface. They revealed that NiO has a relatively uniform surface. The heat of adsorption ranging 80–90 kJ·mol^–1 indicates the production of surface hydroxyl groups on the (100) plane of NiO. It is relatively small compared with that of other metal oxides, which suggests a weak nature of the Ni²⁺ ion sites for chemisorption of water. It is suspected that half of the surface Ni²⁺ ions are covered with hydroxyl groups and the remainings act as relatively strong physisorption sites for water molecules.The authors are grateful for the help of Prof. S. Kittaka of Okayama University of Science in taking electron micrographs. This work was partly supported by Grant-in-Aid for Scientific Research No. 02640348 from the Ministry of Education, Science and Culture of Japanese Government.     

Direct observation of substrate-enzyme complexation by surface forces measurement

The substrate-enzyme complexation of heptaprenyl diphosphate synthase was directly investigated using colloidal probe atomic force microscopy (AFM) and a quartz crystal microbalance (QCM) in order to obtain new insights into the molecular mechanism of the enzyme reaction. This enzyme is composed of two dissociable subunits that exhibit a catalytic activity only when they are associated together in the presence of a cofactor, Mg2+, and a substrate, farnesyl diphosphate (FPP). The QCM measurement revealed that FPP was preferentially bound to subunit II in the presence of Mg2+, while the AFM measurement showed that the adhesive force between the subunits was observed only in the presence of both Mg2+ and FPP. This is the first direct demonstration of the specific interaction involved in the enzyme reaction. The dependence of the Mg2+ concentration on the specific interaction between subunits I and II well agreed with that on the enzyme activity of heptaprenyl diphosphate synthase. This indicated that the observed adhesive forces were indeed involved in the catalytic reaction of this enzyme. On the basis of these results, we discussed the processes involved in the substrate-enzyme complexation. The first, the substrate FPP bound to subunit II using Mg2+, followed by the formation of the subunit I-FPP-Mg2+-subunit II complex. Our study showed a very useful methodology for examining the elemental processes of biological reactions such as an enzyme reaction.     

Rapid radio-proteinbinding measurement of urine folates

A method is presented for the determination of urine folates by a commercial radio-proteinbinding assay widely used in clinical diagnostics for assessing plasma folate levels. Good recovery of urine folates over the range of the calibration curve was observed. Because of the speed, sensitivity and precision of this test, urine folate levels can be measured in bioavailability studies or for the assessment of folate status.     

Rapid measurement of three-dimensional diffusion tensor

In this article, the authors demonstrate a rapid NMR method to measure a full three-dimensional diffusion tensor. This method is based on a multiple modulation multiple echo sequence and utilizes static and pulsed magnetic field gradients to measure diffusion along multiple directions simultaneously. The pulse sequence was optimized using a well-known linear inversion metric (condition number) and successfully tested on both isotropic (water) and anisotropic (asparagus) diffusion systems.     

Investigations of local electrical surface characteristics by dynamical scanning force microscopy

A technique is presented that allows to obtain information about sample surface topography and local electrical surface properties simultaneously. A scanning electrical force microscope is used for that purpose which is based on an atomic force microscope (AFM) working in the dynamical mode. Different information channels contained in the cantilever excitation spectrum are separated by a lock-in technique. The physical content of the technique is discussed in detail and the influence of surface topography on the non-topographic imaging is demonstrated. Finally, the real advantages of cross-sectional sample preparation (as known from electron microscopy) for this kind of scanning probe microscopy with respect to various applications is presented.     

Rapid measurement of polymer photo-degradation by FTIR spectrometry of evolved carbon dioxide

A novel method, allowing simultaneous UV exposure of a polymer sample and IR interrogation of the vapour in a specially constructed cell, has been applied to polyethylene (PE) samples containing TiO₂ pigments with different photoactivities. Measurements of the CO₂ generated by films exposed to ultraviolet irradiation (UV) were completed in 5 h - very much less than conventional accelerated tests. The TiO₂ pigments used included anatase and rutiles with different surface treatments. Anatase pigmented material gave significantly higher CO₂ emission than unpigmented PE whilst rutile-pigmented PEs either gave reduced CO₂ emission or enhanced emission, according to the surface treatment. The ranking of the pigments as protectants or pro-degradants correlated well with the carbonyl index measured after more than 300 h exposure to UVA fluorescent tubes in a QUV machine.The method was then used to probe mechanistic aspects of the photo-oxidation of pigmented polyethylene (PE) film. For unpigmented polymer the photo-degradation was sensitive to changes in the small fraction of incident UV below 300 nm, but for pigmented films this was much less important. This is because unpigmented film degrades by direct photochemical attack whereas, for pigmented film, photocatalysis by TiO₂, which absorbs in the 300-400 nm region, is important. For films whose photo-oxidation was dominated by photocatalysis by the TiO₂ the rate of oxidation was shown to vary as the square root of the UV intensity. By contrast, for unpigmented films the rate of direct photochemical oxidation was linearly proportional to UV intensity. The difference is a consequence of the controlling role of electron-hole recombination in photocatalytic processes. For both unpigmented and pigmented films the rate of oxidation was shown to increase with increasing humidity and oxygen content of the atmosphere.     

Rapid measurement of pseudocontact shifts in metalloproteins by proton-detected solid-state NMR spectroscopy

Pseudocontact shifts (PCSs) arise in paramagnetic systems in which the susceptibility tensor is anisotropic. PCSs depend upon the distance from the paramagnetic center and the position relative to the susceptibility tensor, and they can be used as structural restraints in protein structure determination. We show that the use of (1)H-detected solid-state correlations provides facile and rapid detection and assignment of site-specific PCSs, including resolved (1)H PCSs, in a large metalloprotein, Co(2+)-substituted superoxide dismutase (Co(2+)-SOD). With only 3 mg of sample and a small set of experiments, several hundred PCSs were measured and assigned, and these PCSs were subsequently used in combination with (1)H-(1)H distance and dihedral angle restraints to determine the protein backbone geometry with a precision paralleling those of state-of-the-art liquid-state determinations of diamagnetic proteins, including a well-defined active site.     

Tissue surface tension measurement by rigorous axisymmetric drop shape analysis

Certain behaviours of embryonic cell aggregates can be modelled by ascribing to them a tissue surface tension, with each cell analogous to a liquid molecule. Under normal gravity, aggregates are nearly spherical, but they can be partially flattened in a centrifuge. This allows measurement of their tissue surface tensions by a drop shape method such as axisymmetric drop shape analysis (ADSA). We study ectodermal embryonic cells from the frog Xenopus laevis subjected to centrifugation at 100 × g and 200 × g. We show that ADSA can be applied to irregular aggregate profiles and compare results with those from a previous, simpler version called ADSA-IP. With a modification in the experimental method, the two algorithms give similar results and the aggregate profiles more closely follow Laplacian curves. The ADSA fitting error allows an estimate of the relative uncertainty in the results.     

Numerical method of non-isothermal curve analysis by means of electrical resistance measurement during cooling

The temperature-dependence of the electrical resistance of Al-Zn 78 wt.% was measured during linear cooling of the samples in the range of eutectoidal decomposition. The resulting resistancevs. temperature curves were analysed by:

deriving the temperature-dependence of the volume fractionx(T) of theη precipitate;

fitting the theoretical functionx(T)=x _h (T)+x _c (T) following from numerical integration of the reaction rate equations for the simultaneously occurring homogeneous (H) and cellular (C) precipitation processes.

As a result, the activation energiesE _h andE _c , the JMA exponentsn _h andn _c , the rate constantsk _h andk _c , and the critical temperaturesT _o of the two processes were estimated.     

Rapid measurement of oestradiol and oestriol by high-performance liquid chromatography after automatic pretreatment

A fluorometric liquid chromatographic method was developed for measurements of unconjugated oestradiol and oestriol in the serum of pregnant women. The serum samples are injected directly into the apparatus and pass to a pretreatment column, where oestrogens are adsorbed while hydrophilic components such as proteins and carbohydrates are not. The oestrogens then pass into a separation column containing a new type of polymer gel. The mobile phase consists of an acetonitrile-water mixture, and separation is achieved by a reversed-phase mechanism. The eluent is monitored for fluorescence. Data on the reproducibility and recovery by this method and the correlation of values with those obtained by radioimmunoassay are reported. Results on the increases of oestradiol and oestriol in the serum during pregnancy are also reported.     

Rapid measurement of cyclosporin a plasma levels by HPLC in allograft transplant recipients

Summary An HPLC-method for the measurement of blood Cyclosporin A levels (CyA) of renal allograft transplanted patients within 9min is described. After a simple protein precipitation of the blood the supernatant is transferred to an HPLC-system. The short time of analysis is obtained by a step gradient elution technique and a precolumn separation of the fractions of interest followed by a backflush regeneration step of the precolumn. The analysis of the fraction of interest takes place on a column with high resolution power as long as the precolumn is regenerated. CyA is monitored by UV-absorption at 206nm. Detection of 20 to 2000ng/ml CyA allows the use of the method for patient monitoring and for research purposes. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Calculation of the surface potential and surface charge density by measurement of the three-phase contact angle

The silica/silicon wafer is widely used in the semiconductor industry in the manufacture of electronic devices, so it is essential to understand its physical chemistry and determine the surface potential at the silica wafer/water interface. However, it is difficult to measure the surface potential of a silica/silicon wafer directly due to its high electric resistance. In the present study, the three-phase contact angle (TPCA) on silica is measured as a function of the pH. The surface potential and surface charge density at the silica/water surface are calculated by a model based on the Young-Lippmann equation in conjunction with the Gouy-Chapman model for the electric double layer. In measurements of the TPCA on silica, two distinct regions were identified with a boundary at pH 9.5-showing a dominance of the surface ionization of silanol groups below pH 9.5 and a dominance of the dissolution of silica into the aqueous solution above pH 9.5. Since the surface chemistry changes above pH 9.5, the model is applied to solutions below pH 9.5 (ionization dominant) for the calculation of the surface potential and surface charge density at the silica/aqueous interface. In order to evaluate the model, a galvanic mica cell was made of a mica sheet and the surface potential was measured directly at the mica/water interface. The model results are also validated by experimental data from the literature, as well as the results obtained by the potentiometric titration method and the electro-kinetic measurements.     

Rapid fabrication of large-area colloidal crystal monolayers by a vortical surface method

We have developed a simple approach for rapidly fabricating large-scale colloidal crystal arrays on substrates. Latex particles were first assembled into a close-packed monolayer on a vortical water surface; the monolayer was then transferred onto substrates by a withdrawer. Such an assembly method is conceptually similar to the Langmuir-Blodgett (L-B) methods for film deposition but does not require an L-B trough. The samples exhibit a large-scale periodic feature based on optical microscopy and scanning electron microscopy observations and diffract the laser beam, acting as crystals. This newly developed technique is timesaving, widely accessible, and applicable to large particles (up to 2 microm). It promises to be useful in nanofabrication.     

Direct electrical measurement of the conversion of metal acetates to metal sulfides by hydrogen sulfide

Copper acetate and related metal salt films react directly with hydrogen sulfide at room temperature to form metal sulfides, resulting in conductivity changes as large as 108. The observed changes in conductivity are related to the solubility product constant (Ksp) and the difference in conductivity between the metal salt and the resulting metal sulfide. A smaller Ksp indicates a more stable metal sulfide and, therefore, greater metal salt reactivity. Polyaniline nanofiber/metal salt composites were also examined and show metal sulfide conversion with changes in resistance up to 106. The direct electrical measurement of the conversion of metal salt to metal sulfide has the potential to be the basis of a new type of sensitive, thin-film chemical sensor.     

Mg-doping experiment and electrical transport measurement of boron nanobelts

We measured electrical conductance of single crystalline boron nanobelts having α-tetragonal crystalline structure. The doping experiment of Mg was carried out by vapor diffusion method. The pure boron nanobelt is a p-type semiconductor and its electrical conductivity was estimated to be on the order of 10^-3 (Ω cm)⁻¹ at room temperature. The carrier mobility of pure boron nanobelt was measured to be on the order of 10⁻³ (cm² Vs⁻¹) at room temperature and has an activation energy of ∼0.19 eV. The Mg-doped boron nanobelts have the same α-tetragonal crystalline structure as the pristine nanobelts. After Mg vapor diffusion, the nanobelts were still semiconductor, while the electrical conductance increased by a factor of 100-500. Transition to metal or superconductor by doping was not observed.