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Quan, De,Nagarale, R. K.,Shin, Woonsup WILEY-VCH Verlag 2010 Electroanalysis Vol.22 No.20
<P>Copper containing nitrite reductase (Cu-NiR) and viologen-modified sulfonated polyaminopropylsiloxane (PAPS-SO<SUB>3</SUB>H-V) were co-immobilized on glassy carbon electrode (GCE) by hydrophilic polyurethane (HPU) drop-coating, and the electrode was tested as a reagentless electrochemical biosensor for nitrite detection. The newly synthesized PAPS-SO<SUB>3</SUB>H-V as an electron transfer (ET) mediator between electrode and NiR was effective, and could be effectively immobilized in HPU membrane. The NiR and PAPS-SO<SUB>3</SUB>H-V co-immobilized GCE used as a nitrite biosensor showed the following performance factors: sensitivity=12.0 nA μM<SUP>−1</SUP>, limit of detection (LOD)=60 nM (S/N=3), linear response range=0–18 μM (r<SUP>2</SUP>=0.996) and response time (t<SUB>90%</SUB>)=60 s, respectively. Lineweaver–Burk plot shows that apparent Michaelis–Menten constant (K<TEX>$\rm{{_{M}^{app}})}$</TEX> is 101 μM. Storage stability of the sensor is 51 days (80% of initial activity) in condition of storing in ambient air at room temperature. The sensor showed a relative standard deviation (RSD) of 3.2% (n=5) even in condition of injection of 1 μM nitrite. Interference study showed that common anions in water sample such as chlorate, chloride, sulfate and sulfite do not interfere with the nitrite detection. However, nitrate interfered with a relative sensitivity of 80% due to inherent character of the enzyme used.</P>
Saravanakumar, D.,Nagarale, Rajaram Krishna,Jirimali, Harish Chandra,Lee, Jong Myung,Song, Jieun,Lee, Junghyun,Shin, Woonsup The Korean Electrochemical Society 2016 Journal of electrochemical science and technology Vol.7 No.4
The development of non-precious metal based electrocatalysts is highly desired for the oxygen reduction reaction (ORR) as alternates to noble metal based ORR electrocatalysts. Herein, we report mononulcear copper(II) complex $[CuLbpy]ClO_4$ (L=4-[(2-hydroxyphenylimino)methyl]benzoic acid) containing poly(allylamine.HCl) polymer (PAlACuLbpy) as an electrocatalyst for oxygen reduction reaction (ORR). PAlACuLbpy was mixed with poly(acrylic acid) and tetraethylortho silicate to prepare a composite and then deposited on the screen printed electrode surface. The modified electrode (PAlACuLbpy/PCE) is highly stable and showed a quasi-reversible redox behavior with $E_{1/2}=-0.2V$ vs. Ag/AgCl(3 M KCl) in 0.1 M phosphate buffer at pH 7 under argon atmosphere. PAlACuLbpy/PCE exhibited a remarkable ORR activity with an onset potential of -0.1 V vs Ag/AgCl in 0.1 M PB (pH 7) in the presence of oxygen. The kinetics for ORR was studied by rotating disk voltammetry in neutral aqueous medium and the results indicated that the number of electrons involving in the ORR is four and the conversion products are water and hydrogen peroxide.
Jirimali, Harishchandra Digambar,Nagarale, Rajaram Krishna,Lee, Jong Myung,Saravanakumar, Durai,Shin, Woonsup WILEY‐VCH Verlag 2013 Chemphyschem Vol.14 No.10
<P><B>Abstract</B></P><P>A new family of chitosan‐cross‐linked osmium polymer composites was prepared and its electrochemical properties were examined. The composites were prepared by quaternization of the poly(4‐vinylpyridine) osmium bipyridyl polymer (PVP‐Os) which was then cross‐linked with chitosan, yielding PVP‐Os/chitosan. Films made of the composites showed improved mass and electron transport owing to the porous and hydrophilic structure which is derived from the cross‐links between the Os polymer and chitosan. The rate for glucose oxidation was enhanced four times when glucose oxidase (GOx) was immobilized on PVP‐Os/chitosan compared immobilization on PVP‐Os.</P>
Shin, Woonsup,Zhu, Enhua,Nagarale, Rajaram Krishna,Kim, Chang Hwan,Lee, Jong Myung,Shin, Samuel Jaeho,Heller, Adam American Chemical Society 2011 ANALYTICAL CHEMISTRY - Vol.83 No.12
<P>When a current or a voltage is applied across the ceramic membrane of the nongassing Ag/Ag<SUB>2</SUB>O-SiO<SUB>2</SUB>-Ag/Ag<SUB>2</SUB>O pump, protons produced in the anodic reaction 2Ag(s) + H<SUB>2</SUB>O → Ag<SUB>2</SUB>O(s) + 2H<SUP>+</SUP> + 2e<SUP>–</SUP> are driven to the cathode, where they are consumed by the reaction Ag<SUB>2</SUB>O(s) + H<SUB>2</SUB>O + 2e<SUP>–</SUP> → 2Ag(s) + 2 OH<SUP>–</SUP>. The flow of water is induced by momentum transfer from the electric field-driven proton-sheet at the surface of the ceramic membrane. About 10<SUP>4</SUP> water molecules flowed per reacted electron. Because dissolved ions decrease the field at the membrane surface, the flow decreases upon increasing the ionic strength. For this reason Ag<SUP>+</SUP> ions introduced through the anodic reaction and by dissolution of Ag<SUB>2</SUB>O decrease the flow. Their accumulation is reduced by applying Nafion-films to the electrodes. The 20 μL min<SUP>–1</SUP> flow rate of 6 mm i.d. pumps with Nafion coated electrodes operate daily for 5 min at 1 V for 1 month, for 70 h when the pump is pulsed for 30 s every 30 min, and for 2 h when operating continuously.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancham/2011/ancham.2011.83.issue-12/ac201118t/production/images/medium/ac-2011-01118t_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ac201118t'>ACS Electronic Supporting Info</A></P>
Singh, Pramod K,Kim, Kang-Wook,Nagarale, R K,Rhee, Hee-Woo Institute of Physics [etc.] 2009 Journal of physics. D, applied physics Vol.42 No.12
<P>Solid polymer electrolyte membranes of polyethylene oxide, KI and I<SUB>2</SUB> doped with low viscosity ionic liquid (IL) are developed and used in dye sensitized solar cells. Free charge carriers and reduced crystallinity of polymer electrolyte matrix provided by IL assist in ionic conductivity (σ) enhancement, and the maximum σ is 4.72 × 10<SUP>−4</SUP> S cm<SUP>−1</SUP> at 40 wt% IL concentration. XRD and DSC results affirm the reduction of crystallinity while AFM suggests the good incorporation of IL. The fabricated solar cells with IL-doped polymer electrolytes show improved efficiency (2%) in comparison with solar cells without IL. This improvement is due to the high σ by IL doping.</P>
Song, Ji-Eun,Hong, Zhenyu,Nagarale, Rajaram Krishna,Shin, Woon-Sup The Korean Electrochemical Society 2011 Journal of electrochemical science and technology Vol.2 No.3
Nicotinamide adenine dinucleotide, $NAD^+$, and its reduced form, NADH, play important roles as coenzymes in many enzymatic reactions. Electrochemical methods for $NAD^+$ or NADH detection or generation are drawn attention because it can provide the simple and low cost platform with fairly good sensitivity. In this study, the polysiloxane viologen polymer/diaphorase/hydrophilic polyurethane (PSV/DI/HPU) modified electrodes were simply prepared and demonstrated for bio-electrocatalytic $NAD^+$ sensors. The electrodes were co-immobilized with diaphorase and polysiloxane viologen polymer as an electron mediator followed by the overcoating with HPU membrane. The mixture of the enzyme and the electron mediator was well stabilized within HPU membrane and exhibited good reversibility and stability. The sensitivity was 0.2 $nA{\cdot}{\mu}M^{-1}$ and the detection limit was 28 ${\mu}M$ with a response time of 50 s ($t_{90%}$). The capability for NADH sensor was also observed on the PSV/DI/HPU electrode.
Shin, Woonsup,Shin, Samuel Jaeho,Lee, Jong Myung,Nagarale, Rajaram Krishna,Heller, Adam Springer US 2011 Drug delivery and translational research Vol.1 No.4
<P>A programmable, skin-attached, 36??30??8?mm system for subcutaneous infusion of 1.2?mL of a drug solution is described. The system is intended to be replaced daily. It comprises a 20??14??8?mm electronic controller and power source, an 8?mm diameter 2?mm thick electroosmotic pump, a two-compartment reservoir for a pumped water and a drug solution, an adhesive tape for attachment to the skin, and a 6?mm long 27 gauge needle. Its removable electronic controller programs the dose rate and dose and is re-used. The electroosmotic pump consists of a porous ceramic membrane sandwiched between a pair of Ag/Ag2O plated carbon paper electrodes. It operates below 1.23?V, the thermodynamic threshold for water electrolysis without gassing. The flow rate can be adjusted between 4 and 30?μL?min(-1) by setting either by the voltage (0.2-0.8?V) or the current (30-200?μA). For average flow rates below 4?μL?min(-1), the pump is turned on and off intermittently. For example, a flow rate of 160?μL?day(-1), i.e., 0.13?μL?min(-1) for basal insulin infusion in type 1 diabetes management, is obtained when 10?s pulses of 75?μA is applied every 15?min. High flow rates of 10-30?μL?min(-1), required for prandial insulin administration, are obtained when the pump operates at 50-200?μA. To prevent fouling by the drug, only pure water passes the pump; the water pushes a drop of oil, which, in turn, pushes the drug solution.</P>