A fast and sensitive continuous flow nanobiodetector based on polyaniline nanofibrils

Polyaniline nanofibrils, fabricated as a freestanding nanonetwork in a micro gap between two gold electrodes, have been applied in a fast and sensitive analytical device for detecting microorganism cells in a flowing liquid, including the “on-line” regime. The electrical response of the device (in this case an increase in the electrical conductivity of the nanonetwork) depends on the number of cells in the sample analyzed: it is linear within the range of 0–5000 and 0–15 × 10⁶ cells injected for yeast and bacteria examined, respectively. The detection limit depends on the type of microorganism: it is about 300 and 1.9 × 10⁵ (per mL) for yeast (Saccharomyces cerevisiae) and bacteria cells (Lactobacillus rhamnosus), respectively. The results are registered within few seconds (typically 5–15 s). The device is designed to detect a low level of bio-contamination and it is expected to be useful in biomedical applications, environmental protection and anti bioterrorism systems, including “on-line” monitoring.     

The microenvironment of iron in (Ba,Ca)(Fe,Co)O3−δ catalyst system: A Mössbauer study

Undisturbed, non-fertilized woodland soil (“loamy sandy soil” type) from 1 m below surface was dry and wet sieved. Sieving fractions of <10–1000 μm were analyzed for total alpha-activity. Thorium and uranium contents were determined by alpha-spectrometry after radiochemical separation. Soluble and insoluble parts of thorium and uranium were determined in the sieved fractions indicating that the isotope distribution in soil correlates with the particle size distribution: The smaller the size fraction the higher the isotope content. Isotope ratios of²²⁸Th/²³²Th, and²³⁴U/²³⁸U are discussed.     

Electrorheology and creep-recovery behavior of conducting polythiophene/poly(oxymethylene)-blend suspensions

Electrorheological properties and creep-recovery behavior of polythiophene/polyoxymethylene-blend having PT（50%）/POM（50%） composition were investigated.Particle size,conductivity and dielectric values were measured to be 24.77μm,3.85×10^-5 S·m^-1 and 26.75,respectively.Sedimentation ratio was measured to be 64%at the end of 16 days.The effects of dispersed particle volume fraction,external electric field strength,shear rate,frequency and temperature on ER properties and storage modulus of PT/POM-blend/silicone oil（SO） suspensions were examined.Enhancement were observed in the electric field viscosities of the suspensions and thus they were classified as a smart material.Shear thinning non-Newtonian viscoelastic behavior was determined for PT/POM-blend/SO system.Further,time-dependent deformation was examined by creep-recovery tests and recoverable viscoelastic deformation established.     

Characterization of a capacitance-coupled contactless conductivity detection system with sidewall electrodes on a low-voltage-driven electrophoresis microchip

A new type of capacitance-coupled contactless conductivity detection (C⁴D) system with sidewall electrodes was proposed for integration on a silicon-on-isolator–poly(dimethylsiloxane) (SOI-PDMS) hybrid low-voltage-driven electrophoresis microchip. By a microelectromechanical system process, the sidewall electrodes were fabricated precisely at either side of the separation channel. The area of the capacitor electrodes was the maximum value to improve the detection sensitivity with an enhanced capacitance effect. According to the simulation results, the structural parameters of the sidewall electrodes were determined as 550-μm length, 15-μm width, 80-μm separation distance, and 1-μm isolator thickness. The integrated microdevice with the SOI-PDMS hybrid electrophoresis microchip was very compact and the size was only 15 cm × 15 cm × 10 cm (width × length × height), which permitted miniaturization and portability. The detector performance was evaluated by K⁺ testing. The detection limit of the conductivity detector was determined to be 10^-9 and 10^-6 M for K⁺ in the static and electric-driven modes, respectively. Finally, the C⁴D was applied to low-voltage-driven electrophoresis on a microchip to carry out real-time measurement of the separation of amino acids. The separations of 10^-4 M lysine and phenylalanine in the low-voltage-driven electrophoresis mode were performed with an electric field of 300 V/cm and were completed in less than 15 min with a resolution of 1.3. The separation efficiency was found to be 1.3 × 10³ and 2.8 × 10³ plates for lysine and phenylalanine, respectively, with a migration time reproducibility of 2.7 and 3.2%. The conductivity detection limit of amino acids achieved was 10^-6 M. The proposed method for the construction of a novel C⁴D integrated on an SOI-PDMS hybrid low-voltage-driven electrophoresis microchip showed the most extensive integration and miniaturization of a microdevice, which is a further crucial step toward the realization of the “lab-on-a-chip” concept.     

The europium/samarium-2-benzoyl-indane-1,3-dione-cetyltrimethylammonium bromide fluorescence system and its analytical application

The fluorescence system of the Eu³⁺ (or/and Sm³⁺)-2-benzoyl-indane-1,3-dione(BID)-cetyltrimethylammonium bromide (CTMAB) was investigated at excitation wavelengths of 350 nm, and emission wavelengths at 612 nm for europium and 565, 606 and 650 nm for samarium, respectively. The system was used for the determination of Eu and Sm in rare earth oxides and of BID in water. Europium or/and samarium could be determined in the range of 1.0 × 10^–9–1.0 × 10^–5 mol/L and 2.0 × 10^–8–5.0 × 10^–5 mol/L, respectively; 1.0 × 10^–6–2.0 × 10^–5 mol/L of BID could also be determined. Received: 5 March 1997 / Revised: 6 August 1997 / Accepted: 20 September 1997     

The europium/samarium-2-benzoyl-indane-1,3-dione-cetyltrimethylammonium bromide fluorescence system and its analytical application

The fluorescence system of the Eu³⁺ (or/and Sm³⁺)-2-benzoyl-indane-1,3-dione(BID)-cetyltrimethylammonium bromide (CTMAB) was investigated at excitation wavelengths of 350 nm, and emission wavelengths at 612 nm for europium and 565, 606 and 650 nm for samarium, respectively. The system was used for the determination of Eu and Sm in rare earth oxides and of BID in water. Europium or/and samarium could be determined in the range of 1.0 × 10^–9–1.0 × 10^–5 mol/L and 2.0 × 10^–8–5.0 × 10^–5 mol/L, respectively; 1.0 × 10^–6–2.0 × 10^–5 mol/L of BID could also be determined. Received: 5 March 1997 / Revised: 6 August 1997 / Accepted: 20 September 1997     

EPMA and Quantitative MCs+-SIMS of Metal-DLC Coating Materials

 Compositional characterization of metal-DLC (metal-containing diamond-like carbon) hard coatings is carried out by (WDS)-EPMA and MCs⁺-SIMS. EPMA enables accurate (± 5% relative) quantitative analysis including minor concentrations (0.1–10 at%) of N, O and Ar. Under conditions of “near-surface” EPMA (E₀ < 10 keV) the influence of surface oxide films on “pure” metal standards may be a limiting factor in respect of accuracy. Depth profiling of sufficiently “thick” layered structures (film thickness ≥ 2 μm) is carried out by EPMA-line scans along mechanically prepared bevels. The depth resolution is about 0.2 μm. SIMS in the MCs⁺-mode enables high resolution (< 20 nm) depth profiling of metal-DLC layered structures including the determination of H (1–20 at%). MCs⁺-SIMS, i.e. employing Cs⁺ primary ions and monitoring MCs⁺ molecular secondary ions (M is the element of interest) is presented as a promising route towards sufficiently accurate (10–20%) SIMS-quantification. Matrix-independent relative sensitivity factors for MCs⁺-SIMS are derived from homogeneous coating materials defined by EPMA. EPMA proves to be also useful to detect problems related to SIMS of Ar in metal-DLC materials. The combination EPMA-SIMS is demonstrated as an effective analytical strategy for quality control in industrial production and to support the development of metal DLC layered structures with optimum tribological properties.     

Experimental evidence for the formation of doubly charged oxide and hydroxide ions in inductively coupled plasma mass spectrometry

The formation of doubly charged polyatomic ions in inductively coupled plasma mass spectrometers was investigated using commercially available instruments. The species observed were ThO²⁺ and ThOH²⁺, which were found in similar amounts with the different instruments used in this study, when operated under routine analytical conditions. The signal ratios for ThO²⁺ were between 1.8 × 10^–4 and 4.2 × 10^–4 relative to the singly charged elemental ion and between 1.4 × 10^–2 and 2.2 × 10^–2 relative to the doubly charged elemental ion. The formation of ThOH²⁺ was between 1.1 × 10^–4 and 2.8 × 10^–4 relative to the singly charged elemental ion and between 0.72 × 10^–2 and 1.3 × 10^–2 relative to the doubly charged elemental ion. A mechanism is proposed for the formation of the doubly charged oxide and hydroxide ions that is based on the condensation of the doubly charged elemental ion with water or oxygen molecules in the interface region of the mass spectrometer. Received: 20 December 2000 / Revised: 19 March 2001 / Accepted: 22 March 2001     

Investigation of the electrical resistance of single-walled carbon nanotube films in the temperature range 4.2–290 K

Electrical resistance of films made of the source material and purified HiPCO and Arc single-walled carbon nanotubes (SWCNTs) with a thickness of 20−40 μm is 2.4 to 45 Ω (electrical conductivity of 0.42 × 10³ to 5.03 × 10³ S/m) at room temperature. The films have been formed by vacuum microfiltration of SWCNT suspensions in toluene and characterized by Raman and X-ray photoelectron spectroscopy and scanning electron microscopy. The conductivity of the films at room temperature depends on the type and degree of purity of the material of nanotubes. The resistance of the films decreases with the increasing temperature over the range of 4.2–290 K, and the rate of the step-down decreases with increasing purity of the material of the nanotubes. The conductivity of the films is semiconducting in character, and the electron transport is consistent with three-dimensional hopping conductivity.     

Synthesis of highly dispersed super-refractory tantalum-zirconium carbide Ta<Subscript>4</Subscript>ZrC<Subscript>5</Subscript> and tantalum-hafnium carbide Ta<Subscript>4</Subscript>HfC<Subscript>5</Subscript> via sol-gel technology

Nanocrystalline powders of super-refractory complex carbides Ta₄HfC₅ and Ta₄ZrC₅ were synthesized using a hybrid method comprising sol-gel technology for preparing highly dispersed metal oxidescarbon starting mixtures and a relatively low-temperature (1300–1500°C) carbothermal synthesis under a dynamic vacuum (P = 1 × 10⁻³ to 1 × 10⁻⁵ MPa). The elemental and phase compositions of the products and average crystallite sizes were determined. TEM was used to study particle morphology and dispersion. Microstructures were observed by SEM. BET specific surface areas were determined for powders prepared at 1400°C.     

An “off–on” fluorescence probe for chromium(III) ion determination in aqueous solution

An “off–on” rhodamine-based fluorescence probe for the selective signaling of Cr(III) has been designed by exploiting the guest-induced structure transform mechanism. This system shows a sharp Cr(III)-selective fluorescence enhancement response in 100% aqueous system under physiological pH value and possesses high selectivity against the background of environmentally and biologically relevant metal ions including Cr(VI), Al(III), Fe(III), Cd(II), Co(II), Cu(II), Ni(II), Zn(II), Mg(II), Ba(II), Pb(II), Na(I), and K(I). Under optimum conditions, the fluorescence intensity enhancement of this system is linearly proportional to Cr(III) concentration from 5.0 × 10⁻⁸ to 7.0 × 10⁻⁶ mol L⁻¹ with a detection limit of 1.6 × 10⁻⁸ mol L⁻¹.     

Voltammetric determination of 2,4-dinitrophenol and 2,5-dinitrophenol using a poly-aspartic acid modified electrode1

In pH 5.0, 0.1 mol l⁻¹ NaAc-HAc buffer solution, 2,4-dinitrophenol and 2,5-dinitrophenol exhibited sensitive and distinguishable voltammetric responses at the glassy carbon electrode modified with poly-aspartic acid. By measuring the reduction peak currents of nitro groups in different positions, dinitrophenol isomers have been determined simultaneously and quantitatively. The linear calibration ranges were 1.1 × 10⁻⁶–6.0 × 10⁻⁴ mol l⁻¹ for 2,4-dinitrophenol and 7.0 × 10⁻⁷–6.0 × 10⁻⁴ mol l⁻¹ for 2,5-dinitrophenol, with detection limits of 2.7 × 10⁻⁷ and 1.1 × 10⁻⁷ mol l-1 respectively. This method has been applied to the detection of dinitrophenols in simulation water sample, and the recovery was from 96.7 to 102.5%.     

Preparation and evaluation of a functionalized polymer-coated silica based sorbent for metal ion separation

A silica based sorbent with an anion complexone polymer coating, [24]ane-N₆ macrocycle, was prepared. The chelation properties of this material were investigated by elemental analysis, infrared spectra and Voige’s method. The polymer-coated silica column (25– 40 μm, 100 × 4.6 mm i.d.) was employed for trace metal analyses. Oxalic acid, malonic acid, succinic acid, citric acid, phthalic acid and acetic acid were used as mobile phases. Their retention characteristics were elucidated. Oxalic acid was found to be the most effective eluent. With a mobile phase consisting of oxalic acid (25 mM) and sodium nitrate (25 mM) at pH 4.2, the separation of copper(II), cadmium(II), cobalt(II) and zinc(II) in sea water could be achieved. The identification of metal ions was performed at 510 nm using 4(2-pyridylazo)resorcinol (1 × 10^–4 M) as post column reagent. The limits of detection were 5 × 10^–7 M, 1 × 10^–5 M, 3 × 10^–5 M and 2 × 10^–6 M for copper(II), cadmium(II), cobalt(II) and zinc(II) based on three times the standard deviation of the response for the lowest concentration (n = 5) in the chromatogram with a sample volume of 50 μL. For evaluation of data reliability, oyster tissue (NIST SRM 1566 a) was studied with the proposed system. Received: 9 February 1998 / Revised: 15 May 1998 / Accepted: 16 June 1998     

A direct chemiluminescence method for the determination of nucleic acids using Ru(phen)32+–Ce(IV) system

A direct chemiluminescence method for the determination of nucleic acids has been developed based on the enhancement of nucleic acids on the chemiluminescence light emission of the reaction between Ru(phen)₃ ²⁺(phen = 1,10-phenanthroline) and Ce(IV). Under the optimum conditions, the calibration graphs are linear in the range of 5.0 × 10^–8–5.0 × 10^–5 g/mL for calf thymus DNA, 8.0 × 10^–8–5.0 × 10^–5 g/mL for fish sperm DNA and 1.0 × 10^–7–3.0 × 10^–5 g/mL for yeast RNA, respectively. The limits of detection are 1.0 × 10^–8 g/mL for calf thymus DNA, 3.1 × 10^–8 g/mL for fish sperm DNA and 5.2 × 10^–8 g/mL for yeast RNA, respectively. The final procedure allows the successful determination of calf thymus DNA, fish sperm DNA and yeast RNA in six synthetic samples. This method is simple, rapid and specific. Received: 22 January 1999 / Revised: 29 April 1999 / Accepted: 3 May 1999     

Influence of water on the dielectric behaviour of chitosan films

 The dielectric properties of chitosan films with a degree of deacetylation of 86% have been investigated in the frequency range of 10^3–10⁶ Hz covering a broad range of temperatures from −150 to 150 °C. The variation of the dielectric pro-perties with temperature has been associated with two dielectric processes: (a) a local relaxation attributed to the presence of hydrogen-bonded water appearing at low temperatures (b) a conduction process related to water molecules which becomes desorbed upon heating at T>80 °C. Isothermal dielectric experiments have been performed in order to follow, in real time, the occurrence of both, the water sorption and desorption processes. Received: 20 June 1996 Accepted: 19 November 1996     

Study on the Catalytic Determination of Vanadium (V) Using the Rhodamine 6G-Periodate Redox Reaction and its Analytical Application

 A fluorescence quenching method for the determination of vanadium (V) based on the vanadium- catalyzed oxidation of rhodamine 6G (R6G) with periodate in the presence of ethylenediaminetetraacetic acid disodium salt (EDTA) in sulfuric acid medium is described. The fluorescence was measured with excitation and emission wavelengths of 525 and 555 nm, respectively. The calibration graph for vanadium (V) had linear ranges of 3.0 × 10⁻⁹–1.5 × 10⁻⁸ mol/l and 1.5 × 10⁻⁸–4.0 × 10⁻⁸ mol/l, respectively. The detection limit was 1.7 × 10⁻⁹ mol/l. The proposed method was successfully applied to the determination of vanadium (V) in river water, rain water and cast iron samples. Received June 29, 2001 Revision October 9, 2001     

Aggregation and sedimentation stability of microcrystalline cellulose suspensions in aqueous aluminum nitrate solutions

The aggregation and sedimentation stability of dilute suspensions of microcrystalline cellulose in aqueous solutions of Al(NO₃)₃(2 × 10⁻⁵–2 × 10⁻³ mol/l) is studied by the photometric method at pH 2–11. It is found that, in the absence of Al(NO₃)₃, microcrystalline cellulose suspensions are stable with respect to aggregation throughout the pH range in question. The addition of Al(NO₃)₃ induces the coagulation and accelerates the sedimentation of microcrystalline cellulose aggregates. At all concentrations of Al(NO₃)₃, the maximum loss in stability is observed at pH 7–9. Original Russian Text ? P.M. Mosur, A.V. Lorentsson, Yu.M. Chernoberezhskii, 2009, published in Kolloidnyi Zhurnal, 2009, Vol. 71, No. 4, pp. 566–568.     

Determination of cocaine on banknotes through an aptamer-based electrochemiluminescence biosensor

A novel electrochemiluminescence (ECL) “sandwich” biosensor has been developed to detect cocaine. The sandwich biosensor was fabricated on the basis of the fact that a single aptamer could be split into two fragments and the two dissociated parts could form a folded, associated complex in the presence of targets. One of these (capture probe), which had hexane–thiol at its 5′-terminus, was immobilized on a gold electrode via thiol–gold binding. The other one (detection probe) was labeled with the ECL reagent tris(2,2′-bipyridyl)ruthenium(II)-doped silica nanoparticles (RuSiNPs) at its 3′-terminus. Owing to the weak interaction between the two fragments, the sensor exhibited a low ECL signal in the absence of cocaine. After the target cocaine had been added to the solution, it induced association of the two fragments and stabilized the associated complexes, leading to immobilization of RuSiNPs on the electrode surface, and the ECL detected on the electrode surface was enhanced. The enhanced ECL intensity was directly proportional to the logarithm of the cocaine concentration in the range from 1.0 × 10⁻⁹ to1.0 × 10⁻¹¹ mol/L, with a detection limit of 3.7 × 10⁻¹² mol/L. The biosensor was applied to detect trace amounts of cocaine on banknotes with satisfactory results.     

Structure of mechanically activated high-energy Al + polytetrafluoroethylene nanocomposites

The structure of high-energy Al/polytetrafluoroethylene nanocomposites prepared by mechanochemical synthesis is studied by X-ray diffraction analysis, scanning electron microscopy, atomic force microscopy, and chemical analysis. It is revealed that the composite consists of aluminum particles with sizes of 100–150 nm separated by the polymer layers. The formation of nanocomposite is accompanied by the accumulation of dislocations with the density ρ = (4 ± 1.5) × 10¹⁰ cm⁻². Upon the shock-wave initiation of activated samples, Al + (-C₂ F₄-) → AlF₃ + C reaction propagates in detonation-similar regime at supersonic speed. The velocity of detonation is the highest at the stoichiometric component ratio.     

Flow injection chemiluminescence determination of isoniazid with electrogenerated hypochlorite

A flow-injection chemiluminescence method for the determination of isoniazid based on the sensitizing effect of isoniazid on the chemiluminescence generating luminol-hypochlorite reaction is described. The hypochlorite was electrogenerated on-line by constant current electrolysis, thus, eliminating instability of hypochlorite solution prepared from commercially available sodium hypochlorite. The calibration graph is linear in the range 1 × 10^–8 to 1 × 10^–6 g mL^–1, and the detection limit is 6 × 10^–9 g mL^–1. The relative standard deviation for determination of 5 × 10^–8 g mL^–1 is 2.8%. The proposed method has been successfully applied to the determination of isoniazid in pharmaceutical preparations. Reveived: 2 May 1998 / Revised: 27 July 1998 / Accepted: 7 August 1998