E.A. Zvereva

Rapid pretreatment-free immunochromatographic assay of chloramphenicol in milk.

A pretreatment-free immunochromatographic assay for detection of chloramphenicol (CAP) in milk was developed. The assay is based on competition between CAP molecules in the sample and immobilized CAP-protein conjugate for binding to monoclonal anti-CAP antibodies conjugated with colloidal gold particles (average diameter 30nm). The assay is carried out in the course of sample flowing along test strip with immobilized reactants, and its results can be detected by the naked eye or by a photometric device. Effect of the concentration of immunoreactants on assay characteristics was studied. The assay protocol with maximal sensitivity and reliability was optimized using measured values of brightness of lines. Detection limit for CAP is 10ngmL(-1). Assay duration is 10min, and it can be carried out at room temperature without any additional devices and reactants. The developed test strip has been applied to CAP detection in dairy products.

Pretreatment-free immunochromatographic assay for the detection of streptomycin and its application to the control of milk and dairy products

A rapid pretreatment-free immunochromatographic assay was developed for the control of the streptomycin (STR) content in milk and dairy products. The assay is based on the competition between an immobilized STR-protein conjugate and STR in a sample to be tested for the binding to monoclonal anti-STR antibodies conjugated to colloidal gold during the flow of the sample along a membrane strip with immobilized reactants. It is possible to improve the cut-off level of positive and negative samples distinguished by a change in the molar STR to protein ratio in the immobilized conjugate. The cut-off level (500 ng mL(-1)) thus achieved corresponds to the stated MRL of STR in milk and dairy products. For STR concentrations in the range of 16-250 ng mL(-1) its content can be quantitatively measured based on the degree of binding of a colloidal gold label in the test strip zone with the immobilized STR-protein conjugate. The duration of the assay is 10 min. The selected sizes of membrane pores and colloidal gold particles allow the assay to be carried out at room temperature without additional reactants and pretreatment. The applicability of the assay for milk, whole milk, sour clotted milk, and kefir with different fat content (from 0.5% to 6%) was confirmed. The results of quantitative immunochromatographic assay show good correlation with traditional ELISA (r was equal to 0.935 and 0.940 for the series tested).

Phosphonium ionic liquids based on bulky phosphines: synthesis, structure and properties

A series of new ionic liquids based on sterically hindered decyl(tri-tert-butyl)phosphonium (DTBP) or decyl(tricyclohexyl)phosphonium (DCHP) cations were prepared using quaternisation of tri-tert-butyl- or tricyclohexylphosphine with decylbromide and subsequent bromide exchange with the weakly-coordinating anions BF(4)(-), PF(6)(-), SO(3)CF(3)(-), N(SO(2)CF(3))(2)(-). The salts obtained melt below 100 degrees C and possess a broad electrochemical window. Density functional theory combined with X-ray crystallography, IR and Raman spectroscopy has been used to analyze the molecular and supramolecular structures of the compounds obtained and their possible influence on their physical properties.

Complex Formation of d-Metal Ions at the Interface of TbIII-Doped Silica Nanoparticles as a Basis of Substrate-Responsive TbIII-Centered Luminescence

The complex formation of d-metal ions at the interface of Tb(III)-doped silica nanoparticles modified by amino groups is introduced as a route to sensing d-metal ions and some organic molecules. Diverse modes of surface modification (covalent and noncovalent) are used to fix amino groups onto the silica surface. The interfacial binding of d-metal ions and complexes is the reason for the Tb(III)-centered luminescence quenching. The regularities and mechanisms of quenching are estimated for the series of d-metal ions and their complexes with chelating ligands. The obtained results reveal the interfacial binding of Cu(II) ions as the basis of their quantitative determination in the concentration range 0.1-2.5 μM by means of steady-state and time-resolved fluorescence measurements. The variation of chelating ligands results in a significant effect on the quenching regularities due to diverse binding modes (inner or outer sphere) between amino groups at the interface of nanoparticles and Fe(III) ions. The applicability of the steady-state and time-resolved fluorescence measurements to sense both Fe(III) ions and catechols in aqueous solution by means of Tb(III)-doped silica nanoparticles is also introduced.

Stabilization of the fermi level by a resonant gallium level in Pb1−x SnxTe alloys

Electrical properties of gallium-doped n-Pb1−xSnxTe alloys (x=0.09−0.21) are studied. Ahomalous temperature dependences of the Hall coefficient which indicate the Fermi level pinning by a resonant gallium level in the conduction band were detected. The dependences of the electron concentration and Fermi energy on the alloy composition and temperature are calculated from experimental data in terms of the two-band Kane dispersion relation. It is shown that the gallium resonant level position relative to the valence band top is almost independent of the matrix composition. The dependence of the thermal coefficient of the resonant level shift with respect to the midgap on the alloy composition is obtained.

On Fermi level pinning in lead telluride based alloys doped with mixed valence impurities

Abstract The galvanomagnetic (4.2≤T≤300 K, B≤0.1 T) properties of n-Pb1−yMnyTe (0.07≤y≤0.11) and n-Pb1−xGexTe (0.04≤x≤0.08) doped with In and Ga (CIn≈0.5 mol%, CGa≈1.5–2 mol%, respectively) before and after the irradiation with fast electron (E=6 MeV, Φ≤1.85×1017 cm−2) have been investigated. Impurity-induced deep levels EIn and EGa were observed in the alloys studied. Their energy position was determined and the energy level diagrams as a function of alloy composition were constructed. It was found that the electron irradiation has nearly no effect on the properties of Pb1−yMnyTe〈In〉, while in Pb1−xGexTe〈Ga〉 it causes a transition to metal-type conductivity. It was concluded that the gallium-induced level EGa, unlike the level EIn does not stabilize the Fermi level in PbTe based alloys.

Gallium-induced defect states in Pb1-xGexTe alloys

Galvanomagnetic effects (B ≤ 0.1 T, 4.2 ≤ T < 300 K) in n-Pb 1-x Ge x Te( (0.04 ≤ x ≤ 0.08) alloys doped with gallium (1.5-3 at%) have been investigated as well as before and after the irradiation with fast electrons (T 300 K, E = 6 MeV, Φ ≤ 2.4 × 10 16 cm -2 ). Low-temperature activation range on temperature dependencies of the resistivity and the Hall constant has been revealed in the alloys with low initial gallium concentration. Increasing in the gallium content as well as fast-electron irradiation lead to the transition to the metal-type conductivity in the samples. The results were explained under assumption that gallium doping induced the appearance of deep impurity level in the gap of the alloys. The position of the gallium level in depending on the alloy composition was determined.

Crystal structure, physical properties, and electronic and magnetic structure of the spin S = 5/2 zigzag chain compound Bi2Fe(SeO3)2OCl3.

We report the synthesis and characterization of the new bismuth iron selenite oxochloride Bi2Fe(SeO3)2OCl3. The main feature of its crystal structure is the presence of a reasonably isolated set of spin S = 5/2 zigzag chains of corner-sharing FeO6 octahedra decorated with BiO4Cl3, BiO3Cl3, and SeO3 groups. When the temperature is lowered, the magnetization passes through a broad maximum at Tmax ≈ 130 K, which indicates the formation of a magnetic short-range correlation regime. The same behavior is demonstrated by the integral electron spin resonance intensity. The absorption is characterized by the isotropic effective factor g ≈ 2 typical for high-spin Fe(3+) ions. The broadening of ESR absorption lines at low temperatures with the critical exponent β = 7/4 is consistent with the divergence of the temperature-dependent correlation length expected for the quasi-one-dimensional antiferromagnetic spin chain upon approaching the long-range ordering transition from above. At TN = 13 K, Bi2Fe(SeO3)2OCl3 exhibits a transition into an antiferromagnetically ordered state, evidenced in the magnetization, specific heat, and Mössbauer spectra. At T < TN, the (57)Fe Mössbauer spectra reveal a low saturated value of the hyperfine field Hhf ≈ 44 T, which indicates a quantum spin reduction of spin-only magnetic moment ΔS/S ≈ 20%. The determination of exchange interaction parameters using first-principles calculations validates the quasi-one-dimensional nature of magnetism in this compound.

Magnetic phase diagram and first-principles study ofPb3TeCo3V2O14

An antiferromagnetic ordering in Pb3TeCo3V2O14 takes place through formation of short range correlation regime with T* ~ 10.5 K and succession of second order phase transition at TN1 = 8.9 K and first order phase transition at TN2 = 6.3 K. An external magnetic field rapidly destroys magnetic structure at T < TN2 and influences the magnetic order at TN2 < T < TN1 resulting in complex magnetic phase diagram of Pb3TeCo3V2O14 as derived from magnetization and specific heat measurements. The first principles calculations indicate that in variance with layered crystal structure the magnetic subsystem of Pb3TeCo3V2O14 is quasi-one-dimensional and highly unusual consisting of weakly coupled triangular tubes.

Enzyme immunoassay and proteomic characterization of troponin I as a marker of mammalian muscle compounds in raw meat and some meat products

The skeletal muscle protein troponin I (TnI) has been characterized as a potential thermally stable and species-specific biomarker of mammalian muscle tissues in raw meat and meat products. This study proposed a technique for the quantification of TnI comprising protein extraction and sandwich enzyme-linked immunosorbent assay (ELISA). The technique is characterized by a TnI detection limit of 4.8 ng/ml with quantifiable concentrations ranging from 8.7 to 52 ng/ml. The method was shown to be suitable for detection of TnI in mammalian (beef, pork, lamb, and horse) meat but not in poultry (chicken, turkey, and duck) meat. In particular, the TnI content in beef was 0.40 3 ± 0.058 mg/g of wet tissue. The TnI estimations obtained for the pork and beef samples using ELISA were comparable to the proteomic analysis results. Thus, the quantitative study of TnI can be a convenient way to assess the mammalian muscle tissue content of various meat products.