单分子层修饰生物芯片基片的电化学研究

构建了一种亲和素单分子层修饰的电化学分析生物芯片基片，并且以二茂铁和亚铁氰化钾为指示剂对该基片的电化学性能进行了研究．循环伏安实验结果表明，单分子层的存在增强了二茂铁在基片上的响应电流，二茂铁可以作为该基片的高效电子媒介体，实验结果具有良好的重现性和一致性，基片产生的背景噪声可以忽略不计．文中对这些结果产生的原因进行了讨论．     

Imaging cytoplasmic cAMP in mouse brainstem neurons

Background  

cAMP is an ubiquitous second messenger mediating various neuronal functions, often as a consequence of increased intracellular Ca²⁺ levels. While imaging of calcium is commonly used in neuroscience applications, probing for cAMP levels has not yet been performed in living vertebrate neuronal tissue before.     

Ultrafast study of 9-diazofluorene: direct observation of the first two singlet states of fluorenylidene

Ultrafast photolysis of 9-diazofluorene (DAF) produces a broadly absorbing transient within the instrument time resolution (300 fs), which is assigned to an excited state of the diazo compound. The diazo excited state fragments to form fluorenylidene (Fl) in both its lowest energy singlet state (1Fl, 405-430 nm, depending on the solvent) and a higher energy singlet state (370 nm, 1Fl*). The excited singlet carbene has a lifetime of 20.9 ps in acetonitrile and decays to the lower energy singlet state (1Fl), which relaxes to the triplet ground state (3Fl) in acetonitrile, cyclohexane, benzene, and hexafluorobenzene. The equilibrium mixture of singlet and triplet fluorenylidene reacts with these solvents. Singlet fluorenylidene reacts with methanol and cyclohexene in competition with relaxation to 3Fl. One of the reaction products in methanol is the 9-fluorenyl cation. The rate of intersystem crossing (ISC) in hexafluorobenzene and other halogenated solvents is remarkably slow given that carbene ISC rates are generally fastest in nonpolar solvents. An explanation of this effect is advanced.     

Stable isotopic studies of earthworm feeding ecology in tropical ecosystems of Puerto Rico

Feeding strategies of earthworms and their influence on soil processes are often inferred from morphological, behavioral and physiological traits. We used (13)C and (15)N natural abundance in earthworms, soils and plants to explore patterns of resource utilization by different species of earthworms in three tropical ecosystems in Puerto Rico. In a high altitude dwarf forest, native earthworms Trigaster longissimus and Estherella sp. showed less (15)N enrichment ((15)N = 3-6 per thousand) than exotic Pontoscolex corethrurus ((15)N =7-9 per thousand) indicating different food sources or stronger isotopic discrimination by the latter. Conversely, in a lower altitude tabonuco forest, Estherella sp. and P. corethrurus overlapped completely in (15)N enrichment ((15)N = 6-9 per thousand), suggesting the potential for interspecific competition for N resources. A tabonuco forest converted to pasture contained only P. corethrurus which were less enriched in (15)N than those in the forest sites, but more highly enriched in (13)C suggesting assimilation of C from the predominant C(4) grass. These results support the utility of stable isotopes to delineate resource partitioning and potential competitive interactions among earthworm species. Copyright 1999 John Wiley & Sons, Ltd.     

Identification of additives in poly(vinylacetate) artist’s paints using PY-GC-MS

Commercial poly(vinyl acetate) (PVAc) paint formulations for artists include a number of compounds in addition to the PVAc polymer and pigments to improve the physical and chemical properties of the resulting product. Among the most common additives are surfactants, coalescing agents, defoamers, freeze–thaw agents and thickeners. These products significantly influence the behaviour of the dried film. Nevertheless, they are usually difficult to detect with conventional analytical methods given their low concentration. In order to identify these additives, present in the dried film as minor components, an analytical method based on in situ thermally assisted pyrolysis–silylation gas chromatography–mass spectrometry (GC-MS) using hexamethyldisilazane as a derivatisation reagent is proposed. This method improves the conventional GC-MS analysis performed by direct pyrolysis and enables the simultaneous identification of the PVAc binding medium and the additives included by the manufacturer in the commercial paint. Five different commercial PVAc paints have been analysed, namely, armour green, burnt umber, oriental red, raw umber and white from Flashe®. Internal plasticiser VeoVa consisting of C₁₀ fatty acids with highly branched chains has been recognised from the MS spectra. On the other hand, the differences found in the additive content of the studied paints, in particular the poly(ethylene glycol)-type surfactant, are in good agreement with their mechanical properties.

Radiometric holdup measurements: Differential mass holdup of americium and plutonium oxides during preparation of traceable non-destructive assay standards

Summary Traceable non-destructive assay standards containing mixtures of well characterized americium and plutonium oxides were prepared by blending weighed quantities with a diatomaceous earth matrix and encapsulating in welded zirconium cylinders. Am and Pu retained in fabrication process materials (e.g., emptied blend bottles), termed holdup, was quantified by gamma-spectroscopy in order to accurately state the total nuclear material content of the standards. The observed holdup data indicate that the common assumption that Am and Pu holdup behavior is similar does not hold up well in the case of mixed oxides.     

Crystal quality boosts responsiveness of magnetic shape memory single crystals

Magnetic shape memory alloys are promising materials to replace giant magnetostrictive materials and piezoelectrical ceramics in actuating devices due to the large magnetically induced strains. Ni-Mn-Ga is the most intense studied system due to its relatively high operational temperatures and the huge magnetically induced strains reported. Up to now the application of these materials is still limited by the operational temperature range. Additionally twin boundary mobility suffers from structural defects increasing the magnetic fields needed for significant and reproducible strains. The sample quality is affected by crystal inhomogeneity, porosity and impurities. Here new results are reported for the Ni-Mn-Ga class based on a set of single crystals grown by the SLARE method, recently developed by Mecklenburg et al. Single crystalline samples of Ni_49.7Mn_29.3Ga₂₁ of tetragonal martensitic structure exhibit a magnetic field induced strain of more than 4% below 170 mT and 6.5% at only 340 mT. Furthermore the operational temperature regimen could be expanded up to 65 °C.     

GlycoChip: multiarray for the study of carbohydrate-binding proteins

Biotinylated glycoconjugates which were designed as oligosaccharides attached to 30 kDa polyacrylamide were coated on a microarray platform XNAonGOLD, which was developed earlier for an oligonucleotide assay. The specificity of antibodies to carbohydrate antigens was analyzed using the glyco-microarray. Comparison of the obtained results with those of common 96-well plate ELISA completely coincided with the found antibody specificities. However, parameters such as the analytical sensitivity of the method and the amount of biotinylated material coated on the microarray platform proved to be worse than expected.     

Investigation of sera from various species by using lectin affinity arrays and scanning ellipsometry

Serum proteins of different species and of different human blood groups exhibit various protein glycosylation patterns. Sera from human, pig, sheep and guinea pig have been applied to a panel of eight different lectins immobilized on a gold wafer. The biorecognition has been evaluated with scanning ellipsometry and the two-dimensional matrices obtained have been treated with image analysis and MVDA for evaluation. The results showed a clear difference in protein binding pattern between the different species and thereby separation of the different sera could be made. Dendograms indicate that human and pig sera are the most related of the four different sera investigated.