Application of high-resolution EFTEM SI in an AEM

In this work we show how energy-filtered imaging can be used to obtain spectrum images of electron energy-loss spectrometric data. Focus is placed on improved energy resolution within these data sets. Using two multilayer samples (GaN/AlN and InP/InAs), we demonstrate the advantages of spectrum-imaging and its extended mapping capabilities. Plasmon-ratio maps are used to quickly create high-contrast material maps with high signal-to-noise ratio, ratio-contrast plots are used to gain optimum settings for the ratio maps, and plasmon-position maps are used to map small shifts of the energy position of bulk plasmon peaks. Figure Scheme of EELS SI and derived plasman-position map     

Nuclear magnetic resonance of mass-limited samples using small RF coils

Figure Schematic diagram of a typical arrangement used for hyphenating chemical microseparations (e.g. capillary HPLC, CE, or CEC) with microcoil NMR detection     

Application of anodized aluminum in fluorescence detection of biological species

Thin nanoporous alumina obtained by anodization of aluminum films offers promising advantages for application in fluorescence-based biological sensors including convenient preparation, increased density of binding sites, and improved collection efficiency of fluorescence. These advantages are illustrated in the detection of streptavidin using biotin covalently bound to the surface of alumina nanopores. Fluorescence intensity enhancement as high as 7 times is observed in nanopores in comparison to flat glass surface.      

Aptamers as molecular recognition elements for electrical nanobiosensors

Recent advances in nanotechnology have enabled the development of nanoscale sensors that outperform conventional biosensors. This review summarizes the nanoscale biosensors that use aptamers as molecular recognition elements. The advantages of aptamers over antibodies as sensors are highlighted. These advantages are especially apparent with electrical sensors such as electrochemical sensors or those using field-effect transistors. Figure Feeling proteins with aptamer-functionalized carbon nanotubes     

Investigation of sample-purification procedures for MALDI-based proteomic studies

Purification methods for proteomics samples are of crucial concern for improving the quality of the sample delivered to the mass spectrometer. They constitute the link between the mass spectrometer and protein processing and peptide isolation steps that usually require solvents, buffers, or detergents completely incompatible with MS-analysis conditions. This work describes three new clean-up procedures using synthetic membranes and polymer media and compares them with standard procedures. The efficiency of each of the purification procedures was studied via application to four standards and two membrane proteins. This work highlights the importance of versatility in sample preparation, especially for MS-based proteomic investigations. Figure PMF spectra obtained after MALDI-TOF measurements of bovine mitochondrial complex III (A) and complex IV (B) in-solution digests, with and without purification     

On-line NMR detection of microgram quantities of heparin-derived oligosaccharides and their structure elucidation by microcoil NMR

The isolation and purification of sufficient quantities of heparin-derived oligosaccharides for characterization by NMR is a tedious and time-consuming process. In addition, the structural complexity and microheterogeneity of heparin makes its characterization a challenging task. The improved mass-sensitivity of microcoil NMR probe technology makes this technique well suited for characterization of mass-limited heparin-derived oligosaccharides. Although microcoil probes have poorer concentration sensitivity than conventional NMR probes, this limitation can be overcome by coupling capillary isotachophoresis (cITP) with on-line microcoil NMR detection (cITP-NMR). Strategies to improve the sensitivity of on-line NMR detection through changes in probe design and in the cITP-NMR experimental protocol are discussed. These improvements in sensitivity allow acquisition of cITP-NMR survey spectra facilitating tentative identification of unknown oligosaccharides. Complete structure elucidation for microgram quantities of the purified material can be carried out through acquisition of 2D NMR spectra using a CapNMR microcoil probe. Survey NMR spectrum obtained by cITP-NMR using a second-generation probe (the microcoil of which is shown) facilitates tentative identification of unknown oligosaccharides (e.g., the heparin-derived tetrasaccharide illustrated)     

Simultaneous use of multiple fluorescent reporter dyes for glucose sensing in aqueous solution

The simultaneous use of several fluorescent reporter dyes in a multicomponent boronic acid-based glucose sensing system is reported. In one application, two dyes with widely different emission wavelengths are used to report changes in glucose concentration. A third glucose-insensitive dye was then added to act as a reference dye and provide for a ratiometric correction to the two reporter dye signals. The inclusion of such a reference dye reduces errors arising from sources such as fluctuations in lamp intensity and sample dilution. The simultaneous use of multiple fluorescent reporter dyes     

Rapid response behavior,at room temperature,of a nanofiber-structured TiO<Subscript>2</Subscript> sensor to selected simulant chemical-warfare agents

A chemical prototype sensor was constructed based on nanofiber-structured TiO₂ and highly sensitive quartz resonators. The gas-sensing behavior of this new sensor to selected simulant warfare agents was investigated at room temperature. Results showed rapid response and good reversibility of this sensor when used with high-purity nitrogen. This provides a simple approach to preparation of materials needed as chemical sensors for selected organic volatiles or warfare agents. Figure Sensing behavior of TiO₂ nanofiber sensor to chemical vapors     

Molecular characterization of brominated persistent pollutants using extended X-ray absorption fine structure (EXAFS) spectroscopy

X-ray absorption fine structure (EXAFS) spectroscopy spectra were collected for three brominated persistent pollutants: 6-bromo-2,4,5-trichlorophenol (BrTriClP), pentabromophenol (PentaBrP) and 3,3′,5,5′-tetrabromobisphenol A (TBBA). The substances were selected to be symmetrical (BrTriClP and TBBA) or asymmetrical (PentaBrP) with respect to the atomic Br positions and to differ in the number of bromine and other halide atoms, as well as their relative positions. The asymmetrical PentaBrP was modelled with special detail as not all bromine atoms have identical coordination environments. The studied substances displayed unique EXAFS spectra, which could be used to determine the molecular structure in fair detail. We conclude that EXAFS spectroscopy is a suitable technique for molecular characterization of the comparatively complex molecules within the class of compounds of brominated organic persistent pollutants. A detailed understanding of the EXAFS spectra of the pure compounds opens up possibilities to study the interactions with soil and sediment matrices by means of EXAFS spectroscopy. Figure Brominated organic persistent pollutants are characterized by EXAFS spectroscopy     

Analysis of glycans in glycoproteins by diffusion-ordered nuclear magnetic resonance spectroscopy

Enzymatically cleaved glycans from sub-milligram quantities of erythropoietin (EPO) and ovalbumin have been analyzed, without further purification, by two-dimensional diffusion-ordered nuclear magnetic resonance spectroscopy. At NMR sample concentrations below 50 μmol L⁻¹ the major components of the oligosaccharide fractions could be distinguished by their anomeric proton chemical shift and their size-dependent diffusion coefficients. Figure ¹H NMR diffusion decay curves of anomeric protons in the EPO glycan fraction     

Spectroscopic and electrochemical studies of cocaine–opioid interactions

The drugs of abuse cocaine (C), heroin (H), and morphine (M) have been studied to enable understanding of the occurrence of cocaine–opioid interactions at a molecular level. Electrochemical, Raman, and NMR studies of the free drugs and their mixtures were used to study drug–drug interactions. The results were analyzed using data obtained from quantum-mechanical calculations. For the cocaine–morphine mixture (C–MH), formation of a binary complex was detected; this involved the 3-phenolic group and the heterocyclic oxygen of morphine and the carbonyl oxygen and the methyl protons of cocaine’s methyl ester group. NMR studies conducted simultaneously also revealed C–MH binding geometry consistent with theoretical predictions and with electrochemical and vibrational spectroscopy results. These results provide evidence for the occurrence of a cocaine–morphine interaction, both in the solid state and in solution, particularly for the hydrochloride form. A slight interaction, in solution, was also detected by NMR for the cocaine–heroin mixture. Figure "Schematic representation of the proposed model for cocaine:morphine salt interaction"     

Characterization of imazamox degradation by-products by using liquid chromatography mass spectrometry and high-resolution Fourier transform ion cyclotron resonance mass spectrometry

The photodecomposition of imazamox, a herbicide of the imidazolinone family, was investigated in pure water. The main photoproducts from the photolysis were followed over time by liquid chromatography mass spectrometry and structures were proposed from exact mass determinations obtained by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The method comprised exact mass determination with better than 0.2 ppm mass accuracy and a corresponding structural visualization taking care of respective isotopes with an adapted van Krevelen diagram that enabled a systematic approach to the characterisation of the elementary composition of each photoproduct. By taking advantage of the high resolving power of FT-ICR MS to make precise formula assignments, the derived 2D van Krevelen diagram (O/C; H/C; m/z) enabled one to structurally differentiate the formed photoproducts and to propose a degradation pathway for imazamox. Figure Overview of applied method to analyse the photolysis process of imazamox herbicide     

Multivariate classification and modeling in surface water pollution estimation

The present study deals with the application of self-organizing maps (SOM) and multiway principal-components analysis to classify, model, and interpret a large monitoring data set for surface water quality. The chemometric methods applied made it possible to reveal specific quality patterns of the chemical and biological parameters used to monitor the water quality (relation between water temperature, turbidity, hardness, colibacteria), seasonal impacts during the long period of observation and the relative independence on the spatial location of the sampling sites (water supply sources for the City of Trieste). Figure The schematic procedure for surface water pollution estimation supported by neural network-based classification and multivariate factor analysis     

Amplification of noble gas ion lines in the afterglow of a pulsed hollow cathode discharge and possible benefit for analytical glow discharge mass spectrometry

A high-current pulsed hollow cathode discharge was used to study the role of atomic and ionic metastables involved in ionization plasma processes. We observed the enhancement of the spectral emission lines of noble gas ions in the afterglow. A study of the processes that involve atomic and ionic metastables is of great interest since it should lead to a better understanding of and enhanced control over the ionization mechanisms crucial to analytical glow discharge mass spectrometry (GDMS) analysis. Figure Time profile of Ti, Ti⁺, and Ne⁺ spectral lines     

Raman spectroscopic investigation of cocaine hydrochloride on human nail in a forensic context

This study describes the application of Raman spectroscopy to the detection of drugs of abuse and noncontrolled substances used in the adulteration of drugs of abuse on human nail. Contamination of the nail may result from handling or abusing these substances. Raman spectra of pure cocaine hydrochloride, a seized street sample of cocaine hydrochloride (77%), and paracetamol could be acquired from drug crystals on the surface of the nail. An added difficulty in the analytical procedure is afforded by the presence of a nail varnish coating the nail fragment. By using confocal Raman spectroscopy, spectra of the drugs under nail varnish could be acquired. Spectra of the drugs could be readily obtained nondestructively within three minutes with little or no sample preparation. Raman spectra could be acquired from drug particles with an average size of 5–20 μm. Acquisition of Raman point maps of crystals from both pure and street samples of cocaine hydrochloride under nail varnish is also reported. Figure Raman spectrum and point Raman map of cocaine HCI     

Results of an interlaboratory comparison on the determination of polybrominated flame retardants in poly(ethyleneterephthalate)

An intercomparison to establish the performance of routine laboratories in the determination of polybrominated flame retardants in polymers was organised. Commercial poly(ethyleneterephthalate) was fortified with technical pentabromodiphenyl ether, octabromodiphenyl ether and decabromodiphenyl ether mixtures and with a decabromobiphenyl technical mixture at 0.4–0.8 g/kg. Homogeneity and stability of the total Br content in the material was confirmed. Thirty-seven laboratories from Europe, Asia and the Americas submitted results. Relative repeatability standard deviations for individual congeners ranged from 7 to 17%. Relative between-laboratory standard deviations ranged from 22 to 61%. No significant influence of a common standard, application of a standard method or method parameters could be identified. The quality and uncertainty of the results of this study are significantly worse than those reported in the environmental field and indicate a clear need for a learning process among the laboratories involved. Figure Mandel’s h (between labs): critical level: 1.91     

Impedimetric genosensors for the detection of DNA hybridization

Impedance spectroscopy is proposed as the transduction principle for detecting the hybridization of DNA complementary strands. In our experiments, different DNA oligonucleotides were used as model gene substances. The gene probe is first immobilized on a graphite-epoxy composite working electrode based genosensor. Detection principle is based on changes of impedance spectra of a redox marker, the ferro/ferricyanide couple, after hybridization with target DNA. Resistance offered to the electrochemical reaction serves as the working signal, allowing for an unlabelled gene assay.      

Smoothing and passivation of special Si(111) substrates: studied by SPV,PL, AFM and SEM measurements

Surface sensitive techniques, the field-modulated surface photovoltage, photoluminescence measurements, atomic force microscopy and scanning electron microscopy, were employed to yield detailed information on the influence of wet-chemical treatments on the preparation induced microroughness and electronic properties of wet-chemically passivated Si(111) substrates with special surface morphology. Stepped substrates with evenly distributed atomically flat terraces were prepared and passivated by thin oxide layers, which were used as a starting point for the subsequent H-termination after long storage in air. It was shown that their surface morphology and electronic properties do not degrade. Applying this preparation method to solar cell substrates with randomly distributed Si(111) pyramids, we achieved significantly lower densities of surface states and reduced recombination loss at a-Si:H/c-Si interfaces, compared with conventional pretreatments. The surface microroughness, the density of rechargeable states and the resulting recombination loss on a-Si:H/c-Si heterojunctions were found to be mainly influenced by two steps of surface pretreatment: firstly, the wet-chemical smoothing procedure of structured substrates and, secondly, the removal of native and wet-chemical oxides during the final etching in HF- or NH₄F- containing solutions. Figure After wet-chemical oxidation in H₂SO₄/H₂O₂ and storage in air     

‘Gate effect’ in templated polyacrylamide membranes influences the electrotransport of proteins and finds applications in proteome analysis

Templating is an effective way for the structural modifications of a material and hence for altering its functional properties. Here protein imprinting was exploited to alter polymeric polyacrylamide (PAA) membranes. The sieving properties and selection abilities of the material formed were evaluated by studying the electrically driven transport of various proteins across templated PAA membranes. The sieving properties correlated with the templating process and depended on the quantity of template used during the polymerisation. For 1 mg/mL protein-templated membranes a ‘gate effect’ was shown, which induced a preferential migration of the template and of similar-size proteins. Such template preferential electrotransport was exploited for the selective removal of certain proteins in biological fluids prior to proteome analysis (depletion of albumin from human serum); the efficiency of the removal was demonstrated by analysing the serum proteome by two-dimensional electrophoresis experiments. Figure PAA templeted membrane for the electroremoval of serum albumin before proteome analysis     

Determination of acetone in seawater using derivatization solid-phase microextraction

Acetone plays an important role in the chemistry of both the atmosphere and the ocean, due to its potential effect on the tropospheric HO_x (= HO + HO₂) budget, as well as its environmental and health effects. We discuss the development of a mobile, sensitive, selective, economical and facile method for the determination of acetone in seawater. The method consists of derivatizing acetone to its pentafluorobenzyl oxime using 1,2,3,4,5-pentafluorobenzylhydroxylamine (PFBHA), followed by solid-phase microextraction (SPME) and analysis by gas chromatography/mass spectrometry (GC/MS). A detection limit of 3.0 nM was achieved. The buffering capacity of seawater imposes challenges in using the method’s optimum pH (3.7) on seawater samples, requiring calibration standards to be made in buffered salt water and the acidification of seawater samples and standards prior to extraction. We employed the technique for analysis of selected surface seawater samples taken on the Nordic seas during the ARK-XX/1 cruise (R.V. Polarstern). An upper limit of 5.5–9.6 nM was observed for acetone in these waters, the first acetone measurements reported for far North Atlantic and Arctic waters. Simplified schematic of transformations of organic compounds at the atmosphere–ocean interface