Enhanced rapidity for qualitative detection of Listeria monocytogenes using an enzyme-linked immunosorbent assay and immunochromatography strip test combined with immunomagnetic bead separation

An enzyme-linked immunosorbent assay (ELISA), immunochromatography (ICG) strip test, and immunomagnetic bead separation (IMBS) system based on a monoclonal antibody were individually developed for the detection and isolation of Listeria monocytogenes in meat samples. The three methods showed a strong reaction with Listeria species and a weak reaction with Staphylococcus aureus. To increase the rapidity of L. monocytogenes detection, combinations of the ELISA and ICG strip test with the IMBS system (ELISA-IMBS and ICG-IMBS) were investigated. In comparative analyses of artificially inoculated meat and samples of processed meat, the ELISA and ICG strip test required 24 h of enrichment time to detect the inoculated meat samples with > or =1 X 10(2) CFU/10 g, whereas the ELISA-IMBS and ICG-IMBS required only 14 h of enrichment. Analyses of naturally contaminated meat samples (30 pork samples, 20 beef samples, 26 chicken samples, 20 fish samples, and 20 processed meat samples) performed by ELISA-IMBS, ICG-IMBS, and API kit produced similar results. The ELISA-IMBS and ICG-IMBS provide a more rapid assay than the individual ELISA and the ICG strip test and are appropriate for rapid and qualitative detection of L. monocytogenes (or Listeria species) in meat samples. With the ICG-IMBS, L. monocytogenes could be detected in meat samples within 15 h and the method has potential as a rapid, cost-effective on-site screening tool for the detection of L. monocytogenes in food samples and agricultural products at a minimum detection level of approximately 100 CFU/10 g.     

A Direct Enzyme Immunoassay to Detect Erythrosine in Foods

As a synthetic food dye, erythrosine is associated with serious toxicity in inducing thyroid tumors, and the use of erythrosine is strictly regulated in most counties including China. In this study, a direct enzyme-linked immunosorbent assay (ELISA) has been developed for analysis of erythrosine in food products. A highly specific monoclonal antibody (MAb) for erythrosine was produced using erythrosine–bovine serum albumin (BSA) conjugate as an artificial antigen, and horseradish peroxidase (HRP)-labeled MAb for erythrosine was utilized as the detection antibody. Under the optimized condition, the UV absorbance in microplate related well with erythrosine concentration in the range of 0.1–10.0 μg/g. The proposed method could be applied to determine erythrosine in beverage and cookie, with good recoveries (80 –103 %) for the three spiked levels (30, 50, and 100 μg/g), and the relative standard deviations of detected amount were <12.3 %.     

Fluorescence polarization immunoassay based on a monoclonal antibody for the detection of ochratoxin A

A fluorescence polarization immunoassay (FPIA) based on a monoclonal antibody for the determination of ochratoxin A (OTA) was developed. Fluorescein‐labelled OTA derivative (tracer) was synthesized and purified by thin‐layer chromatography. The optimized OTA FPIA had a dynamic range from 5 to 200 ng mL^?1 with IC₅₀ value of 30 ng mL^?1 and a detection limit of 3 ng mL^?1. The method developed was characterized by high specificity and reproducibility. Cross‐reactivity with other mycotoxins (zearalenone, aflatoxins, patulin and T‐2 toxin) was negligible (<0.1%). Methanol extracts of barley samples were used for the analysis. The results of OTA determination in barley were compared with those determined by indirect competitive enzyme‐linked immunosorbent assay (ELISA). Recoveries for the samples spiked at 50, 100 and 500 ng g^?1 levels were 91, 90 and 97%, respectively, for FPIA, and 98, 98 and 102%, for ELISA. Naturally contaminated barley samples were analysed by these methods but some disagreement was observed between the results. The FPIA method can be applied for screening of food samples for OTA residues without a complicated clean‐up.     

Effects of Humic Substances Obtained from Shives on Flax Yield Characteristics

The effects of humic substances (HS) extracted from flax shives on the fiber and seed yield of fiber flax were examined during 3 years field experiment. HS from shives consists of humic acids—5.3 gL^?1 and fulvic acids—0.7 gL^?1 were applied (6·10^–2 gL^?1 concentration, with 300 Lha^?1 of spraying liquid) in “herring-bone” stage (BBCH 13 growth stage). The HS action was evaluated in different climatic conditions and in three varieties. Application of HS on early stage of vegetation of flax plants increased fiber yield (exceeding control on 16.0–28.1%) and quality (5% of cellulose content), protein and oil content in seeds (up to 1.9–4.2% and 1.6–3.5%, respectively). Positive reply of flax plants on HS from flax shives in tested cultivars allows saying about prospects of this type of humic substances.     

Electromechanical Imaging and Spectroscopy of Ferroelectric and Piezoelectric Materials: State of the Art and Prospects for the Future

Piezoresponse force microscopy (PFM) has emerged as a powerful and versatile tool for probing nanoscale phenomena in ferroelectric materials on the nanometer and micrometer scales. In this review, we summarize the fundamentals and recent advances in PFM, and describe the nanoscale electromechanical properties of several important ferroelectric ceramic materials widely used in memory and microelectromechanical systems applications. Probing static and dynamic polarization behavior of individual grains in PZT films and ceramics is discussed. Switching spectroscopy PFM is introduced as a useful tool for studying defects and interfaces in ceramic materials. The results on local switching and domain pinning behavior, as well as nanoscale fatigue and imprint mapping are presented. Probing domain structures and polarization dynamics in polycrystalline relaxors (PMN-PT, PLZT, doped BaTiO₃) are briefly outlined. Finally, applications of PFM to dimensionally confined ferroelectrics are demonstrated. The potential of PFM for studying local electromechanical phenomena in polycrystalline ferroelectrics where defects and other inhomogeneities are essential for the interpretation of their macroscopic properties is illustrated.     

Triplet state absorption in carbon nanotubes: a TD-DFT study

We predict properties of triplet excited states in single-walled carbon nanotubes (CNTs) using a time-dependent density-functional theory (TD-DFT). We show that the lowest triplet state energy in CNTs to be about 0.2-0.3 eV lower than the lowest singlet state energies. Like in pi-conjugated polymers, the lowest CNT triplets are spatially localized. These states show strong optical absorption at about 0.5-0.6 eV to the higher lying delocalized triplet states. These results demonstrate striking similarity of the electronic features between CNTs and pi-conjugated polymers and provide explicit guidelines for spectroscopic detection of CNT triplet states.     

Optimization and application of ICPMS with dynamic reaction cell for precise determination of 44Ca/40Ca isotope ratios

An inductively coupled plasma mass spectrometer with dynamic reaction cell (ICP-DRC-MS) was optimized for determining (44)Ca/(40)Ca isotope ratios in aqueous solutions with respect to (i) repeatability, (ii) robustness, and (iii) stability. Ammonia as reaction gas allowed both the removal of (40)Ar+ interference on (40)Ca+ and collisional damping of ion density fluctuations of an ion beam extracted from an ICP. The effect of laboratory conditions as well as ICP-DRC-MS parameters such a nebulizer gas flow rate, rf power, lens potential, dwell time, or DRC parameters on precision and mass bias was studied. Precision (calculated using the "unbiased" or "n - 1" method) of a single isotope ratio measurement of a 60 ng g(-1) calcium solution (analysis time of 6 min) is routinely achievable in the range of 0.03-0.05%, which corresponded to the standard error of the mean value (n = 6) of 0.012-0.020%. These experimentally observed RSDs were close to theoretical precision values given by counting statistics. Accuracy of measured isotope ratios was assessed by comparative measurements of the same samples by ICP-DRC-MS and thermal ionization mass spectrometry (TIMS) by using isotope dilution with a (43)Ca-(48)Ca double spike. The analysis time in both cases was 1 h per analysis (10 blocks, each 6 min). The delta(44)Ca values measured by TIMS and ICP-DRC-MS with double-spike calibration in two samples (Ca ICP standard solution and digested NIST 1486 bone meal) coincided within the obtained precision. Although the applied isotope dilution with (43)Ca-(48)Ca double-spike compensates for time-dependent deviations of mass bias and allows achieving accurate results, this approach makes it necessary to measure an additional isotope pair, reducing the overall analysis time per isotope or increasing the total analysis time. Further development of external calibration by using a bracketing method would allow a wider use of ICP-DRC-MS for routine calcium isotopic measurements, but it still requires particular software or hardware improvements aimed at reliable control of environmental effects, which might influence signal stability in ICP-DRC-MS and serve as potential uncertainty sources in isotope ratio measurements.     

Derivation of plasmonic resonances in the Fourier modal method with adaptive spatial resolution and matched coordinates

A very stable approach for finding optical resonances is to solve an eigenvalue equation that evolves from the linearization of the inverse scattering matrix. In this paper, we show how to use this approach in the Fourier modal method so that advanced coordinate transformation methods such as adaptive spatial resolution and matched coordinates can be included. Furthermore, we present a way that accelerates the computation of the inverse scattering matrix tremendously and allows the derivation of the resonant field distribution inside the structure efficiently.     

Electrochemical strain microscopy of local electrochemical processes in solids: mechanism of imaging and spectroscopy in the diffusion limit

Changes in ionic concentration and electrochemical processes in solids are invariably associated with changes in molar volume. Correspondingly, materials with mobile ions develop strain in response to applied electric bias. This electromechanical coupling mediated by mobile ions lays the foundation for the electrochemical strain microscopy (ESM) of energy storage and conversion materials. Here, we analyze the imaging and spectroscopic mechanism in ESM in the diffusion limit and discuss the similarities between ESM and macroscopic current-based electrochemical measurements. The theoretical challenges in ESM are formulated.