Integrated capillary electrophoresis amperometric detection microchip with replaceable microdisk working electrode. II. Influence of channel cross-sectional area on the separation and detection of dopamine and catechol

The interference of separation high voltage with the electrochemical detection is a major challenge to the microchip capillary electrophoresis-electrochemical detection systems with end-channel detection mode. Using dopamine and catechol as model analytes, the influences of channel cross-sectional area and channel-to-electrode distance on the high-voltage interference, accordingly on the separation and detection performances of the microchip capillary electrophoresis-electrochemical detection system were investigated. With the increase of the channel cross-sectional area from 312 through 450-615 microm2, the apparent half-wave potentials of hydrodynamic voltammetry for dopamine at the field strength of 288 V/cm shifted positively from 285 through 330-400 mV. By using a chip with the smallest channel cross-section (312 microm2 with top width of 37.3 microm and depth of 8.9 microm) the residual high-voltage field in the detection cell was small, so that detection was conducted at a channel-to-electrode distance of 20 microm to achieve better performances of separation and detection.     

Early metabolic characterization of brain tissues after whole body radiation based on gas chromatography–mass spectrometry in a rat model

Radiation‐induced brain injury involves acute, early delayed and late delayed damage based on the time‐course and clinical manifestations. The acute symptoms are mostly transient and reversible, whereas the late delayed radiation‐induced changes are progressive and irreversible. Therefore, evaluation of the organ‐specific early response to ionizing radiation exposure is necessary for improving treatment strategies and minimizing possible damage at an early stage after radiation exposure. In the current study, the gas chromatography–mass spectrometry technique based on metabolomics coupled with metabolic correlation network was applied to investigate the early metabolic characterization of rat brain tissues following irradiation. Our findings showed that the metabolic response to irradiation was not just limited to the variations of individual metabolite levels, but also accompanied by alterations of network correlations among various metabolites. Metabolite clustering indicated that energy metabolism disorder and inflammation response were induced following radiation exposure. The correlation networks revealed that the strong positive correlations of differential metabolites were highly reduced and significant negative linkages were highlighted in irradiated groups even without statistical changes in metabolic levels. Our findings provided new insights into our understanding of the radiation‐induced acute brain injury mechanism and clues as to the therapy target for clinical applications.     

Fabrication of a gold microelectrode for amperometric detection on a polycarbonate electrophoresis chip by photodirected electroless plating

A novel method of photoresist-free micropatterning coupled with electroless gold plating is described for the fabrication of an integrated gold electrode for electrochemical detection (ED) on a polycarbonate (PC) electrophoresis microchip. The microelectrode layout was photochemically patterned onto the surface of a PC plate by selective exposure of the surface coated without photoresist to 254 nm UV light through a chromium/quartz photomask. Thus, the PC plate was selectively sensitized by formation of reactive chemical moieties in the exposed areas. After a series of wet chemistry reactions, the UV-exposed area was activated with a layer of gold nanoparticles that served as a seed to catalyze the electroless plating. The gold microelectrode was then selectively plated onto the activated area by using an electroless gold plating bath. Nonselective gold deposition on the unwanted areas was eliminated by sonication of the activated PC plate in a KSCN solution before electroless plating, and the adhesion of the plated electrodes to the PC surface was strengthened with thermal annealing. Compared with the previously reported electroless plating technique for fabrication of microelectrodes on a microchip, the present method avoided the use of a membrane stencil with an electrode pattern to restrict the area to be wet-chemically sensitized. The CE with integrated ED (CE-ED) microchip was assembled by thermal bonding an electrode-plated PC cover plate to a microchannel-embossed PC substrate. The novel method allows one to fabricate low-cost, electrode-integrated, complete PC CE-ED chips with no need of a clean room. The fabricated CE-ED microchip was demonstrated for separation and detection of model analytes, including dopamine (DA) and catechol (CA). Detection limits of 0.65 and 1.03 microM were achieved for DA and CA, respectively, and theoretical plate number of 1.4 x 10(4) was obtained for DA. The plated gold electrode can be used for about 4 h, bearing usually more than 100 runs before complete failure.     

On short cycles in triangle-free oriented graphs

An orientation of a simple graph is referred to as an oriented graph. Caccetta and Häggkvist conjectured that any digraph on n vertices with minimum outdegree d contains a directed cycle of length at most ?n/d?. In this paper, we consider short cycles in oriented graphs without directed triangles. Suppose that α0 is the smallest real such that every n-vertex digraph with minimum outdegree at least α₀n contains a directed triangle. Let ε < (3 ? 2α₀)/(4 ? 2α₀) be a positive real. We show that if D is an oriented graph without directed triangles and has minimum outdegree and minimum indegree at least (1/(4 ? 2α₀)+ε)|D|, then each vertex of D is contained in a directed cycle of length l for each 4 ≤ l < (4 ? 2α₀)ε|D|/(3 ? 2α₀) + 2.     

完全交替结构乙烯-丙烯共聚物的制备与表征

对顺-1,4含量为100%的高顺式聚异戊二烯(HCPI)进行加氢反应,得到了序列结构高度规整的乙烯-丙烯交替共聚物(alt-EP).所用的HCPI有适当的分子量(Mn=41×104)和极窄的分子量分布(Mw/Mn=1.02).HCPI的加氢反应以环烷酸镍和三异丁基铝为催化剂,在60℃和4.0MPa氢压的条件下反应3h,加氢产物的加氢度为100%.GPC测试结果显示所得乙烯-丙烯交替共聚物保持了窄分布的特点,表明HCPI加氢后未发生交联和降解反应;NMR,FTIR和广角X射线衍射测试结果表明此乙烯-丙烯交替共聚物具有高度规整的序列结构,为完全交替结构的乙烯-丙烯共聚物.并通过TGA和DSC对乙烯-丙烯交替共聚物的热性能进行了表征.     

Synthesis and Functional Properties of Symmetrically Naphthyl-Based Oligoarylenes with High Glass-Transition Temperatures

Symmetrically naphthyl‐based π‐conjugated oligoarylenes, OPP(4)Ph‐TNp, OPP(4)An‐TNp and OPP(4)OX‐TNp have successfully been synthesized by a divergent approach using Pd‐catalyzed Suzuki cross‐coupling reaction of diiodo‐ or dibromo‐oligoarylene and arylboronic acid as a key step. Their optical, electrochemical and thermal properties have also been characterized. These newly synthesized naphthyl‐based oligoarylenes show highly morphological (T_g 149–187°C) and thermal (T_dec 509–597°C) stabilities as well as exhibit potential applications in optoelectronic fields.