Development and validation of a rapid multiplex ELISA for pyrrolizidine alkaloids and their N-oxides in honey and feed

Pyrrolizidine alkaloids (PAs) are a group of plant secondary metabolites with carcinogenic and hepatotoxic properties. When PA-producing plants contaminate crops, toxins can be transferred through the food chain and cause illness in humans and animals, most notably hepatic veno-occlusive disease. Honey has been identified as a direct risk of human exposure. The European Food Safety Authority has recently identified four groups of PAs that are of particular importance for food and feed: senecionine-type, lycopsamine-type, heliotrine-type and monocrotaline-type. Liquid or gas chromatography methods are currently used to detect PAs but there are no rapid screening assays available commercially. Therefore, the aim of this study was to develop a rapid multiplex ELISA test for the representatives of three groups of alkaloids (senecionine, lycopsamine and heliotrine types) that would be used as a risk-management tool for the screening of these toxic compounds in food and feed. The method was validated for honey and feed matrices and was demonstrated to have a detection capability less than 25 μg/kg for jacobine, lycopsamine, heliotrine and senecionine. The zinc reduction step introduced to the extraction procedure allows for the additional detection of the presence of N-oxides of PAs. This first multiplex immunoassay for PA detection with N-oxide reduction can be used for the simultaneous screening of 21 samples for >12 PA analytes. Honey samples (n?=?146) from various origins were analysed for PA determination. Six samples were determined to contain measurable PAs >25 μg/kg by ELISA which correlated to >10 μg/kg by LC-MS/MS.     

Twisting DNA: single molecule studies

Over the past 10 years a number of new techniques have emerged that allow the manipulation of single DNA molecules and other biopolymers (RNA, proteins, etc.). These experiments have permitted the measurement of the DNA stretching and twisting elasticity and have consequently revealed the essential role played by the DNA mechanical properties in its interactions with proteins. We shall first describe the different methods used to stretch and twist single DNA molecules. We will then focus on its behaviour under torsion, especially by discussing the different methods used to estimate its torsional modulus.     

Spectral analysis of wall turbulence with a bicircular electrochemical probe

The calculation of the mass flux/velocity gradient transfer function at a wall in the direction parallel to the wall and perpendicular to the mean flow direction, has been performed in linear conditions. This transfer function is relevant to the difference of the mass fluxes between two semicircular surfaces separated by an infinitely thin gap aligned with the flow direction.Electrochemical measurements in turbulent flow were performed with segmented electrodes having this geometry and devised by a photolithographic technique. The spectra of the velocity gradient fluctuations in the longitudinal and transverse directions were calculated and hence the turbulence intensities.     

Application à la viscoélasticité non linéaire du calcul symbolique à plusieurs variables

Résumé Nous présentons une tentative pour étendre à la viscoélasticité non linéaire les méthodes du calcul symbolique, dont on sait qu'ils ramènent, dans le cas linéaire, tous les problèmes de viscoélasticité, tant dynamiques que statiques, à des problèmes d'élastostatique (Mandel, 1955).Nous partons d'un développement deFréchet, limité à l'ordren, de la fonctionnelle non linéaire donnant l'expression du tenseur des contraintes deKirchhoff II en fonction de la représentation lagrangienne (en déformations finies) du tenseur de la déformation pure E(t).Nous appliquons successivement deux transformations. La première dissymétriseII(t) en(t ₁,,t _k ,,t _n ) ce qui transforme le développement deFréchet limité en une somme des produits de convolution multiples, multilinéaires par rapport aux _i = ( _i ) et à leurs invariants simples tr _i , ou composés tr( _j ... _k ) (ces derniers étant eux-mêmes multilinéaires par rapport aux _i ).Pour un choix convenable de l'origine des temps, l'application à de la transformation deCarson àn variable (CS _n ) transforme cette somme en un polynôme ^n*(p₁, p_n) multilinéaire par rapport aux E _i ^* = E^*(p _i ) (en CS₁) et à leurs invariants simples trE _i ^* ou composés tr[E _j ^* E _k ^* ]. Ses coefficients (scalaires) sont les transformésr _ki ^k* (p₁, , p _k ) des noyauxr _ki(t₁, ,t _k ).Dans le cas d'un corps initialement isotrope, le résultat deSpencer etRivlin (1960) permet de se limiter au CS₁₁. Dans la pratique, on peut même se limiter au CS₃ si l'on tient compte de la remarque deGradowczyk (1969) sur le rôle de la précision expérimentale escomptable.Dans tous les cas, a même forme que l'expression obtenue en dissymétrisant le développement utilisé parGoldenblatt dans le cas de l'élasticité non linéaire en déformations finies, à ceci près que le nombre d'invariants de base étant supérieur à 3, il ne peut se réduire à un développement d'ordre 2 par rapport à l'ensemble des E _i ^* .Le retour àII(t) se fait en inversant (par des tables) la transformation deCarson, ce qui donne(t₁, t_n), puis en faisantt _i = t i = 1, n dans. L'inversion se ramène àn inversions d'ordre 1 lorsque les noyauxK sont sous forme produit ou sous forme de polynômes deDirichlet par rapport aux _i. Dans ce dernier cas, elle est immédiate (par décomposition en éléments simples) si la sollicitation fonction du temps est elle-même représentée par un polynôme deDirichlet, propriété qui se transmet à la solution.     

Mid-wave QWIPs for the [3–4.2 μm] atmospheric window

We report two approaches using Quantum Well Infrared Photodetectors for detection in the [3–4.2 μm] atmospheric window. Taking advantage of the large band gap discontinuity we demonstrated a strained AlInAs/InGaAs heterostructure on InP. The optical coupling in this structure has been experimentally and numerically investigated. The results show that the coupling is mainly due to guided modes. The second approach is based on double barrier strained AlGaAs/AlAs/GaAs/InGaAs active layers on GaAs. The segregation of the elements III in these structures has been investigated using a transmission electron microscope. The results show a strong modification of the conduction band profile. We demonstrate peak wavelengths at 3.9 μm for the InP based detector and 4.0 μm for the GaAs based detector. We report a background limited peak detectivity (2π field of view, 300 K background) at 4.0 μm of about 2 × 10¹¹ cm Hz^1/2 W^?1 at 77 K, and 1.5 × 10¹¹ cm Hz^1/2 W^?1 at 100 K.     

13C NMR spectra of 2,3-dihydro-1H-benzo[b]azepines: Differentiation of diastereomers

The ¹³C NMR spectra of 23 2,3-dihydro-1H-benzo[b]azepines, including nine pairs of diastereomers separated by chromatography, [(2R*, 3R^*) and (2R^*), 3S^*)] are hereby assigned and discussed. The relative configurations of the diastereomers were assigned by two methods. The first, based on the chemical shifts of the asymmetric carbons C-2 and C-3 (with regression analysis), shows that the values for (R^*, R^*) are approximately 1 ppm lower than those for (R^*, S^*) diastereomers. The second method uses the chemical shifts, δ₃, of the R₃(CH₃) substituents. When these δ₃ values are compared by means of the δ₃-δ_m difference (δ_m is the mean value obtained from compounds where R₂=H), the difference is always negative for (R^*, R^*) and positive for (R^*, S^*). This is attributed to a γ-gauche effect between R₂ and R₃ in the case of (R^*, R^*) diastereomers (R₂ and R₃ are cis). The results corroborate those already obtained by ¹H NMR [J(23)(R^*, R^*)<J(23)(R^*, S^*)] and are a confirmation of the results of a radiocrystallographic examination carried out on two nitrogen acetylated diastereomers.     

Development of a 4–15 μm infrared GaAs hyperspectral QWIP imager

In the on-going evolution of GaAs quantum well infrared photodetectors (QWIPs) we have developed a four band, 640 × 512, 23 μm × 23 μm pixel array which we have subsequently integrated with a linear variable etalon (LVE) filter providing over 200 spectral bands across the 4–15.4 μm wavelength region. This effort was a collaboration between NASA’s Goddard Space Flight Center (GSFC), the Jet Propulsion Laboratory (JPL) and the Army Research Laboratory (ARL) sponsored by the Earth Science Technology Office of NASA. The QWIP array was fabricated by graded molecular beam epitaxial (MBE) growth that was specifically tailored to yield four distinct bands (FWHM): Band 1; 4.5–5.7 μm, Band 2; 8.5–10 μm, Band 3; 10–12 μm and Band 4; 13.3–14.8 μm. Each band occupies a swath that comprises 128 × 640 elements. The addition of the LVE (which is placed directly over the array) further divides the four “broad” bands into 209 separate spectral bands ranging in width from 0.02 μm at 5 μm to 0.05 μm at 15 μm. The detector is cooled by a mechanical cryocooler to 46 K. The camera system is a fully reflective, f/4.2, 3-mirror system with a 21° × 25° field of view. The project goals were: (1) develop the 4 band GaAs QWIP array; (2) develop the LVE and; (3) implement a mechanical cryocooler. This paper will describe the efforts and results of this undertaking with emphasis on the overall system characteristics.