Fluorescence ratiometric pH sensor prepared from covalently immobilized porphyrin and benzothioxanthene

A fluorescence ratiometric sensor for pH determination is described in this paper. The sensor incorporated the pH-sensitive dye meso-5,10,15,20-tetra-(4-allyloxyphenyl)porphyrin (TAPP) as an indicator and a pH-insensitive dye N-(2-methacryloxyethyl)benzo[k,l]thioxanthene-3,4-dicarboximide (MBTD), a benzothioxanthene derivative, as a reference for fluorescence ratiometric measurement. To prevent leakage of the dyes, both were photocopolymerized with acrylamide, hydroxyethyl methacrylate, and triethylene glycol dimethacrylate on the silanized glass surface. The reproducibility and response time of the prepared sensor were sufficient. Most common coexisting inorganic ions and organic compounds did not interfere with pH sensing. In the acidic pH range from 1.5 to 5.0 the fluorescence intensity ratio of the two dyes varied linearly as a function of pH. The sensing membrane was found to have a lifetime of at least one month. The sensor was applied to the analysis of waste water and artificial samples.     

Determination of Copper at a Glassy Carbon Electrode Modified with Langmuir–Blodgett Film of p‐tert‐Butylthiacalix[4]arene

A new type of voltammetric sensor, Langmuir–Blodgett film of p‐tert‐butylthiacalix[4]arene modified glassy carbon electrode, was advanced and used for determining copper at trace levels by differential pulse stripping voltammetry. Calibration plot was found to be linear in the range of 2×10^?8 M to 5×10^?6 M; the detection limit was 2×10^?9 M. Possible recognition mechanism was also discussed. From determination of Copper in real samples (river, lake and tap water) it can be concluded that the method is rapid, sensitive in determining of copper and can be used in the analysis of natural water samples.     

Immobilization of glucose oxidase with the blend of regenerated silk fibroin and poly(vinyl alcohol) and its application to a 1,1′- dimethylferrocene-mediating glucose sensor

The structure and properties of the blend of regenerated silk fibroin (RSF) and poly(vinyl alcohol) (PVA) were investigated. The two polymers in the blend are in the state of phase segregation. Infrared (IR) spectra indicate that the RSF in the blend maintains its intrinsic properties, thus, ethanol treatment can transfer silk I structure of RSF to silk II structure. The water absorption property and mechanical property of the blend are improved in comparison with those of RSF. The blend maintains the major merit of RSF, that is, it can immobilize glucose oxidase on the basis of the conformational transition from silk I structure to silk II structure. The properties of the immobilized enzyme are examined. Moreover, the second generation of glucose sensor based on the immobilized enzyme is fabricated and it has a variety of advantages including easy maintenance of enzyme, simplicity of construction, fast response time and high stability.     

Determination of dopamine in synthetic cerebrospinal fluid by SWV with a graphite–polyurethane composite electrode

This work describes an electroanalytical investigation of dopamine using cyclic voltammetry (CV) and the graphite–polyurethane composite electrode (GPU). In CV studies, well-defined redox peaks characterize the oxidation process at the GPU electrode, which is indicative of electrocatalytic effects associated with active sites on the GPU electrode surface. A new analytical methodology was developed using the GPU electrode and square wave voltammetry (SWV) in BR buffer solution (0.1 mol L^–1; pH 7.4). Analytical curves were constructed under optimized conditions (f=60s^–1, E_a=50 mV, E_I=2 mV) and detection and quantification limits of 6.4×10^–8 mol L^–1 (12.1 g L^–1) and 5.2×10^–6 mol L^–1 (0.9 mg L^–1), respectively, were achieved. The precision of the method was checked by performing ten successive measurements for a 9.9×10^–6 mol L^–1 dopamine solution. For intra-assay and inter-assay precisions, the relative standard deviations were 1.9 and 2.3%, respectively. In order to evaluate the developed methodology, the determination of dopamine was performed with good sensitivity and selectivity, without the interference of ascorbic acid in synthetic cerebrospinal fluid, which indicates that the new methodology enables reliable analysis of dopamine.     

An LCEC method for the analysis of synthetic amino acids in fruit juices

Summary A fast and simple HPLC-method for the determination of synthetic amino acids in adulterated orange juice has been developed. The amino acid enantiomers were derivatized with a chiral reagent and the derivatives separated on a 3 m particle size C₁₈ column. An electrochemical detector operating in the oxidative mode was used for detection. The potential at which the derivatives are oxidized was determined by cyclic voltammetry.By using selective (electrochemical) detection it is possible to reduce the sample clean-up to simple centrifugation and filtration steps.     

无机胶体法制备Pt/C催化剂及其性能表征

采用无机胶体法制备用于质子交换膜燃料电池(PEMFC)的Pt/C催化剂。研究了影响PtO₂胶体生成和稳定性的因素(溶液的pH值、浓度和温度条件等)以及不同还原剂浓度对Pt/C催化剂性能的影响。透射电子显微镜测试结果表明，采用经优化的工艺条件所制备的Pt/C催化剂平均粒径为3 nm，且分散性好、粒度均匀。X-射线衍射分析表明，催化剂中Pt(111)晶面的相对含量较高，有利于加速氧还原反应。单体PEMFC的电压/电流密度曲线测试表明，所制备的Pt/C催化剂具有良好的电化学性能。     

水相锌二次电池正极材料V2O5/C的电化学性能研究

采用溶胶－凝胶法合成了一种V₂O₅/C复合材料.扫描电镜（SEM）和红外光谱（FTIR）分析表明,这是一种外层V₂O₅胶体包覆内层乙炔分子的多孔复合材料.以V₂O₅/C作正极,锌片为负极,Zn(ClO₄)₂溶液为电解质组成水相锌二次电池,采用循环伏安（CV）和电化学阻抗谱（EIS）等方法研究发现:V₂O₅:C质量比为1:1时电极具有最好的电化学性能,电池开路电压达1.64 V; Zn^2＋能分别在1.01 V和1.26 V处分步嵌入V₂O₅/C结构中A、B两种位置,其嵌入电流密度峰值最高可达70 mA•g^－1,并且具有较好的循环充放电性能;在一定放电深度下,V₂O₅/C电极反应速率受Zn^2＋的扩散过程控制.     

Label-Free Impedance Biosensors: Opportunities and Challenges

Impedance biosensors are a class of electrical biosensors that show promise for point-of-care and other applications due to low cost, ease of miniaturization, and label-free operation. Unlabeled DNA and protein targets can be detected by monitoring changes in surface impedance when a target molecule binds to an immobilized probe. The affinity capture step leads to challenges shared by all label-free affinity biosensors; these challenges are discussed along with others unique to impedance readout. Various possible mechanisms for impedance change upon target binding are discussed. We critically summarize accomplishments of past label-free impedance biosensors and identify areas for future research.     

NdOx作为助催化剂对PtRu/C电催化氧化甲醇活性的影响

采用沉积-还原法制备了PtRu-NdOx/C催化剂, 借助TEM、EDS和XRD等测试手段对其进行了微结构和组成的表征. 结果表明, 催化剂中Pt与Ru以合金形式存在, 而Nd的氧化物则以无定形形态存在. 催化剂粒子的平均粒径在2 nm左右, 晶胞参数为0.3896 nm, Nd氧化物的加入对PtRu合金的晶体结构影响不明显. 采用循环伏安法和计时电流法, 比较了PtRu-NdOx/C催化剂和PtRu /C催化剂对甲醇氧化的电催化活性, 结果表明, 加入Nd的氧化物作为助催化剂能明显提高PtRu /C催化剂对甲醇氧化的电催化性能.     

The surface and materials science of tin oxide

The study of tin oxide is motivated by its applications as a solid state gas sensor material, oxidation catalyst, and transparent conductor. This review describes the physical and chemical properties that make tin oxide a suitable material for these purposes. The emphasis is on surface science studies of single crystal surfaces, but selected studies on powder and polycrystalline films are also incorporated in order to provide connecting points between surface science studies with the broader field of materials science of tin oxide. The key for understanding many aspects of SnO₂ surface properties is the dual valency of Sn. The dual valency facilitates a reversible transformation of the surface composition from stoichiometric surfaces with Sn⁴⁺ surface cations into a reduced surface with Sn²⁺ surface cations depending on the oxygen chemical potential of the system. Reduction of the surface modifies the surface electronic structure by formation of Sn 5s derived surface states that lie deep within the band gap and also cause a lowering of the work function. The gas sensing mechanism appears, however, only to be indirectly influenced by the surface composition of SnO₂. Critical for triggering a gas response are not the lattice oxygen concentration but chemisorbed (or ionosorbed) oxygen and other molecules with a net electric charge. Band bending induced by charged molecules cause the increase or decrease in surface conductivity responsible for the gas response signal. In most applications tin oxide is modified by additives to either increase the charge carrier concentration by donor atoms, or to increase the gas sensitivity or the catalytic activity by metal additives. Some of the basic concepts by which additives modify the gas sensing and catalytic properties of SnO₂ are discussed and the few surface science studies of doped SnO₂ are reviewed. Epitaxial SnO₂ films may facilitate the surface science studies of doped films in the future. To this end film growth on titania, alumina, and Pt(1 1 1) is reviewed. Thin films on alumina also make promising test systems for probing gas sensing behavior. Molecular adsorption and reaction studies on SnO₂ surfaces have been hampered by the challenges of preparing well-characterized surfaces. Nevertheless some experimental and theoretical studies have been performed and are reviewed. Of particular interest in these studies was the influence of the surface composition on its chemical properties. Finally, the variety of recently synthesized tin oxide nanoscopic materials is summarized.