SciCombinator

Discover the most talked about and latest scientific content & concepts.

Journal: Analytical chemistry

28

Sensitive detection of black powder (BP) by stand-alone ion mobility spectrometry (IMS) is full of challenges. In conventional air-based IMS, overlap between reactant ion O2-(H2O)n peak and sulfur ion peak occurs severely; and common doping methods, providing alternative reactant ion Cl-(H2O)n, would hinder the formation of ionic sulfur allotropes. In this work, an ion mobility spectrometer embedded a titration region (TR-IMS) downstream from ionization region was developed for selective and sensitive detection of sulfur in BP with CH2Cl2 as titration reagent. Sulfur ions were produced via reactions between sulfur molecules and O2-(H2O)n ions in the ionization region and the remaining O2-(H2O)n ions that entered the titration region were converted to Cl-(H2O)n ions, which avoided the peak overlap as well as the negative effect of CH2Cl2 on sulfur ions. The limit of detection for sulfur was measured to be 5 pg. Furthermore, it was demonstrated that this TR-IMS was qualified for detecting less than 5 ng BP and other nitro-organic explosives.

Concepts: Mass spectrometry, Chemical bond, Ion, Sodium, Chloride, Ions, Ion mobility spectrometry, Ion mobility

28

We report the first in situ and real-time monitoring of the interconversion of L- and D-alanine-d3 by alanine racemase from Bacillus Stearothermophilus directly observed by 2H-NMR spectroscopy in anisotropic phase. The enantiomers are distinguished by the difference of their 2H quadrupolar splittings in a chiral liquid-crystalline environment made of short DNA fragments. The proof-of-principle, the reliability and the robustness of this new method is demonstrated by the determination of the turnover rates of the enzyme using the Michaelis-Menten model.

Concepts: Scientific method, Bacteria, Polymerase chain reaction, Stereochemistry, DNA polymerase, Object-oriented programming, Activation energy

28

We report the detection and analysis of a suspected counterfeit sample of the anti-malarial medicine Metakelfin through developing Nitrogen-14 Nuclear Quadrupole Resonance (14N NQR) spectroscopy at a quantitative level. The sensitivity of quadrupolar parameters to the solid-state chemical environment of the molecule enables development of a technique capable of discrimination between the same pharmaceutical preparations made by different manufacturers. The 14N NQR signal returned by a tablet (or tablets) from a Metakelfin batch suspected to be counterfeit was compared with that acquired from a tablet(s) from a known-to-be-genuine batch from the same named manufacturer. Metakelfin contains two active pharmaceutical ingredients, sulfalene and pyrimethamine and NQR analysis revealed spectral differences for the sulfalene component indicative of differences in the processing history of the two batches. Furthermore, the NQR analysis provided quantitative information that the suspected counterfeit tablets contained only 43  3 % as much sulfalene as the genuine Metakelfin tablets. Conversely, conventional non-destructive analysis by FT-Raman and FT-NIR spectroscopies only achieved differentiation between batches, but no ascription. HPLC-UV analysis of the suspect tablets revealed a sulfalene content of 42  2 % of the labelled claim. The degree of agreement shows the promise of NQR as a means of the non-destructive identification and content-indicating first-stage analysis of counterfeit pharmaceuticals.

Concepts: Pharmacology, Medicine, Nuclear magnetic resonance, Pharmaceutical drug, Antimalarial drug, Active ingredient, Nuclear quadrupole resonance, Authentication

28

Solid-state nanopores have emerged as versatile single-molecule sensors for applications including DNA sequencing, protein unfolding, micro-RNA detection, label-free detection of single nucleotide polymorphisms, and mapping of DNA-binding proteins involved in homologous recombination. While machining nanopores in dielectric membranes provides nanometer-scale precision, the rigid silicon support for the membrane contributes capacitive noise and limits integration with microfluidic networks for sample pre-processing. Herein, we demonstrate a technique to directly transfer solid-state nanopores machined in dielectric membranes from a silicon support into a microfluidic network. The resulting microfluidic-addressable nanopores can sense single DNA molecules at high bandwidths and with low noise, owing to significant reductions in membrane capacitance. This strategy will enable large-scale integration of solid-state nanopores with microfluidic upstream and downstream processing and permit new functions with nanopores such as complex manipulations for multidimensional analysis and parallel sensing in two and three-dimensional architectures.

Concepts: DNA, Gene, Bioinformatics, Transcription, Molecular biology, RNA, DNA repair, Capacitor

28

A study combining high resolution mass spectrometry (LC-QTof-MS) and chemometrics for the analysis of post-mortem brain tissue from subjects with Alzheimer’s disease (AD) (n=15) and healthy age-matched controls (n=15) was undertaken. The huge potential of this metabolomics approach for distinguishing AD cases is underlined by the correct prediction of disease status in 94%-97% of cases. Predictive power was confirmed in a blind test set of 60 samples, reaching 100% diagnostic accuracy. The approach also indicated compounds significantly altered in concentration following the onset of human AD. Using orthogonal partial least squares discriminant analysis (OPLS-DA) a multivariate model was created for both modes of acquisition explaining the maximum amount of variation between sample groups (Positive Mode-R2=97%; Q2=93 %; RMSEV=13 %; Negative Mode-R2=99 %; Q2=92 %; RMSEV=15%). In brain extracts 1264 and 1457 ions of interest were detected for the different modes of acquisition (positive and negative, respectively). Incorporation of gender into the model increased predictive accuracy and decreased RMSEV values. High resolution LC-QTof-MS has not previously been employed to biochemically profile post-mortem brain tissue and the novel methods described and validated herein prove its potential for making new discoveries related to the aetiology, pathophysiology and treatment of degenerative brain disorders.

Concepts: Nervous system, Medicine, Neuron, Neuroanatomy, Brain, Human brain, Cerebral cortex, Cerebellum

28

Method of highly sensitive registration of magnetic nanoparticles by their non-linear magnetization is used in a novel sandwich-type immunoassay for detection of staphylococcal toxins in complex media of virtually any volume, with increasing sensitivity at higher sample volume. The signal is read out from the entire volume of a non-transparent 3D fiber structure employed as a solid phase, which provides large reaction surface, quick reagent mixing as well as antigen immunofiltration directly in the course of the assay. The method has demonstrated near-linear dose-response curves within wide range of ~3 decades while detection of staphylococcal enterotoxin A (SEA) and toxic shock syndrome toxin (TSST) in neat milk without sample preparation. The limits of detection (LOD) as low as 4 and 10 pg/mL for TSST and SEA, respectively, were obtained in 2-hour format using 30-mL samples. The second, 25-minute format, showed the LOD of 0.1 and 0.3 ng/mL for the same toxins in a 150 µL sample. The developed immunoassay can be applied in food safety control, in vitro diagnostics and veterinary for a variety of research from express tests in the field to highly sensitive laboratory tests.

Concepts: Magnetic field, Staphylococcus aureus, Streptococcus pyogenes, ELISA, Toxic shock syndrome, Exotoxin, Necrotizing fasciitis, Magnetic immunoassay

28

Use of elevated electric fields and helium-rich gases has recently enabled differential ion mobility spectrometry (IMS) with a resolving power up to R ∼ 300. Here we applied that technique to a protein (ubiquitin), achieving R up to ∼80 and separating previously unresolved conformers. While still limited by conformational multiplicity, this resolution is some 4 times greater than that previously reported using either conventional (drift-tube or traveling-wave) or differential IMS. The capability for fine resolution of protein conformers may open new avenues for proteoform separations in top-down and intact-protein proteomics.

Concepts: Electric charge, Mass spectrometry, Proteomics, Display resolution, Resolution, Separation, Ion mobility spectrometry

28

The forensic analysis of textile fibers uses a variety of techniques from microscopy to spectroscopy. One such technique that is often used to identify the dye(s) within the fiber is mass spectrometry. In the traditional direct infusion method, the dye must be extracted from the fabric and the dye components separated by chromatography prior to mass spectrometric analysis. Direct analysis of the dye from the fabric allows the omission of the lengthy sample preparation involved in extraction, thereby significantly reducing the overall analysis time. Herein, a direct analysis of dyed textile fabric was performed using the infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) source for mass spectrometry (MS). In MALDESI, an IR laser with wavelength tuned to 2.94 µm is used to desorb the dye from the fabric sample with the aid of water as the matrix. The desorbed dye molecules are then post-ionized by electrospray ionization. A variety of dye classes were analyzed from various fabrics with little to no sample preparation allowing for the identification of the dye mass and in some cases the fiber polymer. Those dyes that were not detected using MALDESI were also not observed using the traditional method of direct infusion.

Concepts: Mass spectrometry, Nylon, Electrospray ionization, Ion source, Matrix-assisted laser desorption/ionization, Textile, Infrared, Desorption electrospray ionization

28

Polystyrene electrospun optical fibrous membrane (EOF) was fabricated using a one-step electrospinning technique, functionalized with glucose oxidases (GOD/EOF), and used as a quick and highly sensitive optical biosensor. Due to the doped iridium complex, the fibrous membrane emitted yellow luminescence (562 nm) when exited at 405 nm. Its luminescence was significantly enhanced with the presence of extremely low concentration glucose. The detection limit was of 1.0 × 10-10 M (S/N=3), superior to that of reported glucose biosensor. A linear range between the relative intensity increase and the logarithm of glucose concentration was exhibited from 3.0 × 10-10 M to 1.3 × 10-4 M, which was much wider than reported results. Notable, the response time was less than 1 second. These high sensitivity and fast response were attributed to the high surface-area-to-volume of the porous fibrous membrane, the efficient GOD biocatalyst reaction on the fibers surface, as well as the fast electron or energy transfer between dissolved oxygen and the optical fibrous membrane.

Concepts: Oxygen, Light, Sensitivity and specificity, Blood sugar, Fiber, Dietary fiber, Biosensor, Vaska's complex

28

A direct, sensitive and rapid method for the detection of smokeless powder components, from five different types of ammunition, is demonstrated using laser electrospray mass spectrometry (LEMS). Common components found in powder, such as ethyl centralite, methyl centralite, dibutyl phthalate and dimethyl phthalate, are detected under atmospheric conditions without additional sample preparation. LEMS analysis of the powders revealed several new mass spectral features that have not been identified previously. Offline principal component analysis and discrimination of the LEMS mass spectral measurements resulted in perfect classification of the smokeless powder with respect to manufacturer.

Concepts: Mass spectrometry, Multivariate statistics, Principal component analysis, Electrospray ionization, The Unscrambler, Plasticizers, Smokeless powder, Centralite