Validation of three rapid screening methods for detection of verotoxin-producing Escherichia coli in foods: interlaboratory study

An interlaboratory study was conducted for the validation of 3 methods for the detection of all verotoxin-producing Escherichia coli (VTEC) in foods. The methods were a multi-analyte 1-step lateral flow immunoassay (LFIA) for detection of E. coli O157 and verotoxin (VT); an enzyme-linked immunosorbent assay targeted against VT1, VT2, and VT2c (VT-ELISA); and a polymerase chain reaction (PCR) method for detection of VT genes (VT-PCR). Aliquots (25 g or 25 mL) of 4 food types (raw minced [ground] beef, unpasteurized milk, unpasteurized apple juice [cider], and salami) were individually inoculated with low numbers (<9 to 375 cells/25 g) of 6 test strains of E. coli (serogroups O26, O103, O111, O145, and O157) with differing VT-producing capabilities. Five replicates for each test strain and 5 uninoculated samples were prepared for each food type. Fourteen participating laboratories analyzed samples using the LFIA, 9 analyzed the samples by ELISA, and 9 by PCR. The LFIA for O157 and VT had a specificity (correct identification of negative samples) of 92 and 94%, respectively, and a sensitivity (correct identification of positive samples) of 94 and 55%, respectively. The VT-ELISA and VT-PCR had a specificity of 98 and 99%, respectively, and a sensitivity of 89 and 72%, respectively.     

Detailed chemomechanistic sensitivity study on the alkoxylation of fatty amines

The mechanism of the autocatalytic alkoxylation of fatty amines was elucidated using a combined experimental and theoretical approach. The kinetic parameters of the elementary reaction steps are fitted to the experimental data gained in semibatch for propylene and butylene oxides with dodecylamine. A quality-of-fit sensitivity study was conducted to assess the robustness and accuracy of the model. Herein, we identified the kinetic parameters that are either crucial for a good fit or rate controlling in terms of the overall kinetics. It was found that the critical steps are the activation of the epoxide ring by a hydroxyl group present on either the intermediate or final product, highlighting the autocatalytic nature of the reaction. Furthermore, we introduced a so-called degree of conversion control to characterize the importance of each elementary reaction step toward the epoxide conversion. The degree of conversion control showed that the uncatalyzed route toward the secondary amine is only influential at low conversion. At higher conversion the route via the catalytic intermediate dominates. Alternative mechanisms were investigated as well but did not significantly improve the quality of fitting and were thus discarded.     

Characterization of thin polymer‐like films formed by plasma polymerization of methylmethacrylate: A neutron reflectivity study

The microstructure of the plasma‐polymerized methylmethacrylate (ppMMA) films is characterized using neutron reflectivity (NR) as a function of the plasma reaction time or film thickness. Variation in the crosslink density normal to the substrate surface is examined by swelling the film with a solvent, d‐nitrobenzene (dNB). In the presence of dNB, uniform swelling is observed throughout the bulk as well as at the air surface, and silicon oxide interfaces. The results indicate that the MMA film prepared by plasma polymerization (ppMMA) has a uniform crosslink density from air surface to substrate surface. Additionally, the scattering length density of the plasma‐polymerized MMA film (SLD ≈ 0.750 × 10⁻⁶ Å⁻²) is much lower than that of a conventional PMMA film (SLD = 1.177 × 10⁻⁶ Å⁻²). The increase in film thickness following dNB sorption is 7.5% and at least 36% for the ppMMA and PMMA films, respectively. This suggests that the films formed by plasma polymerization are different from conventional polymers in chemical structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2522–2530, 2004     

Reconstruction of the time-dependent wave function exclusively from position data

A method is presented that reconstructs the amplitude and phase of an unknown time-dependent pure-state wave function entirely from experimental position data. No assumptions about the wave function are needed. At a series of times, a large collection of position data is taken, but no measurements of momentum or energy are necessary. The momenta, however, are required for the reconstruction of the wave function and are supplied by analysis of the position data via quantum particle trajectories. Simulations of the method are provided for helium atoms in single and double slit experiments.     

Accurate mass measurement by matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry. I. Measurement of positive radical ions using porphyrin standard reference materials

A method for the accurate mass measurement of positive radical ions by matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry (MALDI‐TOFMS) is described. Initial use of a conjugated oligomeric calibration material was rejected in favour of a series of meso‐tetraalkyl/tetraalkylaryl‐functionalised porphyrins, from which the two calibrants required for a particular accurate mass measurement were chosen. While all measurements of monoisotopic species were within ±5 ppm, and the method was rigorously validated using chemometrics, mean values of five measurements were used for extra confidence in the generation of potential elemental formulae. Potential difficulties encountered when measuring compounds containing multi‐isotopic elements are discussed, where the monoisotopic peak is no longer the lowest mass peak, and a simple mass‐correction solution can be applied. The method requires no significant expertise to implement, but care and attention is required to obtain valid measurements. The method is operationally simple and will prove useful to the analytical chemistry community. Copyright © 2010 John Wiley & Sons, Ltd.     

Liposome-templated supramolecular assembly of responsive alginate nanogels

Nanosized gel particles (nanogels) are of interest for a variety of applications, including drug delivery and single-molecule encapsulation. Here, we employ the cores of nanoscale liposomes as reaction vessels to template the assembly of calcium alginate nanogels. For our experiments, a liposome formulation with a high bilayer melting temperature (Tm) is selected, and sodium alginate is encapsulated in the liposomal core. The liposomes are then placed in an aqueous buffer containing calcium chloride, and the temperature is raised up to Tm. This allows permeation of Ca2+ ions through the bilayer and into the core, whereupon these ions gel the encapsulated alginate. Subsequently, the lipid bilayer covering the gelled core is removed by the addition of a detergent. The resulting alginate nanogels have a size distribution consistent with that of the template liposomes (ca. 120-200 nm), as confirmed by transmission electron microscopy and light scattering. Nanogels of different average sizes can be synthesized by varying the template dimensions, and the gel size can be further tuned after synthesis by the addition of monovalent salt to the solution.     

Light-sensitive lamellar phases

Light sensitive lamellar (L(alpha)) phases have been generated in glycerol/water mixtures from blends of an inert ABA tri-block co-polymer (dimethylsiloxane-polyethylenoxide, (EO)(15)-(PDMS)(15)-(EO)(15)), and a photodestructible anionic surfactant C(6)PAS (sodium 4-hexylphenylazosulfonate). These L(alpha) systems have been formulated in a 6/4 glycerol/water (v/v) mixed solvent. Rheology, small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS) and dynamic light scattering (DLS) have been used to characterize the change in phase behavior and structure after the incorporated C(6)PAS is selectively degraded by UV light incident on the L(alpha) phases. The ABA co-polymer alone forms weakly structured lamellar mesophases, which are stabilized by thermal fluctuations and characterized by low shear moduli (L(alpha) phase-A). Addition of C(6)PAS (10 mM) introduces charge stabilization, generating more ordered and stiffer L(alpha) systems (L(alpha) phase-B). After UV irradiation (Hg lamp) of the L(alpha)-B phases, and subsequent degradation of the ionic C(6)PAS, the results of rheological and scattering studies are consistent with an irreversible change back to L(alpha) phase-A type systems. These formulations display a novel transition between electrostatically- and thermally-stabilized lamellae, which may be controlled by incident UV light.