Comparison of different extraction methods to determine free and bound forms of B-group vitamins in quinoa

The distribution of free and bound forms of B-group vitamins (B₁, B₂, B₃, B₅, and B₆) was quantified in quinoa seeds using LC-MS-TOF combined with a stable isotope dilution assay. The effectiveness of liberating thiamine, riboflavin, nicotinic acid, pantothenic acid, pyridoxal, and pyridoxine from the food matrix and cofactors was evaluated for a variety of extraction conditions, including the addition of enzymes. Phosphatase and protease inhibitors, as well as ultrafiltration, were evaluated for their ability to suppress vitamer liberation via enzymes endogenous to quinoa. Cold extraction, together with a mixture of phosphatase and protease inhibitors, is identified as the most efficient treatment to prevent the conversion of cofactors into simple vitamers. Overnight incubation at 37 °C both with and without additional hydrolytic enzyme preparations containing phosphatase and β-glucosidase activity was almost equally effective in releasing the bound forms of the vitamers. This indicates that the endogenous enzymes within quinoa seeds have high activity. β-Glucosidase should be used when the total pyridoxine content is to be determined, and thermal treatment followed by enzymatic treatment with phosphatase activity is recommended to liberate the bound forms of pyridoxal prior to quantification. Graphical Abstract

Free and bound forms of B-group vitamins in quinoa     

Photocatalytic activity of nitrogen-modified TiO2/SiO2

The physicochemical characteristics of nitrogen-modified TiO₂/SiO₂ and its photocatalytic activity in the oxidation of methyl orange (MO) were studied. Nitrogen-modified TiO₂/SiO₂ had higher activity than the unmodified samples. The photocatalytic oxidation of MO obeys the Langmuir-Hinshelwood model.     

Direct electrochemistry of glucose oxidase and a biosensor for glucose based on a glass carbon electrode modified with MoS2 nanosheets decorated with gold nanoparticles

An electrochemical glucose biosensor was developed by immobilizing glucose oxidase (GOx) on a glass carbon electrode that was modified with molybdenum disulfide (MoS₂) nanosheets that were decorated with gold nanoparticles (AuNPs). The electrochemical performance of the modified electrode was investigated by cyclic voltammetry, and it is found that use of the AuNPs-decorated MoS₂ nanocomposite accelerates the electron transfer from electrode to the immobilized enzyme. This enables the direct electrochemistry of GOx without any electron mediator. The synergistic effect the MoS₂ nanosheets and the AuNPs result in excellent electrocatalytic activity. Glucose can be detected in the concentration range from 10 to 300 μM, and down to levels as low as 2.8 μM. The biosensor also displays good reproducibility and long-term stability, suggesting that it represents a promising tool for biological assays. Figure

A MoS₂-based glucose sensor has been prepared by gold nanoparticles-decorated MoS₂ nanocomposite, which exhibited excellent electrocatalytic activity, reproducibility and long-term stability. It was applied to determine glucose concentration in human serum, suggest the sensor maybe promising for practical application.     

Electrochemistry and voltammetric determination of L-tryptophan and L-tyrosine using a glassy carbon electrode modified with a Nafion/TiO2-graphene composite film

We describe a glassy carbon electrode (GCE) modified with a film composed of Nafion and TiO₂-graphene (TiO₂-GR) nanocomposite, and its voltammetric response to the amino acids L-tryptophane (Trp) and L-tyrosine (Tyr). The incorporation of TiO₂ nanoparticles with graphene significantly improves the electrocatalytic activity and voltammetric response compared to electrodes modified with Nafion/graphene only. The Nafion/TiO₂-GR modified electrode was used to determine Trp and Tyr with detection limits of 0.7 and 2.3 μM, and a sensitivity of 75.9 and 22.8 μA mM^?1 for Trp and Tyr, respectively.

Characterization of poly(2-vinylpyridine)-block-poly(methyl methacrylate) copolymers and blends of their homopolymers by liquid chromatography at critical conditions

Poly(2-vinylpyridine)s (P2VPs) are important polymers with extensive applications in modern day material science. P2VP is an exceptional case for liquid chromatography because of certain polar interactions with most of the stationary phases. In the present study, we established the critical adsorption point (CAP) of P2VP for the first time. The effectiveness of the method is demonstrated by analyses of blends and block copolymers of P2VP and PMMA. The CAP of PMMA is established for determination of molar mass of P2VP component of above mentioned blends and block copolymers. The methods successfully demonstrate the separation of both types of homopolymers from the rest of the samples in conjunction with the determination of molar mass distribution of noncritical block or component. Graphical Abstract

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A turn-on fluorescence-sensing technique for glucose determination based on graphene oxide–DNA interaction

Graphene is a two-dimensional carbon nanomaterial one atom thick. Interactions between graphene oxide (GO) and ssDNA containing different numbers of bases have been proved to be remarkably different. In this paper we propose a novel approach for turn-on fluorescence sensing determination of glucose. Hydrogen peroxide (H₂O₂) is produced by glucose oxidase-catalysed oxidation of glucose. In the presence of ferrous iron (Fe²⁺) the hydroxyl radical (?OH) is generated from H₂O₂ by the Fenton reaction. This attacks FAM-labelled long ssDNA causing irreversible cleavage, as a result of the oxidative effect of ?OH, producing an FAM-linked DNA fragment. Because of the weak interaction between GO and short FAM-linked DNA fragments, restoration of DNA fluorescence can be achieved by addition of glucose. Due to the excellent fluorescence quenching efficiency of GO and the specific catalysis of glucose oxidase, the sensitivity and selectivity of this method for GO-DNA sensing are extremely high. The linear range is from 0.5 to 10 μmol L^?1 and the detection limit for glucose is 0.1 μmol L^?1. The method has been successfully used for analysis of glucose in human serum. Figure

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Uncertainty measurement for automated macro program-processed quantitative proton NMR spectra

The evaluation of a fully automated quantitative proton nuclear magnetic resonance spectroscopy (qNMR) processing program, including the determination of its processing uncertainty, and the calculations of the combined uncertainty of the qNMR result, is presented with details on the use of a trimmed purity average. Quantitative NMR spectra (1359) were collected over a 4-month period on various concentrations of pseudoephedrine HCl dissolved in D₂O (0.0610 to 93.60 mg/mL) containing maleic acid (the internal standard) to yield signal-to-noise ratios ranging from 3 to 72,000 for analyte integral regions. The resulting 5436 purities exhibited a normal distribution about the best estimate of the true value. The median absolute deviation (MAD) statistical method was used to obtain a model of uncertainty relative to the signal-to-noise of the analyte’s integral peaks. The model was then tested using different concentrations of known purity chloroquine diphosphate. qNMR results of numerous illicit heroin HCl samples were compared to those obtained by capillary electrophoresis. Graphical Abstract

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Biomolecular Imaging with a C60-SIMS/MALDI Dual Ion Source Hybrid Mass Spectrometer: Instrumentation,Matrix Enhancement,and Single Cell Analysis

We describe a hybrid MALDI/C₆₀-SIMS Q-TOF mass spectrometer and corresponding sample preparation protocols to image intact biomolecules and their fragments in mammalian spinal cord, individual invertebrate neurons, and cultured neuronal networks. A lateral spatial resolution of 10 μm was demonstrated, with further improvement feasible to 1 μm, sufficient to resolve cell outgrowth and interconnections in neuronal networks. The high mass resolution (>13,000 FWHM) and tandem mass spectrometry capability of this hybrid instrument enabled the confident identification of cellular metabolites. Sublimation of a suitable matrix, 2,5-dihydroxybenzoic acid, significantly enhanced the ion signal intensity for intact glycerophospholipid ions from mammalian nervous tissue, facilitating the acquisition of high-quality ion images for low-abundance biomolecules. These results illustrate that the combination of C₆₀-SIMS and MALDI mass spectrometry offers particular benefits for studies that require the imaging of intact biomolecules with high spatial and mass resolution, such as investigations of single cells, subcellular organelles, and communities of cells. Graphical Abstract

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Cytotoxicity Evaluation and Subcellular Location of Titanium Dioxide Nanotubes

TiO₂ nanotubes (TiO₂-NTs) are currently attracting a high interest because the intrinsic properties of TiO₂ provide the basis for many outstanding functional features. Herein, we focus on the cytotoxicity and sublocation of TiO₂-NTs in neural stem cells (NSCs). The cytotoxicity of TiO₂-NTs is investigated using the methyl tetrazolium cytotoxicity and reactive oxygen species assay, the apoptosis assay by flow cytometry. Cell viability assay shows that TiO₂-NTs inside cells are nontoxic at the low concentration. A time-dependent relationship is observed, while a dose-dependent relationship is seen only at the concentration higher than 150 μg/ml. The uptake happens shortly after incubation with cells. TiO₂-NTs can easily pass through the cell membrane and enter into the cells. The uptake amount is increased with prolonging incubation time and reach to maximum at 48 h. Transmission electron microscopy and confocal is used to study subcellular location of TiO₂-NTs. It is found that TiO₂-NTs traversed cell membrane and localized in many vesicles (endosomes and lysosomes) and cytoplasm. TiO₂-NTs in NSCs firstly disperse or metabolism by lysosomal enzymes and then exocytosis from NSCs.

Investigation of bn-44 Peptide Fragments Using High Resolution Mass Spectrometry and Isotope Labeling

An N-terminal deuterohemin-containing hexapeptide (DhHP-6) was designed as a short peptide cytochrome c (Cyt c) mimetic to study the effect of N-terminal charge on peptide fragmentation pathways. This peptide gave different dissociation patterns than normal tryptic peptides. Upon collision-induced dissociation (CID) with an ion trap mass spectrometer, the singly charged peptide ion containing no added proton generated abundant and characteristic b_n-44 ions instead of b_n-28 (a_n) ions. Studies by high resolution mass spectrometry (HRMS) and isotope labeling indicate that elimination of 44 Da fragments from b ions occurs via two different pathways: (1) loss of CH₃CHO (44.0262) from a Thr side chain; (2) loss of CO₂ (43.9898) from the oxazolone structure in the C-terminus. A series of analogues were designed and analyzed. The experimental results combined with Density Functional Theory (DFT) calculations on the proton affinity of the deuteroporphyrin demonstrate that the production of these novel b_n-44 ions is related to the N-terminal charge via a charge-remote rather than radical-directed fragmentation pathway. Graphical Abstract

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Simultaneous sensing of L-tyrosine and epinephrine using a glassy carbon electrode modified with nafion and CeO2 nanoparticles

An electrochemical sensor was developed and tested for detection of L-tyrosine in the presence of epinephrine by surface modification of a glassy carbon electrode (GCE) with Nafion and cerium dioxide nanoparticles. Fabrication parameters of a surfactant-assisted precipitation method were optimized to produce 2–3 nm CeO₂ nanoparticles with very high surface-to-volume ratio. The resulting nanocrystals were characterized structurally and morphologically by X-ray diffractometery (XRD), scanning and high resolution transmission electron microscopy (SEM and HR-TEM). The nanopowder is sonochemically dispersed in a Nafion solution which is then used to modify the surface of a GCE electrode. The electrochemical activity of L-tyrosine and epinephrine was investigated using both a Nafion-CeO₂ coated and a bare GCE. The modified electrode exhibits a significant electrochemical oxidation effect of L-tyrosine in a 0.2 M Britton-Robinson (B-R) buffer solution of pH 2. The electro-oxidation peak current increases linearly with the L-tyrosine concentration in the molar concentration range of 2 to 160 μM. By employing differential pulse voltammetry (DPV) for simultaneous measurements, we detected two reproducible peaks for L-tyrosine and epinephrine in the same solution with a peak separation of about 443 mV. The detection limit of the sensor (signal to noise ratio of 3) for L-tyrosine is ~90 nM and the sensitivity is 0.20 μA μM^?1, while for epinephrine these values are ~60 nM and 0.19 μA μM^?1. The sensor exhibited excellent selectivity, sensitivity, reproducibility and stability as well as a very good recovery time in real human blood serum samples.

Simultaneous electrochemical determination of L-tyrosine and epinephrine in blood plasma with Nafion-CeO₂/GCE modified electrode showing a 443 mV peak-to-peak potential difference between species oxidation peak currents.     

Energetics and Kinetics of Thermal Ionization Models of MALDI

Thermal models of ultraviolet MALDI ionization based on the polar fluid concept are re-examined. Key components are very high solvating power of the fluidized matrix and consequent low reaction-free energy, attainment of thermal equilibrium in the fluid, and negligible recombination losses. None of these are found to hold in a MALDI event. The reaction-free energy in the hot matrix must be near the gas phase value, ion formation is too slow to approach equilibrium, and geminate recombination of autoprotolysis pairs greatly increases the initial loss rate. The maximum thermal ion yield is estimated to be many orders of magnitude below experimental values. Figure

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Magnetic ion imprinted polymer nanoparticles for the preconcentration of vanadium(IV) ions

An ion imprinted polymer coated onto magnetite (Fe₃O₄) nanoparticles is shown to be a useful magnetic sorbent for the fairly selective preconcentration of vanadium. The sorbent was prepared by radical copolymerization of 3-(triethoxysilyl)propyl methacrylate (the monomer), ethylene glycol dimethacrylate (the cross-linker), and the vanadium(IV) complex of 1-(2-pyridylazo-2-naphthol) in the presence of magnetite nanoparticles. The material was characterized by IR spectroscopy, scanning electron microscopy, and thermal analysis. The vanadium(IV) ions were removed from the imprint by a solution containing thiourea and HCl, and the eluent was submitted to AAS. The analytical efficiency and relative standard deviation are 99.4 and ±2.3 %, respectively, under optimum conditions, and the limit of detection is 20 ng mL^?1. The method was successfully applied to the preconcentration and determination of vanadium(IV) ions in crude oil. Figure

An ion imprinted polymer is coated on to magnetite nanoparticles as a useful magnetic sorbent for the fairly selective preconcentration of vanadium which can be used for vanadium determination in crude oil.     

Electrochemical in-vivo sensors using nanomaterials made from carbon species,noble metals,or semiconductors

Electrochemical analytical methods have the advantages of simplicity, direct measurements, and ease of miniaturization which pave the way for real time detection and sensing. However, the complexity of living systems usually requires electrochemical sensors to display high selectivity, sensitivity, accuracy, biocompatibility and stability over time. Nanomaterials possess attractive properties in terms of surface modification, catalysis, and functionality. These open new avenues with respect to electrochemical enzymatic determination of neurochemicals such as dopamine, serotonin and ascorbate, biological small molecules such as H₂O₂ and metal ions such as copper(II) in-vivo. Three properties of nanomaterials make their use particularly attractive, namely the larger surface-to-volume ratio area, their unique surface, and the ease of electron transfer between enzymes and electrodes. These properties make them more sensitive, selective and stable. The article is subdivided into sections that cover applications of the following materials: carbonaceous materials (mainly carbon nanotube), noble metal particles (mainly gold and platinum particles), and semiconductor (mainly metal oxide) nanomaterials. A conclusion and outlook section addresses current chances and limitations. The review contains 99 references. Figure

Three attractive properties of nanomaterials: the larger surface-to-volume ratio area, unique surface, and facilitating the electron transfer between enzyme and electrode, can improve the analytical performance of electrode, fulfilling the requirements in sensitivity, selectivity and stability for in vivo electrochemistry.     

Survey of pyrrolizidine alkaloids in teas and herbal teas on the Swiss market using HPLC-MS/MS

Pyrrolizidine alkaloids (PAs) are a large class of natural compounds amongst which the esterified 1,2-unsaturated necine base is toxic for humans and livestock. In the present study, a method was developed and validated for the screening and quantification of nine PAs and one PA N-oxide in teas (Camellia sinensis (L.) O. Kuntze) and herbal teas (camomile, fennel, linden, mint, rooibos, verbena). Samples were analysed by HPLC on a RP-column, packed with sub-2 μm core-shell particles, and quantified using tandem mass spectrometry operating in the positive electrospray ionisation mode. These PAs and some of their isomers were detected in a majority of the analysed beverages (50/70 samples). In 24 samples, PA concentrations were above the limit of quantification and the sum of the nine targeted PAs was between 0.021 and 0.954 μg per cup of tea. Thus, in some cases, total concentrations exceed the maximum daily intake recommended by the German Federal Institute for Risk Assessment and the UK’s Committee On Toxicity (i.e. 0.007 μg kg^?1 bw). Graphical Abstract

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Direct electrochemistry of glucose oxidase and sensing glucose using a screen-printed carbon electrode modified with graphite nanosheets and zinc oxide nanoparticles

We have studied the direct electrochemistry of glucose oxidase (GOx) immobilized on electrochemically fabricated graphite nanosheets (GNs) and zinc oxide nanoparticles (ZnO) that were deposited on a screen printed carbon electrode (SPCE). The GNs/ZnO composite was characterized by using scanning electron microscopy and elemental analysis. The GOx immobilized on the modified electrode shows a well-defined redox couple at a formal potential of ?0.4 V. The enhanced direct electrochemistry of GOx (compared to electrodes without ZnO or without GNs) indicates a fast electron transfer at this kind of electrode, with a heterogeneous electron transfer rate constant (K_s) of 3.75 s^?1. The fast electron transfer is attributed to the high conductivity and large edge plane defects of GNs and good conductivity of ZnO-NPs. The modified electrode displays a linear response to glucose in concentrations from 0.3 to 4.5 mM, and the sensitivity is 30.07 μA mM^?1 cm^?2. The sensor exhibits a high selectivity, good repeatability and reproducibility, and long term stability. Figure

Graphical representation for the fabrication of GNs/ZnO composite modified SPCE and the immobilization of GOx     

Analysis of urinary vitamin D3 metabolites by liquid chromatography/tandem mass spectrometry with ESI-enhancing and stable isotope-coded derivatization

The determination of the urinary vitamin D₃ metabolites might prove helpful in the assessment of the vitamin D status. We developed a method for the determination of trace vitamin D₃ metabolites, 25-hydroxyvitamin D₃ [25(OH)D₃] and 24,25-dihydroxyvitamin D₃ [24,25(OH)₂D₃], in urine using liquid chromatography/electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS) combined with derivatization using an ESI-enhancing reagent, 4-(4′-dimethylaminophenyl)-1,2,4-triazoline-3,5-dione (DAPTAD), and its isotope-coded analogue, ²H₄-DAPTAD (d-DAPTAD). The urine samples were treated with β-glucuronidase, purified with an Oasis® hydrophilic–lipophilic balanced (HLB) cartridge, and then subjected to the derivatization. The DAPTAD derivatization enabled the highly sensitive detection (detection limit, 0.25 fmol on the column), and the use of d-DAPTAD significantly improved the assay precision [the intra- (n?=?5) and inter-assay (n?=?3) relative standard deviations did not exceed 9.5 %]. The method was successfully applied to urine sample analyses and detected the increases of the urinary 25(OH)D₃ and 24,25(OH)₂D₃ levels due to vitamin D₃ administration. Graphical Abstract

Scheme of procedure for urinary vitamin D₃ metabolite analysis based on LC/MS/MS with ESI-enhancing and isotope-coded derivatization.     

Determination of neurotransmitters and their metabolites using one- and two-dimensional liquid chromatography with acidic potassium permanganate chemiluminescence detection

High-performance liquid chromatography with chemiluminescence detection based on the reaction with acidic potassium permanganate and formaldehyde was explored for the determination of neurotransmitters and their metabolites. The neurotransmitters norepinephrine and dopamine were quantified in the left and right hemispheres of rat hippocampus, nucleus accumbens and prefrontal cortex, and the metabolites vanillylmandelic acid, 3,4-dihydrophenylacetic acid, 5-hydroxyindole-3-acetic acid and homovanillic acid were identified in human urine. Under optimised chemiluminescence reagent conditions, the limits of detection for these analytes ranged from 2.5?×?10^?8 to 2.5?×?10^?7 M. For the determination of neurotransmitter metabolites in urine, a two-dimensional high-performance liquid chromatography (2D-HPLC) separation operated in heart-cutting mode was developed to overcome the peak capacity limitations of the one-dimensional separation. This approach provided the greater separation power of 2D-HPLC with analysis times comparable to conventional one-dimensional separations. Figure

2D-HPLC separation and permanganate chemiluminescence detection of neurotransmitter metabolites     

Lactate biosensor based on a bionanocomposite composed of titanium oxide nanoparticles, photocatalytically reduced graphene, and lactate oxidase

We have developed a lactate biosensor based on a bionanocomposite (BNC) composed of titanium dioxide nanoparticles (TiO₂-NPs), photocatalytically reduced graphene, and lactate oxidase. Graphene oxide was photochemically reduced (without using any chemical reagents) in the presence of TiO₂-NPs to give graphene nanosheets that were characterized by atomic force microscopy, Raman and X-ray photoelectron spectroscopy. The results show the nanosheets to possess few oxygen functionalities only and to be decorated with TiO₂-NPs. These nanosheets typically are at least 1 μm long and have a thickness of 4.2 nm. A BNC was obtained by mixing lactate oxidase with the nanosheets and immobilized on the surface of a glassy carbon electrode. The resulting biosensor was applied to the determination of lactate. Compared to a sensor without TiO₂-NPs, the sensor exhibits higher sensitivity (6.0 μA mM^?1), a better detection limit (0.6 μM), a wider linear response (2.0 μM to 0.40 mM), and better reproducibility (3.2 %).

Sensitive determination of nitric oxide using an electrochemical sensor based on MWCNTs decorated with spherical Au nanoparticles

This paper describes the synthesis, characterisation and application of a very sensitive electrochemical sensor based on a glassy carbon electrode modified with multiwalled carbon nanotubes (MWCNTs) decorated with homogeneously distributed spherical gold nanoparticles (AuNPs). These AuNPs presented diameters ranging from 2 to 10 nm. The AuNPs were prepared directly on the MWCNTs’ surface via a synthesis using HAuCl₄ and citric acid as the reducing agent. The resulting material (Au/MWCNTs) was characterised by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and Raman spectroscopy. The developed Au/MWCNTs sensor was used in the determination of nitric oxide (NO) in phosphate buffer solution at pH 4.4 by differential pulse voltammetry. In the potential window between 0.5 and 0.65 V, a well-defined oxidation peak was observed, whose height was proportional to the NO concentration in the solution. The Au/MWCNTs-modified electrode exhibited high sensitivity for the determination of nitric oxide, with the limit of detection being 0.21 nmol L^?1 (S/N?=?3). No significant interference was detected for nitrite and CO₂ in the NO detection. Our study demonstrated that the resultant Au/MWCNT-modified electrode can be used for nitric oxide detection in the presence of ascorbic acid, dopamine and uric acid, being potentially useful for determinations of NO in real samples. Figure

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