金纳米粒子在氨基表面上的组装-pH值的影响

用原子力显微镜（AFM）和表面增强喇曼光谱（SERS）研究了pH值对金纳米粒子在Au／巯基苯胺自组装膜表面上组装效果的影响．AFM结果表明，金纳米粒子在表面上的覆盖度随pH值表现出规律性的变化，巯基苯胺自组装膜的SERS强度随pH值的变化也有类似的趋势．在磁性环境下，氨基未质子化，金粒子难以组装上，而在酸性条件下，氨基质子化带正电，金粒子与基底容易结合．我们认为金纳米粒子和氨基之间的作用属于静电力，pH值同时影响膜表面氨基的质子化程度和金纳米粒子表面的带电量．     

Electrochemical Behavior and Determination of Uric Acid at Single-Walled Carbon Nanotube Modified Gold Electrodes

The voltammetric behavior of uric acid was studied at a single-walled carbon nanotube (SWNT) modified gold electrode. Uric acid can effectively accumulate at this electrode and produce an anodic peak at about 0.45 V (vs. SCE) in pH 5.0 sodium acetate buffer solutions (HAc-NaAc). The experimental parameters, such as solution pH, accumulation time, and amount of SWNT, were optimized for determination. Under the optimum conditions, the anodic peak current is linear to the uric acid concentration over the range of 1.0×10⁻⁷ M to 2.5×10⁻⁵ M with a correlation coefficient of 0.998. The detection limit was 5.0×10⁻⁸ M for 60 s accumulation. The electrode could be easily regenerated and exhibited good stability. A 5.0×10⁻⁶ M uric acid solution was measured ten times using the same electrode, and the relative standard deviation of the peak current was 1.3%. This method was successfully applied to the determination of uric acid in human urine samples, and the recovery was 97–99%. The feasibility for simultaneous determination of xanthine, ascorbic acid and uric acid was discussed. These species did not interfere with each other in a certain concentration range. The influence of some surfactants on the anodic peak was also examined.     

Grain boundary diffusion coefficients in gold–nickel thin films

Polycrystalline gold–nickel thin films are deposited on silicon (111) wafers by evaporation in a vacuum of 2 × 10^?6 mbar. Concentration profiles of heat‐treated specimens are obtained by Auger electron depth profiling. The heat treatments are carried out in a vacuum furnace of 4 × 10^?6 mbar in the temperature interval 473–773 K. The grain boundary diffusion coefficient is determined, using a modified Wipple model, to be (3 × 10^?4 cm² s^?1) exp (?0.94 eV kT^?1). It is concluded that interdiffusion in the investigated system is characterized by type B kinetics, and that grain boundary diffusion plays a dominant role in the mass transport process of such films. Copyright © 2003 John Wiley & Sons, Ltd.     

Superoxide sensor based on cytochrome c immobilized on mixed-thiol SAM with a new calibration method

Cytochrome c was immobilized on a mixed-thiol (mercaptoundecanoic acid/mercaptoundecanol) modified gold electrode (MUA:MU/cyt c electrode). Characterization of the cyt c electrode showed a quasi-reversible, electrochemical redox behavior with a formal potential of −13±5 mV (versus Ag/AgCl) for the surface adsorbed protein and 3±5 mV for covalently immobilized cyt c. The heterogeneous electron transfer rate constants were determined to be about 70 and 40 s⁻¹ for both states of the protein, respectively. They were found to be significantly higher than those of pure MUA-modified cyt c electrodes (MUA/cyt c electrodes). The interaction of superoxide radicals (O₂⁻) with the (MUA:MU)/cyt c electrode was characterized and used for an amperometric O₂⁻ detection. The influence of H₂O₂ and uric acid on the sensor signal was investigated. The sensitivity of the (MUA:MU)/cyt c electrode to O₂⁻ was significantly improved compared with that of the MUA/cyt c electrode. Based on a kinetic model for the superoxide detection system, a new calibration method was established. This simple and fast method used the spontaneous dismutation of KO₂ and was compared with the enzymatic superoxide generation system using xanthine oxidase.     

Superconductivity in copper, silver, and gold compounds

High-temperature superconductivity exists in layered, square-planar cuprates, but is almost absent in most other Cu(II) compounds and in most Ag(II) and Au(II) compounds. Valence state II is quite unusual in silver and gold and often disproportionates to valence states I and III ("negative-U compounds"). The two-electron difference in oxidation state is suggestive of electron pairing, a prerequisite for superconductivity. In the present paper the connection between disproportionation and geometrical structure on one hand and superconductivity on the other is discussed by using the accepted theory for mixed valence complexes. It is concluded that absence of superconductivity in gold and silver compounds can be connected to the instability of oxidation state II and the large difference in equilibrium geometry between oxidation states I and III.     

负载型Au-Pd双金属催化剂的制备及其对CO氧化的催化活性

采用改性的等体积浸渍法制备了SiO2负载的Au-Pd双金属催化剂,考察了催化剂的焙烧温度对CO氧化反应活性的影响.与623,723和773K的条件下焙烧的催化剂相比,673K焙烧的催化剂具有良好的催化CO氧化活性,CO完全转化温度低于398K.应用N2物理吸附、X射线衍射、程序升温还原、CO程序升温脱附及X射线光电子能谱等技术对催化剂进行了表征.结果表明,673K焙烧的催化剂具有最大的比表面积和最小的孔径,存在Au0,Pd0和PdO相,AuxPdy合金相很少;而773K焙烧的催化剂上除了含有Au0,Pd0和PdO相外,还存在明显的AuxPdy合金相.具有大比表面积,小孔径,Au0,Pd0和PdO多相共存的催化剂可使CO的吸附量增加,催化活性提高;而AuxPdy合金相的生成并不能提高催化剂的催化活性.     

Formation of supported size-controlled nanoparticles of sulfated zirconia

Methods of the preparation of catalysts for alkane skeletal isomerization based on uniform nanoparticles of sulfated zirconia anchored to different supports were investigated. These catalysts were characterized by using the ICP, HRTEM and BET techniques. The activities of the catalysts in the reaction of n-butane isomerization were measured and compared with those of bulk catalysts.     

The partial hydrogenation of benzene to cyclohexene by nanoscale ruthenium catalysts in imidazolium ionic liquids

The controlled decomposition of an Ru(0) organometallic precursor dispersed in 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMI.PF(6)), tetrafluoroborate (BMI.BF(4)) or trifluoromethane sulfonate (BMI.CF(3)SO(3)) ionic liquids with H(2) represents a simple and efficient method for the generation of Ru(0) nanoparticles. TEM analysis of these nanoparticles shows the formation of superstructures with diameters of approximately 57 nm that contain dispersed Ru(0) nanoparticles with diameters of 2.6+/-0.4 nm. These nanoparticles dispersed in the ionic liquids are efficient multiphase catalysts for the hydrogenation of alkenes and benzene under mild reaction conditions (4 atm, 75 degrees C). The ternary diagram (benzene/cyclohexene/BMI.PF(6)) indicated a maximum of 1 % cyclohexene concentration in BMI.PF(6), which is attained with 4 % benzene in the ionic phase. This solubility difference in the ionic liquid can be used for the extraction of cyclohexene during benzene hydrogenation by Ru catalysts suspended in BMI.PF(6). Selectivities of up to 39 % in cyclohexene can be attained at very low benzene conversion. Although the maximum yield of 2 % in cyclohexene is too low for technical applications, it represents a rare example of partial hydrogenation of benzene by soluble transition-metal nanoparticles.     

Determination of Human Alpha-Fetoprotein (AFP) by Solid Substrate Room Temperature Phosphorescence Enzyme-Linked Immune Response Using Luminescent Nanoparticles

Luminescent nanoparticles of silicon dioxide (SiO₂) containing fluorescein isothiocyanate (FITC) with a particle size of 20 nm were synthesized using the Sol–Gel method (abbreviated FITC–SiO₂). FITC–SiO₂ nanoparticles whose surfaces are modified (FITC–SiO₂–S–CH₂COOH) can emit strong and stable solid substrate room temperature phosphorescence (SS-RTP) on acetyl cellulose membranes. When the original color-producing agent (R) in the enzyme-linked immunosorbent assay (ELISA) kits for determination of alpha-fetoprotein (AFP) was substituted with (FITC–SiO₂–S–CH₂COOH), the system maintained good FITC–SiO₂ phosphorescence properties. Furthermore, the phosphorescence intensity enhanced markedly after the ELISA reaction. The relationship between the phosphorescence intensity and the content of AFP obeyed Beer’s law. Based on the facts stated above, a new method for the determination of human AFP by SS-RTP-ELISA (using the luminescent nanoparticle as marker) was established. The linear range of this method is 0.040–16.0 pg of human AFP per spot (sample volume: 0.40 μL spot⁻¹, corresponding concentration: 0.10–40.0 ng mL⁻¹). The regression equation of the working curve is ΔIp = −6.289+18.075 m_AFP (pg spot⁻¹) (r = 0.9960, n = 6). The detection limit (LD) of this method calculated by 3 S_b/k is 6.7 fg spot⁻¹ (corresponding concentration: 17 ng L⁻¹). Compared to the ELISA method using a traditional color-producing agent, the new method exhibited a 34.8 times higher sensitivity and a wider linear range. The method has been successfully applied to the determination of human AFP in serum.     

纳米银修饰电极差分脉冲伏安法测定盐酸金霉素

建立了快速测定盐酸金霉素(CTC)的方法。通过NaBH4还原法制备纳米银(AgNPs)溶胶,并利用X射线衍射和紫外-可见光谱进行表征。将制备好的AgNPs滴涂到玻碳电极表面制备修饰电极(AgNPs/GCE),研究了CTC在AgNPs/GCE上的电化学行为及伏安法测定,优化了缓冲溶液和pH等检测条件。结果表明,CTC在pH 3.3的柠檬酸-NaOH-HCl缓冲溶液中检测效果最佳。CTC在AgNPs/GCE上发生2个电子和2个质子的不可逆电化学氧化反应,且反应受吸附控制。最佳条件下,CTC的氧化峰电流与其浓度呈现良好的线性关系,线性范围为0.5~100μmol/L,检出限为0.14μmol/L。该修饰电极可用于河水样品检测。