Voltammetric determination of B<Subscript>1</Subscript> and B<Subscript>6</Subscript> vitamins using a pencil graphite electrode

Due to the importance of B₁ and B₆ vitamins for human health it is useful to develop new cheap and rapid methods for their determination. Voltammetric behavior of these vitamins on a pencil graphite electrode was investigated using cyclic voltammetry in different media. Direct quantitative determination of the two vitamins, one in the presence of the other, was done by differential pulse voltammetry. Vitamin B₁ was electroactive only in a NaOH solution generating two irreversible oxidation peaks; the first peak obtained at 250 mV is well-defined and was used in quantitative determinations. In case of vitamin B₆, a well-defined oxidation peak was observed in all investigated supporting electrolytes except for HCl. The linear concentration ranges were 10^?5–10^?3 M for vitamin B₁ in a NaOH solution and 5 × 10^?6–10^?3 M for vitamin B₆ in an acetate buffer solution. The obtained detection limits were 5.34 × 10^?6 M and 2.81 × 10^?6 M for vitamin B₁ and vitamin B₆, respectively. The developed method is simple and rapid and it was successfully applied in the determination of the two vitamins in pharmaceuticals.     

Uncertainty in aflatoxin B<Subscript>1</Subscript> analysis using information from proficiency tests

We describe how to calculate uncertainty in the determination of aflatoxin B₁ in nuts and maize using an HPLC method with prederivatisation with trifluoroacetic acid and fluorescence detection. The uncertainty is easily calculated using the information obtained from the participation in several proficiency tests. All the sources of uncertainty are grouped in two terms: (1) matrix variability, intermediate precision and sample heterogeneity, and (2) method concordance. This methodology has the advantage that no extra work needs to be done because all the information to calculate uncertainty comes from proficiency tests. The uncertainty values were calculated using samples whose concentration ranged between 2 and 20 g L^–1. The relative standard uncertainty computed for aflatoxin B₁ was 16.3%.     

Controlled synthesis,characterization and thermal properties of Mg<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>

Optimum conditions for synthesizing monoclinic and triclinic Mg₂B₂O₅ compounds by high-temperature solid-state reactions were investigated. Mixtures composed of boric acid and magnesium oxide at MgO:B₂O₃ mole ratios of 1:0.25, 1:0.5 and 1:1.5 were heated for 1 hour at temperatures between 600–1050°C and the formed phases were identified by XRD analysis. Monoclinic Mg₂B₂O₅ was formed by heating at 850°C for 4 hours together with minimum amounts of triclinic Mg₂B₂O₅, while triclinic Mg₂B₂O₅ was formed as a single phase at 1050°C for the same reaction time. The products obtained at optimum conditions were subjected to a series of tests to determine their chemical compositions, particle size distributions, surface area values, IR spectra and TG/DTA patterns.      

Determination of vitamin B<Subscript>1</Subscript> in seawater and microalgal fermentation media by high-performance liquid chromatography with fluorescence detection

A highly sensitive high-performance liquid chromatographic method with fluorescence detection has been developed for determination of vitamin B₁. Vitamin B₁ was converted into a fluorescent compound by treatment with hydrogen peroxide–horseradish peroxidase and the derivative was subsequently analyzed by HPLC on a Waters Spherisorb ODS2 column (250 mm×4.6 mm ID, 5 μm) with 40:60 methanol–pH 8.5 acetate buffer solution as mobile phase and fluorescence detection at 440 nm (with excitation at 375 nm). The calibration graph was linear from 5.00×10⁻¹⁰ mol L⁻¹ to 5.00×10⁻⁷ mol L⁻¹ for vitamin B₁ with a correlation coefficient of 0.9991 (n=9). The detection limit was 1.0×10⁻¹⁰ mol L⁻¹. The method was successfully used for determination of vitamin B₁ at pg mL⁻¹ levels in microalgal fermentation media and seawater after solid-phase extraction. Recovery was from 89 to 110% and the relative standard deviation was in the range 1.1 to 4.3%.     

Transmission Electron Microscopy Study on the Formation of Al<Subscript>18</Subscript>B<Subscript>4</Subscript>O<Subscript>33</Subscript> Whiskers

The aim of this paper is to report the results of a systematic high-resolution transmission electron microscopy study on Al₁₈B₄O₃₃. The fluxing agent method permits the formation of needle-shaped whiskers of Al₁₈B₄O₃₃, having sub-micron thickness with a tendency to come and fuse together. Amounts of 25% and 50% K₂SO₄, K₂CO₃ or KCl were used liked fluxing agents. Using this method, the optimum temperature for the synthesised compound was found to be 1000°C. The investigation techniques were X-ray diffraction and electron microscopy.     

Synthesis and crystal structure of strontium borate Sr<Subscript>4</Subscript>B<Subscript>14</Subscript>O<Subscript>25</Subscript>

The new compound Sr₄B₁₄O₂₅ (4SrO · 7B₂O₃) corresponding to an oxide ratio of 4: 7 has been identified and synthesized in the SrO-B₂O₃ system. The crystal structure of the compound has been determined (space group Cmc2₁, a = 7.734(5) Å, b = 16.332(5) Å, c = 14.556(5) Å, Z = 4, 702 F(hkl), R = 0.078). The borate anions form a three-dimensional framework consisting of borate groups of two types: three-ring structures (2□, Δ) and BO₃ triangles. Layers formed by 14-membered rings composed of boron-oxygen tetrahedra and triangles packed within the layer according to the herringbone pattern can be distinguished in the framework. The strontium atoms are located on the mirror symmetry planes between these layers. The compound is metastable and decomposes, on long-term storage, into strontium di- and metaborate.     

Bismuth aluminoborate Bi<Subscript>0.96</Subscript>Al<Subscript>2.37</Subscript>(B<Subscript>4</Subscript>O<Subscript>10</Subscript>)O: Synthesis and crystal structure

The crystal structure of a new bismuth aluminoborate Bi_0.96Al_2.37(B₄O₁₀)O is studied by single-crystal X-ray diffraction. The Bi_0.96Al_2.37(B₄O₁₀)O single crystals are hexagonal (space group \(P\bar 6\) 2m). The unit cell parameters are as follows: a = b = 4.587(4) Å, c = 2.253(9) Å, α = β = 90°, γ = 120°, V = 168.60 ų, Z = 1.     

Synthesis of IR phosphors based on germanatoborate Gd<Subscript>14</Subscript>Ge<Subscript>2</Subscript>B<Subscript>6</Subscript>O<Subscript>34</Subscript>

Processes of the formation of germanatoborates Gd₁₄B₆Ge₂O₃₄ and Gd_13.02Nd_0.98B₆Ge₂O₃₄ have been studied using different methods of synthesis (solid-state interaction, direct and inverse co-precipitation, self-propagating high-temperature synthesis (SHS)). It has been established that the synthesis of germanatoborates Gd₁₄B₆Ge₂O₃₄ and Gd_13.02Nd_0.98B₆Ge₂O₃₄ using the inverse precipitation and SHS methods occurs with the formation of an intermediate apatite-like phase, which upon heating to above 1100°С is reconstructed into the Ln₁₄B₆Ge₂O₃₄ (Ln = Gd, Nd) structure. The germanatoborates synthesized crystallize in the trigonal system (space group P3₁). The lattice parameters of Gd_13.02Nd_0.98B₆Ge₂O₃₄ are a = 9.746(4) Å and c = 25.795(13) Å. The thermal stability of the Gd₁₄B₆Ge₂O₃₄ and Gd_13.02Nd_0.98B₆Ge₂O₃₄ germanatoborates has been studied. The obtained materials of composition Gd_13.02Nd_0.98B₆Ge₂O₃₄ show luminescence properties and can be employed as infrared phosphors.     

Carbon in boron carbide: The crystal structure of B<Subscript>11.4</Subscript>C<Subscript>3.6</Subscript>

A single crystal of boron carbide obtained from a self-propagating high-temperature synthesis (SHS) product was studied by X-ray crystallography: B_11.4C_3.6, a = 5.594(2) Å, c = 11.977(7) Å, V = 324.6(7) ų, space group R3m, Z = 3, ρ_calcd = 2.56 g/cm³, R = 0.048. The content of carbon in the single crystal was estimated at ～24 at % from analysis of the unit cell parameters, bond lengths, and the volume of B_{12 ? x} C _x icosahedra, which demonstrated the possibility of obtaining by SHS carbon-rich boron carbide crystals due to the substitution of carbon atoms for boron atoms in icosahedra. Comparison of the X-ray crystallographic data for single crystals of boron carbide with the results of quantum-chemical calculations (an ab initio method (the 3–21G basis set) with geometry optimization) showed that the C-B-C group in a crystal has a nonlinear structure.     

A Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript>@graphene quantum dot core-shell structured nanomaterial as a fluorescent probe and for magnetic removal of mercury(II) ion

The authors describe the synthesis of a multifunctional nanocomposite with an architecture of type Fe₃O₄@SiO₂@graphene quantum dots with an average diameter of about 22 nm. The graphene quantum dots (GQDs) were covalently immobilized on the surface of silica-coated magnetite nanospheres via covalent linkage to surface amino groups. The nanocomposite displays a strong fluorescence (with excitation/emission peaks at 330/420 nm) that is fairly selectively quenched by Hg²⁺ ions, presumably due to nonradiative electron/hole recombination annihilation. Under the optimized experimental conditions, the linear response to Hg²⁺ covers the 0.1 to 70 μM concentration range, with a 30 nM lower detection limit. The high specific surface area and abundant binding sites of the GQDs result in a good adsorption capacity for Hg²⁺ (68 mg?g^?1). The material, due to its superparamagnetism, can be separated by using a magnet and also is recyclable with EDTA so that it can be repeatedly used for simultaneous detection and removal of Hg²⁺ from contaminated water.

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Graphical abstract A schematic view of preparation process for the Fe₃O₄@SiO₂@graphene quantum dots nanocomposite (denoted as Fe₃O₄@SiO₂@GQDs). The graphene quantum dots were covalently immobilized on the surface of silica-coated magnetite nanospheres (Fe₃O₄@SiO₂) via covalent linkage to surface amino groups.

     

A DFT study on electronic and optical properties of aspirin-functionalized B<Subscript>12</Subscript>N<Subscript>12</Subscript> fullerene-like nanocluster

In this work, the interaction of an aspirin (AS) molecule with the external surface of a boron nitride fullerene-like nanocage (B₁₂N₁₂) is studied by means of density functional theory (DFT) calculations. Equilibrium geometry, electronic properties, adsorption energy and thermodynamic stability are identified for all of the adsorbed configurations. Four stable configurations are obtained for the interaction of AS molecule with the B₁₂N₁₂ nanocage, with adsorption energies in the range of ?10.1 to ?37.7 kcal/mol (at the M06-2X/6-31 + G** level). Our results clearly indicate that Al-doping of the B₁₂N₁₂ tends to increase the adsorption energy and thermodynamic stability of AS molecule over this nanocage. We further study the adsorption of AS over the B₁₂N₁₂ and B₁₁N₁₂Al in the presence of a protic (water) or aprotic (benzene) solvent. It is found that the calculated binding distances and adsorption energies by the PCM and CPCM solvent models are very similar, especially for the B₁₂N₁₂ complexes. According to time-dependent DFT calculations, the Al-doping can shift estimated λ _max values toward longer wavelengths (redshift). Solvent effects also have an important influence on the calculated electronic absorption spectra of AS-B₁₂N₁₂ complexes.     

Electro-deposition of gold nanostructures on carbon paste electrode: a platform with signal amplification for voltammetric study and determination of pyridoxine (vitamin B<Subscript>6</Subscript>)

For the first time, the electrochemical synthesis of gold nanostructures was done at the surface of carbon paste electrode. This device was used as a simple and sensitive electrochemical sensor for measurement of pyridoxine (Vitamin B₆, VB₆). The diffusion coefficient (D) and the kinetic parameters such as electron transfer coefficient (α) and catalytic rate constant (k) for VB₆ were also determined using electrochemical approaches. The cyclic voltammetry method showed VB₆ oxidation reaction with irreversible characteristics was diffusion-controlled at low scan rates. Using differential pulse voltammetry (DPV), the peak current was linearly dependent on VB₆ concentration in the ranges of 1.9–110.8 and 110.8–257.0 μM, with detection limit of 74.0 nM, respectively. Results showed there is no interference of other vitamins in oxidation of VB₆. DPV was used to quantify of VB₆ in some real samples by the standard addition method. The modified electrode showed good sensitivity and stability.     

Aptamer-based fluorescent platform for ultrasensitive adenosine detection utilizing Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic nanoparticles and silver nanoparticles

The authors describe an aptamer-based fluorescent assay for adenosine (Ade). It is based on the interaction between silver nanoparticles (AgNPs) and CdTe quantum dots (QDs). The beacon comprises a pair of aptamers, one conjugated to Fe₃O₄ magnetic nanoparticles, the other to AgNPs. In the presence of Ade, structural folding and sandwich association of the two attachments takes place. After magnetic separation, the associated sandwich structures are exposed to the QDs. The AgNPs in sandwich structures act as the signaling label of Ade by quenching the fluorescence of QDs (at excitation/emission wavelengths of 370/565 nm) via inner filter effect, electron transfer and trapping processes. As a result, the fluorescence of QDs drops with increasing Ade concentration. The assay has a linear response in the 0.1 nM to 30 nM Ade concentration range and a 60 pM limit of detection. The assay only takes 40 min which is the shortest among the aptamer-based methods ever reported. The method was successfully applied to the detection of Ade in spiked biological samples and satisfactory recoveries were obtained.

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Graphical abstract Schematic of a highly efficient and convenient adenosine (Ade) fluorometric assay. It is based on the interaction between Ag nanoparticles (NPs) and CdTe quantum dots (QDs). Ade aptamers (ABA1 and ABA2) are used as recognition unit and Fe₃O₄ magnetic nanoparticles act as magnetic separator. The assay exhibits superior sensitivity and speediness.

     

Determination of vitamin B<Subscript>12</Subscript> using a chemiluminescence flow system

A method to determine vitamin B₁₂ by measuring the chemiluminescence (CL) intensities using a flow injection (FI) system has been proposed. It is based on the catalytic effect of cobalt(II) in vitamin B₁₂ on the CL reaction between luminol and hydrogen peroxide in a basic medium. The increment of the CL intensity is proportional to the concentration of vitamin B₁₂ in the range 8.68–86.9 ng/mL (r ² = 0.9984) with a detection limit (3σ) of 0.89 ng/mL. The CL response is obtained in 10 s at a flow rate of 3.0 mL/min with a relative standard deviation (RSD) of less than 2.5% (n = 6). The method has been successfully applied to the determination of vitamin B₁₂ in pharmaceutical injections. The text was submitted by the authors in English.     

Urchin-like gold nanoparticle-based immunochromatographic strip test for rapid detection of fumonisin B<Subscript>1</Subscript> in grains

An immunochromatographic strip (ICS) using urchin-like gold nanoparticles (UGNs) for sensitive detection of fumonisin B₁ (FB₁) was developed to meet the requirement for rapidly monitoring FB₁ in grain samples. The sensitivity of the ICS was 5.0 ng/mL, which represents a fourfold increase in sensitivity over conventional strip preparation using colloidal gold as the antibody-labeled probe. Analysis of FB₁ in grain samples showed that data obtained from the strip tests were in a good agreement with those obtained from HPLC and enzyme-linked immunosorbent assays (ELISAs). This qualitative test did not require any specialized equipment, and the detection time was less than 5 min, which is suitable for on-site testing of FB₁ in grain samples. Overall, to our knowledge, this is the first report of using a UGN as the antibody-labeled probe for sensitive detection of FB₁ in grains using an ICS.

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Graphical Abstract Preparation of ICS using conventional colloidal gold and urchin-like gold nanoparticle, respectively

     

An oligosorbent-based aptamer affinity column for selective extraction of aflatoxin B<Subscript>2</Subscript> prior to HPLC with fluorometric detection

The article describes an aptamer affinity column for selective solid-phase extraction of aflatoxin B₂ (AFB₂). Amino-modified aptamer against AFB₂ was immobilized on CNBr-activated Sepharose through a covalent bond. The effects of oligosorbents based on 3′- or 5′-amino-modified sequences with a C6 or a C7 spacer arm were evaluated by UV spectroscopy at 260 nm. The extraction recovery was evaluated by HPLC with fluorometric detection. The extraction of AFB₂ was optimized. Under the optimum conditions, the aptamer affinity column has a linear response to AFB₂ in the range of 0.5–80 ng, with a capacity of 84.6 ng. Control supports without immobilized aptamers and a nonspecific oligosorbent immobilized with a negative control oligonucleotide were studied in order to demonstrate selectivity. The method was tested with spiked peanut sample (0.5–50 μg·kg^?1 AFB₂) and gave average recoveries of 80.9% and a mean relative standard deviation of 1.9%. The limit of detection is 25 pg·mL^?1. This is much lower than the maximum residue limits suggested by the European Union. The columns can be re-used up to five times without any loss of performance. The oligosorbent was also applied to clean-up of AFB₂ from peanut sample extracts before HPLC analysis. Results were further confirmed by ultra-fast liquid chromatography with tandem mass spectrometry. Conceivably, the method may also be applied to other samples, such as food, agricultural products, and traditional Chinese medicines.

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Graphical abstract Schematic illustration of the fabrication procedures of aptamer affinity column, AAC (a), its principle of aptamer bound to aflatoxin B₂ (b) and the obtained AAC (c).

     

Aptamer based lysozyme assay using fluorescent CuInS<Subscript>2</Subscript> quantum dots and graphene oxide,and its application to inhibitor screening

We report on a widely applicable approach for protein detection by using triple-helix DNA mediated CuInS₂ quantum dot (QD) and graphene oxide (GO) nanocomposite. The CuInS₂ QDs were coated with mercaptopropionic acid and then covalently linked to a hairpin aptamer against lysozyme (HLA). Single-stranded DNA (triple helix-forming oligonucleotide; THFO) readily absorbs on the surface of GO via π-stacking interaction, and this results in the formation of THFO-GO. If HLA-CuInS₂ QDs are added to the THFO-GO system, the fluorescence of HLA-CuInS₂ QDs (at excitation/emission wavelengths of 590/665 nm) is quenched. Lysozyme has a higher affinity for HLA than THFO. Therefore, in the presence of lysozyme, it will bind to the HLA-CuInS₂ QD and displace the THFO-GO. This results in the restoration of fluorescence that is related to the concentration of lysozyme. The fluorescence of the QDs is turned on. The calibration plot is linear in the 0.01 to 1.8 ng·mL￣¹ concentration range, with a 3 pg·mL￣¹ detection limit (at a signal-to-noise ratio of 3). The method was also applied to study the inhibition of lysozyme by Ivy _Ec . In our perception, this method has a wide scope in that it may become applicable to any protein for which an appropriate aptamer is available.

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Graphical abstract A novel convenient and universal fluorescence nanoprobe for sensitive and selective detection of lysozyme and inhibitor screening was established using triple-helix DNA mediated CuInS₂ QDs and GO nanocomposites

     

Water-soluble MoS<Subscript>2</Subscript> quantum dots are a viable fluorescent probe for hypochlorite

A method is described for the fluorometric determination of hypochlorite. It is making use of molybdenum disulfide quantum dots (MoS₂ QDs) as a fluorescent probe. The QDs are prepared by hydrothermal reaction of sodium molybdate with glutathione. They possess diameters typically ranging from 1.4 to 3.8 nm, excellent stability in water, and blue photoluminescence (with excitation/emission peaks located at 315/412 nm and a quantum yield of 3.7%). The fluorescence of the QDs is statically quenched by hypochlorite, and the Stern-Volmer plot is linear. Hypochlorite can be detected in the 5–500 μM concentration range with a 0.5 μM detection limit. The method has been successfully applied to the determination of hypochlorite in spiked samples of tap water, lake water, and commercial disinfectants.

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Graphical abstract Schematic of a method for the fluorometric determination of hypochlorite using MoS₂ quantum dots as a fluorescent probe. It has been applied to hypochlorite assay in spiked samples of tap water, lake water, and commercial disinfectants.

     

Voltammetric determination of vitamin B<Subscript>6</Subscript> (pyridoxine) at a graphite screen-printed electrode modified with graphene oxide/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanocomposite

The preparation and study of electrochemical properties of a graphite screen-printed electrode (SPE) modified with the GO/Fe₃O₄@SiO₂ (GO is graphene oxide) nanocomposites are described. The morphologies of the GO/Fe₃O₄@SiO₂ nanocomposites were examined by scanning electron microscopy. The electrochemical oxidation of vitamin B₆ (pyridoxine) on SPE modified with the GO/Fe₃O₄@SiO₂ nanocomposite was investigated by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. Under optimum conditions (pH 7.0), the vitamin B₆ oxidation at the surface of the modified SPE occurs at a potential about 190 mV less positive than that at the unmodified SPE. A linear voltammetric response for vitamin B₆ was obtained in the concentration range 1.0?10 ⁶—9.0?10 ⁴ mol L^–1 with a detection limit of 5.2?10 ⁷ mol L^–1 using differential pulse voltammetry. The developed sensor was also successfully applied for determination of trace level of vitamin B₆ in both the standard vitamin B₆ sample and biological samples (urine).