Manganese oxide nanoparticles electrodeposited on platinum are superior to platinum for oxygen reduction.
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Journal Article↗
Biomedical subjects
Takeo Ohsaka
Publications and source records attributed to Takeo Ohsaka.
Eccentric phenomena at liquid mercury electrode/solution interfaces: upward, downward, and circular motions.
The present paper describes a visualization of unidirectional and circular motions triggered by an electrochemical redox reaction at a charged, bent, and streamed liquid electrode/liquid solution interface. The novel circular motion that induces a conversion of electrochemical energy into mechanical energy could be visualized for the first time at a hanging mercury drop electrode (HMDE)/dimethyl sulfoxide (DMSO) solution interface via the electrochromic reaction of 2,1,3-benzothiadiazole (BTD) by using a CCD-color video camera. The observed motions are self-insisting in nature and are tunable into upward, downward, clockwise, and anticlockwise ones by an appropriate choice of the experimental conditions. This circular motion is visualized for the first time as the cause of the well-known cyclic voltammetric anodic current oscillation at the HMDE. Several small perturbations, for example, surface tension, surface motion, bulk motion, diffusional mass transport, and surface electrochemical potential are considered to be endlessly amplified by their coupling in a cyclic chain, resulting in such macroscopic motions at the electrode/solution interface. All of the phenomena can be explained on the basis of the modern theory proposed by Aogaki et al. for the polarographic streaming maxima of the first kind.
Journal Article↗
Fabrication and electrochemical application of three-dimensional gold nanoparticles: self-assembly.
Multilayers film of nanostructured citrate-stabilized gold particles (AuNPs) has been fabricated based on the layer-by-layer (LBL) technique using a self-assembled monolayer of 1,4-benzenedimethanethiol (BDMT). The formation of AuNPs and BDMT self-assemblies as alternative multilayers was confirmed by transmission electron microscopy (TEM), X-ray photoelectron spectroscope (XPS), and quartz crystal microbalance (QCM). The formation of uniform AuNP layers with an average monolayer thickness of 5-6 nm was obvious in the TEM images. The existence of BDMT molecules as cross linkers for the AuNPs' layers was proved by XPS measurements. The greater affinity of AuNPs' layers to bind BDMT molecules in comparison with the bare Au bulk electrode was revealed by QCM measurements. Electrochemically, the AuNPs' layers on the electrode surface did not only catalyze the reduction of oxygen (ca. 100-mV positive shift of the reduction peak potential compared with that at the bare Au bulk electrode) but also showed a fascinating nature of working as a renewed activated-electrode surface; a zigzag response was observed for oxygen reduction during alternative immobilization of BDMT and the AuNP layer. The self-assembly of a new AuNPs layer restored the catalytic activity that was entirely blocked by the preceding BDMT layer.
Journal Article↗
Cathodic detection of H2O2 using iodide-modified gold electrode in alkaline media.
Oxidative chemisorption and cathodic stripping reductive desorption of iodide have been studied at a smooth polycrystalline gold (Au (poly)) electrode. Potential-dependent surface coverage of iodide has been controlled on the basis of its reductive desoprtion in 0.1 M KOH alkaline media and its quantitative oxidation to aqueous iodates in acidic media. The Au (poly) electrode surface catalyzes the decomposition of H2O2 to O2. Specific adsorption of iodide on the Au electrode inhibits fully the catalytic decomposition and electrochemical oxidation of H2O2 as well as the adsorption of unknown impurities and the oxidative degradation of the electrode surface by H2O2. A quantitative characterization/detection of H2O2 at the iodide-modified Au (poly) electrode in the alkaline media has, thus, been achieved. Performance of the electrode toward the detection of H2O2 with respect to response time and sensitivity as well as operational stability has been evaluated. It has a sensitivity of 0.272 mA cm(-2) mM(-1) in amperometric measurements with a detection limit of 1.0 x 10(-5) M H2O2, and the response time to achieve 95% of the steady-state current is <20 s. The effect of O2 in the air-saturated solution can be minimized by subtracting the additional current for the O2 reduction. Experimental measurements were based upon cyclic voltametric and amperometric techniques.
Journal Article↗
A carbon fiber microelectrode-based third-generation biosensor for superoxide anion.
Implantable and miniature carbon fiber microelectrode (CFME)-based third-generation biosensor for superoxide anion (O(2)(-)) was fabricated for the first time. The CFME-based biosensor was constructed by electro-deposition of Au nanoparticles on the CFMEs and then modification of the Au nanoparticles by cysteine followed by immobilization of superoxide dismutase (SOD) on the electrodes. The direct electrochemistry of the SOD immobilized on the CFME-based electrodes was efficiently realized by electron transfer promoter - cysteine molecules confined on the Au nanoparticles deposited on the CFMEs. The CFME-based biosensors were demonstrated to possess striking analytical properties for O(2)(-) determination, such as optional operation potentials, high selectivity and sensitivity as well as good stability. Along with the implantable capacity inherent in the CFMEs, these striking analytical properties of the CFME-based biosensors substantially make them potential for in vivo determination of O(2)(-).
Adsorption↗
Electrochemistry and electrocatalytic activities of superoxide dismutases at gold electrodes modified with a self-assembled monolayer.
In this article, the electrochemical properties and electrocatalytic activity of three kinds of superoxide dismutases (SODs), that is, bovine erythrocyte copper-zinc superoxide dismutase (Cu/Zn-SOD), iron superoxide dismutase from Escherichia coli (Fe-SOD), and manganese superoxide dismutase from E. coli (Mn-SOD), in the SOD family were studied. It was revealed that the direct electron transfer of the three kinds of SODs could be efficiently promoted by a self-assembled monolayer (SAM) of 3-mercaptopropionic acid (MPA) confined on a gold electrode. The electrochemical properties of the SODs at the MPA-SAM electrode vary with the sort of SOD with respect to the formal potential, reversibility of electrode reactions, kinetic parameters, and pH dependence, suggesting different mechanisms for the electrode reactions of the individual SODs. A combination of the facilitated direct electron transfer and the bifunctional enzymatic catalytic activities of the SODs via a redox cycle of their active metals substantially offered a flexible electrochemical route to determination of O(2)(*)(-) where O(2)(*)(-) can be sensed with the SOD-based biosensors in both anodic and cathodic polarizations. Such an intrinsic feature of the SOD-based biosensors successfully enabled a sensitive determination scheme for O(2)(*)(-) free from the interference from some coexisting electroactive species, such as ascorbic acid (AA) and uric acid (UA). Further potential applications for in vivo determination of O(2)(*)(-) is also suggested.
3-Mercaptopropionic Acid↗
A novel electrochemical strategy for developing alkaline air electrodes by a combined use of dual functional catalysts.
A novel electrochemical strategy for the development of new alkaline air electrodes has been proposed based on a combined use of dual catalysts for redox-mediating O2 reduction and disproportionating the reduction intermediates, i.e., superoxide and peroxide in alkaline media.
Journal Article↗
Simultaneous potentiometric determination of peracetic acid and hydrogen peroxide.
A rapid and highly selective potentiometric method for the simultaneous analysis of peracetic acid (PAA) and hydrogen peroxide (H2O2) has been proposed, for the first time, using glassy carbon (GC) as an indicator electrode and I2/I- potential buffer. On the basis of the large difference in the reaction rates of PAA and H2O2 with I-, which was confirmed using stopped-flow spectrophotometry, a transient potential response corresponding to the reactions of the two species with I- was observed. The response times were typically a few seconds and several minutes for PAA and H2O2, respectively. The effects of the concentrations of molybdate catalyst, H+, I2, and I- in the potential buffer on the selectivity as well as the sensitivity were examined. The potential response obtained using the GC indicator electrode was found to be Nernstian over a wide range of their concentrations (typically from micromolar to millimolar) with slopes of 30.5 and 29.5 mV for PAA and H2O2, respectively (in close agreement with the theoretical value, that is, 29.6 mV). O2 was found to have no substantial effect on the potential change at the GC electrode in the present potential buffer.
Journal Article↗
Simultaneous electroanalysis of dopamine and ascorbic acid using poly (N,N-dimethylaniline)-modified electrodes.
Glassy carbon (GC) electrode is modified with an electropolymerized film of N,N-dimethylaniline (DMA). This polymer (PDMA) film-coated GC electrode is used to electrochemically detect dopamine (DA) in the presence of ascorbic acid (AA). Polymer film has the positive charge in its backbone, and in neutral solution DA exists as the positively charged species whereas AA exists as the negatively charged one. In cyclic voltammetric measurements, favorable ionic interaction (i.e., electrostatic attraction) between AA and PDMA film causes a large negative shift of the oxidation potential for AA compared to that at the bare electrode. Oxidation potential for DA is positively shifted due to the electrostatic repulsion. The PDMA film shows hydrophobicity by incorporating uncharged hydroquinone molecule within the film. DA is also incorporated into the film due to hydrophobic attraction even though DA has a positive charge. The responses of DA and AA at polymer-modified electrodes largely change with the concentration of the monomer (i.e., 0.2, 0.1 and 0.05 M DMA) used in electropolymerization and thus with the film thickness. Hydrophobicity of the polymer film shows great influence on the voltammetric responses of both DA and AA. In square wave voltammetric measurements, the PDMA film-coated electrode can separate the DA and AA oxidation potentials by about 300 mV and can detect DA at its low concentration (e.g., 0.2 microM) in the presence of 1000 times higher concentration of AA, which is close to the physiological level. AA oxidizes at more negative potential than DA. The electrode response is not affected by the oxidized product of AA. So unlike the bare electrode, the fouling effect as well as the catalytic oxidation of AA by the oxidized form of DA are eliminated at the PDMA film-coated GC electrode. The electrode exhibits the stable and sensitive response to DA.
Aniline Compounds↗
Superoxide dismutase-based third-generation biosensor for superoxide anion.
A third-generation biosensor for superoxide anion (O2-) was developed by immobilizing superoxide dismutase (SOD) on a self-assembled monolayer of cysteine on gold electrode; i.e., a SOD/cysteine-modified gold electrode (SOD/Cys/Au) was fabricated. A rapid and direct electron transfer of SOD was realized at the gold electrode by using the cysteine molecule as an electron-transfer promoter. The promoted direct electron transfer of SOD and biomolecular recognition by the exploitation of specific and significant enzyme-substrate reactivity of SOD toward O2- combined with the low operating potential enabled a sensitive measurement of O2-. At SOD/Cys/Au, O2- could be specifically oxidized and reduced to O2 and hydrogen peroxide, respectively, through the inherent catalytic reaction of SOD. This allowed us to measure O2- by polarizing the electrode both anodically and cathodically. We could successfully measure O2- by suitably polarizing the electrode, typically at 300 and -200 mV versus Ag/AgCl without the virtual interference from physiological levels of H2O2, ascorbic acid, uric acid, and metabolites of neurotransmitters. The response mechanism of SOD/Cys/Au to O2- and its sensor characteristics are also presented and discussed.
Animals↗
A superoxide dismutase-modified electrode that detects superoxide ion.
A superoxide dismutase (SOD)-modified electrode, in which SOD is oriented on the gold electrode via a self-assembled monolayer of cysteine so as to allow its direct electrode reaction, possesses a bi-directional electrocatalysis for both the oxidation of superoxide ion (O2-) to O2 and the reduction of O2- to H2O2 and functions as a third generation O2- biosensor.
Electrochemistry↗
A facilitated electron transfer of copper--zinc superoxide dismutase (SOD) based on a cysteine-bridged SOD electrode.
The direct electrochemical redox reaction of bovine erythrocyte copper--zinc superoxide dismutase (Cu(2)Zn(2)SOD) was clearly observed at a gold electrode modified with a self-assembled monolayer (SAM) of cysteine in phosphate buffer solution containing SOD, although its reaction could not be observed at the bare electrode. In this case, SOD was found to be stably confined on the SAM of cysteine and the redox response could be observed even when the cysteine-SAM electrode used in the SOD solution was transferred to the pure electrolyte solution containing no SOD, suggesting the permanent binding of SOD via the SAM of cysteine on the electrode surface. The electrode reaction of the SOD confined on the cysteine-SAM electrode was found to be quasi-reversible with the formal potential of 65 +/- 3 mV vs. Ag/AgCl and its kinetic parameters were estimated: the electron transfer rate constant k(s) is 1.2 +/- 0.2 s(-1) and the anodic (alpha(a)) and cathodic (alpha(c)) transfer coefficients are 0.39 +/- 0.02 and 0.61 +/- 0.02, respectively. The assignment of the redox peak of SOD at the cysteine-SAM modified electrode could be sufficiently carried out using the native SOD (Cu(2)Zn(2)SOD), its Cu- or Zn-free derivatives (E(2)Zn(2)SOD and Cu(2)E(2)SOD, E designates an empty site) and the SOD reconstituted from E(2)Zn(2)SOD and Cu(2+). The Cu complex moiety, the active site for the enzymatic dismutation of the superoxide ion, was characterized to be also the electroactive site of SOD. In addition, we found that the SOD confined on the electrode can be expected to possess its inherent enzymatic activity for dismutation of the superoxide ion.
Aminobutyrates↗
Square wave voltammetric sensing of uric acid using the self-assembly of mercaptobenzimidazole.
The self-assembled monolayer of a heterocyclic thiol, mercaptobenzimidazole (MBI) on gold (Au) electrode is successfully utilized for the voltammetric sensing of uric acid (UA). The self-assembly of MBI separates the voltammetric signal of UA from the interfering ascorbate (AA). Selective detection of UA in the presence of a large excess of AA or the simultaneous detection of UA and AA is achieved at the MBI monolayer-modified electrode. This electrode can detect as low as 1 microM of UA in the presence of 100-fold excess of AA with excellent reproducibility. The practical utility of the electrode is demonstrated by measuring the concentration of UA in human serum.
Benzimidazoles↗
Chemiluminescence of lucigenin by electrogenerated superoxide ions in aqueous solutions.
The chemiluminescence reaction of lucigenin (Luc(2+)c2NO(3) (-), N,N'-dimethyl-9,9'-biacridinium dinitrate) at gold electrodes in dioxygen-saturated alkaline aqueous solutions (pH 10) was investigated in detail by the use of electrochemical emission spectroscopy. We noted that both O(2) and Luc(2+) are reduced on a gold electrode in aqueous solution of pH 10 in almost the same potential region. From this fact, we expected chemiluminescence based on a radical-radical coupling reaction of superoxide ion (O(2).(-)) and one-electron reduced form of Luc(2+) (Luc.(+), a radical cation). Chemiluminescence was actually observed in the potential range where O(2) and Luc(2+) were simultaneously reduced at the electrodes. The effects were examined upon addition of enzymes, i.e. superoxide dismutase (SOD) and catalase, into the solution and the substitution of heavy water (D(2)O) for light water (H(2)O) as a solvent on the chemiluminescence. In the presence of native and active SOD, chemiluminescence was completely absent. On the other hand, chemiluminescence was observed, unchanged in the presence of either denatured and inert SOD or catalase. In addition, the amount of chemiluminescence in D(2)O solution was about three times greater than that in H(2)O solution. These results, together with cyclic voltammetric results, suggest that O(2).(-) participates directly in the chemiluminescence but H(2)O(2) does not, and the chemiluminescence results from the coupling reaction between O(2).(-) and Luc(.+) under the present experimental conditions. These chemically unstable species, O(2).(-) and Luc.(+), are produced during the simultaneous electroreduction of O(2) and Luc(2+). The coupling reaction between those radical species would lead to the formation of a dioxetane-type intermediate and, finally, to chemiluminescence. The chemiluminescence reaction mechanism is discussed.
Acridines↗