Direct electrochemical assay of glucose using boron-doped diamond electrodes

We report linear sweep and square wave voltammetric studies on glucose oxidation at boron-doped diamond (BDD) electrodes in an alkaline medium in efforts to evaluate the techniques for electrochemically assaying glucose. The bare BDD electrode showed good linear responses to glucose oxidation for a concentration range from 0.5 to 10 mM glucose, which well encompasses the physiological range of 3-8 mM. The BDD electrodes did not experience interferences from ascorbic acid or uric acid during glucose detection. This method, when applied to real blood samples, gave results similar to those obtained by a commercial glucose monitor.     

Pressure and volume dependence of thelo-to phonons in InAs

The pressure dependence of thelo-to phonons in InAs has been investigated by Raman scattering using the diamond anvil cell. Indium arsenide transforms, presumably to the rock-salt structure at 70±1 kbar. The mode Grüneisen parameters for thelo-to phonons are γ _lo =0.99±0.03, γ _to =1.2±0.03 respectively. The effective charge,e* _T , for InAs decreases slightly with pressure and this trend is in accordance with the behaviour of other III–V zinc blende structured semiconductors: The structural phase transition is discussed in the light of theoretical calculations for phase stability of III–V compounds, as well as recent high pressure x-ray diffraction studies.     

Modeling of H2 and H2/CH4 Moderate-Pressure Microwave Plasma Used for Diamond Deposition

One-dimensional transport models of moderate-pressure H ₂ and H ₂ /CH ₄ plasmas obtained in a diamond deposition microwave reactor are presented. These models describe the plasma as a thermochemically nonequilibrium flow with three different energy modes. The solution of the one-dimensional plasma transport equations enabled the estimation of plasma species concentrations and temperatures on the axis of the reactor. As far as pure H ₂ plasmas are concerned, results showed that the model predictions of gas and vibration temperatures are in good agreement with experimental measurements. The model also yields a relatively good qualitative prediction of the variations of H-atom mole fraction with the power density absorbed by the plasma. The results obtained for H ₂ /CH ₄ discharges showed that the model prediction on the variations of H-atom mole fraction with methane percentage in the discharge is in good qualitative agreement with experimental results. They also showed that methane is rapidly converted to acetylene before reaching the discharge zone. The concentrations of neutral hydrocarbon species in the reactor are mainly governed by thermal chemistry. The addition of methane strongly affects the ionization kinetics of the plasma. Three major ions are generally obtained in H ₂ /CH ₄ plasmas: C ₂ H ₂ ⁺ , C ₂ H ₃ ⁺ , and C ₂ H ₅ ⁺ . The relative predominance of these ions depends on the considered plasma region and on the discharge conditions. The ionic species concentrations are also mainly governed by chemistry, except very near the substrate surface. Finally the use of this transport model along with the surface chemistry model of Goodwin ⁽¹⁾ enabled us to estimate the diamond growth rate for several discharge conditions.     

Diamond paste-based electrodes for determination of Cr(III) in pharmaceutical compounds

A new class of monocrystalline diamond paste-based electrodes is proposed for the determination of chromium(III) at trace levels in vitamins. Three types of monocrystalline diamond—natural diamond 1 (natural diamond), synthetic diamond 50 (synthetic-1), and synthetic diamond 1 (synthetic-2)—were used for electrode construction. The linear concentration ranges are between 10^–10 and 10^–8; 10^–9 and 10^–7, and 10^–10 to 10^–8 mol L^–1, with limits of detection of 10^–12, 10^–12, and 10^–11 mol L^–1, when natural diamond, synthetic-1, and synthetic-2, respectively, are used as electrode materials. For electrodes based on natural diamond and synthetic-1 it was found that Cr(III) yields a peak at about +0.275±0.015 V (vs. Ag/AgCl) within a predetermined positive potential range situated between +0.4 and +0.2 V, while for the electrode based on synthetic-2 the peaks are found at +0.300±0.015 V (vs. Ag/AgCl). The proposed method is reliable for the determination of chromium(III) at trace levels in two vitamin tablets (RSD<0.2%).     

掺硼多晶金刚石膜的电化学性能研究

采用EACVD(Electron Assisted Chemical Vapor Deposition)方法制备了掺硼金刚石膜, 并用扫描电镜、拉曼光谱及霍尔效应等测试方法对其表面形貌、生长特性、载流子浓度以及导电性能进行了分析. 测试结果表明, 掺硼金刚石膜是由微米级晶粒组成的多晶膜, 其载流子浓度为4.88×1020 cm-3, 电阻率为0.03 Ω·cm, 是高品质金刚石膜. 用该金刚石膜制作电化学电极, 利用循环伏安法分别测量了金刚石膜电极在氯化钾空白底液、亚铁氰化钾溶液和左旋半胱氨酸溶液中的循环伏安曲线, 发现该金刚石膜电极在水溶液中具有宽的电化学窗口(约为3.7 V)和接近零的背景电流, 在生物制剂的检测中具有很高的灵敏度和良好的稳定性, 是一种理想的电化学电极材料.     

Selective Detection of Dopamine and Its Metabolite,DOPAC, in the Presence of Ascorbic Acid Using Diamond Electrode Modified by the Polymer Film

The surface of boron‐doped diamond (BDD) electrode is modified by the polymer film for the first time. The cationic polymer film of N,N‐dimethylaniline (DMA) is electrochemically deposited on BDD electrode surface. This polymer (PDMA) film‐coated BDD electrode is used as a sensor which selectively detect dopamine (DA) in the presence of ascorbic acid (AA). This electrode also can detect both DA and its metabolite, 3,4‐dihydroxy phenyl acetic acid (DOPAC) in the presence of AA in the range of the physiological concentrations of these species. Favorable ionic interaction (i.e., electrostatic attraction) between the PDMA film and AA or DOPAC lowers their oxidation potentials and enhances the current response for AA and DOPAC compared to that at the bare electrode. The PDMA film also shows a hydrophobic interaction with DA and DOPAC. In cyclic voltammetric measurements, the PDMA film‐coated electrode can successfully separate the oxidation potentials for AA and DA coexisting in the same solution and the separation is about 200 mV. AA oxidizes at more negative potential than DA. In square‐wave voltammetry, the sensitivity of the PDMA film‐coated BDD electrode for DA in the presence of higher concentration of AA is higher than that of the PDMA film‐coated glassy carbon electrode. The hydrodynamic amperometric experiments confirm that the oxidation of AA is not affected by the oxidized product of DA and vice versa. So, unlike the bare electrode the catalytic oxidation of AA by the oxidized DA is eliminated at the PDMA film‐coated BDD electrode. The sensitivities of the modified electrode for AA, DA and DOPAC, which are present in the same solution with their physiological concentration ratios, are calculated to be 0.070, 0.363 and 0.084 μA μM^?1, respectively. The modified electrode exhibits a stable and sensitive response to DA.     

A novel zirconocene/ultradispersed diamond black powder supported catalytic system for ethylene polymerization

A novel carrier of ultradispersed diamond black powder (UDDBP) was used to support metallocene catalyst. Al₂O₃ was also used as carrier in order to compare with UDDBP. Supported catalysts for ethylene polymerization were synthesized by two different reaction methods. One way was direct immobilization of the metallocene on the support, the other was adsorption of MAO onto the support followed by addition of the metallocene. Four supported catalysts Cp₂ZrCl₂/UDDBP, Cp₂ZrCl₂/Al₂O₃, Cp₂ZrCl₂/MAO/UDDBP and Cp₂ZrCl₂/Al₂O₃/MAO were obtained. The content of the zirconium in the supported catalyst was determined by UV spectroscopy. The activity of the ethylene polymerization catalyzed by supported catalyst was investigated. The influence of Al/Zr molar ratio and polymerization temperature on the activity was discussed. The polymerization rate was also observed.     

Manganese detection in marine sediments: anodic vs. cathodic stripping voltammetry

Three different electroanalytical techniques for the detection of manganese in marine sediments are evaluated. The anodic stripping voltammetry of manganese at an in situ bismuth-film-modified boron-doped diamond electrode and cathodic stripping voltammetry at a carbon paste electrode are shown to lack the required sensitivity and reproducibility whereas cathodic stripping voltammetry at a bare boron-doped diamond electrode is shown to be reliable and selective with a limit of detection, from applying a 60 s accumulation period of 7.4 × 10⁻⁷ M and a sensitivity of 0.24 A M⁻¹. The method was used to evaluate the manganese content of marine sediments taken from Šibenik, Croatia.     

Electroanalytical Determination of Carbaryl in Natural Waters on Boron Doped Diamond Electrode

The anodic voltammetric behavior of carbaryl on a boron‐doped diamond electrode in aqueous solution is reported. The results, obtained by square‐wave voltammetry at 0.1 mol L^?1 Na₂SO₄ and pH 6.0, allow the development of a method to determine carbaryl, without any previous step of extraction, clean‐up, preconcentration or derivatization, in the range 2.5–30.0×10^?6 mol L^?1, with a detection limit of 8.2±0.2 μg L^?1 in pure water. The analytical sensitivity of this electrochemical method diminished slightly, from 3.07 mA mmol^?1 L to 2.90 mA mmol^?1L, when the electrolyte was prepared with water samples collected from two polluted points in an urban creek. In these conditions, the recovery efficiencies obtained were around 104%. The effect of other pesticides (fenthion and 4‐nitrophenol) was evaluated and found to exert a negligible influence on carbaryl determination. The square‐wave voltammetric data obtained for carbaryl were typical of an irreversible electrode process with mass transport control. The combination of square‐wave voltammetry and diamond electrodes is an interesting and desirable alternative for analytical determinations.     

Electrocatalytic Reduction of Chromium(VI) by Thionin: Electrochemical Properties and Mechanistic Study

The electrochemical properties of aqueous thionin (an electroactive water soluble dye) of pH 1–12 were investigated by cyclic voltammetry at a boron doped diamond(BDD) electrode. A well defined reversible redox couple was observed in acidic, neutral and alkaline solutions. The standard potential and kinetic parameters for thionin were obtained by fitting experimental cyclic voltammograms to those generated by the DigiSim program. The electrogenerated reduced form of thionin has been used as an efficient organic catalyst for the reduction of Cr(VI) at a BDD electrode immersed in aqueous media. The cyclic voltammetry measurements indicate that an electrocatalytic process occurs, where electrochemically generated thionin reduced species (Leucothionin) is oxidized by Cr(VI) back to the parent thionin species via a EC' reaction mechanism. The determination of catalytic rate constant (K_cat) was accomplished again by fitting experimental cyclic voltammograms with simulated ones.