Development of a sensitive surface plasmon resonance immunosensor for detection of 2,4-dinitrotoluene with a novel oligo (ethylene glycol)-based sensor surface

A surface plasmon resonance (SPR) immunosensor for detection of 2,4-dinitrotoluene (2,4-DNT), which is a signature compound of 2,4,6-trinitrotoluene-related explosives, was developed by using a novel oligo (ethylene glycol) (OEG)-based sensor surface. A rabbit polyclonal antibody against 2,4-DNT (anti-DNPh-KLH-400 antibody) was prepared, and the avidity for 2,4-DNT and recognition capability were investigated by indirect competitive ELISA. The sensor surface was fabricated by immobilizing a 2,4-DNT analog onto an OEG-based self-assembled monolayer formed on a gold surface via an OEG linker. The fabricated surface was characterized by Fourier-transform infrared-refractive absorption spectrometry (FTIR-RAS). The immunosensing of 2,4-DNT is based on the indirect competitive principle, in which the immunoreaction between the anti-DNPh-KLH-400 antibody and 2,4-DNT on the sensor surface was inhibited in the presence of free 2,4-DNT in solution. The limit of detection for the immunosensor, calculated as three times the standard deviation of a blank value, was 20 pg mL⁻¹, and the linear dynamic range was found to be between 1 and 100 ng mL⁻¹. Additionally, the fabricated OEG-based surface effectively prevented non-specific adsorption of proteins, and the specific response to anti-DNPh-KLH-400 antibody was maintained for more than 30 measurement cycles.     

Measuring metal homogeneity in a matrix via the measurement of the ratio metal to matrix oxide using ICP-MS

A simple method has been developed that allows a fast determination of the homogeneity of an element M in an alloy, even for minor components. This is done by measuring a ratio of ion currents I, I ^M/I ^M’O, whereby M’ is the matrix element, by inductively coupled plasma mass spectrometry (ICP-MS). The method can be used to determine the homogeneity of one component in a binary alloy and allows to estimate the sample size necessary to minimise uncertainty contributions due to inhomogeneity in the analysis of such an alloy. In this work the homogeneity of a niobium/0.1% zirconium alloy was determined on 1 mg samples. Accurate weighings of these small samples are not required, as the method is based on the measurement of the niobium/zirconium amount ratio in the dissolved samples. As this ratio is fairly large, the Zr/NbO amount ratio was measured instead to decrease the magnitude of the measured ratio. This ratio was found to be sufficiently stable over time for homogeneity testing. In this particular case the Zr/NbO ratio in the samples was found to vary by 0.049 relative for a 1 mg samples size.     

Measuring metal homogeneity in a matrix via the measurement of the ratio metal to matrix oxide using ICP-MS

A simple method has been developed that allows a fast determination of the homogeneity of an element M in an alloy, even for minor components. This is done by measuring a ratio of ion currents I, I ^M/I ^M’O, whereby M’ is the matrix element, by inductively coupled plasma mass spectrometry (ICP-MS). The method can be used to determine the homogeneity of one component in a binary alloy and allows to estimate the sample size necessary to minimise uncertainty contributions due to inhomogeneity in the analysis of such an alloy. In this work the homogeneity of a niobium/0.1% zirconium alloy was determined on 1 mg samples. Accurate weighings of these small samples are not required, as the method is based on the measurement of the niobium/zirconium amount ratio in the dissolved samples. As this ratio is fairly large, the Zr/NbO amount ratio was measured instead to decrease the magnitude of the measured ratio. This ratio was found to be sufficiently stable over time for homogeneity testing. In this particular case the Zr/NbO ratio in the samples was found to vary by 0.049 relative for a 1 mg samples size. Received: 30 November 1998 / Revised: 22 March 1999 / Accepted: 27 March 1999     

Enhanced degradation of 2,4-dinitrotoluene by ozonation in the presence of manganese(II) and oxalic acid

Manganese catalytic ozonation of 2,4-dinitrotoluene (DNT) in the presence of oxalic acid was studied. The addition of manganese ion (Mn²⁺) or oxalic acid alone in ozonation process did not enhance DNT degradation, but the addition of Mn²⁺ coupled with oxalic acid accelerated degradation of DNT. The DNT degradation efficiency was influenced by carbonate in the catalytic ozonation process. Kinetics study showed that Mn²⁺ catalytic ozonation significantly promoted the decomposition of ozone. Experimental results of electron spin resonance (ESR) demonstrated that addition of Mn²⁺ and oxalic acid produced much hydroxyl radicals in catalytic ozonation system than that in single ozonation system. These results suggested that catalytic ozonation followed hydroxyl radical-type mechanism. Mn²⁺ promoted decomposition of ozone to produce hydroxyl radical and it was oxidized into manganese oxide. Manganese oxide was reduced into Mn²⁺ by oxalic acid, which is the key step of catalytic process. Based on above results, a cycle catalytic mechanism of Mn²⁺ was proposed. Intermediates were determined by HPLC and GC–MS, and they mainly included aromatic organics and aliphatic carboxylic acids.     

Catalytic activity of a zirconium(IV) oxide surface supported with transition metal ions

The kinetics of H₂O₂ decomposition have been investigated using ZrO₂ supported with transition metal ions including Cu^II, Ag^I, Hg^II, Co^II, Mn^II, Ni^II and Fe^III. At pH = 6.8, the reaction rate exhibits a first order dependence on the initial H₂O₂ concentration at low concentrations. The order of activity of the different catalysts is strongly dependent on the [H₂O₂]₀ used. The reaction proceed via the formation of the peroxo-intermediate which has an inhibiting effect on the reaction rate. The rate increases with increasing pH, and attains a limiting rate at higher pH's. A reaction mechanism is proposed involving liberation of HO₂ radicals from the peroxo-intermediate as the rate-determining step.     

Structure and dynamics of CO overlayers on a hydroxylated metal oxide: the polar ZnO(0001) surface

The adsorption and desorption of CO on the hydroxylated, O-terminated polar ZnO(0001) surface has been studied using He-atom scattering. The experimental results reveal the formation of a physisorbed ordered CO overlayer. In addition to recording angular distributions of elastically scattered He atoms, also the dynamical properties of the CO overlayer have been investigated using inelastic He-atom scattering. With the aid of electronic structure calculations a loss peak with an energy transfer of 7.2 meV is assigned to the frustrated translation of the CO molecule normal to the surface.     

Highly sensitive detection of mercury (II) in aqueous media by tetraphenylporphyrin with a metal ion receptor

We provide a highly sensitive and selective assay to detect Hg²⁺ in aqueous solutions using a novel β-functionalised porphyrin-based chemosensor 5 at room temperature. The binding properties of the chemosensor 5 for cations were examined by UV–vis spectroscopy and ¹H NMR. The results indicate that a 1:1 stoichiometric complex is formed between chemosensor 5 and mercury (II) ion. The recognition mechanism between chemosensor 5 and metal ion was discussed based on their absorbance changes and the chemical shift changes when they interact with each other. Control experiments revealed that chemosensor 5 has a selective response to mercury (II) ion compared with other metal ions.     

A label-free thrombin binding aptamer as a probe for highly sensitive and selective detection of lead(II) ions by a resonance Rayleigh scattering method

The binding of lead(II) ions with unusually high affinity to a thrombin binding aptamer resulted in an enhancement of resonance Rayleigh scattering (RRS). A simple, sensitive, and selective assay for the direct determination of trace amounts of Pb(2+) on the basis of RRS has been proposed.     

Kinetics and mechanism of the liquid-phase reaction of 2,4-dinitrotoluene with ozone in the presence of manganese(II) acetate

The kinetics and the mechanism of the liquid-phase oxidation of 2,4-dinitrotoluene with ozone in the presence of manganese(II) acetate have been investigated. The major products of 2,4-dinitrotoluene oxidation with ozone in acetic anhydride are 2,4-dinitrobenzyl acetate (65.8%) and 2,4-dinitrobenzylidene diacetate (18.8%). The effect of the manganese(II) acetate concentration on the selectivity of substrate oxidation at the methyl group is reported. A redox catalysis mechanism providing an explanation to experimental data is considered.     

An unprecedented strategy for selective and sensitive fluorescence detection of nitric oxide based on its reaction with a selenide

A new strategy that utilizes the interaction between NO and a selenide is reported for fluorescence detection of NO, in which rhodamine B selenolactone serves as a model selenide.     

A sensitive fluorescence anisotropy method for detection of lead (II) ion by a G-quadruplex-inducible DNA aptamer

Sensitive and selective detection of Pb²⁺ is of great importance to both human health and environmental protection. Here we propose a novel fluorescence anisotropy (FA) approach for sensing Pb²⁺ in homogeneous solution by a G-rich thrombin binding aptamer (TBA). The TBA labeled with 6-carboxytetramethylrhodamine (TMR) at the seventh thymine nucleotide was used as a fluorescent probe for signaling Pb²⁺. It was found that the aptamer probe had a high FA in the absence of Pb²⁺. This is because the rotation of TMR is restricted by intramolecular interaction with the adjacent guanine bases, which results in photoinduced electron transfer (PET). When the aptamer probe binds to Pb²⁺ to form G-quadruplex, the intramolecular interaction should be eliminated, resulting in faster rotation of the fluorophore TMR in solution. Therefore, FA of aptamer probe is expected to decrease significantly upon binding to Pb²⁺. Indeed, we observed a decrease in FA of aptamer probe upon Pb²⁺ binding. Circular dichroism, fluorescence spectra, and fluorescence lifetime measurement were used to verify the reliability and reasonability of the sensing mechanism. By monitoring the FA change of the aptamer probe, we were able to real-time detect binding between the TBA probe and Pb²⁺. Moreover, the aptamer probe was exploited as a recognition element for quantification of Pb²⁺ in homogeneous solution. The change in FA showed a linear response to Pb²⁺ from 10 nM to 2.0 μM, with 1.0 nM limit of detection. In addition, this sensing system exhibited good selectivity for Pb²⁺ over other metal ions. The method is simple, quick and inherits the advantages of aptamer and FA.     

Sol-gel processing of a bimetallic alkoxide precursor confined in a porous glass matrix: a route to novel glass/metal oxide nanocomposites

In this work we present the utilization of the heterometallic alkoxide [FeCl{Ti(2)(OPr(i))(9)}] as the first sol-gel single-source precursor to achieve nanocomposites made of iron and titanium oxides incorporated into Porous Vycor Glass (PVG). The nanocomposites were prepared by the impregnation of the precursor in a PVG plate followed by hydrolysis reactions. Different samples were obtained by further thermal treatment of the hydrolyzed sample. The nanocomposites were characterized by UV-vis-NIR, Raman and EPR spectroscopies, XRD and TEM. The results indicate that the room-temperature hydrolyzed samples are formed by nanoparticles of FeOOH and brookite-TiO(2) embedded on a glassy matrix. After the heat treatment at temperatures above 900 degrees C, a pseudobrookite Fe(2)TiO(5) was formed. All samples present high transparency and homogeneity. The results showed here indicate that the sol-gel process using the single-source precursor [FeCl{Ti(2)(OPr(i))(9)}] should be a novel and efficient approach to the preparation of nanometric Fe/Ti oxides incorporated into a glassy matrix.     

Dynamic elasticity of triblock copolymer of poly(ethylene oxide) and poly(propylene oxide) on a water surface

Dilatational viscoelasticity of adsorbed and spread films of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer at the air-water interface is studied by the capillary waves and oscillating barrier techniques. At the surface pressure below 10 mN/m, dynamic surface properties of these films coincide with those of poly(ethylene oxide). At higher surface pressures, the results obtained indicate the desorption of poly(propylene oxide) segments from the monolayer and their interaction with poly(ethylene oxide) segments in an aqueous phase. At a surface pressure close to 19 mN/m, the behavior of adsorbed and spread poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) films becomes different. The real part of dynamic surface elasticity of spread films tends toward its maximum value (20 mN/m) and, upon further compression, films begin to dissolve. At the same time, the surface elasticity of adsorbed films decreases nearly twofold upon the achievement of the maximum value that testifies the formation of looser structure of the surface layer.     

Spin-state dynamics of a photochromic iron(II) complex and its immobilization on oxide surfaces via phenol anchors

This work presents a detailed study of the photo-induced spin-state dynamics of the photochromic iron(II) complex 1, where the metal ion is in the field of a tripodal hexa-imine ligand with protolysable phenol groups. The nature of the complex’s ground state has been identified as a spin singlet by ¹H NMR and steady-state UV/vis spectroscopies, and its distorted octahedral structure was analyzed via crystal structure determination. Sub-picosecond and nanosecond time-resolved laser flash photolysis experiments identify the long-lived quintet state of 1 as the selective product of photoexcitation in the UV/vis spectral region. Thermal barriers of spin-state interconversion as a function of solvent and added base are derived from temperature-dependent rates of transient decay. Ground-state recovery is found to be significantly affected by the solvent and is strongly enhanced, in particular, by base-driven solvolysis of the ligand’s phenol groups. Partial spontaneous deprotonation of the phenolic hydroxyl groups of 1 seems to prevail on metal oxide surfaces, i.e. on alumina. Composite materials, like 1 at Al₂O₃, that retain the characteristic spectral features of the parent iron(II) complex can be readily obtained by wet impregnation of hydrous alumina with solutions of 1.     

Dynamics of a poly(ethylene oxide) tracer in a poly(methyl methacrylate) matrix: remarkable decoupling of local and global motions

The tracer diffusion coefficient of unentangled poly(ethylene oxide) (PEO, M=1000 gmol) in a matrix of poly(methyl methacrylate) (PMMA, M=10 000 gmol) has been measured over a temperature range from 125 to 220 degrees C with forced Rayleigh scattering. The dynamic viscosities of blends of two different high molecular weight PEO tracers (M=440 000 and 900 000 gmol) in the same PMMA matrix were also measured at temperatures ranging from 160 to 220 degrees C; failure of time-temperature superposition was observed for these systems. The monomeric friction factors for the PEO tracers were extracted from the diffusion coefficients and the rheological relaxation times using the Rouse model. The friction factors determined by diffusion and rheology were in good agreement, even though the molecular weights of the tracers differed by about three orders of magnitude. The PEO monomeric friction factors were compared with literature data for PEO segmental relaxation times measured directly with NMR. The monomeric friction factors of the PEO tracer in the PMMA matrix were found to be from two to six orders of magnitude greater than anticipated based on direct measurements of segmental dynamics. Additionally, the PEO tracer terminal dynamics are a much stronger function of temperature than the corresponding PEO segmental dynamics. These results indicate that the fastest PEO Rouse mode, inferred from diffusion and rheology, is completely separated from the bond reorientation of PEO detected by NMR. This result is unlike other blend systems in which global and local motions have been compared.     

A label-free and self-assembled electrochemical biosensor for highly sensitive detection of cyclic diguanylate monophosphate (c-di-GMP) based on RNA riboswitch

Cyclic diguanylate monophosphate (c-di-GMP) is an important second messenger that regulates a variety of complex physiological processes involved in motility, virulence, biofilm formation and cell cycle progression in several bacteria. Herein we report a simple label-free and self-assembled RNA riboswitch-based biosensor for sensitive and selective detection of c-di-GMP. The detectable concentration range of c-di-GMP is from 50 nM to 1 μM with a detection limit of 50 nM.     

Carbon nanotube/metal oxide dispersed poly(ortho‐aminophenol) as a ternary nanocomposite film: Facile electrosynthesis,surface characterization,and electrochemical pseudocapacitive performance

In this work, CNT‐NiCo₂O₄ was first synthesized via a chemical strategy in order to fabricate the ternary nanocomposite of a p‐type conductive polymer. Subsequently, hybrid poly(o‐aminophenol) POAP/CNT‐NiCo₂O₄ ternary composite films were prepared via the electropolymerization of POAP in the presence of CNT‐NiCo₂O₄ to be used in electrochemical storage devices as the active electrode. Electrochemical analyses including galvanostatic charge–discharge experiments, cyclic voltammetry, and electrochemical impedance spectroscopy were conducted to study the system performance. Furthermore, surface analyses were carried out to characterize the POAP/CNT‐NiCo₂O₄ composite film. Novel nanocomposite materials with the merits of extraordinarily high active surface area, ease of fabrication, and superior stability in aqueous electrolytes are presented for use in electrochemical redox capacitors.     

Modulation of surface reactivity via electron confinement in metal quantum well films: O2 adsorption on PbSi(111)

Pb quantum well films with atomic-scale uniformity in thickness over macroscopic areas were prepared on Si(111)-7x7 surfaces. As a probe molecule, O(2) was used to explore the effect of electron confinement in the metal films on the surface reactivity. X-ray photoelectron spectroscopy results showed clear oscillations of oxygen adsorption and Pb oxidation with the thickness of the Pb films. The higher reactivity to O(2) on the films with 23 and 25 ML Pb has been attributed to their highest occupied quantum well states being close to the Fermi level (E(F)) and the high density of the electron states at E(F) (DOS-E(F)), as evidenced by the corresponding ultraviolet photoelectron spectroscopy. A dominant role of DOS-E(F) was suggested to explain the quantum modulation of surface reactivity in metal quantum well films.     

Adsorption of poly(ethylene oxide) at the air/water interface: a dynamic and static surface tension study

The adsorption of polyethylene oxide (PEO) homologues in a wide range of molecular weight (from M(PEO)=200 to 10(6)) at the air/aqueous solution interface was investigated by dynamic and static surface tension measurements. An approximate estimate for the lower limit of PEO concentration was given at which reliable equilibrium surface tension can be determined from static surface tension measurements. It was shown that the observed jump in the earlier published sigma-lg(c(PEO)) curves is attributable to the nonequilibrium surface tension values at low PEO concentrations. The adsorption behavior of short chain PEO molecules (M(PEO)1000) is similar to that of the ordinary surfactants. The estimated standard free energy of PEO adsorption, DeltaG(0), increases linearly with the PEO molecular weight until M(PEO)=1000. In this molecular weight range, DeltaG(0) was found to be approximately the fifth of the hydrophobic driving force related to the adsorption of a surfactant with the same number of methylene groups. In the case of the longer chain PEOs the driving force of adsorption is so high that the adsorption isotherm is near saturation in the experimentally available polymer concentration range. Above a critical molecular weight the PEO adsorption reveals universal features, e.g., the surface tension and the surface density of segments do not depend on the polymer molecular weight.