Demetallation of methemoglobin in cellulose nanofibril–TiO2 nanoparticle composite membrane electrodes

Porous composite films containing cellulose nanofibrils (from sisal) and TiO₂ nanoparticles (ca. 6 nm diameter) are obtained in a layer-by-layer assembly process. Each layer consists of ca. 0.18 μg cellulose nanofibrils and ca. 0.72 μg TiO₂ (determined by QCMB) and adds a thickness of ca. 16 nm (by AFM) to the uniform deposit. The TiO₂ nanophase is creating conducting pathways for electrons in a relatively open cellulose structure (ca. 82% open pores) potentially suitable for the immobilization of large redox proteins such as methemoglobin.Methemoglobin is shown to readily adsorb into the cellulose–TiO₂ film. However, electrochemical responses for the immobilized methemoglobin in aqueous 0.1 M phosphate buffer at pH 5.5 suggest that facile demetallation occurs. Experiments with Fe³⁺ in the absence of protein result in voltammetric responses indistinguishable from those observed for immobilized methemoglobin. In the presence of ethylenediamine tetraacetic acid (EDTA) the voltammetric signals for the Fe³⁺ immediately disappear. Complementary experiments conducted in 0.1 M acetate buffer at pH 5.5 demonstrate that methemoglobin can indeed be immobilized in electrochemically active form and without demetallation loss of the voltammetric signal in the presence of EDTA. Demetallation appears to occur (i) in the presence of phosphate, (ii) at pH 5.5, (iii) and in the presence of a charged surface.     

Electrochemical properties of core-shell TiC-TiO2 nanoparticle films immobilized at ITO electrode surfaces

Titanium carbide (TiC) nanoparticles are readily deposited onto tin-doped indium oxide (ITO) electrodes in the form of thin porous films. The nanoparticle deposits are electrically highly conducting and electrochemically active. In aqueous media (at pH 7) and at applied potentials positive of 0.3 V vs. SCE partial anodic surface oxidation and formation (at least in part) of novel core-shell TiC-TiO2 nanoparticles is observed. Significant thermal oxidation of TiC nanoparticles by heating in air occurs at a temperature of 250 degrees C and leads first to core-shell TiC-TiO2 nanoparticles, next at ca. 350 degrees C to TiO2 (anatase), and finally at temperatures higher than 750 degrees C to TiO2 (rutile). Electrochemically and thermally partially oxidized TiC nanoparticles still remain very active and for some redox systems electrocatalytically active. Scanning and transmission electron microscopy (SEM and TEM), temperature dependent XRD, quartz crystal microbalance, and voltammetric measurements are reported. The electrocatalytic properties of the core-shell TiC-TiO2 nanoparticulate films are surveyed for the oxidation of hydroquinone, ascorbic acid, and dopamine in aqueous buffer media. In TiC-TiO2 core-shell nanoparticle films TiO2 surface reactivity can be combined with TiC conductivity.     

Hemoglobin adsorption into TiO2 phytate multi-layer films: particle size and conductivity effects

Hemoglobin (molecular weight 64.5 kDa, isoelectric point 7.4) in 0.1 M phosphate buffer solution at pH 5.5 readily adsorbs onto mesoporous TiO₂ phytate films, which have been formed in a layer-by-layer deposition process from TiO₂ nanoparticles (ca. 6–10 nm diameter) and phytic acid at tin-doped indium oxide (ITO) electrodes. Quartz crystal microbalance data, voltammetry, and SEM evidence are consistent with hemoglobin adsorption only into the outer TiO₂ phytate surface layer. The size of the tetrametric hemoglobin protein (ca. 6 nm diameter) appears to be too big for a homogeneous film to form.The modified ITO electrode immersed in 0.1 M phosphate buffer solution at pH 5.5 allows reversible electron transfer for hemoglobin to be observed with a midpoint potential of 0.01 vs. SCE. Characteristic TiO₂ phytate film thickness and pH effects are observed with both thicker films and lower proton activity causing ‘decoupling’ of the protein redox chemistry due to a reduced electrical conductivity of the TiO₂ phytate film connecting hemoglobin with the electrode. This is the first example of a bi-layer nanofilm structure where the underlying TiO₂ phytate film controls the electrochemical properties of the hemoglobin modified top-layer.     

Layer-by-layer assembly of Ru3+ and $$ {\text{Si}}_{{\text{8}}} {\text{O}}^{{8 - }}_{{20}} $$ into electrochemically active silicate films

A porous silicate is obtained from octa-anionic cage-like poly-silicate (PS) and Ru³⁺ cations in an ethanol-based layer-by-layer assembly process. Electrochemical experiments (voltammetry and impedance spectroscopy) confirm the formation of redox-active ruthenium centers in the form of hydrous ruthenium oxide throughout the film deposit. Oxidation of Ru(III) to Ru(IV) at a potential below 0.5 V vs saturated Calomel electrode (SCE) is reversible, but a potential positive of 0.5 V vs SCE is associated with an irreversible change in reactivity, which is characteristic for very small hydrous ruthenium oxide nanoparticles. Further voltammetric experiments are performed in aqueous phosphate buffer solutions, and the effects of number of layers, scan rate, and pH are investigated. Three aqueous redox systems are studied in contact with the PS–Ru³⁺ films. The reduction of cationic methylene blue adsorbed onto the negative surface of the nanocomposite silicate is shown to occur, although most of the bound methylene blue appears to be electrochemically inactive either bound to silicate or buried into small pores. The PS–Ru³⁺-catalyzed oxidations of hydroquinone and arsenite(III) are investigated. Scanning electron microscopy images show that a macroscopically uniform porous surface is formed after deposition of 50 layers of the PS–Ru³⁺ nanocomposite. However, atomic force microscopy images demonstrate that in the initial deposition stages, irregular island growth occurs. The average rate of thickness increase for PS–Ru³⁺ nanocomposite films is 6 nm per deposition cycle.     

头孢噻甲羧肟的伏安行为及其单扫描极谱法测定

以多种电化学手段研究了头孢噻甲羧肟的伏安行为。在磷酸盐缓冲溶液中，ＣＴＤ产生２个不可逆吸附还原波，峰电位分别为－０．６５Ｖ和－１．２０Ｖ。分别有１个电子与２个电子和１个质子参与了峰１与峰２的电极过程。探讨了电极反应机理。     

Reactivity of methemoglobin immobilized on TiO2 nanoparticle films

Facile demetallation occurs upon contact of the methemoglobin with a mesoporous TiO2 host in phosphate buffer media at pH 5.5 but not in acetate buffer media. As a result, voltammetric signals previously attributed to hemoglobin-based redox processes have to be re-interpreted.     

维脑路通的伏安行为及其二阶导数卷积伏安法测定

以多种电化学手段研究了维脑路通的伏安行为。在磷酸盐缓冲溶液中( p H 4) ,维脑路通产生一个不可逆吸附还原波 ,峰电位 - 1 .55V ( vs.SCE)。建立了二阶导数卷积伏安法测定的新方法 ,并将此法应用于维脑路通注射液及模拟尿样中维脑路通的测定。     

Ultrathin Carbon Nanoparticle Composite Film Electrodes: Distinguishing Dopamine and Ascorbate

Ultrathin carbon nanoparticle–poly(diallyldimethylammonium chloride) films (CNP‐PDDAC films) are formed on tin‐doped indium oxide (ITO) electrodes in a layer‐by‐layer electrostatic deposition process employing 9–18 nm diameter carbon particles. Transparent and strongly adhering films of high electrical conductivity are formed and characterized in terms of their electrochemical reactivity. When immersed in aqueous 0.1 M phosphate buffer pH 7, each layer of CNP‐PDDAC (of ca. 5–6 nm average thickness) is adding an interfacial capacitance of ca. 10 μF cm^?2. Absorption into the CNP–PDDAC nanocomposite film is dominated by the sites in the PDDAC cationomer and therefore anionic molecules such as indigo carmine are strongly bound and retained within the film (cationic binding sites per layer ca. 150 pmol cm^?2). In contrast, cationic redox systems such as ferrocenylmethyltrimethyl‐ammonium⁺ fail to bind. For solution phase redox systems such as hydroquinone, the rate of electron transfer is dramatically affected by the CNP‐PDDAC film and switched from completely irreversible to highly reversible even with a single layer of carbon nanoparticles. For the mixed redox system ascorbate–dopamine in 0.1 M phosphate buffer pH 7 cyclic voltammograms suggest a rapid and selective temporary poisoning process which causes the ascorbate oxidation to be suppressed in the second potential cycle. This effect is exploited for the detection of micromolar concentrations of dopamine in the presence of millimolar ascorbate.     

Direct reversible voltammetry and electrocatalysis with surface-stabilised Fe2O3 redox states

Nanoparticle film voltammetry is employed to explore the presence and reactivity of surface-stabilised iron redox centers at the interface of immobilised Fe₂O₃ nanoparticles of ca. 4 nm diameter and aqueous buffer media. Mesoporous films of Fe₂O₃ nanoparticles on tin-doped indium oxide (ITO) substrates are formed in a layer-by-layer deposition process from aqueous colloidal Fe₂O₃ and aqueous cyclohexyl-hexacarboxylate followed by thermal (500 °C) removal of the organic binder content. Both reversible oxidation and reversible reduction responses for Fe(III) are observed in phosphate and carbonate buffer media in the “underpotential” zone. Higher oxidation states of iron formed anodically (here tentatively assigned to Fe(IV)) are shown to be inert in phosphate buffer media but reactive towards the oxidation of glucose in carbonate buffer media.     

电沉积二氧化钛纳米微粒膜的光电化学性能和表面形貌研究

采用光电流谱、透射光谱和扫描微探针显微镜技术对电沉积法制备的二氧化钛纳米微粒膜的光电化学性能和表面形貌进行了研究.结果表明,不同制备条件下的二氧化钛纳米微粒膜具有与紧密的半导体电极不同的光电化学性质,并探讨了其光电化学性能与表面形貌的关系.     

Tuning percolation speed in layer-by-layer assembled polyaniline�Cnanocellulose composite films

Polyaniline of low molecular weight (ca. 10?kDa) is combined with cellulose nanofibrils (sisal, 4?C5?nm average cross-sectional edge length, with surface sulphate ester groups) in an electrostatic layer-by-layer deposition process to form thin nano-composite films on tin-doped indium oxide (ITO) substrates. AFM analysis suggests a growth in thickness of ca. 4?nm per layer. Stable and strongly adhering films are formed with thickness-dependent coloration. Electrochemical measurements in aqueous H₂SO₄ confirm the presence of two prominent redox waves consistent with polaron and bipolaron formation processes in the polyaniline?Cnanocellulose composite. Measurements with a polyaniline?Cnanocellulose film applied across an ITO junction (a 700?nm gap produced by ion beam milling) suggest a jump in electrical conductivity at ca. 0.2?V vs. SCE and a propagation rate (or percolation speed) two orders of magnitude slower compared to that observed in pure polyaniline This effect allows tuning of the propagation rate based on the nanostructure architecture. Film thickness-dependent electrocatalysis is observed for the oxidation of hydroquinone.     

Gelatin-functionalized carbon nanotubes for the bioelectrochemistry of hemoglobin

In this paper, we compared the use of gelatin-functionalized carbon nanotubes (CNTs) as substrates for Hemoglobin (Hb) immobilization and as electrodes for electrochemical reduction of the absorbed Hb. The non-covalently gelatin-functionalized CNTs possessed an improved solubility in aqueous solution and may have an enhanced biocompatibility with Hb. The characteristics of Hb/gelatin-CNTs composite films were studied by using UV–vis spectroscopy, FTIR spectroscopy and electrochemical methods. The immobilized Hb showed a couple of quasi-reversible redox peaks with a formal potential of −0.35 V (vs. SCE) in 0.10 M pH 7.0 phosphate buffer solution (PBS). The surface concentration of electroactive Hb immobilized on gelatin-CNT/GC electrode was about 4.34 × 10⁻¹⁰ mol cm⁻².     

TiO2 phytate films as hosts and conduits for cytochrome c electrochemistry

Cytochrome c is accumulated into a film of TiO(2) nanoparticles and phytate by adsorption from an aqueous solution into the mesoporous structure. Stable voltammetric responses and high concentrations of redox protein within the TiO(2) phytate layer can be achieved. Two types of electrode systems are reported with (i) the modified TiO(2) phytate film between electrode and aqueous solution phase and (ii) the modified TiO(2) phytate film buried under a porous gold electrode ('porotrode'). The electrical conductivity of TiO(2) phytate films is measured and compared in the dry and in the wet state. Although in the dry state essentially insulating, the TiO(2) phytate film turns into an electrical conductor (with approximately 4 Omega cm specific resistivity assuming ohmic behaviour) when immersed in aqueous 0.1 M phosphate buffer solution at pH 7. The redox protein cytochrome c is therefore directly connected to the electrode via diffusion and migration of electrons in the three dimensional mesoporous TiO(2) phytate host structure. Electron transfer from cytochrome c to TiO(2) is proposed to be the rate-determining step for this conduction mechanism.     

Tuning percolation speed in layer-by-layer assembled polyaniline–nanocellulose composite films

Polyaniline of low molecular weight (ca. 10 kDa) is combined with cellulose nanofibrils (sisal, 4–5 nm average cross-sectional edge length, with surface sulphate ester groups) in an electrostatic layer-by-layer deposition process to form thin nano-composite films on tin-doped indium oxide (ITO) substrates. AFM analysis suggests a growth in thickness of ca. 4 nm per layer. Stable and strongly adhering films are formed with thickness-dependent coloration. Electrochemical measurements in aqueous H₂SO₄ confirm the presence of two prominent redox waves consistent with polaron and bipolaron formation processes in the polyaniline–nanocellulose composite. Measurements with a polyaniline–nanocellulose film applied across an ITO junction (a 700 nm gap produced by ion beam milling) suggest a jump in electrical conductivity at ca. 0.2 V vs. SCE and a propagation rate (or percolation speed) two orders of magnitude slower compared to that observed in pure polyaniline This effect allows tuning of the propagation rate based on the nanostructure architecture. Film thickness-dependent electrocatalysis is observed for the oxidation of hydroquinone.

     

云芝漆酶在N,N'-亚甲基双丙烯酰胺（BIS）交联聚甲基丙烯酸基元上的固定及其修饰玻碳电极电化学行为

以N,N′-亚甲基双丙烯酰胺（BIS）交联聚甲基丙烯酸作为固定漆酶的载体,以共价偶联法固定云芝漆酶并测定了固定基元的酶固定量和固定漆酶的比活力。 还研究了固定漆酶热稳定性、重复使用性以及固定漆酶催化2,6-二甲氧基苯酚（DMP）氧化的酶动力学参数。 实验结果表明,这种交联聚合物基元通过共价偶联法固定漆酶的量和固定漆酶的比活力分别可达26.37 mg/g和1.202 U/mg;在交联聚合物基元上固定的漆酶在50 ℃下放置2 h后仍然保持初始活力的83％,重复使用10次后仍保持初始活力的80％以上;交联聚合物固定漆酶催化DMP氧化的表观速率常数k_cat可达1090 min^-1,以固定漆酶的BIS交联聚甲基丙烯酸功能化碳纳米管修饰的玻碳电极在pH=4.4磷酸盐缓冲液中氧还原发生在+724 mV(vs.SCE)。     

肌红蛋白在碳纳米管修饰电极上的直接电化学和电催化性能

将肌红蛋白(Mb)通过吸附的方法固定在碳纳米管(CNT)表面, 用AFM、XPS、UV-Vis和FTIR对其进行了表征, 研究了CNT对Mb直接电子转移反应的促进作用. 循环伏安结果表明, Mb在CNT表面能进行有效和稳定的直接电子转移反应, 其循环伏安曲线上表现出一对良好的、几乎对称的氧化还原峰; 在20−160 mV•s−1的扫速范围内, 式量电位E0′几乎不随扫速而变化, 其平均值为(−0.343±0.001) V (vs SCE, pH 7.0); Mb在CNT表面直接电子转移的表观速率常数为(3.11±0.98) s−1; 式量电位E0′与溶液pH的关系表明, Mb的直接电化学过程是一个有H+参与的电极过程. 进一步的实验结果显示, 固定在CNT表面的Mb能保持其对H2O2和O2还原的生物电催化活性.     

电化学方法对农药啶虫脒的间接测定

啶虫脒本身不具有电化学性质,而其在NaOH溶液中的水解产物为电活性物质。采用循环伏安法(CV)、示差脉冲伏安法(DPV)研究了啶虫脒水解产物在碳糊电极上的电化学行为,并初步探讨了其反应机理。在pH9.0的磷酸盐缓冲液(PBS)中,啶虫脒水解产物在约0.9 V(vs.SCE)产生一灵敏的氧化峰,表明电极反应是受扩散控制的不可逆氧化过程。基于啶虫脒水解产物的氧化行为,以0.9 V为工作电位,采用计时安培法进行测定,其响应电流与啶虫脒的浓度在2.0×10-7~2.8×10-5mol/L范围内呈良好的线性关系,方法的检出限为1.0×10-7mol/L。该方法成本低、操作方便、重复性好,对人体与环境无毒害,将其用于啶虫脒实际样品的测定,结果满意。     

过硫酸钾存在下曲匹布通极谱平行催化波的研究及其应用

采用平行催化波法、循环伏安法等手段研究了在KH2PO4-Na2HPO4介质中过二硫酸钾存在下曲匹布通平行催化波产生的机理。曲匹布通的羰基官能团C=O在KH2PO4-Na2HPO4介质中以2e-,2H+方式极谱还原,产生了单个还原波。加入氧化剂过二硫酸钾时,曲匹布通还原中间体自由基在电极表面上能被过二硫酸钾及其中间还原体硫酸根阴离子自由基氧化,再生为原可还原基团C=O,从而产生了曲匹布通的平行催化波。基于此,提出了一种测定曲匹布通的新方法。     

Phenols monitoring and Hill coefficient evaluation using tyrosinase-based amperometric biosensors

Sensitive amperometric biosensors for phenols compounds, based on tyrosinase (polyphenoloxidase, PPO) immobilized on a Pt electrode in an electropolymerized poly-amphiphilic pyrrole matrix or cross-linked with glutaraldehyde, were constructed and compared. Steady-state amperometric measurements, performed at -50 mV vs. SCE in aqueous phosphate buffer containing LiClO(4) 0.1 M (pH 7) as well as in a chloroform solution containing 0.1 M C(6)H(5)CH(2)N(CH(3))(3)Cl, were used in order to compare the electroanalytical and kinetic parameters of the investigated amperometric biosensors in aqueous and nonaqueous media. It was established that the polypyrrole matrix has a higher efficiency for enzyme retention resulting in higher bioelectrode sensitivity, both in aqueous buffer (690 microA M(-1)) and in chloroform (149 microA M(-1)).     

Direct Electrochemistry of Hemoglobin Immobilized in Sodium Alginate Film on the Ionic Liquid [BMIM]PF6 Modified Carbon Paste Electrode

In recent years the direct electron transfer of redox protein on electrode surface has attracted great attentions1. Different kind of modified electrode and various supporting films for immobilization of proteins had been proposed. But most of them are ba…