Fast wave forms for pulsed electrochemical detection of glucose by incorporation of reductive desorption of oxidation products

The electrochemical activity of Au electrodes held at constant potential for anodic detection of carbohydrates in alkaline media eventually decays to zero. This loss of response is a consequence of the accumulation of adsorbed oxidation products on the electrode surface. Although it is well-known that these "poisons" can be removed by oxidative desorption simultaneously with formation of surface oxide, we have discovered that electrodes fouled during the detection of glucose yield a cathodic peak at -0.77 V vs SCE resulting from reductive desorption of these species. Incorporation of the reductive desorption process into wave forms for pulsed electrochemical detection (PED) permits a significant decrease in the time periods traditionally allowed for the oxidative and reductive reactivation of the electrode with a resulting increase in wave form frequency. A 6.7-Hz wave form using E(red) = -1.00 V (t(red) = 10 ms), E(oxd) = +0.60 V (t(oxd) = 10 ms), and E(det) = +0.10 V (t(del) = 50 ms, t(int) = 50 ms) is applied for detection of glucose in a LC-PED system and is demonstrated to yield a sub-picomole detection limit with a linear dynamic range extending over three decades.     

Electrochemical identification of the property of peripheral nerve fiber based on a biocompatible polymer film via in situ incorporating gold nanoparticles

We report a simple electrochemical method for the identification of properties of peripheral nerve fibers, based on the detection of a neurotransmitter enzyme, acetylcholinesterase (AChE). A poly(diallydimethylammonium) (PDDA) adulterated poly(dimethylsiloxane) (PDMS) film is spin-coated on the surface of gold electrodes. Gold nanoparticles (AuNPs) are in situ synthesized on the polymer film, which act as "electron antennae" between the film and the electrode surface and also provide a biocompatible interface. This PDMS-PDDA/AuNPs film shows different adsorption sites to choline oxidase (ChO) and AChE; after incubation with ChO, the polymer-gold nanocomposite film also shows excellent adsorption ability to AChE. Moreover the adsorption sites of AChE would not be blocked by bovine serum albumin (BSA) which provides a good platform for the quantitative amperometric determination of AChE via the oxidation of the enzymatically generated H 2O 2 in the bienzyme system in the presence of acetylcholine. The detection limit is down to 1.0 unit/mL. The polymer-gold nanocomposite film shows excellent anti-interference ability to the coexistent electroactive substances such as ascorbic acid. Thus it was applied to determine AChE in peripheral nerve fibers homogenates and identify the motor and sensory fibers for the first time. Compared with histochemical staining methods, the electrochemical technique shows good accurate rate and faster response, which has good potential for a clinical application.     

Enlargement of gold nanoparticles on the surface of a self-assembled monolayer modified electrode: a mode in biosensor design

Gold nanoparticle (Au-NP) seeds were adsorbed onto the surface of a self-assembled monolayer (SAM)-modified electrode. With the treatment of this modified electrode by Au-NPs growth solution containing different concentrations of H2O2 or cholesterol along with cholesterol oxidase (ChOx), the Au-NP seeds on the electrode surface were enlarged in varying degrees. As a result, the peak currents in corresponding cyclic voltammograms were inversely proportional to the concentration of H2O2 or cholesterol. ChOx was also further modified onto the surface of Au/SAM/Au-NP electrode to prepare Au/SAM/Au-NP/ChOx electrode. Using the enzyme-modified electrode to detect cholesterol, which also utilized the enlargement of the NPs, an extraordinary low detection limit of 5 x 10(-9) M was achieved and two linear dependence ranges of 7.5 x 10(-8)-1 x 10(-6) and 1 x 10(-6)-5 x 10(-5) M were obtained. Consequently, new kinds of H2O2 and cholesterol biosensors could be fabricated.     

Electrooxidation of ascorbic acid on a polyaniline-deposited nickel electrode: surface modification of a non-platinum metal for an electrooxidative analysis

The electrooxidation of ascorbic acid (H2A), which does not occur on a bare Ni electrode, has been shown to take place on a polyaniline (PANI)-coated Ni electrode in aqueous electrolytes of a wide pH range. The characteristic voltammetric peak of PANI in 0.1 M H2SO4 at 0.2 V vs SCE corresponding to the transformation of leucoemeraldine to emeraldine gradually diminishes with an increase in concentration of H2A as a result of adsorption. This peak disappears before the appearance of another peak corresponding to the oxidation of H2A at a concentration of 1 mM. The irreversible oxidation current of H2A exhibits a linear dependence on the concentration. The effect of adsorption of H2A on PANI has been shown to increase the voltammetric peak current. A study on the variation of the PANI thickness and its influence on the voltammetric oxidation of H2A has led to an optimum thickness of 1.6 microm. The oxidation currents on the porous PANI/Ni electrode have been found to be several times higher at lower potentials in comparison with the data of a Pt electrode. The reaction has also been studied by ac impedance spectroscopy. In alkaline electrolytes, the Nyquist impedance plot is characterized by two semicircles instead of a single semicircle in acidic electrolytes. Thus, Ni, which is a non-platinum metal, has been found to be useful, by surface modification with PANI, for electrooxidation of H2A. The data are reproducible in the electrolytes of a wide pH range, thus suggesting a good stability, reusability and a long life for the PANI/Ni electrodes.     

Effects of poly(ethylene glycol) tert-octylphenyl ether on tris(2-phenylpyridine)iridium(III)-tripropylamine electrochemiluminescence

The effects of the nonionic surfactant Triton X-100 (poly(ethylene glycol) tert-octylphenyl ether) on the properties of tris(2-phenylpyridine)iridium(III) (Ir(ppy)3, where ppy = 2-phenylpyridine, electrochemiluminescence (ECL) have been investigated. Anodic oxidation of Ir(ppy)3 produces ECL in the presence of tri-n-propylamine (TPrA) in aqueous surfactant solution. Increases in ECL efficiency (> or = 10-fold) and TPrA oxidation current (> or = 2.0-fold) have been observed in surfactant media. The data support adsorption of surfactant on the electrode surface, thus facilitating TPrA and Ir(ppy)3 oxidation and leading to higher ECL efficiencies.     

Scanning Electrochemical Microscopy of Metal/Metal Oxide Electrodes. Analysis of Spatially Localized Electron-Transfer Reactions during Oxide Growth

Scanning electrochemical microscopy (SECM) has been used to study the oxidation of iodide at Ta electrodes covered by a thin (～2.5 nm) film of Ta(2)O(5). SECM images of surface activity reveal that the voltammetric response of a macroscopic Ta electrode comprises the individual responses of a large number of microscopic sites, each with its own unique electrochemical behavior. Oxide film growth and metal dissolution occur simultaneously with iodide oxidation, resulting in a complex voltammetric response. The component of the voltammetric current due to iodide oxidation can be separated from the total current by SECM analysis. The growth of nanometer-thick oxide films can also be studied using SECM by monitoring the rate at which iodide is oxidized at the electrode surface.     

Selective Etching Induced Synthesis of Hollow Rh Nanospheres Electrocatalyst for Alcohol Oxidation Reactions

The hollow noble metal nanostructures have attracted wide attention in catalysis/electrocatalysis. Here a two‐step procedure for constructing hollow Rh nanospheres (Rh H‐NSs) with clean surface is described. By selectively removing the surfactant and Au core of Au‐core@Rh‐shell nanostructures (Au@Rh NSs), the surface‐cleaned Rh H‐NSs are obtained, which contain abundant porous channels and large specific surface area. The as‐prepared Rh H‐NSs exhibit enhanced inherent activity for the methanol oxidation reaction (MOR) compared to state‐of‐the‐art Pt nanoparticles in alkaline media. Further electrochemical experiments show that Rh H‐NSs also have high activity for the electrooxidation of formaldehyde and formate (intermediate species in the course of the MOR) in alkaline media. Unfortunately, Rh H‐NSs have low electrocatalytic activity for the ethanol and 1‐propanol oxidation reactions in alkaline media. All electrochemical results indicate that the order of electrocatalytic activity of Rh H‐NSs for alcohol oxidation reaction is methanol (C₁) > ethanol (C₂) > 1‐propanol (C₃). This work highlights the synthesis route of Rh hollow nanostructures, and indicates the promising application of Rh nanostructures in alkaline direct methanol fuel cells.     

Degradation of bisphenol A in aqueous solution by H2O2-assisted photoelectrocatalytic oxidation

A series of titanium dioxide (TiO(2)/Ti) film electrodes were prepared from titanium (Ti) metal mesh by an improved anodic oxidation process and were further modified by photochemically depositing gold (Au) on the TiO(2) film surface as Au-TiO(2)/Ti film electrodes. The morphological characteristics, crystal structure and photoelectroreactivity of both the TiO(2)/Ti and Au-TiO(2)/Ti electrodes were studied. The experiments confirmed that the gold modification of TiO(2) film could enhance the efficiency of e(-)/h(+) separation on the TiO(2) conduction band and resulted in the higher photocatalytic (PC) and photoelectrocatalytic (PEC) activity under UV or visible illumination. To further enhance the TiO(2) PEC reaction, a reticulated vitreous carbon (RVC) electrode was applied in the same reaction system as the cathode to electrically generate H(2)O(2) in the aqueous solution. The experiments demonstrated that such a H(2)O(2)-assisted TiO(2) PEC reaction system could achieve a much better performance of BPA degradation in aqueous solution due to an interactive effect among TiO(2), Au, and H(2)O(2). It may have good potential for application in water and wastewater treatment in the future.     

One-dimensional TiO2 nanomaterials: preparation and catalytic applications

This work reports on the syntheses of one-dimensional (1D) H2Ti3O7 materials (nanotubes, nanowires and their mixtures) by autoclaving anatase titania (Raw-TiO2) in NaOH-containing ethanol-water solutions, followed by washing with acid solution. The synthesized nanosized materials were characterized using XRD, TEM/HRTEM, BET and TG techniques. The autoclaving temperature (120-180 degrees C) and ethanol-to-water ratio (V(EtOH)/V(H2O) = 0/60 approximately 30/30) were shown to be critical to the morphology of H2Ti3O7 product. The obtained H2Ti3O7 nanostructures were calcined at 400-900 degrees C to prepare 1D-TiO2 nanomaterials. H2Ti3O7 nanotubes were converted to anatase nanorods while H2Ti3O7 nanowires to TiO2(B) nanowires after the calcination at 400 degrees C. The calcination at higher temperatures led to gradual decomposition of the wires to rods and phase transformation from TiO2(B) to anatase then to rutile. Photocatalytic degradation of methyl orange was conducted to compare the photocatalytic activity of these 1D materials. These 1D materials were used as new support to prepare Au/TiO2 catalysts for CO oxidation at 0 degrees C and 1,3-butadiene hydrogenation at 120 degrees C. For the CO oxidation reaction, Au particles supported on anatase nanorods derived from the H2Ti3O7 nanotubes (Au/W-180-400) were 1.6 times active that in Au/P25-TiO2, 4 times that in Au/Raw-TiO2, and 8 times that on TiO2(B) nanowires derived from the H2Ti3O7 nanotubes (Au/M-180-400). For the hydrogenation of 1,3-butadiene, however, the activity of Au particles in Au/M-180-400 was 3 times higher than those in Au/W-180-400 but similar to those in Au/P25-TiO2. These results demonstrate that the potential of 1D-TiO2 nanomaterials in catalysis is versatile.     

Highly selective and sensitive electrochemical detection of dopamine using a nafion coated hybrid macroporous gold modified electrode with platinum nanoparticles

A coral-like macroporous Au electrode with electroplated Pt nanoparticles (hybrid macroporous Au-/nPts) coated with Nafion has been fabricated for the first time and used for highly selective and sensitive determination of dopamine (DA). The physically characterized results indicated that the electroplated Pt nanoparticles were dispersed uniformly on the macroporous Au electrode. The porosity and window pore size of the fabricated macroporous Au electrode were 50% and 100-300 nm, respectively. Also the electroplated Pt nanoparticles size was approximately 10-20 nm. The cyclic voltammograms results showed that the hybrid macroporous Au-/nPts exhibited a much larger surface activation area, a roughness factor (RF) of 2024.7, much higher than that of the macroporous Au electrode, which is 46.07. The electrochemical experimental results showed that the hybrid macroporous Au-/nPts coated with Nafion exhibited a dramatic electrocatalytic effect on the oxidation of DA. At 0.1 V, it responded linearly to DA concentrations ranging from 20 μ M to 160 μ M with a detection sensitivity of 90.9 μA mM (-1) cm (-2). Furthermore, it showed wide detection ranging from 20 nM to 900 μ M. At the same time, the interference of ascorbic acid (AA) was effectively avoided because of the Nafion film coated on the surface of the hybrid electrode.     

Following the biocatalytic activities of glucose oxidase by electrochemically cross-linked enzyme-Pt nanoparticles composite electrodes

An integrated platinum nanoparticles (NPs)/glucose oxidase (GOx) composite film associated with a Au electrode is used to follow the biocatalytic activities of the enzyme. The film is assembled on a Au electrode by the electropolymerization of thioaniline-functionalized Pt NPs and thioaniline-modified GOx. The resulting enzyme/Pt NPs-functionalized electrode stimulates the O 2 oxidation of glucose to gluconic acid and H 2O 2. The modified electrode is then implemented to follow the activity of the enzyme by the electrochemical monitoring of the generated H 2O 2. The effect of the composition of the Pt NPs/GOx cross-linked nanostructures and the optimal conditions for the preparation of the electrodes are discussed.     

Vertical α-FeOOH nanowires grown on the carbon fiber paper as a free-standing electrode for sensitive H<Subscript>2</Subscript>O<Subscript>2</Subscript> detection

Highly sensitive,selective,and stable hydrogen peroxide (H2O2) detection using nanozyme-based catalysts are desirable for practical applications.Herein,vertical α-FeOOH nanowires were successfully grown on the surface of carbon fiber paper (CFP) via a low-temperature hydrothermal procedure.The formation of vertical α-FeOOH nanowires is ascribed to the structure-directing role of sodium dodecyl sulfate.The resulting free-standing electrode with one-dimensional (1D)nanowires offers oriented channels for fast charge transfer,excellent electrical contact between the electrocatalyst and the current collector,and good mechanical stability and reproducibility.Thus,it can serve as an efficient electrocatalyst for the reduction and sensitive detection of H2O2.The relation of the oxidation current of H2O2 with the concentration is linear from 0.05 to 0.5 mM with a sensitivity of-0.194 mA/(mM.cm2) and a low detection limit of 18 μM.Furthermore,the portability in the geometric tailor and easy device fabrication allow extending the general applicability of this free-standing electrode to chemical and biological sensors.     

Electrochemical and quartz crystal microbalance detection of the cholera toxin employing horseradish peroxidase and GM1-functionalized liposomes.

An ultrasensitive method for the detection of the cholera toxin (CT) using electrochemical or microgravimetric quartz crystal microbalance transduction means is described. Horseradish peroxidase (HRP) and GM1-functionalized liposomes act as catalytic recognition labels for the amplified detection of the cholera toxin based on highly specific recognition of CT by the ganglioside GM1. The sensing interface consists of monoclonal antibody against the B subunit of CT that is linked to protein G, assembled as a monolayer on an Au electrode or an Au/ quartz crystal. The CT is detected by a "sandwich-type" assay on the electronic transducers, where the toxin is first bound to the anti-CT-Ab and then to the HRP-GM1-ganglioside-functionalized liposome. The enzyme-labeled liposome mediates the oxidation of 4-chloronaphthol (2) in the presence of H2O2 to form the insoluble product 3 on the electrode support or the Au/quartz crystal. The biocatalytic precipitation of 3 provides the amplification route for the detection of the CT. Formation of the insulating film of 3 on the electrode increases the interfacial electron-transfer resistance, Ret, or enhances the electrode resistance, R', parameters that are quantitatively derived by Faradaic impedance measurements and chronopotentiometric analyses, respectively. Similarly, the precipitate 3 formed on the Au/quartz crystal results in a mass increase on the transducer that is reflected by a decrease in the resonance frequency of the crystal. The methods allow the detection of the CT with an unprecedented sensitivity that corresponds to 1.0 x 10(-13) M.     

Au(111)电极表面溴离子吸附诱导的表面应力的理论研究

以Br~-为例,应用格子气模型,建立了阴离子吸附层对Au(111)电极表面应力贡献的统计热力学理论,计算了吸附层Br~-间的相互作用能及表面应力的贡献.计算结果表明,总的表面应力是压缩性的;在高覆盖度区域,表面应力与覆盖度近似呈直线关系;在表面吸附层应力的多种物理起源中,通过底物的分子间作用力有着决定性的贡献,揭示了分子的吸附能间接地起着重要作用.     

Electrochemical behavior of gold nanoparticles modified nitrogen incorporated tetrahedral amorphous carbon and its application in glucose sensing

Gold nanoparticles (NPs) with 10-50 nm in diameter were synthesized on nitrogen incorporated tetrahedral amorphous carbon (ta-C:N) thin film electrode by electrodeposition. The deposition and nucleation processes of Au on ta-C:N surface were investigated by cyclic voltammetry and chronoamperometry. The morphology of Au NPs was characterized by scanned electron microscopy. The electrochemical properties of Au NPs modified ta-C:N (ta-C:N/Au) electrode and its ability to sense glucose were investigated by voltammetric and amperometric measurements. The potentiostatic current-time transients showed a progressive nucleation process and diffusion growth of Au on the surface of ta-C:N film according to the Scharifker-Hills model. The Au NPs acted as microelectrodes improved the electron transfer and electrocatalytic oxidation of glucose on ta-C:N electrode. The ta-C:N/Au electrode exhibited fast current response, a linear detection range of glucose from 0.5 to 25 mM and a detection limit of 120 microM, which hinted its potential application as a glucose biosensor.     

Sensing of H2O2 at low surface density assemblies of Pt nanoparticles in polyelectrolyte

Amperometric detection of H2O2 was studied at random arrays of 2.5 nm polyacrylate-capped Pt nanoparticles (NP) assembled in poly(diallydimethylammonium chloride), PDDA, as a function of NP surface coverage. The arrays were assembled by varying the adsorption time of PDDA-modified electrodes in the nanoparticles solution. Pt NP-on-PDDA assemblies exhibited significant sensitivity and stability facing constant anodic polarization and a low limit of detection at small Pt mass in submonolayer coverage. The current output was measured at approximately 0.5 A M(-1) cm(-2)(geom) over a linear range from 42 nM to 0.16 mM H2O2 at a loading of 0.87 microg(Pt)/cm(2) or an estimated coverage of 0.4 of an assumed monolayer, or higher, and decreased with decreasing NP surface density to 0.2 A M(-1) cm(-2)(geom) at a Pt loading of 190 ng/cm. On the other hand, the intrinsic sensitivity measured relative to the real Pt surface area increased with decreasing coverage and reached a significant limiting value of 0.9 A M(-1) cm(-2) real at approximately 190-380 ng/cm(2). The behavior shows a significant effective turnover rate per Pt site and mass (1 A M(-1)/microg of Pt) in loosely packed assemblies, while overlap of individual diffusion fields (of particles or islands) and inaccessibility of some active sites lowers the sensitivity per nanoparticle in densely packed arrays. The reported trend agrees with the behavior of ultramicroelectrode arrays.     

Electrochemical biosensor based on multi-walled carbon nanotubes and Au nanoparticles synthesized in chitosan

A new biosensor is prepared by cross-linking glucose oxidase (GOD) with glutaradehyde at the electrode combining Au nanoparticles (AuNP) with multi-walled carbon nanotubes (MWCNTs). Au nanoparticles-doped chitosan (CS) solution (AuNP-CS) is prepared by treating the CS solution followed by chemical reduction of Au (III) with NaBH4. MWCNTs are then dispersed in AuNP-CS solution. TEM, FT-IR, and UV-Vis show that the AuNP-CS solution is highly dispersed and stable. The synergistic effect between AuNP and CNTs of the AuNP-CNTs-CS material has been investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and amperometric methods. The modified glassy carbon electrode (GCE) allows low-potential detection of H2O2 with high sensitivity and fast response time. With the immobilization of GOD, a biosensor has been constructed. In phosphate buffer solutions (PBS, pH 7.0), nearly free interference determination of glucose has been realized at 0.4 V(vs. Ag/AgCl/3.0 M KCI) with a wide linear range from 2.0 x 10(-5) to 1.5 x 10(-2) M and a fast response time within 5s. The biosensor has been used to determine glucose in human serum samples and the results are satisfactory.     

Liposomes labeled with biotin and horseradish peroxidase: a probe for the enhanced amplification of antigen--antibody or oligonucleotide--DNA sensing processes by the precipitation of an insoluble product on electrodes

Liposomes labeled with biotin and the enzyme horseradish peroxidase (HRP) are used as a probe to amplify the sensing of antigen-antibody interactions or oligonucleotide-DNA binding. The HRP-biocatalyzed oxidation of 4-chloro-1-naphthol (1) in the presence of H2O2, and the precipitation of the insoluble product 2 on electrode supports, are used as an amplification route for the sensing processes. The anti-dinitrophenyl antibody (DNP-Ab) is sensed by a dinitrophenyl-L-cysteine antigen monolayer associated with an Au electrode. A biotinylated anti-IgG-antibody (Fc-specific) is linked to the antigen-DNP-Ab complex, and the biotin-labeled HRP-liposomes associate with the assembly through an avidin bridge. The biocatalyzed precipitation of 2 on the electrode increases the electron-transfer resistances at the electrode-solution interface or the electrode resistance itself. The binding events of the different proteins on the electrode and the biocatalyzed precipitation of 2 on the conductive support are followed by Faradaic impedance spectroscopy or constant-current chronopotentiometry. DNP-Ab concentrations as low as 1 x 10(-11) g x mL(-1) can be detected by this method. The labeled liposomes were also used for the amplified detection of DNA 3. The oligonucleotide 4, complementary to a part of the target DNA 3 that is a model nucleic acid sequence for the Tay-Sachs genetic disorder, is assembled on an Au electrode. Hybridization of the analyte 3 followed by the association of the biotin-tagged oligonucleotide 5 yields a three-component double-stranded assembly. Sensing of the analyte 3 is amplified by the association of avidin, the labeled liposomes, and the subsequent biocatalyzed precipitation of 2 on the electrodes. The DNA 3 is detected with a sensitivity that corresponds to 6.5 x 10(-13) M. Faradaic impedance spectroscopy and chronopotentiometry were employed to follow the stepwise assembly of the systems and the electronic transduction of the detection of the analyte DNA 3.     

Surfactant chain length effects on the light emission of tris(2,2'-bipyridyl)ruthenium(II)/ tripropylamine electrogenerated chemiluminescence

The effects of nonionic surfactant chain length on the properties of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3(2+) where bpy = 2,2'-bipyridine) electrochemiluminescence (ECL) have been investigated. The electrochemistry, photophysics, and ECL of Ru(bpy)3(2+) in the presence of a series of nonionic surfactants are reported (Triton X-100, 114, 165, 405, 305, and 705-70). These surfactants differ in the number of poly(ethylene oxide) units incorporated into the surfactant molecule. The anodic oxidation of Ru(bpy)3(2+) produces ECL in the presence of tri-n-propylamine (TPrA) in aqueous surfactant solution. Increases in ECL efficiency (> or = 5-fold) and TPrA oxidation current (> or = 2-fold) have been observed in surfactant media. Slight decreases in ECL intensity are observed as the chain length of the nonionic surfactant increases. The data supports adsorption of surfactant on the electrode surface, thus facilitating TPrA and Ru(bpy)3(2+) oxidation and leading to higher ECL efficiencies.     

Selective detection of As(III) at the Au(111)-like polycrystalline gold electrode

Selective electrochemical detection of As(III) using a highly sensitive platform based on a Au(111)-like surface is described. The Au(111)-like surface was achieved for the first time by the partial reductive desorption of n-butanethiol (n-BT) from polycrystalline gold (poly-Au), on which a self-assembled monolayer (SAM) of n-BT was formed previously, which allows the selective blockage of the Au(100) and Au(110) surface domains by n-BT while the Au(111) domain remains bare. Square wave anodic stripping voltammetry (SWASV) using the Au(111)-like poly-Au electrode confirms the successful detection of As(III) without any interference from Cu(II). The fabricated electrode is stable and highly sensitive even in the presence of Cu(II), and it shows a linear response for As(III) up to 15 μM. The detection limit (S/N = 3) toward As(III) is 0.28 ppb, which is far below the guideline value given by World Health Organization (WHO). The electrode was applicable for the analysis of spiked arsenic in tap water containing a significant amount of various other ion elements. The results indicate that the Au(111)-like poly-Au electrode could be promising for the electrochemical detection of trace level of As(III) in real samples without any interference from Cu(II).