Mi-Sook Won

Electrochemistry of Conductive Polymers VIII In Situ Spectroelectrochemical Studies of Polyaniline Growth Mechanisms

The earlier stage of the polymerization reaction of polyaniline has been studied. The results indicate that the nitrene cation appears to be a key intermediate species, which leads to all three possible dimers including a head-to-tail dimer (N-phenyl-p-phenylenediamine), a tail-to-tail dimer (benzidine), and a head-to-head dimer (hydrazobenzene). The oxidized forms of these dimers were all shown to be capable of growing polyaniline in the presence of aniline, even though aniline was not oxidized

Gold Nanoparticles Doped Conducting Polymer Nanorod Electrodes: Ferrocene Catalyzed Aptamer-Based Thrombin Immunosensor

Au nanoparticles-doped conducting polymer nanorods electrodes (AuNPs/CPNEs) were prepared by coating Au nanorods (AuNRs) with a conducting polymer layer. The AuNRs were prepared through an electroless deposition method using the polycarbonate membrane (pore diameter, 50 nm, pore density, 6 x 10(8) pores/cm(2)) as a template. The AuNPs/CPNEs combining catalytic activity of ferrocene to ascorbic acid were used for the fabrication of an ultrasensitive aptamer sensor for thrombin detection. The AuNPs/3D-CPNEs were characterized employing cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Sandwiched immunoassay for alpha-human thrombin with NH(2)-functionalized-thrombin binding aptamer (Apt) immobilized on AuNPs/3D-CPNEs was studied through the electrocatalytic oxidation of ascorbic acid by the ferrocene moiety that was bound with an antithrombin antibody and attached with the Apt/3D-CPNEs probe through target binding. Various experimental parameters affecting thrombin detection were optimized, and the performance of the thrombin aptamer sensor was examined. The Apt/AuNPs/3D-CPNEs based thrombin sensor exhibited a wide dynamic range of 5-2000 ng L(-1) and a low detection limit of 5 ng L(-1) (0.14 pM). The selectivity and the stability of the proposed thrombin aptamer sensor were excellent, and it was tested in a real human serum sample for the detection of spiked concentrations of thrombin.

Voltammetric determination of the iodide ion with a quinine copper(II) complex modified carbon paste electrode

Abstract A Cu(Qui)(NO 3 ) 2 modified-carbon paste electrode (where Qui is quinine) was constructed by incorporating Cu(Qui)(NO 3 ) 2 into a carbon-paste composed of graphite powder and Nujol. The modification with Cu(Qui)(NO 3 ) 2 resulted in a deposit of iodide ions on the electrode surface through a ligand exchange reaction. This exchange reaction was completed within 20 ms in a CHCl 3 +CH 3 OH solution. The rate constant, k 0 , of the ion exchange reaction was determined to be 27 s −1 by the stopped flow spectroscopic method. The anodic peak of the pre-deposited iodide ion on the electrode surface was observed at +0.54 V in a cyclic voltammogram. Various experimental parameters such as pH, deposition time, temperature, and electrode composition were optimized to analyze the iodide ion employing linear sweep and differential pulse voltammetry. With the exception of thiosulfate ions, inorganic anions did not interfere with the determination of the iodide ion. Using linear sweep voltammetry, a calibration curve was attained over the concentration ranges of the iodide ion from 1.0×10 −4 –2.5×10 −6 M at the deposition time of 10 min, with the detection limit determined as 1.0×10 −6 M. Using differential pulse voltammetry, the logarithmic linear response range for the iodide ion was between 10 −6 and 10 −8 M, and the detection limit was 1.0×10 −8 M. This method was evaluated by analyzing the iodide ion content in a commercial disinfectant.

Water sensor for a nonaqueous solvent with poly(1,5-diaminonapthalene) nanofibers.

A water sensor for a nonaqueous solvent was fabricated using poly(1,5-diaminonapthalene (DAN) nanofibers, which were prepared through a catalytic chemical polymerization of the DAN monomer using Fe(III) salt as the catalyst. Poly(1,5-DAN) nanofibers were characterized by atomic force microscope (AFM), transmission electron microscope (TEM), scanning electron microscope (SEM), and UV-vis spectroscopy. The electrochemical properties of poly(1,5-DAN) nanofibers were investigated using cyclic voltammetry (CV). The electrochemical activity of poly(1,5-DAN) nanofibers was utilized for water sensing. The fabrication of water sensor was followed by placing one drop (about 2 microL) of 0.01% poly(1,5-DAN) nanofibers solution in the gap between two split gold electrodes (PBSA) and completely dried. The response of the water sensor in an acetonitrile solution was evaluated under optimized conditions. The linear dynamic range was from 0.05 to 20%, and the detection limit was determined to be 0.01%. The response of this sensor was shown to be comparable to that obtained with the Karl Fischer titration method.

Cathodic properties of a lithium-ion secondary battery using LiCoO2 prepared by a complex formation reaction

Abstract A LiCoO2 precursor is prepared by a complex formation reaction in a solution that contains LiOH, Co(NO3)2, and humic acid it is used as a cathode for a lithium-ion rechargeable battery. Layered LiCoO2 powders are prepared in air at 700 or 850°C after preheating the precursor at 350 and 450°C, respectively. X-ray diffraction spectra of the powders display a high intensity (003) peak and two low intensity (104) and (101) peaks. This indicates that the powders are well crystallized. Cyclic voltammetry, a galvanostatic charge/discharge experiment, and impedance spectroscopy are used to characterize the LiCoO2 electrode in a 1 M LiClO4/propylene carbonate electrolyte solution during the intercalation/de-intercalation of lithium ions through the electrode. The voltammogram recorded at a scan rate of 0.01 mV s−1 shows a set of redox waves that are caused by the de-intercalation/intercalation of lithium ions through the electrode. A cell, composed of u LiCoO2 cathode and a Li anode, shows an initial discharge specific capacity of 1 12.5 mA h g−1 at a current density of 1 mA cm−2 (43.25 mA g−1) between 3.6 and 4.2 V vs. Li/Li+ electrode. 100 charge/discharge cycles were achieved for a cell composed of a LiCoO2, cathode and graphite (MCMB 6–28) anode separated by Cellgard 2300. X-ray diffraction, charge/discharge, and cyclic voltammetric data shows that there is only a single phase reaction below 4.3 V during charge/discharge for a electrode prepared at 700°C. The diffusivity of lithium ions. DLi+, as determined by AC. impedance, is 5.2 × 10−12 m2 s−1.

An all-solid-state reference electrode based on the layer-by-layer polymer coating.

A solid-state reference electrode (SSRE) was fabricated by layering a silicone rubber (SR) film containing KCl on an AgCl surface, then a perfluorinated ionomer film, and finally a polyurethane-based membrane containing an ionophore, a lipophilic ionic additive, and a plasticizer, respectively. The addition of SiCl4 to the polyurethane-based membrane layer enhanced the strength of the membrane in an aqueous solution. The morphologies of the membranes were studied separately by SEM. The fabrication of the Ag/AgCl electrode through this layer-by-layer polymer coating improved the electrode stability enormously. In addition, the potential drift of the SSRE according to the pH of the medium was minimized by introducing a H+-ion-selective ionophore (tridodecylamine; TDDA) into the outmost polymer membrane. The cyclic voltammetric and potentiometric responses using the SSRE and a conventional reference electrode, respectively, were consistent. The SSRE exhibited little potential variation even in the case of the addition of very high concentrations of various salts, such as Na salicylate, LiCl, KCl, CaCl2, MgCl2, KNO3, NaCl, and NaHCO3. The practicability of the proposed SSRE was tested for the determination of blood pH and pCO2 in a flow cell system. The SSRE fabricated in the present study was stable over two years.

Characterization of protein-attached conducting polymer monolayer.

Cytochrome c (cyt c)-immobilized monolayers and multiple monolayers of a conducting polymer [poly(terthiophene-3-carboxylic acid) polymer (poly-TTCA)] were prepared, where the monolayer of monomer precursor was fabricated with the Langmuir-Blogett technique. Covalent immobilization of cyt c was achieved by the formation of an amide bond between the carboxylic groups of the conducting polymer and amines groups of lysine in cyt c. The monolayer of poly-TTCA and poly-TTCA/cyt c was characterized by cyclic voltammetry, XPS, EQCM, Auger electron spectra (AES), and atomic force microscopy (AFM). The immobilization of cyt c on the polymer layer reveals the direct electron-transfer processes of cyt c. Cyclic voltammetry of the poly-TTCA/cyt c-modified electrode showed a pair of reversible peaks at approximately +212/+201 mV (Epa/Epc) versus Ag/AgCl in a 0.2 M phosphate buffer solution (pH 7.0). The peak separation and the redox peak current of the poly-TTCA/cyt c-modified electrodes were gradually increased by increasing the number of poly-TTCA/cyt c layers on the electrode. The heterogeneous electron-transfer rate constant (ks) of cyt c at the poly-TTCA/cyt c-monolayer-modified electrode was estimated to be 0.874 s(-1). The method provides a novel route for the fabrication of protein (cyt c)-immobilized and/or lipid (palmitoyloleoylphosphatidic acid)-immobilized monolayers and multiple monolayers of a conducting polymer. Cyt c bonded on the conductive polymer layers was applied for bioelectronic devices with unique functionality.

Selective nonenzymatic bilirubin detection in blood samples using a Nafion/Mn–Cu sensor

The specific detection of biological organics without the use of an enzyme is challenging, and it is crucial for analytical and clinical chemistry. We report specific nonenzymatic bilirubin detection through the catalytic oxidation of bilirubin molecule on the Nafion/Mn-Cu surface. The catalytic ability, true surface area, morphology, crystallinity, composition, and oxidation state of the sensor surface were assessed using voltammetry, coulometry, XPS, XRD, Brunauer-Emmett-Teller (BET), SEM, EDXS, and TOF-SIMS experiments. The results showed that the surface was composed of microporous Mn-Cu bimetallic crystal in flake shape with a large BET surface area (3.635 m(2)g(-1)), where the surface area and crystallinity mainly affected the sensor performance. Product analysis of the catalytic reaction on the sensor probe revealed a specific two-electron oxidation of dipyrromethane moiety to dipyrromethene in the bilirubin molecule. Experimental variables affecting the analysis of bilirubin were optimized in terms of probe composition, temperature, pH, and potential. At the optimized condition, the dynamic range was between 1.2 μM and 0.42 mM, which yielded the equation of ΔI (μA)=(1.03 ± 0.72)+(457.0 ± 4.03) [C] (mM) with 0.999 of correlation coefficient, and the detection limit was 25.0 ± 1.8 nM (n=5, k=3). The stability test, interference effects, and analysis of real clinical samples, human whole blood and certified serum samples were demonstrated to confirm the reliability of the proposed bilirubin sensor.

Stability and Sensitivity Enhanced Electrochemical In Vivo Superoxide Microbiosensor Based on Covalently Co-immobilized Lipid and Cytochrome c

Enhanced stability and sensitivity of a superoxide anion radical (O(2)(•-)) microbiosensor were achieved through the sequential immobilization of lipid and cytochrome c (Cyt c) covalently bonded onto a conducting polymer layer that showed a clear quasi-reversible direct electron transfer (DET) process. The formal potential and the apparent standard rate constant were determined to be -0.24 V and 0.62 ± 0.05 s(-1), respectively. The detection of O(2)(•-) was attained through the catalytic activity of the haem group of Cyt c stabilized by coimmobilized lipid molecules (1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-n-dodecanylamine (DGPD)). The linear dynamic range and the detection limit of the O(2)(•-) analysis were determined to be 0.2-6.0 nM and 30.0 ± 0.9 pM, respectively. The in vivo microbiosensor implanted into rat brain successfully determined the extracellular level of O(2)(•-) produced by acute and repeated injections of cocaine. The present O(2)(•-) microbiosensor could be an effective tool for monitoring the change in extracellular O(2)(•-) levels in response to stimulant drug exposure.

Development of compact linear accelerator in KBSI.

The compact linear accelerator using a 28 GHz ECRIS is under construction in KBSI, South Korea. The main capability of this facility is the production of fast neurons for the neutron radiography. The designing of a superconducting magnet, microwave transmission system, beam extraction, and plasma chamber of ECRIS were finished. The nominal axial design fields of the magnets are 3.6 T at injection and 2.2 T at extraction; the nominal radial design field strength at the plasma chamber wall is 2.1 T. We already installed 10 kW, 28 GHz gyrotron, and tested a microwave power from gyrotron using a dummy load. The current status will be discussed in this paper.