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Sample records for iridium oxide microelectrode

  1. Iridium material for hydrothermal oxidation environments

    DOEpatents

    Hong, Glenn T.; Zilberstein, Vladimir A.

    1996-01-01

    A process for hydrothermal oxidation of combustible materials in which, during at least a part of the oxidation, corrosive material is present and makes contact with at least a portion of the apparatus over a contact area on the apparatus. At least a portion of the contact surface area comprises iridium, iridium oxide, an iridium alloy, or a base metal overlaid with an iridium coating. Iridium has been found to be highly resistant to environments encountered in the process of hydrothermal oxidation. Such environments typically contain greater than 50 mole percent water, together with oxygen, carbon dioxide, and a wide range of acids, bases and salts. Pressures are typically about 27.5 to about 1000 bar while temperatures range as high as 800.degree. C.

  2. Iridium oxide-polymer nanocomposite electrode materials for water oxidation.

    PubMed

    Lattach, Youssef; Rivera, Juan Francisco; Bamine, Tahya; Deronzier, Alain; Moutet, Jean-Claude

    2014-08-13

    Nanocomposite anode materials for water oxidation have been readily synthesized by electrodeposition of iridium oxide nanoparticles into poly(pyrrole-alkylammonium) films, previously deposited onto carbon electrodes by oxidative electropolymerization of a pyrrole-alkylammonium monomer. The nanocomposite films were characterized by electrochemistry, transmission electron microscopy, and atomic force microscopy. They showed an efficient electrocatalytic activity toward the oxygen evolution reaction. Data from Tafel plots have demonstrated that the catalytic activity of the iridium oxide nanoparticles is maintained following their inclusion in the polymer matrix. Bulk electrolysis of water at carbon foam modified electrodes have shown that the iridium oxide-polymer composite presents a higher catalytic activity and a better operational stability than regular oxide films.

  3. Homogeneous and heterogenized iridium water oxidation catalysts

    NASA Astrophysics Data System (ADS)

    Macchioni, Alceo

    2014-10-01

    The development of an efficient catalyst for the oxidative splitting of water into molecular oxygen, protons and electrons is of key importance for producing solar fuels through artificial photosynthesis. We are facing the problem by means of a rational approach aimed at understanding how catalytic performance may be optimized by the knowledge of the reaction mechanism of water oxidation and the fate of the catalytic site under the inevitably harsh oxidative conditions. For the purposes of our study we selected iridium water oxidation catalysts, exhibiting remarkable performance (TOF > 5 s-1 and TON > 20000). In particular, we recently focused our attention on [Cp*Ir(N,O)X] (N,O = 2-pyridincarboxylate; X = Cl or NO3) and [IrCl(Hedta)]Na water oxidation catalysts. The former exhibited a remarkable TOF whereas the latter showed a very high TON. Furthermore, [IrCl(Hedta)]Na was heterogenized onto TiO2 taking advantage of the presence of a dandling -COOH functionality. The heterogenized catalyst maintained approximately the same catalytic activity of the homogeneous analogous with the advantage that could be reused many times. Mechanistic studies were performed in order to shed some light on the rate-determining step and the transformation of catalysts when exposed to "oxidative stress". It was found that the last oxidative step, preceding oxygen liberation, is the rate-determining step when a small excess of sacrificial oxidant is used. In addition, several intermediates of the oxidative transformation of the catalyst were intercepted and characterized by NMR, X-Ray diffractometry and ESI-MS.

  4. Iridium-Doped Ruthenium Oxide Catalyst for Oxygen Evolution

    NASA Technical Reports Server (NTRS)

    Valdez, Thomas I.; Narayan, Sri R.; Billings, Keith J.

    2011-01-01

    NASA requires a durable and efficient catalyst for the electrolysis of water in a polymer-electrolyte-membrane (PEM) cell. Ruthenium oxide in a slightly reduced form is known to be a very efficient catalyst for the anodic oxidation of water to oxygen, but it degrades rapidly, reducing efficiency. To combat this tendency of ruthenium oxide to change oxidation states, it is combined with iridium, which has a tendency to stabilize ruthenium oxide at oxygen evolution potentials. The novel oxygen evolution catalyst was fabricated under flowing argon in order to allow the iridium to preferentially react with oxygen from the ruthenium oxide, and not oxygen from the environment. Nanoparticulate iridium black and anhydrous ruthenium oxide are weighed out and mixed to 5 18 atomic percent. They are then heat treated at 300 C under flowing argon (in order to create an inert environment) for a minimum of 14 hours. This temperature was chosen because it is approximately the creep temperature of ruthenium oxide, and is below the sintering temperature of both materials. In general, the temperature should always be below the sintering temperature of both materials. The iridium- doped ruthenium oxide catalyst is then fabricated into a PEM-based membrane- electrode assembly (MEA), and then mounted into test cells. The result is an electrolyzer system that can sustain electrolysis at twice the current density, and at the same efficiency as commercial catalysts in the range of 100-200 mA/sq cm. At 200 mA/sq cm, this new system operates at an efficiency of 85 percent, which is 2 percent greater than commercially available catalysts. Testing has shown that this material is as stable as commercially available oxygen evolution catalysts. This means that this new catalyst can be used to regenerate fuel cell systems in space, and as a hydrogen generator on Earth.

  5. Mercury Underpotential Deposition to Determine Iridium and Iridium Oxide Electrochemical Surface Areas

    DOE PAGES

    Alia, Shaun M.; Hurst, Katherine E.; Kocha, Shyam S.; Pivovar, Bryan S.

    2016-06-02

    Determining the surface areas of electrocatalysts is critical for separating the key properties of area-specific activity and electrochemical surface area from mass activity. Hydrogen underpotential deposition and carbon monoxide oxidation are typically used to evaluate iridium (Ir) surface areas, but are ineffective on oxides and can be sensitive to surface oxides formed on Ir metals. Mercury underpotential deposition is presented in this study as an alternative, able to produce reasonable surface areas on Ir and Ir oxide nanoparticles, and able to produce similar surface areas prior to and following characterization in oxygen evolution. Reliable electrochemical surface areas allow for comparativemore » studies of different catalyst types and the characterization of advanced oxygen evolution catalysts. Lastly, they also enable the study of catalyst degradation in durability testing, both areas of increasing importance within electrolysis and electrocatalysis.« less

  6. Excimer laser deinsulation of Parylene-C on iridium for use in an activated iridium oxide film-coated Utah electrode array

    PubMed Central

    Yoo, Je-Min; Negi, Sandeep; Tathireddy, Prashant; Solzbacher, Florian; Song, Jong-In; Rieth, Loren W.

    2013-01-01

    Implantable microelectrodes provide a measure to electrically stimulate neurons in the brain and spinal cord and record their electrophysiological activity. A material with a high charge capacity such as activated or sputter-deposited iridium oxide film (AIROF or SIROF) is used as an interface. The Utah electrode array (UEA) uses SIROF for its interface material with neural tissue and oxygen plasma etching (OPE) with an aluminium foil mask to expose the active area, where the interface between the electrode and neural tissue is formed. However, deinsulation of Parylene-C using OPE has limitations, including the lack of uniformity in the exposed area and reproducibility. While the deinsulation of Parylene-C using an excimer laser is proven to be an alternative for overcoming the limitations, the iridium oxide (IrOx) suffers from fracture when high laser fluence (>1000 mJ/cm2) is used. Iridium (Ir), which has a much higher fracture resistance than IrOx, can be deposited before excimer laser deinsulation and then the exposed Ir film area can be activated by electrochemical treatment to acquire the AIROF. Characterisation of the laser-ablated Ir film and AIROF by surface analysis (X-ray photoelectron spectroscopy, scanning electron microscope, and atomic force microscope) and electrochemical analysis (electrochemical impedance spectroscopy, and cyclic voltammetry) shows that the damage on the Ir film induced by laser irradiation is significantly less than that on SIROF, and the AIROF has a high charge storage capacity. The results show the potential of the laser deinsulation technique for use in high performance AIROF-coated UEA fabrication. PMID:23458659

  7. Microelectrode arrays fabricated using a novel hybrid microfabrication method

    PubMed Central

    Merlo, Mark W.; Snyder, Russell L.; Middlebrooks, John C.; Bachman, Mark

    2011-01-01

    We present novel hybrid microfabrication methods for microelectrode arrays that combine microwire assembly, microelectromechanical systems (MEMS) manufacturing techniques and precision tool-based micromachining. This combination enables hybrid microfabrication to produce complex geometries and structures, increase material selection, and improve integration. A 32-channel shank microelectrode array was fabricated to highlight the hybrid microfabrication techniques. The electrode shank was 130 μm at its narrowest, had a 127 μm thickness and had iridium oxide electrode sites that were 25 μm in diameter with 150 μm spacing. Techniques used to fabricate this electrode include microassembly of insulated gold wires into a micromold, micromolding the microelectrode shank, post molding machining, sacrificial release of the microelectrode and electrodeposition of iridium oxide onto the microelectrode sites. Electrode site position accuracy was shown to have a standard deviation of less than 4 μm. Acute in vivo recordings with the 32-channel shank microelectrode array demonstrated comparable performance to that obtained with commercial microelectrode arrays . This new approach to microelectrode array fabrication will enable new microelectrodes, such as multi-sided arrays, drug eluding electrodes and biodegradable shanks. PMID:21979567

  8. Sol-Gel Deposition of Iridium Oxide for Biomedical Micro-Devices

    PubMed Central

    Nguyen, Cuong M.; Rao, Smitha; Yang, Xuesong; Dubey, Souvik; Mays, Jeffrey; Cao, Hung; Chiao, Jung-Chih

    2015-01-01

    Flexible iridium oxide (IrOx)-based micro-electrodes were fabricated on flexible polyimide substrates using a sol-gel deposition process for utilization as integrated pseudo-reference electrodes for bio-electrochemical sensing applications. The fabrication method yields reliable miniature on-probe IrOx electrodes with long lifetime, high stability and repeatability. Such sensors can be used for long-term measurements. Various dimensions of sol-gel iridium oxide electrodes including 1 mm × 1 mm, 500 μm × 500 μm, and 100 μm × 100 μm were fabricated. Sensor longevity and pH dependence were investigated by immersing the electrodes in hydrochloric acid, fetal bovine serum (FBS), and sodium hydroxide solutions for 30 days. Less pH dependent responses, compared to IrOx electrodes fabricated by electrochemical deposition processes, were measured at 58.8 ± 0.4 mV/pH, 53.8 ± 1.3 mV/pH and 48 ± 0.6 mV/pH, respectively. The on-probe IrOx pseudo-reference electrodes were utilized for dopamine sensing. The baseline responses of the sensors were higher than the one using an external Ag/AgCl reference electrode. Using IrOx reference electrodes integrated on the same probe with working electrodes eliminated the use of cytotoxic Ag/AgCl reference electrode without loss in sensitivity. This enables employing such sensors in long-term recording of concentrations of neurotransmitters in central nervous systems of animals and humans. PMID:25686309

  9. Single step radiolytic synthesis of iridium nanoparticles onto graphene oxide

    NASA Astrophysics Data System (ADS)

    Rojas, J. V.; Molina Higgins, M. C.; Toro Gonzalez, M.; Castano, C. E.

    2015-12-01

    In this work a new approach to synthesize iridium nanoparticles on reduced graphene oxide is presented. The nanoparticles were directly deposited and grown on the surface of the carbon-based support using a single step reduction method through gamma irradiation. In this process, an aqueous isopropanol solution containing the iridium precursor, graphene oxide, and sodium dodecyl sulfate was initially prepared and sonicated thoroughly to obtain a homogeneous dispersion. The samples were irradiated with gamma rays with energies of 1.17 and 1.33 MeV emitted from the spontaneous decay of the 60Co irradiator. The interaction of gamma rays with water in the presence of isopropanol generates highly reducing species homogeneously distributed in the solution that can reduce the Ir precursor down to a zero valence state. An absorbed dose of 60 kGy was used, which according to the yield of reducing species is sufficient to reduce the total amount of precursor present in the solution. This novel approach leads to the formation of 2.3 ± 0.5 nm Ir nanoparticles distributed along the surface of the support. The oxygenated functionalities of graphene oxide served as nucleation sites for the formation of Ir nuclei and their subsequent growth. XPS results revealed that the interaction of Ir with the support occurs through Irsbnd O bonds.

  10. Evaluation of oxide-coated iridium-rhenium chambers

    NASA Technical Reports Server (NTRS)

    Reed, Brian D.

    1994-01-01

    Iridium-coated rhenium (Ir-Re) provides long life operation of radiation-cooled rockets at temperatures up to 2200 C. Ceramic oxide coatings could be used to increase Ir-Re rocket lifetimes and allow operation in highly oxidizing environments. Ceramic oxide coatings promise to serve as both thermal and diffusion barriers for the iridium layer. Seven ceramic oxide-coated Ir-Re, 22-N rocket chambers were tested with gaseous hydrogen/gaseous oxygen (GHz/G02) propellants. Five chambers had thick (over 10 mils), monolithic coatings of either hafnia (HfO2) or zirconia (ZrO2). Two chambers had coatings with thicknesses less than 5 mils. One of these chambers had a thin-walled coating of ZrO2 infiltrated with sol gel HfO2. The other chamber had a coating composed of an Ir-oxide composite. The purpose of this test program was to assess the ability of the oxide coatings to withstand the thermal shock of combustion initiation, adhere under repeated thermal cycling, and operate in aggressively oxidizing environments. All of the coatings survived the thermal shock of combustion and demonstrated operation at mixture ratios up to 11. Testing the Ir-oxide composite-coated chamber included over 29 min at mixture ratio 16. The thicker walled coatings provided the larger temperature drops across the oxide layer (up to 570 C), but were susceptible to macrocracking and eventual chipping at a stress concentrator. The cracks apparently resealed during firing, under compression of the oxide layer. The thinner walled coatings did not experience the macrocracking and chipping of the chambers that was seen with the thick, monolithic coatings. However, burn-throughs in the throat region did occur in both of the thin-walled chambers at mixture ratios well above stoichiometric. The burn-throughs were probably the result of oxygen diffusion through the oxide coating that allowed the underlying Ir and Re layers to be oxidized. The results of this test program indicated that the thin-walled oxide

  11. Evaluation of oxide-coated iridium-rhenium chambers

    NASA Astrophysics Data System (ADS)

    Reed, Brian D.

    1994-03-01

    Iridium-coated rhenium (Ir-Re) provides long life operation of radiation-cooled rockets at temperatures up to 2200 C. Ceramic oxide coatings could be used to increase Ir-Re rocket lifetimes and allow operation in highly oxidizing environments. Ceramic oxide coatings promise to serve as both thermal and diffusion barriers for the iridium layer. Seven ceramic oxide-coated Ir-Re, 22-N rocket chambers were tested with gaseous hydrogen/gaseous oxygen (GHz/G02) propellants. Five chambers had thick (over 10 mils), monolithic coatings of either hafnia (HfO2) or zirconia (ZrO2). Two chambers had coatings with thicknesses less than 5 mils. One of these chambers had a thin-walled coating of ZrO2 infiltrated with sol gel HfO2. The other chamber had a coating composed of an Ir-oxide composite. The purpose of this test program was to assess the ability of the oxide coatings to withstand the thermal shock of combustion initiation, adhere under repeated thermal cycling, and operate in aggressively oxidizing environments. All of the coatings survived the thermal shock of combustion and demonstrated operation at mixture ratios up to 11. Testing the Ir-oxide composite-coated chamber included over 29 min at mixture ratio 16. The thicker walled coatings provided the larger temperature drops across the oxide layer (up to 570 C), but were susceptible to macrocracking and eventual chipping at a stress concentrator. The cracks apparently resealed during firing, under compression of the oxide layer. The thinner walled coatings did not experience the macrocracking and chipping of the chambers that was seen with the thick, monolithic coatings. However, burn-throughs in the throat region did occur in both of the thin-walled chambers at mixture ratios well above stoichiometric. The burn-throughs were probably the result of oxygen diffusion through the oxide coating that allowed the underlying Ir and Re layers to be oxidized. The results of this test program indicated that the thin-walled oxide

  12. Development and Testing of High Surface Area Iridium Anodes for Molten Oxide Electrolysis

    NASA Technical Reports Server (NTRS)

    Shchetkovskiy, Anatoliy; McKechnie, Timothy; Sadoway, Donald R.; Paramore, James; Melendez, Orlando; Curreri, Peter A.

    2010-01-01

    Processing of lunar regolith into oxygen for habitat and propulsion is needed to support future space missions. Direct electrochemical reduction of molten regolith is an attractive method of processing, because no additional chemical reagents are needed. The electrochemical processing of molten oxides requires high surface area, inert anodes. Such electrodes need to be structurally robust at elevated temperatures (1400-1600?C), be resistant to thermal shock, have good electrical conductivity, be resistant to attack by molten oxide (silicate), be electrochemically stable and support high current density. Iridium with its high melting point, good oxidation resistance, superior high temperature strength and ductility is the most promising candidate for anodes in high temperature electrochemical processes. Several innovative concepts for manufacturing such anodes by electrodeposition of iridium from molten salt electrolyte (EL-Form? process) were evaluated. Iridium electrodeposition to form of complex shape components and coating was investigated. Iridium coated graphite, porous iridium structure and solid iridium anodes were fabricated. Testing of electroformed iridium anodes shows no visible degradation. The result of development, manufacturing and testing of high surface, inert iridium anodes will be presented.

  13. Development and Testing of High Surface Area Iridium Anodes for Molten Oxide Electrolysis

    NASA Technical Reports Server (NTRS)

    Shchetkovskiy, Anatoliy; McKechnie, Timothy; Sadoway, Donald R.; Paramore, James; Melendez, Orlando; Curreri, Peter A.

    2010-01-01

    Processing of lunar regolith into oxygen for habitat and propulsion is needed to support future space missions. Direct electrochemical reduction of molten regolith is an attractive method of processing, because no additional chemical reagents are needed. The electrochemical processing of molten oxides requires high surface area, inert anodes. Such electrodes need to be structurally robust at elevated temperatures (1400-1600 C), be resistant to thermal shock, have good electrical conductivity, be resistant to attack by molten oxide (silicate), be electrochemically stable and support high current density. Iridium with its high melting point, good oxidation resistance, superior high temperature strength and ductility is the most promising candidate for anodes in high temperature electrochemical processes. Several innovative concepts for manufacturing such anodes by electrodeposition of iridium from molten salt electrolyte (EL-Form process) were evaluated. Iridium electrodeposition to form of complex shape components and coating was investigated. Iridium coated graphite, porous iridium structure and solid iridium anodes were fabricated. Testing of electroformed iridium anodes shows no visible degradation. The result of development, manufacturing and testing of high surface, inert iridium anodes will be presented.

  14. High-Temperature Oxidation Behavior of Iridium-Rhenium Alloys

    NASA Technical Reports Server (NTRS)

    Reed, Brian D.

    1995-01-01

    The life-limiting mechanism for radiation-cooled rockets made from iridium-coated rhenium (Ir/Re) is the diffusion of Re into the Ir layer and the subsequent oxidation of the resulting Ir-Re alloy from the inner surface. In a previous study, a life model for Ir/Re rockets was developed. It incorporated Ir-Re diffusion and oxidation data to predict chamber lifetimes as a function of temperature and oxygen partial pressure. Oxidation testing at 1540 deg C suggested that a 20-wt percent Re concentration at the inner wall surface should be established as the failure criterion. The present study was performed to better define Ir-oxidation behavior as a function of Re concentration and to supplement the data base for the life model. Samples ranging from pure Ir to Ir-40 wt percent Re (Ir-40Re) were tested at 1500 deg C, in two different oxygen environments. There were indications that the oxidation rate of the Ir-Re alloy increased significantly when it went from a single-phase solid solution to a two-phase mixture, as was suggested in previous work. However, because of testing anomalies in this study, there were not enough dependable oxidation data to definitively raise the Ir/Re rocket failure criterion from 20-wt percent Re to a Re concentration corresponding to entry into the two-phase region.

  15. Iridium-based double perovskites for efficient water oxidation in acid media

    NASA Astrophysics Data System (ADS)

    Diaz-Morales, Oscar; Raaijman, Stefan; Kortlever, Ruud; Kooyman, Patricia J.; Wezendonk, Tim; Gascon, Jorge; Fu, W. T.; Koper, Marc T. M.

    2016-08-01

    The development of active, cost-effective and stable oxygen-evolving catalysts is one of the major challenges for solar-to-fuel conversion towards sustainable energy generation. Iridium oxide exhibits the best available compromise between catalytic activity and stability in acid media, but it is prohibitively expensive for large-scale applications. Therefore, preparing oxygen-evolving catalysts with lower amounts of the scarce but active and stable iridium is an attractive avenue to overcome this economical constraint. Here we report on a class of oxygen-evolving catalysts based on iridium double perovskites which contain 32 wt% less iridium than IrO2 and yet exhibit a more than threefold higher activity in acid media. According to recently suggested benchmarking criteria, the iridium double perovskites are the most active catalysts for oxygen evolution in acid media reported until now, to the best of our knowledge, and exhibit similar stability to IrO2.

  16. Iridium-based double perovskites for efficient water oxidation in acid media

    PubMed Central

    Diaz-Morales, Oscar; Raaijman, Stefan; Kortlever, Ruud; Kooyman, Patricia J.; Wezendonk, Tim; Gascon, Jorge; Fu, W. T.; Koper, Marc T. M.

    2016-01-01

    The development of active, cost-effective and stable oxygen-evolving catalysts is one of the major challenges for solar-to-fuel conversion towards sustainable energy generation. Iridium oxide exhibits the best available compromise between catalytic activity and stability in acid media, but it is prohibitively expensive for large-scale applications. Therefore, preparing oxygen-evolving catalysts with lower amounts of the scarce but active and stable iridium is an attractive avenue to overcome this economical constraint. Here we report on a class of oxygen-evolving catalysts based on iridium double perovskites which contain 32 wt% less iridium than IrO2 and yet exhibit a more than threefold higher activity in acid media. According to recently suggested benchmarking criteria, the iridium double perovskites are the most active catalysts for oxygen evolution in acid media reported until now, to the best of our knowledge, and exhibit similar stability to IrO2. PMID:27498694

  17. Iridium-based double perovskites for efficient water oxidation in acid media.

    PubMed

    Diaz-Morales, Oscar; Raaijman, Stefan; Kortlever, Ruud; Kooyman, Patricia J; Wezendonk, Tim; Gascon, Jorge; Fu, W T; Koper, Marc T M

    2016-01-01

    The development of active, cost-effective and stable oxygen-evolving catalysts is one of the major challenges for solar-to-fuel conversion towards sustainable energy generation. Iridium oxide exhibits the best available compromise between catalytic activity and stability in acid media, but it is prohibitively expensive for large-scale applications. Therefore, preparing oxygen-evolving catalysts with lower amounts of the scarce but active and stable iridium is an attractive avenue to overcome this economical constraint. Here we report on a class of oxygen-evolving catalysts based on iridium double perovskites which contain 32 wt% less iridium than IrO2 and yet exhibit a more than threefold higher activity in acid media. According to recently suggested benchmarking criteria, the iridium double perovskites are the most active catalysts for oxygen evolution in acid media reported until now, to the best of our knowledge, and exhibit similar stability to IrO2. PMID:27498694

  18. In vitro electrical properties for iridium oxide versus titanium nitride stimulating electrodes.

    PubMed

    Weiland, James D; Anderson, David J; Humayun, Mark S

    2002-12-01

    Stimulating electrode materials must be capable of supplying high-density electrical charge to effectively activate neural tissue. Platinum is the most commonly used material for neural stimulation. Two other materials have been considered: iridium oxide and titanium nitride. This study directly compared the electrical characteristics of iridium oxide and titanium nitride by fabricating silicon substrate probes that differed only in the material used to form the electrode. Electrochemical measurements indicated that iridium oxide had lower impedance and a higher charge storage capacity than titanium nitride, suggesting better performance as a stimulating electrode. Direct measurement of the electrode potential in response to a biphasic current pulse confirmed that iridium oxide uses less voltage to transfer the same amount of charge, therefore using less power. The charge injection limit for titanium nitride was 0.87 mC/cm2, contradicting other reports estimating that titanium nitride was capable of injecting 22 mC/cm2. Iridium oxide charge storage was 4 mC/cm2, which is comparable to other published values for iridium oxide. Electrode efficiency will lead to an overall more efficient and effective device.

  19. Transformation of a Cp*-iridium(III) precatalyst for water oxidation when exposed to oxidative stress.

    PubMed

    Zuccaccia, Cristiano; Bellachioma, Gianfranco; Bortolini, Olga; Bucci, Alberto; Savini, Arianna; Macchioni, Alceo

    2014-03-17

    The reaction of [Cp*Ir(bzpy)NO3 ] (1; bzpy=2-benzoylpyridine, Cp*=pentamethylcyclopentadienyl anion), a competent water-oxidation catalyst, with several oxidants (H2 O2 , NaIO4 , cerium ammonium nitrate (CAN)) was studied to intercept and characterize possible intermediates of the oxidative transformation. NMR spectroscopy and ESI-MS techniques provided evidence for the formation of many species that all had the intact Ir-bzpy moiety and a gradually more oxidized Cp* ligand. Initially, an oxygen atom is trapped in between two carbon atoms of Cp* and iridium, which gives an oxygen-Ir coordinated epoxide, whereas the remaining three carbon atoms of Cp* are involved in a η(3) interaction with iridium (2 a). Formal addition of H2 O to 2 a or H2 O2 to 1 leads to 2 b, in which a double MeCOH functionalization of Cp* is present with one MeCOH engaged in an interaction with iridium. The structure of 2 b was unambiguously determined in the solid state and in solution by X-ray single-crystal diffractometry and advanced NMR spectroscopic techniques, respectively. Further oxidation led to the opening of Cp* and transformation of the diol into a diketone with one carbonyl coordinated at the metal (2 c). A η(3) interaction between the three non-oxygenated carbons of "ex-Cp*" and iridium is also present in both 2 b and 2 c. Isolated 2 b and mixtures of 2 a-c species were tested in water-oxidation catalysis by using CAN as sacrificial oxidant. They showed substantially the same activity than 1 (turnover frequency values ranged from 9 to 14 min(-1) ). PMID:24523138

  20. Transformation of a Cp*-iridium(III) precatalyst for water oxidation when exposed to oxidative stress.

    PubMed

    Zuccaccia, Cristiano; Bellachioma, Gianfranco; Bortolini, Olga; Bucci, Alberto; Savini, Arianna; Macchioni, Alceo

    2014-03-17

    The reaction of [Cp*Ir(bzpy)NO3 ] (1; bzpy=2-benzoylpyridine, Cp*=pentamethylcyclopentadienyl anion), a competent water-oxidation catalyst, with several oxidants (H2 O2 , NaIO4 , cerium ammonium nitrate (CAN)) was studied to intercept and characterize possible intermediates of the oxidative transformation. NMR spectroscopy and ESI-MS techniques provided evidence for the formation of many species that all had the intact Ir-bzpy moiety and a gradually more oxidized Cp* ligand. Initially, an oxygen atom is trapped in between two carbon atoms of Cp* and iridium, which gives an oxygen-Ir coordinated epoxide, whereas the remaining three carbon atoms of Cp* are involved in a η(3) interaction with iridium (2 a). Formal addition of H2 O to 2 a or H2 O2 to 1 leads to 2 b, in which a double MeCOH functionalization of Cp* is present with one MeCOH engaged in an interaction with iridium. The structure of 2 b was unambiguously determined in the solid state and in solution by X-ray single-crystal diffractometry and advanced NMR spectroscopic techniques, respectively. Further oxidation led to the opening of Cp* and transformation of the diol into a diketone with one carbonyl coordinated at the metal (2 c). A η(3) interaction between the three non-oxygenated carbons of "ex-Cp*" and iridium is also present in both 2 b and 2 c. Isolated 2 b and mixtures of 2 a-c species were tested in water-oxidation catalysis by using CAN as sacrificial oxidant. They showed substantially the same activity than 1 (turnover frequency values ranged from 9 to 14 min(-1) ).

  1. Design, analysis, and fabrication of oxide-coated iridium/rhenium combustion chambers

    NASA Astrophysics Data System (ADS)

    Jang, Q.; Tuffias, R. H.; Laferla, R.; Ghoniem, N. M.

    1993-11-01

    Iridium-coated rhenium (Ir/Re) combustion chambers provide high temperature, oxidation-resistant operation for radiation-cooled liquid-fueled rocket engines. A 22-N (5-lb(sub f)) chamber has been operated for 15 hours at 2200 C (4000 F) using nitrogen tetroxide/monomethyl hydrazine (NTO/MMH) propellant, with negligible internal erosion. The oxidation resistance of these chambers could be further increased by the addition of refractory oxide coatings, providing longer life and/or operation in more oxidizing and higher temperature environments. The oxide coatings would serve as a thermal and diffusion barrier for the iridium coating, lowering the temperature of the iridium layer while also preventing the ingress of oxygen and egress of iridium oxides. This would serve to slow the failure mechanisms of Ir/Re chambers, namely the diffusion of rhenium to the inner surface and the oxidation of iridium. Such protection could extend chamber lifetimes by tens or perhaps hundreds of hours, and allow chamber operation on stoichiometric or higher mixture ratio oxygen/hydrogen (O2/H2) propellant. Extensive thermomechanical, thermochemical, and mass transport modeling was performed as a key material/structure design tool. Based on the results of these analyses, several 22-N oxide-coated Ir/Re chambers were fabricated and delivered to NASA Lewis Research Center for hot-fire testing.

  2. Design, analysis, and fabrication of oxide-coated iridium/rhenium combustion chambers

    NASA Technical Reports Server (NTRS)

    Jang, Q.; Tuffias, R. H.; Laferla, R.; Ghoniem, N. M.

    1993-01-01

    Iridium-coated rhenium (Ir/Re) combustion chambers provide high temperature, oxidation-resistant operation for radiation-cooled liquid-fueled rocket engines. A 22-N (5-lb(sub f)) chamber has been operated for 15 hours at 2200 C (4000 F) using nitrogen tetroxide/monomethyl hydrazine (NTO/MMH) propellant, with negligible internal erosion. The oxidation resistance of these chambers could be further increased by the addition of refractory oxide coatings, providing longer life and/or operation in more oxidizing and higher temperature environments. The oxide coatings would serve as a thermal and diffusion barrier for the iridium coating, lowering the temperature of the iridium layer while also preventing the ingress of oxygen and egress of iridium oxides. This would serve to slow the failure mechanisms of Ir/Re chambers, namely the diffusion of rhenium to the inner surface and the oxidation of iridium. Such protection could extend chamber lifetimes by tens or perhaps hundreds of hours, and allow chamber operation on stoichiometric or higher mixture ratio oxygen/hydrogen (O2/H2) propellant. Extensive thermomechanical, thermochemical, and mass transport modeling was performed as a key material/structure design tool. Based on the results of these analyses, several 22-N oxide-coated Ir/Re chambers were fabricated and delivered to NASA Lewis Research Center for hot-fire testing.

  3. Heterogeneous Catalysis for Water Oxidation by an Iridium Complex Immobilized on Bipyridine-Periodic Mesoporous Organosilica.

    PubMed

    Liu, Xiao; Maegawa, Yoshifumi; Goto, Yasutomo; Hara, Kenji; Inagaki, Shinji

    2016-07-01

    Heterogenization of metal-complex catalysts for water oxidation without loss of their catalytic activity is important for the development of devices simulating photosynthesis. In this study, efficient heterogeneous iridium complexes for water oxidation were prepared using bipyridine-bridged periodic mesoporous organosilica (BPy-PMO) as a solid chelating ligand. The BPy-PMO-based iridium catalysts (Ir-BPy-PMO) were prepared by postsynthetic metalation of BPy-PMO and characterized through physicochemical analyses. The Ir-BPy-PMOs showed high catalytic activity for water oxidation. The turnover frequency (TOF) values for Ir-BPy-PMOs were one order of magnitude higher than those of conventional heterogeneous iridium catalysts. The reusability and stability of Ir-BPy-PMO were also examined, and detailed characterization was conducted using powder X-ray diffraction, nitrogen adsorption, (13) C DD MAS NMR spectroscopy, TEM, and XAFS methods. PMID:27168492

  4. Testing and evaluation of oxide-coated iridium/rhenium chambers

    NASA Technical Reports Server (NTRS)

    Reed, Brian D.

    1993-01-01

    Iridium-coated rhenium provides long life operation of radiation-cooled rockets at temperatures up to 2200 C. Ceramic oxide coatings could be used to increase iridium/rhenium rocket lifetimes and allow operation in highly oxidizing environments. Ceramic oxide coatings promise to serve as both thermal and diffusion barriers for the iridium layer. Seven ceramic oxide-coated iridium/rhenium, 22 N rocket chambers were tested on gaseous hydrogen/gaseous oxygen propellants. Five chambers had thick (over 10 mils), monolithic coatings of either hafnia or zirconia. Two chambers had coatings with thicknesses less than 5 mils. One of these chambers had a thin-walled coating of zirconia infiltrated with sol gel hafnia. The other chamber had a coating composed of an iridium/oxide composite. The purpose of this test program was to assess the ability of the oxide coatings to withstand the thermal shock of combustion initiation, adhere under repeated thermal cycling, and operate in aggressively oxidizing environments. All of the coatings survived the thermal shock of combustion and demonstrated operation at mixture ratios up to 11. The iridium/oxide composite coated chamber included testing for over 29 minutes at mixture ratio 16. The thicker-walled coatings provided the larger temperature drops across the oxide layer (up to 570 C), but were susceptible to macrocracking and eventual chipping at a stress concentrator. The cracks apparently resealed during firing, under compression of the oxide layer. The thinner-walled coatings did not experience the macrocracking and chipping of the chambers seen with the thick, monolithic coatings. However, burnthroughs in the throat region did occur in both of the thin-walled chambers at mixture ratios well above stochiometric. The burn-throughs were probably the result of oxygen-diffusion through the oxide coating that allowed the underlying iridium and rhenium layers to be oxidized. The results of this test program indicated that the thin

  5. Iridium oxide pH sensor for biomedical applications. Case urea-urease in real urine samples.

    PubMed

    Prats-Alfonso, Elisabet; Abad, Llibertat; Casañ-Pastor, Nieves; Gonzalo-Ruiz, Javier; Baldrich, Eva

    2013-01-15

    This work demonstrates the implementation of iridium oxide films (IROF) grown on silicon-based thin-film platinum microelectrodes, their utilization as a pH sensor, and their successful formatting into a urea pH sensor. In this context, Pt electrodes were fabricated on Silicon by using standard photolithography and lift-off procedures and IROF thin films were growth by a dynamic oxidation electrodeposition method (AEIROF). The AEIROF pH sensor reported showed a super-Nerstian (72.9±0.9mV/pH) response between pH 3 and 11, with residual standard deviation of both repeatability and reproducibility below 5%, and resolution of 0.03 pH units. For their application as urea pH sensors, AEIROF electrodes were reversibly modified with urease-coated magnetic microparticles (MP) using a magnet. The urea pH sensor provided fast detection of urea between 78μM and 20mM in saline solution, in sample volumes of just 50μL. The applicability to urea determination in real urine samples is discussed.

  6. Donor-Flexible Nitrogen Ligands for Efficient Iridium-Catalyzed Water Oxidation Catalysis.

    PubMed

    Navarro, Miquel; Li, Mo; Müller-Bunz, Helge; Bernhard, Stefan; Albrecht, Martin

    2016-05-10

    A pyridylideneamide ligand with variable donor properties owing to a pronounced zwitterionic and a neutral diene-type resonance structure was used as a dynamic ligand at a Cp* iridium center to facilitate water oxidation catalysis, a reaction that requires the stabilization of a variety of different iridium oxidation states and that is key for developing an efficient solar fuel device. The ligand imparts high activity (nearly three-fold increase of turnover frequency compared to benchmark systems), and exceptionally high turnover numbers, which indicate a robust catalytic cycle and little catalyst degradation.

  7. Implications of chronic daily anti-oxidant administration on the inflammatory response to intracortical microelectrodes

    NASA Astrophysics Data System (ADS)

    Potter-Baker, Kelsey A.; Stewart, Wade G.; Tomaszewski, William H.; Wong, Chun T.; Meador, William D.; Ziats, Nicholas P.; Capadona, Jeffrey R.

    2015-08-01

    Objective. Oxidative stress events have been implicated to occur and facilitate multiple failure modes of intracortical microelectrodes. The goal of the present study was to evaluate the ability of a sustained concentration of an anti-oxidant and to reduce oxidative stress-mediated neurodegeneration for the application of intracortical microelectrodes. Approach. Non-functional microelectrodes were implanted into the cortex of male Sprague Dawley rats for up to sixteen weeks. Half of the animals received a daily intraperitoneal injection of the natural anti-oxidant resveratrol, at 30 mg kg-1. The study was designed to investigate the biodistribution of the resveratrol, and the effects on neuroinflammation/neuroprotection following device implantation. Main results. Daily maintenance of a sustained range of resveratrol throughout the implantation period resulted in fewer degenerating neurons in comparison to control animals at both two and sixteen weeks post implantation. Initial and chronic improvements in neuronal viability in resveratrol-dosed animals were correlated with significant reductions in local superoxide anion accumulation around the implanted device at two weeks after implantation. Controls, receiving only saline injections, were also found to have reduced amounts of accumulated superoxide anion locally and less neurodegeneration than controls at sixteen weeks post-implantation. Despite observed benefits, thread-like adhesions were found between the liver and diaphragm in resveratrol-dosed animals. Significance. Overall, our chronic daily anti-oxidant dosing scheme resulted in improvements in neuronal viability surrounding implanted microelectrodes, which could result in improved device performance. However, due to the discovery of thread-like adhesions, further work is still required to optimize a chronic anti-oxidant dosing regime for the application of intracortical microelectrodes.

  8. Implications of Chronic Daily Anti-Oxidant Administration on the Inflammatory Response to Intracortical Microelectrodes

    PubMed Central

    Potter-Baker, Kelsey A.; Stewart, Wade G.; Tomaszewski, William H.; Wong, Chun T.; Meador, William D.; Ziats, Nicholas P.; Capadona, Jeffrey R.

    2015-01-01

    Objective Oxidative stress events have been implicated to occur and facilitate multiple failure modes of intracortical microelectrodes. The goal of the present study was to evaluate the ability of a sustained concentration of an anti-oxidant and to reduce oxidative stress-mediated neurodegeneration for the application of intracortical microelectrodes. Approach Non-functional microelectrodes were implanted into the cortex of male Sprague Dawley rats for up to sixteen weeks. Half of the animals received a daily intraperitoneal injection of the natural anti-oxidant resveratrol, at 30 mg/kg. The study was designed to investigate the biodistribution of the resveratrol, and the effects on neuroinflammation/neuroprotection following device implantation. Main Results Daily maintenance of a sustained range of resveratrol throughout the implantation period resulted in fewer degenerating neurons in comparison to control animals at both two and sixteen weeks post implantation. Initial and chronic improvements in neuronal viability in resveratrol-dosed animals were correlated with significant reductions in local superoxide anion accumulation around the implanted device at two weeks after implantation. Controls, receiving only saline injections, were also found to have reduced amounts of accumulated superoxide anion locally and less neurodegeneration than controls at sixteen weeks post-implantation. Despite observed benefits, thread-like adhesions were found between the liver and diaphragm in resveratrol-dosed animals. Significance Overall, our chronic daily anti-oxidant dosing scheme resulted in improvements in neuronal viability surrounding implanted microelectrodes, which could result in improved device performance. However, due to the discovery of thread-like adhesions, further work is still required to optimize a chronic anti-oxidant dosing regime for the application of intracortical microelectrodes. PMID:26015427

  9. Identification of an iridium-containing compound with a formal oxidation state of IX.

    PubMed

    Wang, Guanjun; Zhou, Mingfei; Goettel, James T; Schrobilgen, Gary J; Su, Jing; Li, Jun; Schlöder, Tobias; Riedel, Sebastian

    2014-10-23

    One of the most important classifications in chemistry and within the periodic table is the concept of formal oxidation states. The preparation and characterization of compounds containing elements with unusual oxidation states is of great interest to chemists. The highest experimentally known formal oxidation state of any chemical element is at present VIII, although higher oxidation states have been postulated. Compounds with oxidation state VIII include several xenon compounds (for example XeO4 and XeO3F2) and the well-characterized species RuO4 and OsO4 (refs 2-4). Iridium, which has nine valence electrons, is predicted to have the greatest chance of being oxidized beyond the VIII oxidation state. In recent matrix-isolation experiments, the IrO4 molecule was characterized as an isolated molecule in rare-gas matrices. The valence electron configuration of iridium in IrO4 is 5d(1), with a formal oxidation state of VIII. Removal of the remaining d electron from IrO4 would lead to the iridium tetroxide cation ([IrO4](+)), which was recently predicted to be stable and in which iridium is in a formal oxidation state of IX. There has been some speculation about the formation of [IrO4](+) species, but these experimental observations have not been structurally confirmed. Here we report the formation of [IrO4](+) and its identification by infrared photodissociation spectroscopy. Quantum-chemical calculations were carried out at the highest level of theory that is available today, and predict that the iridium tetroxide cation, with a Td-symmetrical structure and a d(0) electron configuration, is the most stable of all possible [IrO4](+) isomers. PMID:25341786

  10. Identification of an iridium-containing compound with a formal oxidation state of IX

    NASA Astrophysics Data System (ADS)

    Wang, Guanjun; Zhou, Mingfei; Goettel, James T.; Schrobilgen, Gary J.; Su, Jing; Li, Jun; Schlöder, Tobias; Riedel, Sebastian

    2014-10-01

    One of the most important classifications in chemistry and within the periodic table is the concept of formal oxidation states. The preparation and characterization of compounds containing elements with unusual oxidation states is of great interest to chemists. The highest experimentally known formal oxidation state of any chemical element is at present VIII, although higher oxidation states have been postulated. Compounds with oxidation state VIII include several xenon compounds (for example XeO4 and XeO3F2) and the well-characterized species RuO4 and OsO4 (refs 2, 3, 4). Iridium, which has nine valence electrons, is predicted to have the greatest chance of being oxidized beyond the VIII oxidation state. In recent matrix-isolation experiments, the IrO4 molecule was characterized as an isolated molecule in rare-gas matrices. The valence electron configuration of iridium in IrO4 is 5d1, with a formal oxidation state of VIII. Removal of the remaining d electron from IrO4 would lead to the iridium tetroxide cation ([IrO4]+), which was recently predicted to be stable and in which iridium is in a formal oxidation state of IX. There has been some speculation about the formation of [IrO4]+ species, but these experimental observations have not been structurally confirmed. Here we report the formation of [IrO4]+ and its identification by infrared photodissociation spectroscopy. Quantum-chemical calculations were carried out at the highest level of theory that is available today, and predict that the iridium tetroxide cation, with a Td-symmetrical structure and a d0 electron configuration, is the most stable of all possible [IrO4]+ isomers.

  11. Comparative assessment of iridium oxide and platinum alloy wires using an in vitro glial scar assay.

    PubMed

    Ereifej, Evon S; Khan, Saida; Newaz, Golam; Zhang, Jinsheng; Auner, Gregory W; VandeVord, Pamela J

    2013-12-01

    The long-term effect of chronically implanted electrodes is the formation of a glial scar. Therefore, it is imperative to assess the biocompatibility of materials before employing them in neural electrode fabrication. Platinum alloy and iridium oxide have been identified as good candidates as neural electrode biomaterials due to their mechanical and electrical properties, however, effect of glial scar formation for these two materials is lacking. In this study, we applied a glial scarring assay to observe the cellular reactivity to platinum alloy and iridium oxide wires in order to assess the biocompatibility based on previously defined characteristics. Through real-time PCR, immunostaining and imaging techniques, we will advance the understanding of the biocompatibility of these materials. Results of this study demonstrate iridium oxide wires exhibited a more significant reactive response as compared to platinum alloy wires. Cells cultured with platinum alloy wires had less GFAP gene expression, lower average GFAP intensity, and smaller glial scar thickness. Collectively, these results indicated that platinum alloy wires were more biocompatible than the iridium oxide wires.

  12. A pH Sensor Based on a Stainless Steel Electrode Electrodeposited with Iridium Oxide

    ERIC Educational Resources Information Center

    Martinez, C. C. M.; Madrid, R. E.; Felice, C. J.

    2009-01-01

    A simple procedure to make an iridium oxide (IrO[subscript 2]) electrodeposited pH sensor, that can be used in a chemical, biomedical, or materials laboratory, is presented here. Some exercises, based on this sensor, that can be used to teach important concepts in the field of biomedical, biochemical, tissue, or materials engineering, are also…

  13. Luminescent Iridium(III) Complex Labeled DNA for Graphene Oxide-Based Biosensors.

    PubMed

    Zhao, Qingcheng; Zhou, Yuyang; Li, Yingying; Gu, Wei; Zhang, Qi; Liu, Jian

    2016-02-01

    There has been growing interest in utilizing highly photostable iridium(III) complexes as new luminescent probes for biotechnology and life science. Herein, iridium(III) complex with carboxyl group was synthesized and activated with N-hydroxysuccinimide, followed by tagging to the amino terminate of single-stranded DNA (ssDNA). The Ir-ssDNA probe was further combined with graphene oxide (GO) nanosheets to develop a GO-based biosensor for target ssDNA detection. The quenching efficiency of GO, and the photostability of iridium(III) complex and GO-Ir-ssDNA biosensor, were also investigated. On the basis of the high luminescence quenching efficiency of GO toward iridium(III) complex, the GO-Ir-ssDNA biosensor exhibited minimal background signals, while strong emission was observed when Ir-ssDNA desorbed from GO nanosheets and formed a double helix with the specific target, leading to a high signal-to-background ratio. Moreover, it was found that luminescent intensities of iridium(III) complex and GO-Ir-ssDNA biosensor were around 15 and 3 times higher than those of the traditional carboxyl fluorescein (FAM) dye and the GO-FAM-ssDNA biosensor after UV irradiation, respectively. Our study suggested the sensitive and selective Ir-ssDNA probe was suitable for the development of highly photostable GO-based detection platforms, showing promise for application beyond the OLED (organic light emitting diode) area. PMID:26753824

  14. Highly Active Iridium/Iridium Tin/Tin Oxide Heterogeneous Nanoparticles as Alternative Electrocatalysts for the Ethanol Oxidation Reaction

    SciTech Connect

    Du W.; Su D.; Wang Q.; Saxner D.; Deskins N.A.; Krzanowski J.E.; Frenkel A.I.; Teng X.

    2011-08-03

    Ethanol is a promising fuel for low-temperature direct fuel cell reactions due to its low toxicity, ease of storage and transportation, high-energy density, and availability from biomass. However, the implementation of ethanol fuel cell technology has been hindered by the lack of low-cost, highly active anode catalysts. In this paper, we have studied Iridium (Ir)-based binary catalysts as low-cost alternative electrocatalysts replacing platinum (Pt)-based catalysts for the direct ethanol fuel cell (DEFC) reaction. We report the synthesis of carbon supported Ir{sub 71}Sn{sub 29} catalysts with an average diameter of 2.7 {+-} 0.6 nm through a 'surfactant-free' wet chemistry approach. The complementary characterization techniques, including aberration-corrected scanning transmission electron microscopy equipped with electron energy loss spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy, are used to identify the 'real' heterogeneous structure of Ir{sub 71}Sn{sub 29}/C particles as Ir/Ir-Sn/SnO{sub 2}, which consists of an Ir-rich core and an Ir-Sn alloy shell with SnO{sub 2} present on the surface. The Ir{sub 71}Sn{sub 29}/C heterogeneous catalyst exhibited high electrochemical activity toward the ethanol oxidation reaction compared to the commercial Pt/C (ETEK), PtRu/C (Johnson Matthey) as well as PtSn/C catalysts. Electrochemical measurements and density functional theory calculations demonstrate that the superior electro-activity is directly related to the high degree of Ir-Sn alloy formation as well as the existence of nonalloyed SnO{sub 2} on surface. Our cross-disciplinary work, from novel 'surfactant-free' synthesis of Ir-Sn catalysts, theoretical simulations, and catalytic measurements to the characterizations of 'real' heterogeneous nanostructures, will not only highlight the intriguing structure-property correlations in nanosized catalysts but also have a transformative impact on the commercialization of DEFC

  15. Iridium/Iridium Silicide as an Oxidation Resistant Capping Layer for Soft X-ray Mirrors

    SciTech Connect

    Prisbrey, S; Vernon, S

    2004-04-05

    Rust on a sword, tarnish on the silverware, and a loss in reflectivity for soft x-ray mirrors are all caused by oxidation that changes the desired characteristics of a material. Methods to prevent the oxidation have varied over the centuries with the default method of a protective coating being the most common. The protective coating for x-ray mirrors is usually a self-limiting oxidized layer on the surface of the material that stops further oxidation of the material by limiting the diffusion of oxygen to the material underneath.

  16. Half-sandwich iridium complexes for homogeneous water-oxidation catalysis.

    PubMed

    Blakemore, James D; Schley, Nathan D; Balcells, David; Hull, Jonathan F; Olack, Gerard W; Incarvito, Christopher D; Eisenstein, Odile; Brudvig, Gary W; Crabtree, Robert H

    2010-11-17

    Iridium half-sandwich complexes of the types Cp*Ir(N-C)X, [Cp*Ir(N-N)X]X, and [CpIr(N-N)X]X are catalyst precursors for the homogeneous oxidation of water to dioxygen. Kinetic studies with cerium(IV) ammonium nitrate as primary oxidant show that oxygen evolution is rapid and continues over many hours. In addition, [Cp*Ir(H(2)O)(3)]SO(4) and [(Cp*Ir)(2)(μ-OH)(3)]OH can show even higher turnover frequencies (up to 20 min(-1) at pH 0.89). Aqueous electrochemical studies on the cationic complexes having chelate ligands show catalytic oxidation at pH > 7; conversely, at low pH, there are no oxidation waves up to 1.5 V vs NHE for the complexes. H(2)(18)O isotope incorporation studies demonstrate that water is the source of oxygen atoms during cerium(IV)-driven catalysis. DFT calculations and kinetic experiments, including kinetic-isotope-effect studies, suggest a mechanism for homogeneous iridium-catalyzed water oxidation and contribute to the determination of the rate-determining step. The kinetic experiments also help distinguish the active homogeneous catalyst from heterogeneous nanoparticulate iridium dioxide.

  17. Flexible complementary metal oxide semiconductor microelectrode arrays with applications in single cell characterization

    NASA Astrophysics Data System (ADS)

    Pajouhi, H.; Jou, A. Y.; Jain, R.; Ziabari, A.; Shakouri, A.; Savran, C. A.; Mohammadi, S.

    2015-11-01

    A highly flexible microelectrode array with an embedded complementary metal oxide semiconductor (CMOS) instrumentation amplifier suitable for sensing surfaces of biological entities is developed. The array is based on ultrathin CMOS islands that are thermally isolated from each other and are interconnected by meandered nano-scale wires that can adapt to cellular surfaces with micro-scale curvatures. CMOS temperature sensors are placed in the islands and are optimally biased to have high temperature sensitivity. While no live cell thermometry is conducted, a measured temperature sensitivity of 0.15 °C in the temperature range of 35 to 40 °C is achieved by utilizing a low noise CMOS lock-in amplifier implemented in the same technology. The monolithic nature of CMOS sensors and amplifier circuits and their versatile flexible interconnecting wires overcome the sensitivity and yield limitations of microelectrode arrays fabricated in competing technologies.

  18. Anodically Electrodeposited Iridium Oxide Films (AEIROF) from Alkaline Solutions for Electrochromic Display Devices

    NASA Astrophysics Data System (ADS)

    Yamanaka, Kazusuke

    1989-04-01

    Anodically electrodeposited iridium oxide films from alkaline solutions were investigated for application to electrochromic devices. Micro-crystalline (diameter: 15Å) films obtained by the electrolysis of aqueous alkaline solutions containing iridium chloride, oxalic acid and potassium carbonate showed good electrochromic reaction reversibility. The coloration efficiency of the films was about one third that of typical evaporated tungsten oxide films, and the response rate measured by the amount of injected charge was about double. The cycle lives of the cells, composed of electrodeposited films, 1M H3PO4-NaOH (pH{=}3˜ 5), and an activated carbon cloth, were more than 8× 106 with a 0.6 V, 1 Hz continuous square wave.

  19. Strongly improved electrochemical cycling durability by adding iridium to electrochromic nickel oxide films.

    PubMed

    Wen, Rui-Tao; Niklasson, Gunnar A; Granqvist, Claes G

    2015-05-13

    Anodically colored nickel oxide (NiO) thin films are of much interest as counter electrodes in tungsten oxide based electrochromic devices such as "smart windows" for energy-efficient buildings. However, NiO films are prone to suffering severe charge density degradation upon prolonged electrochemical cycling, which can lead to insufficient device lifetime. Therefore, a means to improve the durability of NiO-based films is an important challenge at present. Here we report that the incorporation of a modest amount of iridium into NiO films [Ir/(Ir + Ni) = 7.6 atom %] leads to remarkable durability, exceeding 10000 cycles in a lithium-conducting electrolyte, along with significantly improved optical modulation during extended cycling. Structure characterization showed that the face-centered-cubic-type NiO structure remained after iridium addition. Moreover, the crystallinity of these films was enhanced upon electrochemical cycling. PMID:25919917

  20. A 96-channel neural stimulation system for driving AIROF microelectrodes.

    PubMed

    Hu, Z; Troyk, P; Cogan, S

    2004-01-01

    We present the design and testing of a 96-channel stimulation system to drive activated iridium oxide (AIROF) microelectrodes within safe charge-injection limits. Our system improves upon the traditional capacitively coupled, symmetric charge-balanced biphasic stimulation waveform so as to maximize charge-injection capacity without endangering the microelectrodes. It can deliver computer-controlled cathodic current pulse for to up to 96 AIROF microelectrodes and positively bias them during the inter-pulse interval. The stimulation system is comprised of (1) 12 custom-designed PCB boards each hosting an 8-channel ASIC chip, (2) a motherboard to communicate between these 12 boards and the PC, (3) the PC interface equipped with a DIO card and the corresponding software. We plan to use this system in animal experiments for intracortical neural stimulation of implanted electrodes within our visual prosthesis project. PMID:17271241

  1. Insights into the oxidative dehydrogenation of amines with nanoparticulate iridium oxide.

    PubMed

    Hammond, Ceri; Schümperli, Martin T; Hermans, Ive

    2013-09-23

    The aerobic oxidation of amines offers a promising route towards many versatile chemical compounds. Within this contribution, we extend our previous investigations of iridium oxide-catalyzed alcohol oxidation to amine substrates. In addition to demonstrating the versatility of this catalyst, particular attention is focused on the mechanisms of the reaction. Herein, we demonstrate that although amines are oxidized slower than the corresponding alcohols, the catalyst has a preference for amine substrates, and oxidizes various amines at turnover frequencies greater than other systems found in the open literature. Furthermore, the competition between double amine dehydrogenation, to yield the corresponding nitrile, and amine-imine coupling, to yield the corresponding coupled imine, has been found to arise from a competitive reaction pathway, and stems from an effect of substrate-to-metal ratio. Finally, the mechanism responsible for the formation of N-benzylidene-1-phenylmethanamine was examined, and attributed to the coupling of free benzyl amine substrate and benzaldehyde, formed in situ through hydrolysis of the primary reaction product, benzyl imine. PMID:23939827

  2. Electroanalytical evaluation of antioxidant activity of cerium oxide nanoparticles by nanoparticle collisions at microelectrodes.

    PubMed

    Sardesai, Naimish P; Andreescu, Daniel; Andreescu, Silvana

    2013-11-13

    We describe a simple, cost-effective and rapid electrochemical screening approach to evaluate antioxidant activity of cerium oxide nanoparticles (CeO2 NPs) by single nanoparticle collision at microelectrodes. The method is based on direct monitoring of the interaction between a Pt microelectrode and surface bound superoxo and peroxo anions of CeO2 NPs (Ce-O2(-)/O2(2-)) formed upon exposure to H2O2, selected here as a model reactive oxygen species. We observe an increase in spike current frequency for CeO2 NPs exposed to H2O2, which we attribute to the reduction of surface bound oxygen species when the particles collide with the microelectrode. The results were confirmed with spectroscopic techniques that demonstrate changes in surface reactivity and composition. The spike frequency was found to correlate well with the superoxide dismutase activity of these particles. This approach could enable routine screening of antioxidant NPs using a rapid and inexpensive assay.

  3. Electroanalytical evaluation of antioxidant activity of cerium oxide nanoparticles by nanoparticle collisions at microelectrodes.

    PubMed

    Sardesai, Naimish P; Andreescu, Daniel; Andreescu, Silvana

    2013-11-13

    We describe a simple, cost-effective and rapid electrochemical screening approach to evaluate antioxidant activity of cerium oxide nanoparticles (CeO2 NPs) by single nanoparticle collision at microelectrodes. The method is based on direct monitoring of the interaction between a Pt microelectrode and surface bound superoxo and peroxo anions of CeO2 NPs (Ce-O2(-)/O2(2-)) formed upon exposure to H2O2, selected here as a model reactive oxygen species. We observe an increase in spike current frequency for CeO2 NPs exposed to H2O2, which we attribute to the reduction of surface bound oxygen species when the particles collide with the microelectrode. The results were confirmed with spectroscopic techniques that demonstrate changes in surface reactivity and composition. The spike frequency was found to correlate well with the superoxide dismutase activity of these particles. This approach could enable routine screening of antioxidant NPs using a rapid and inexpensive assay. PMID:24079646

  4. Nanoporous gold supported cobalt oxide microelectrodes as high-performance electrochemical biosensors.

    PubMed

    Lang, Xing-You; Fu, Hong-Ying; Hou, Chao; Han, Gao-Feng; Yang, Ping; Liu, Yong-Bing; Jiang, Qing

    2013-01-01

    Tremendous demands for electrochemical biosensors with high sensitivity and reliability, fast response and excellent selectivity have stimulated intensive research on developing versatile materials with ultrahigh electrocatalytic activity. Here we report flexible and self-supported microelectrodes with a seamless solid/nanoporous gold/cobalt oxide hybrid structure for electrochemical nonenzymatic glucose biosensors. As a result of synergistic electrocatalytic activity of the gold skeleton and cobalt oxide nanoparticles towards glucose oxidation, amperometric glucose biosensors based on the hybrid microelectrodes exhibit multi-linear detection ranges with ultrahigh sensitivities at a low potential of 0.26 V (versus Ag/AgCl). The sensitivity up to 12.5 mA mM⁻¹ cm⁻² with a short response time of less than 1 s gives rise to ultralow detection limit of 5 nM. The outstanding performance originates from a novel nanoarchitecture in which the cobalt oxide nanoparticles are incorporated into pore channels of the seamless solid/nanoporous Au microwires, providing excellent electronic/ionic conductivity and mass transport for the enhanced electrocatalysis.

  5. Iridium in natural waters

    SciTech Connect

    Anbar, A.D.; Wasserburg, G.J.; Papanastassiou, D.A.

    1996-09-13

    Iridium, commonly used as a tracer of extraterrestrial material, was measured in rivers, oceans, and an estuarine environment. The concentration of iridium in the oceans ranges from 3.0 ({+-}1.3) x 10{sup 8} to 5.7 ({+-}0.8) x 10{sup 8} atoms per kilogram. Rivers contain from 17.4 ({+-}0.9) x 10{sup 8} to 92.9 ({+-}2.2) x 10{sup 8} atoms per kilogram and supply more dissolved iridium to the oceans than do extraterrestrial sources. In the Baltic Sea, {approximately}75% of riverine iridium is removed from solution. Iron-manganese oxyhydroxides scavenge iridium under oxidizing conditions, but anoxic environments are not a major sink for iridium. The ocean residence time of iridium is between 2 x 10{sup 3} and 2 x 10{sup 4} years. 32 refs., 3 figs., 1 tab.

  6. Determination of surface coverage of catalysts: Temperature programmed experiments on platinum and iridium sponge catalysts after low temperature ammonia oxidation

    SciTech Connect

    Broek, A.C.M. van den; Grondelle, J. van; Santen, R.A. van

    1999-07-25

    The activity of iridium and platinum sponge catalysts was studied in the low temperature gas phase oxidation of ammonia with oxygen. Under the reaction conditions used, iridium was found to be more active and more selective to nitrogen than platinum. Furthermore it was established from activity measurements that both catalysts lose activity as a function of time on stream due to inhibition of the surface by reaction intermediates. The used catalysts were studied by XPS and temperature programmed techniques. It was found that the surface of the catalysts had a high coverage of NH and OH and some additional NH{sub 2}. It seems most likely that the reaction mechanism proceeds through a stepwise dehydrogenation of the ammonia molecule. It appears that the last dehydrogenation step (NH by OH to N and water) is the rate determining step. The high selectivity of iridium to nitrogen can be explained by the higher activity of iridium in dissociating NO.

  7. Evaluation of microelectrode materials for direct-current electrocorticography

    NASA Astrophysics Data System (ADS)

    Li, Chunyan; Narayan, Raj K.; Wu, Pei-Ming; Rajan, Neena; Wu, Zhizhen; Mehan, Neal; Golanov, Eugene V.; Ahn, Chong H.; Hartings, Jed A.

    2016-02-01

    Objective. Direct-current electrocorticography (DC-ECoG) allows a more complete characterization of brain states and pathologies than traditional alternating-current recordings (AC-ECoG). However, reliable recording of DC signals is challenging because of electrode polarization-induced potential drift, particularly at low frequencies and for more conducting materials. Further challenges arise as electrode size decreases, since impedance is increased and the potential drift is augmented. While microelectrodes have been investigated for AC-ECoG recordings, little work has addressed microelectrode properties for DC-signal recording. In this paper, we investigated several common microelectrode materials used in biomedical application for DC-ECoG. Approach. Five of the most common materials including gold (Au), silver/silver chloride (Ag/AgCl), platinum (Pt), Iridium oxide (IrOx), and platinum-iridium oxide (Pt/IrOx) were investigated for electrode diameters of 300 μm. The critical characteristics such as polarization impedance, AC current-induced polarization, long-term stability and low-frequency noise were studied in vitro (0.9% saline). The two most promising materials, Pt and Pt/lrOx were further investigated in vivo by recording waves of spreading depolarization, one of the most important applications for DC-ECoG in clinical and basic science research. Main results. Our experimental results indicate that IrOx-based microelectrodes, particularly with composite layers of nanostructures, are excellent in all of the common evaluation characteristics both in vitro and in vivo and are most suitable for multimodal monitoring applications. Pt electrodes suffer high current-induced polarization, but have acceptable long-term stability suitable for DC-ECoG. Major significance. The results of this study provide quantitative data on the electrical properties of microelectrodes with commonly-used materials and will be valuable for development of neural recordings inclusive of

  8. Flexible, high-density microphotodiode array with integrated sputtered iridium oxide electrodes for retinal stimulation

    NASA Astrophysics Data System (ADS)

    Yang, Frank; Chang, Mao-Yen; Yang, Chung-Hua; Teng, Chih-Ciao; Fan, Long-Sheng

    2016-01-01

    To assess the charge-injection capacity of the sputtered iridium oxide film (SIROF) electrode on the retinal CMOS image sensor (CIS) chip, a polyimide-based flex device was designed and fabricated to package the retinal CIS chip. The polyimide-flex-based packaging process keeps the surface of photosensors clean, and the measured connection resistance meets the packaging requirement of the low-power retinal CIS chip. The in vitro experimental results show that the small SIROF electrodes can provide a biphasic charge injection per phase of 3.9 nC/ph to achieve the stimulation threshold at a polarization potential of -0.44 V.

  9. An analysis of the kinetics of oxidation of ascorbate at poly(aniline)-poly(styrene sulfonate) modified microelectrodes.

    PubMed

    Bonastre, A M; Sosna, M; Bartlett, P N

    2011-03-28

    A detailed kinetic study is provided for the oxidation of ascorbate at poly(aniline)-poly(styrene sulfonate) coated microelectrodes. Flat films with a low degree of polymer spillover and a thickness much lower than the microelectrode radius were produced by controlled potentiodynamic electrodeposition. The currents for ascorbate oxidation are found to be independent of the polymer thickness, indicating that the reaction occurs at the outer surface of the polymer film. At low ascorbate concentrations, below around 40 mM, the currents are found to be mass transport limited. At higher ascorbate concentrations the currents became kinetically limited. The experimental data for measurements at a range of potentials are fitted to a consistent kinetic model and the results summarized in a case diagram. The results obtained for the poly(aniline)-(polystyrene sulfonate) coated microelectrode are compared to those for a poly(aniline)-poly(vinyl sulfonate) coated microelectrode and to the results of an earlier study of the reaction at poly(aniline)-poly(vinyl sulfonate) coated rotating disc electrodes. For poly(aniline)-poly(styrene sulfonate) the oxidation of ascorbate is found to proceed by one electron reaction whereas for poly(aniline)-poly(vinyl sulfonate) the reaction is found to be a two electron oxidation.

  10. Anodic Deposition of a Robust Iridium-Based Water-Oxidation Catalyst from Organometallic Precursors

    SciTech Connect

    Blakemore, James D; Schley, Nathan D; Olack, G.; Incarvito, Christopher D; Brudvig, Gary W; Crabtree, Robert H

    2011-01-01

    Artificial photosynthesis, modeled on natural light-driven oxidation of water in Photosystem II, holds promise as a sustainable source of reducing equivalents for producing fuels. Few robust water-oxidation catalysts capable of mediating this difficult four-electron, four-proton reaction have yet been described. We report a new method for generating an amorphous electrodeposited material, principally consisting of iridium and oxygen, which is a robust and long-lived catalyst for water oxidation, when driven electrochemically. The catalyst material is generated by a simple anodic deposition from Cp*Ir aqua or hydroxo complexes in aqueous solution. This work suggests that organometallic precursors may be useful in electrodeposition of inorganic heterogeneous catalysts.

  11. Photolytic water oxidation catalyzed by a molecular carbene iridium complex.

    PubMed

    Petronilho, Ana; Rahman, Mahfujur; Woods, James A; Al-Sayyed, Haris; Müller-Bunz, Helge; Don MacElroy, J M; Bernhard, Stefan; Albrecht, Martin

    2012-11-14

    The complex IrCl(2)(Cp*)(trz) (trz = triazolylidene), 2, was prepared from readily available 1,3-dimethyl-4-phenyl-1,2,3-triazolium salt. Under basic conditions, the C-bound phenyl group readily cyclometalates, while under acidic conditions, cyclometalation is reversed. The sensitivity of the C(aryl)-Ir bond but not the C(trz)-Ir bond towards acidolysis provided a basis for using 2 as a catalyst in Ce(IV)-mediated water oxidation. The catalytic activity is characterized by a robust catalytic cycle, affording excellent turnover numbers (TON > 20,000). Under cerium-free conditions and in the presence of hematite as a photoelectrode, light-induced activity was observed. The photoelectrochemical reaction is strongly pH-dependent, which requires pH adjustments when running multiple cycle experiments to regenerate the catalytic activity. Analogous chelating complexes display better stability and higher catalytic activity than the monodentate complex 2.

  12. Characterization of sputtered iridium oxide thin films on planar and laser micro-structured platinum thin film surfaces for neural stimulation applications

    NASA Astrophysics Data System (ADS)

    Thanawala, Sachin

    Electrical stimulation of neurons provides promising results for treatment of a number of diseases and for restoration of lost function. Clinical examples include retinal stimulation for treatment of blindness and cochlear implants for deafness and deep brain stimulation for treatment of Parkinsons disease. A wide variety of materials have been tested for fabrication of electrodes for neural stimulation applications, some of which are platinum and its alloys, titanium nitride, and iridium oxide. In this study iridium oxide thin films were sputtered onto laser micro-structured platinum thin films by pulsed-DC reactive sputtering of iridium metal in oxygen-containing atmosphere, to obtain high charge capacity coatings for neural stimulation applications. The micro-structuring of platinum films was achieved by a pulsed-laser-based technique (KrF excimer laser emitting at lambda=248nm). The surface morphology of the micro-structured films was studied using different surface characterization techniques. In-vitro biocompatibility of these laser micro-structured films coated with iridium oxide thin films was evaluated using cortical neurons isolated from rat embryo brain. Characterization of these laser micro-structured films coated with iridium oxide, by cyclic voltammetry and impedance spectroscopy has revealed a considerable decrease in impedance and increase in charge capacity. A comparison between amorphous and crystalline iridium oxide thin films as electrode materials indicated that amorphous iridium oxide has significantly higher charge capacity and lower impedance making it preferable material for neural stimulation application. Our biocompatibility studies show that neural cells can grow and differentiate successfully on our laser micro-structured films coated with iridium oxide. This indicates that reactively sputtered iridium oxide (SIROF) is biocompatible.

  13. Long life testing of oxide-coated iridium/rhenium rockets

    NASA Astrophysics Data System (ADS)

    Reed, Brian D.

    1995-09-01

    22-N class rockets, composed of a rhenium (Re) substrate, an iridium (Ir) coating, and an additional composite coating consisting of Ir and a ceramic oxide, were tested on gaseous oxygen/gaseous hydrogen (GO2/GH2) propellants. Two rockets were tested, one for nearly 39 hours at a nominal mixture ratio (MR) of 4.6 and chamber pressure (Pc) of 469 kPa, and the other for over 13 hours at a nominal MR of 5.8 and 621 kPa Pc. Four additional Ir/Re rockets, with a composite Ir-oxide coating fabricated using a modified process, were also tested, including one for 1.3 hours at a nominal MR of 16.7 and Pc of 503 kPa. The long lifetimes demonstrated on low MR GO2/GH2 suggest greatly extended chamber lifetimes (tens of hours) in the relatively low oxidizing combustion environments of Earth storable propellants. The oxide coatings could also serve as a protective coating in the near injector region, where a still-mixing flowfield may cause degradation of the Ir layer. Operation at MR close to 17 suggests that oxide-coated Ir/Re rockets could be used in severely oxidizing combustion environments, such as high MR GO2/GH2, oxygen/hydrocarbon, and liquid gun propellants.

  14. Long Life Testing of Oxide-Coated Iridium/Rhenium Rockets

    NASA Technical Reports Server (NTRS)

    Reed, Brian D.

    1995-01-01

    22-N class rockets, composed of a rhenium (Re) substrate, an iridium (Ir) coating, and an additional composite coating consisting of Ir and a ceramic oxide, were tested on gaseous oxygen/gaseous hydrogen (GO2/GH2) propellants. Two rockets were tested, one for nearly 39 hours at a nominal mixture ratio (MR) of 4.6 and chamber pressure (Pc) of 469 kPa, and the other for over 13 hours at a nominal MR of 5.8 and 621 kPa Pc. Four additional Ir/Re rockets, with a composite Ir-oxide coating fabricated using a modified process, were also tested, including one for 1.3 hours at a nominal MR of 16.7 and Pc of 503 kPa. The long lifetimes demonstrated on low MR GO2/GH2 suggest greatly extended chamber lifetimes (tens of hours) in the relatively low oxidizing combustion environments of Earth storable propellants. The oxide coatings could also serve as a protective coating in the near injector region, where a still-mixing flowfield may cause degradation of the Ir layer. Operation at MR close to 17 suggests that oxide-coated Ir/Re rockets could be used in severely oxidizing combustion environments, such as high MR GO2/GH2, oxygen/hydrocarbon, and liquid gun propellants.

  15. Nd2K2IrO7 and Sm2K2IrO7: Iridium(VI) Oxides Prepared under Ambient Pressure

    SciTech Connect

    Mugavero, III, S.; Smith, M; Yoon, W; zur Loye, H

    2009-01-01

    The most-oxidized iridium oxides known to date are prepared in a hydroxide flux under normal pressure. They contain iridium centers exclusively in the +VI oxidation state and are characterized crystallographically. The picture shows the structure of the Ln2K2IrO7 (Ln=Nd, Sm) and its structural components: IrO6 octahedra (black), KO10 polyhedra (beige), LnO10 polyhedra (blue).

  16. Electrodeposition of PANi films on platinum needle type microelectrodes. Application to the oxidation of ascorbate in human plasma.

    PubMed

    Bonastre, A M; Bartlett, P N

    2010-08-31

    Needle type (165 microm(2)) and small Pt disc (3-11 microm(2)) microelectrodes were used for the electrodeposition of composite poly(aniline), PANi, films by cyclic voltammetry and chronoamperometry for the oxidation of ascorbate. PANi electroactivity at neutral pH was retained through polymer alkylation or by using large poly-anions, such as poly(vinylsulfonate), PVS, and poly(styrenesulfonate), PSS. Hence the growth of the composite films was studied in the presence of different counter ions such as SO(4)(2-), Cl(-), NaPVS and NaPSS. The morphology of the resulting films was examined by scanning electron microscopy. Results showed that flat PANi films with thicknesses much lower than the microelectrode radius were obtained by potentiodynamic electrodeposition. On the other hand films with mushroom shapes, with significant spill over, were obtained under constant potential. The resulting polymer modified microelectrodes films were shown to be suitable for the oxidation of ascorbate at 0.1 V vs. SCE and pH 7 with a detection limit of 1 microM for PANi/PSS composites. The current was independent of film thickness, mass transport controlled at low ascorbate concentrations and not affected by the presence of common interferences such as uric acid, glutathione or vitamin E. Due to their excellent properties the PANi-PSS film coated microelectrodes were used for the amperometric detection of ascorbate in human plasma. The results are encouraging for the use of small polymer modified Pt needle type microelectrodes for the detection of ascorbate in biological systems.

  17. Iridium Oxide Nanotube Electrodes for Highly Sensitive and Prolonged Intracellular Measurement of Action Potentials

    PubMed Central

    Lin, Ziliang Carter; Xie, Chong; Osakada, Yasuko; Cui, Yi; Cui, Bianxiao

    2014-01-01

    Intracellular recording of action potentials is important to understand electrically-excitable cells. Recently, vertical nanoelectrodes have been developed to achieve highly sensitive, minimally invasive, and large scale intracellular recording. It has been demonstrated that the vertical geometry is crucial for the enhanced signal detection. Here we develop nanoelectrodes made up of nanotubes of iridium oxide. When cardiomyocytes are cultured upon those nanotubes, the cell membrane not only wraps around the vertical tubes but also protrudes deep into the hollow center. We show that this geometry enhances cell-electrode coupling and results in measuring much larger intracellular action potentials. The nanotube electrodes afford much longer intracellular access and are minimally invasive, making it possible to achieve stable recording up to an hour in a single session and more than 8 days of consecutive daily recording. This study suggests that the electrode performance can be significantly improved by optimizing the electrode geometry. PMID:24487777

  18. Noisy CO oxidation on Iridium(111) surfaces. Experiments explained by theory under realistic assumptions

    NASA Astrophysics Data System (ADS)

    Wehner, S.; Cisternas, J.; Descalzi, O.; Küppers, J.

    2014-01-01

    Noise is an everywhere phenomenon. Its influence could be described theoretically quite easily, but is hard to measure in an experiment. Catalytic reactions on surfaces can be described by nonlinear reaction-diffusion equations. For one of such surface reactions - CO oxidation on Iridium(111) surfaces - the probability distribution of CO2 rates around the mean value - showing the influence of noise - could be measured directly in a ultra high vacuum (UHV) experiment. This opens the way to address such a fundamental phenomenon like noise by all three modern methods of physics - experimental, computational and analytical. We show the measured effect of colored noise on a bistable surface reaction and explain all observations directly with the underlying theoretical description - the Langmuir-Hinshelwood reaction scheme - by solving the equations under realistic assumptions. It is a great pleasure to dedicate this work to Prof. Dr. Helmut R. Brand on the occasion of his 60th birthday.

  19. Te/Pt nanonetwork modified carbon fiber microelectrodes for methanol oxidation

    NASA Astrophysics Data System (ADS)

    Tsai, Hsiang-Yu; Shih, Zih-Yu; Lin, Zong-Hong; Chang, Huan-Tsung

    2013-05-01

    Te/Pt nanonetwork-decorated carbon fiber microelectrodes (CFMEs) have been fabricated and employed as anodic catalysts in a direct methanol fuel cell (DMFC). Te nanowires were prepared from tellurite ions (TeO32-) through a seed-mediated growth process and were deposited onto CFMEs to form three-dimensional Te nanonetworks. The Te nanonetworks then acted as a framework and reducing agent to reduce PtCl62- ions to form Te/Pt through a galvanic replacement reaction, leading to the formation of Te/PtCFMEs. By controlling the reaction time, the amount of Pt and morphology of Te/Pt nanonetworks were controlled, leading to various degrees of electrocatalytic activity. The Te/PtCFMEs provide a high electrochemical active surface area (129.2 m2 g-1), good catalytic activity (1.2 A mg-1), high current density (20.0 mA cm-2), long durability, and tolerance toward the poisoning species for methanol oxidation in 0.5 M sulfuric acid containing 1 M methanol. We have further demonstrated an enhanced current density by separately using 3 and 5 Te/PtCFMEs. Our results show that the low-cost, stable, and effective Te/PtCFMEs have great potential in the fabrication of cost-effective fuel cells.

  20. Highly effective water oxidation catalysis with iridium complexes through the use of NaIO4.

    PubMed

    Codolà, Zoel; Cardoso, João M S; Royo, Beatriz; Costas, Miquel; Lloret-Fillol, Julio

    2013-05-27

    Exceptional water oxidation (WO) turnover frequencies (TOF=17,000 h(-1)), and turnover numbers (TONs) close to 400,000, the largest ever reported for a metal-catalyzed WO reaction, have been found by using [Cp*Ir(III)(NHC)Cl2] (in which NHC=3-methyl-1-(1-phenylethyl)-imidazoline-2-ylidene) as the pre-catalyst and NaIO4 as oxidant in water at 40 °C. The apparent TOF for [Cp*Ir(III)(NHC)X2] (1X, in which X stands for I (1I), Cl (1Cl), or triflate anion (1OTf)) and [(Cp*-NHCMe)Ir(III)I2] (2) complexes, is kept constant during almost all of the O2 evolution reaction when using NaIO4 as oxidant. The TOF was found to be dependent on the ligand and on the anion (TOF ranging from ≈600 to ≈1100 h(-1) at 25 °C). Degradation of the complexes by oxidation of the organic ligands upon reaction with NaIO4 has been investigated. (1)H NMR, ESI-MS, and dynamic light-scattering measurements (DLS) of the reaction medium indicated that the complex undergoes rapid degradation, even at low equivalents of oxidant, but this process takes place without formation of nanoparticles. Remarkably, three-month-old solution samples of oxidized pre-catalysts remain equally as active as freshly prepared solutions. A UV/Vis feature band at λmax =405 nm is observed in catalytic reaction solutions only when O2 evolves, which may be attributed to a resting state iridium speciation, most probably Ir-oxo species with an oxidation state higher than IV.

  1. Iridium Oxide Coatings with Templated Porosity as Highly Active Oxygen Evolution Catalysts: Structure-Activity Relationships.

    PubMed

    Bernicke, Michael; Ortel, Erik; Reier, Tobias; Bergmann, Arno; Ferreira de Araujo, Jorge; Strasser, Peter; Kraehnert, Ralph

    2015-06-01

    Iridium oxide is the catalytic material with the highest stability in the oxygen evolution reaction (OER) performed under acidic conditions. However, its high cost and limited availability demand that IrO2 is utilized as efficiently as possible. We report the synthesis and OER performance of highly active mesoporous IrO2 catalysts with optimized surface area, intrinsic activity, and pore accessibility. Catalytic layers with controlled pore size were obtained by soft-templating with micelles formed from amphiphilic block copolymers poly(ethylene oxide)-b-poly(butadiene)-b-poly(ethylene oxide). A systematic study on the influence of the calcination temperature and film thickness on the morphology, phase composition, accessible surface area, and OER activity reveals that the catalytic performance is controlled by at least two independent factors, that is, accessible surface area and intrinsic activity per accessible site. Catalysts with lower crystallinity show higher intrinsic activity. The catalyst surface area increases linearly with film thickness. As a result of the templated mesopores, the pore surface remains fully active and accessible even for thick IrO2 films. Even the most active multilayer catalyst does not show signs of transport limitations at current densities as high as 75 mA cm(-2) . PMID:25958795

  2. Iridium Oxide Coatings with Templated Porosity as Highly Active Oxygen Evolution Catalysts: Structure-Activity Relationships.

    PubMed

    Bernicke, Michael; Ortel, Erik; Reier, Tobias; Bergmann, Arno; Ferreira de Araujo, Jorge; Strasser, Peter; Kraehnert, Ralph

    2015-06-01

    Iridium oxide is the catalytic material with the highest stability in the oxygen evolution reaction (OER) performed under acidic conditions. However, its high cost and limited availability demand that IrO2 is utilized as efficiently as possible. We report the synthesis and OER performance of highly active mesoporous IrO2 catalysts with optimized surface area, intrinsic activity, and pore accessibility. Catalytic layers with controlled pore size were obtained by soft-templating with micelles formed from amphiphilic block copolymers poly(ethylene oxide)-b-poly(butadiene)-b-poly(ethylene oxide). A systematic study on the influence of the calcination temperature and film thickness on the morphology, phase composition, accessible surface area, and OER activity reveals that the catalytic performance is controlled by at least two independent factors, that is, accessible surface area and intrinsic activity per accessible site. Catalysts with lower crystallinity show higher intrinsic activity. The catalyst surface area increases linearly with film thickness. As a result of the templated mesopores, the pore surface remains fully active and accessible even for thick IrO2 films. Even the most active multilayer catalyst does not show signs of transport limitations at current densities as high as 75 mA cm(-2) .

  3. Assessment of density functional methods for reaction energetics: iridium-catalyzed water oxidation as case study.

    PubMed

    Kazaryan, Andranik; Baerends, Evert Jan

    2013-04-01

    We investigate basis set convergence for a series of density functional theory (DFT) functionals (both hybrid and nonhybrid) and compare to coupled-cluster with single and double excitations and perturbative triples [CCSD(T)] benchmark calculations. The case studied is the energetics of the water oxidation reaction by an iridium-oxo complex. Complexation energies for the reactants and products complexes as well as the transition state (TS) energy are considered. Contrary to the expectation of relatively weak basis set dependence for DFT, the basis set effects are large, for example, more than 10 kcal mol(-1) difference from converged basis for the activation energy with "small" basis sets (DZ/6-31G** for Ir/other atoms, or SVP) and still more than 6 kcal mol(-1) for def2-TZVPP/6-31G**. Inclusion of the dispersion correction in DFT-D3 schemes affects the energies of reactant complex (RC), TS, and product complex (PC) by almost the same amount; it significantly improves the complexation energy (the formation of RC), but has little effect on the activation energy with respect to RC. With converged basis, some pure GGAs (PBE-D3, BP86-D3) as well as the hybrid functional B3LYP-D3 are very accurate compared to benchmark CCSD(T) calculations.

  4. Electrochemical detection of catecholamine release using planar iridium oxide electrodes in nanoliter microfluidic cell culture volumes.

    PubMed

    Ges, Igor A; Currie, Kevin P M; Baudenbacher, Franz

    2012-04-15

    Release of neurotransmitters and hormones by calcium regulated exocytosis is a fundamental cellular/molecular process that is disrupted in a variety of psychiatric, neurological, and endocrine disorders. Therefore, this area represents a relevant target for drug and therapeutic development, efforts that will be aided by novel analytical tools and devices that provide mechanistically rich data with increased throughput. Toward this goal, we have electrochemically deposited iridium oxide (IrOx) films onto planar thin film platinum electrodes (20 μm×300 μm) and utilized these for quantitative detection of catecholamine release from adrenal chromaffin cells trapped in a microfluidic network. The IrOx electrodes show a linear response to norepinephrine in the range of 0-400 μM, with a sensitivity of 23.1±0.5 mA/M mm(2). The sensitivity of the IrOx electrodes does not change in the presence of ascorbic acid, a substance commonly found in biological samples. A replica molded polydimethylsiloxane (PDMS) microfluidic device with nanoliter sensing volumes was aligned and sealed to a glass substrate with the sensing electrodes. Small populations of chromaffin cells were trapped in the microfluidic device and stimulated by rapid perfusion with high potassium (50mM) containing Tyrode's solution at a flow rate of 1 nL/s. Stimulation of the cells produced a rapid increase in current due to oxidation of the released catecholamines, with an estimated maximum concentration in the cell culture volume of ~52 μM. Thus, we demonstrate the utility of an integrated microfluidic network with IrOx electrodes for real-time quantitative detection of catecholamines released from small populations of chromaffin cells. PMID:22398270

  5. Virus-templated iridium oxide-gold hybrid nanowires for electrochromic application

    NASA Astrophysics Data System (ADS)

    Nam, Yoon Sung; Park, Heechul; Magyar, Andrew P.; Yun, Dong Soo; Pollom, Thomas S.; Belcher, Angela M.

    2012-05-01

    A highly porous electrode comprised of biologically templated iridium oxide-gold (IrO2-Au) hybrid nanowires is introduced for electrochromic applications. A filamentous M13 virus is genetically engineered to display IrO2-binding peptides on the viral surface and used as a template for the self-assembly of IrO2 nanoclusters into a nanowire. The open porous morphology of the prepared nanowire film facilitates ion transport. Subsequently, the redox kinetics of the IrO2 nanowires seems to be limited by the electric resistance of the nanowire film. To increase the electron mobility in the nanowires, gold nanoparticles are chemically linked to the virus prior to the IrO2 mineralization, forming a gold nanostring structure along the long axis of the virus. The resulting IrO2-Au hybrid nanowires exhibit a switching time of 35 ms for coloration and 25 ms for bleaching with a transmission change of about 30.5% at 425 nm. These values represent almost an order of magnitude faster switching responses than those of an IrO2 nanowire film having the similar optical contrast. This work shows that genetically engineered viruses can serve as versatile templates to co-assemble multiple functional molecules, enabling control of the electrochemical properties of nanomaterials.A highly porous electrode comprised of biologically templated iridium oxide-gold (IrO2-Au) hybrid nanowires is introduced for electrochromic applications. A filamentous M13 virus is genetically engineered to display IrO2-binding peptides on the viral surface and used as a template for the self-assembly of IrO2 nanoclusters into a nanowire. The open porous morphology of the prepared nanowire film facilitates ion transport. Subsequently, the redox kinetics of the IrO2 nanowires seems to be limited by the electric resistance of the nanowire film. To increase the electron mobility in the nanowires, gold nanoparticles are chemically linked to the virus prior to the IrO2 mineralization, forming a gold nanostring

  6. Mixed N-Heterocyclic Carbene-Bis(oxazolinyl)borato Rhodium and Iridium Complexes in Photochemical and Thermal Oxidative Addition Reactions

    SciTech Connect

    Xu, Songchen; Manna, Kuntal; Ellern, Arkady; Sadow, Aaron D

    2014-12-08

    In order to facilitate oxidative addition chemistry of fac-coordinated rhodium(I) and iridium(I) compounds, carbene–bis(oxazolinyl)phenylborate proligands have been synthesized and reacted with organometallic precursors. Two proligands, PhB(OxMe2)2(ImtBuH) (H[1]; OxMe2 = 4,4-dimethyl-2-oxazoline; ImtBuH = 1-tert-butylimidazole) and PhB(OxMe2)2(ImMesH) (H[2]; ImMesH = 1-mesitylimidazole), are deprotonated with potassium benzyl to generate K[1] and K[2], and these potassium compounds serve as reagents for the synthesis of a series of rhodium and iridium complexes. Cyclooctadiene and dicarbonyl compounds {PhB(OxMe2)2ImtBu}Rh(η4-C8H12) (3), {PhB(OxMe2)2ImMes}Rh(η4-C8H12) (4), {PhB(OxMe2)2ImMes}Rh(CO)2 (5), {PhB(OxMe2)2ImMes}Ir(η4-C8H12) (6), and {PhB(OxMe2)2ImMes}Ir(CO)2 (7) are synthesized along with ToMM(η4-C8H12) (M = Rh (8); M = Ir (9); ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate). The spectroscopic and structural properties and reactivity of this series of compounds show electronic and steric effects of substituents on the imidazole (tert-butyl vs mesityl), effects of replacing an oxazoline in ToM with a carbene donor, and the influence of the donor ligand (CO vs C8H12). The reactions of K[2] and [M(μ-Cl)(η2-C8H14)2]2 (M = Rh, Ir) provide {κ4-PhB(OxMe2)2ImMes'CH2}Rh(μ-H)(μ-Cl)Rh(η2-C8H14)2 (10) and {PhB(OxMe2)2ImMes}IrH(η3-C8H13) (11). In the former compound, a spontaneous oxidative addition of a mesityl ortho-methyl to give a mixed-valent dirhodium species is observed, while the iridium compound forms a monometallic allyl hydride. Photochemical reactions of dicarbonyl compounds 5 and 7 result in C–H bond oxidative addition providing the compounds {κ4-PhB(OxMe2)2ImMes'CH2}RhH(CO) (12) and {PhB(OxMe2)2ImMes}IrH(Ph)CO (13). In 12, oxidative addition results in cyclometalation of the mesityl ortho-methyl similar to 10, whereas the iridium compound reacts with the benzene solvent to give a rare crystallographically characterized cis

  7. Charge injection properties of iridium oxide films produced on Ti-6Al-4V alloy substrates by ion-beam mixing techniques

    SciTech Connect

    Williams, J.M. ); Lee, I-S.; Buchanan, R.A. )

    1991-10-01

    The charge injection capabilities of iridium oxide films, as produced on Ti6Al-4V alloy substrates by ion beam mixing techniques, have been investigated. Iridium oxide is a valence change oxide, and therefore has high values of charge injection density upon voltage cycling in electrolytes. Because of this property, iridium oxide films are useful as working elements in neural prostheses. Iridium films of three thicknesses, produced by sputter deposition followed by ion beam mixing, were tested in cyclic voltammetry out to 1000 cycles or more. Two surface preparations, mechanical polishing and an acid passivation treatment, were also used as controls. Surface analysis was primarily by Rutherford backscattering spectrometry. Both the ion- beam mixing and the acid pretreatment increased the lifetimes of films, in comparison with the mechanically polished standards. Reductions in charge injection capability, when they occurred, were attributed to loss of Ir from the films, and there was a close correlation between the charge injection density and the Ir inventory. 13 refs., 5 figs.

  8. Oxidation and β-Alkylation of Alcohols Catalysed by Iridium(I) Complexes with Functionalised N-Heterocyclic Carbene Ligands.

    PubMed

    Jiménez, M Victoria; Fernández-Tornos, Javier; Modrego, F Javier; Pérez-Torrente, Jesús J; Oro, Luis A

    2015-12-01

    The borrowing hydrogen methodology allows for the use of alcohols as alkylating agents for CC bond forming processes offering significant environmental benefits over traditional approaches. Iridium(I)-cyclooctadiene complexes having a NHC ligand with a O- or N-functionalised wingtip efficiently catalysed the oxidation and β-alkylation of secondary alcohols with primary alcohols in the presence of a base. The cationic complex [Ir(NCCH3 )(cod)(MeIm(2- methoxybenzyl))][BF4 ] (cod=1,5-cyclooctadiene, MeIm=1-methylimidazolyl) having a rigid O-functionalised wingtip, shows the best catalyst performance in the dehydrogenation of benzyl alcohol in acetone, with an initial turnover frequency (TOF0 ) of 1283 h(-1) , and also in the β-alkylation of 2-propanol with butan-1-ol, which gives a conversion of 94 % in 10 h with a selectivity of 99 % for heptan-2-ol. We have investigated the full reaction mechanism including the dehydrogenation, the cross-aldol condensation and the hydrogenation step by DFT calculations. Interestingly, these studies revealed the participation of the iridium catalyst in the key step leading to the formation of the new CC bond that involves the reaction of an O-bound enolate generated in the basic medium with the electrophilic aldehyde.

  9. Oxidation and β-Alkylation of Alcohols Catalysed by Iridium(I) Complexes with Functionalised N-Heterocyclic Carbene Ligands.

    PubMed

    Jiménez, M Victoria; Fernández-Tornos, Javier; Modrego, F Javier; Pérez-Torrente, Jesús J; Oro, Luis A

    2015-12-01

    The borrowing hydrogen methodology allows for the use of alcohols as alkylating agents for CC bond forming processes offering significant environmental benefits over traditional approaches. Iridium(I)-cyclooctadiene complexes having a NHC ligand with a O- or N-functionalised wingtip efficiently catalysed the oxidation and β-alkylation of secondary alcohols with primary alcohols in the presence of a base. The cationic complex [Ir(NCCH3 )(cod)(MeIm(2- methoxybenzyl))][BF4 ] (cod=1,5-cyclooctadiene, MeIm=1-methylimidazolyl) having a rigid O-functionalised wingtip, shows the best catalyst performance in the dehydrogenation of benzyl alcohol in acetone, with an initial turnover frequency (TOF0 ) of 1283 h(-1) , and also in the β-alkylation of 2-propanol with butan-1-ol, which gives a conversion of 94 % in 10 h with a selectivity of 99 % for heptan-2-ol. We have investigated the full reaction mechanism including the dehydrogenation, the cross-aldol condensation and the hydrogenation step by DFT calculations. Interestingly, these studies revealed the participation of the iridium catalyst in the key step leading to the formation of the new CC bond that involves the reaction of an O-bound enolate generated in the basic medium with the electrophilic aldehyde. PMID:26493780

  10. Physicochemical properties of peptide-coated microelectrode arrays and their in vitro effects on neuroblast cells.

    PubMed

    Ghane-Motlagh, Bahareh; Javanbakht, Taraneh; Shoghi, Fatemeh; Wilkinson, Kevin J; Martel, Richard; Sawan, Mohamad

    2016-11-01

    Silicon micromachined neural electrode arrays, which act as an interface between bioelectronic devices and neural tissues, play an important role in chronic implants, in vivo. The biological compatibility of chronic microelectrode arrays (MEA) is an essential factor that must be taken into account in their design and fabrication. In order to improve biocompatibility of the MEAs, the surface of the electrodes was coated with polyethylene glycol (PEG) and parylene-C, which are biocompatible polymers. An in vitro study was performed to test the capacity of poly-d-lysine (PDL) to improve neural-cell adhesion and proliferation. Increased proliferation of the neuroblast cells on the microelectrodes was observed in the presence of the PDL. The presence of the peptide on the electrode surface was confirmed using Fourier transform infrared spectroscopy and scanning electron microscopy (SEM). The impedance of the electrodes was not changed significantly before and after PDL deposition. Mouse neuroblast cells were seeded and cultured on the PDL coated and uncoated neural MEAs with different tip-coatings such as platinum, molybdenum, gold, sputtered iridium oxide, and carbon nanotubes. The neuroblast cells grew preferentially on and around peptide coated-microelectrode tips, as compared to the uncoated microelectrodes. PMID:27524064

  11. Impact of metal nano layer thickness on tunneling oxide and memory performance of core-shell iridium-oxide nanocrystals

    SciTech Connect

    Banerjee, W.; Maikap, S.; Tien, T.-C.; Li, W.-C.; Yang, J.-R.

    2011-10-01

    The impact of iridium-oxide (IrO{sub x}) nano layer thickness on the tunneling oxide and memory performance of IrO{sub x} metal nanocrystals in an n-Si/SiO{sub 2}/Al{sub 2}O{sub 3}/IrO{sub x}/Al{sub 2}O{sub 3}/IrO{sub x} structure has been investigated. A thinner (1.5 nm) IrO{sub x} nano layer has shown better memory performance than that of a thicker one (2.5 nm). Core-shell IrO{sub x} nanocrystals with a small average diameter of 2.4 nm and a high density of {approx}2 x 10{sup 12}/cm{sup 2} have been observed by scanning transmission electron microscopy. The IrO{sub x} nanocrystals are confirmed by x-ray photoelectron spectroscopy. A large memory window of 3.0 V at a sweeping gate voltage of {+-}5 V and 7.2 V at a sweeping gate voltage of {+-} 8 V has been observed for the 1.5 nm-thick IrO{sub x} nano layer memory capacitors with a small equivalent oxide thickness of 8 nm. The electrons and holes are trapped in the core and annular regions of the IrO{sub x} nanocrystals, respectively, which is explained by Gibbs free energy. High electron and hole-trapping densities are found to be 1.5 x 10{sup 13}/cm{sup 2} and 2 x 10{sup 13}/cm{sup 2}, respectively, due to the small size and high-density of IrO{sub x} nanocrystals. Excellent program/erase endurance of >10{sup 6} cycles and good retention of 10{sup 4} s with a good memory window of >1.2 V under a small operation voltage of {+-} 5 V are obtained. A large memory size of >10 Tbit/sq. in. can be designed by using the IrO{sub x} nanocrystals. This study is not only important for the IrO{sub x} nanocrystal charge-trapping memory investigation but it will also help to design future metal nanocrystal flash memory.

  12. Facilitated extracellular electron transfer of Shewanella loihica PV-4 by antimony-doped tin oxide nanoparticles as active microelectrodes

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaojian; Liu, Huan; Wang, Jinrong; Ren, Guangyuan; Xie, Beizhen; Liu, Hong; Zhu, Ying; Jiang, Lei

    2015-11-01

    Dissimilatory metal reducing bacteria are capable of extracellular electron transfer (EET) to insoluble metal oxides as external electron acceptors for their anaerobic respiration, which is recognized as an important energy-conversion process in natural and engineered environments, such as in mineral cycling, bioremediation, and microbial fuel/electrolysis cells. However, the low EET efficiency remains one of the major bottlenecks for its practical application. We report firstly that the microbial current generated by Shewanella loihica PV-4 (S. loihica PV-4) could be greatly improved that is up to ca. 115 fold, by adding antimony-doped tin oxide (ATO) nanoparticles in the electrochemical reactor. The results demonstrate that the biocompatible, electrically conductive ATO nanoparticles acted as active microelectrodes could facilitate the formation of a cells/ATO composite biofilm and the reduction of the outer membrane c-type cytochromes (OM c-Cyts) that are beneficial for the electron transfer from cells to electrode. Meanwhile, a synergistic effect between the participation of OM c-Cyts and the accelerated EET mediated by cell-secreted flavins may play an important role for the enhanced current generation in the presence of ATO nanoparticles. Moreover, it is worth noting that the TCA cycle in S. loihica PV-4 cells is activated by adding ATO nanoparticles, even if the potential is poised at +0.2 V, thereby also improving the EET process. The results presented here may provide a simple and effective strategy to boost the EET of S. loihica PV-4 cells, which is conducive to providing potential applications in bioelectrochemical systems.Dissimilatory metal reducing bacteria are capable of extracellular electron transfer (EET) to insoluble metal oxides as external electron acceptors for their anaerobic respiration, which is recognized as an important energy-conversion process in natural and engineered environments, such as in mineral cycling, bioremediation, and

  13. Oxidation of anthracene on platinum macro- and micro-electrodes: Sonoelectrochemical, cryoelectrochemical and sonocryoelectrochemical studies.

    PubMed

    Paddon, Christopher A; Banks, Craig E; Davies, Ieuan G; Compton, Richard G

    2006-02-01

    The electro- and sonoelectro-chemical oxidation of anthracene in acetonitrile has been explored at room and low temperature (-40 degrees C) at a platinum micro- and macro-electrode, respectively. From both methodologies, the effective number of electrons, n(eff), in the oxidation process is evaluated at both room temperature and at the limit of the solvent-electrolyte freezing point. It is observed that n(eff) is close to 1 at low temperature while at room temperature it is higher, indicating sluggish follow up kinetics at lower temperature. The oxidative electrolysis of anthracene within an undivided cell, under various conditions is investigated with the product(s) obtained analysed and quantified by (1)H NMR. At room temperature under both 'silent' and 'sono' conditions the electrochemical oxidation produces 9,10-anthraquinone and bianthrone while at low temperature with acoustic streaming, anthracene-9,10-diol is additionally produced. Electrolyses with intentionally added water and also with oxygen saturation is investigated and its influence on the reaction pathway reported. In particular, the addition of water (1.4M) favours the formation of anthraquinone in a 3:1 ratio with bianthrone. Overall, the effect of lower temperature is to favour the formation of anthraquinone or its reduced form whilst the addition of insonation at low temperature is to substantially enhance the product yield per Coulomb of charge injected.

  14. Iridium-Tin oxide solid-solution nanocatalysts with enhanced activity and stability for oxygen evolution

    NASA Astrophysics Data System (ADS)

    Li, Guangfu; Yu, Hongmei; Yang, Donglei; Chi, Jun; Wang, Xunying; Sun, Shucheng; Shao, Zhigang; Yi, Baolian

    2016-09-01

    Addressing major challenges from the material cost, efficiency and stability, it is highly desirable to develop high-performance catalysts for oxygen evolution reaction (OER). Herein we explore a facile surfactant-assisted approach for fabricating Irsbnd Sn (Ir/Sn = 0.6/0.4, by mol.) nano-oxide catalysts with good morphology control. Direct proofs from XRD and X-ray photoelectron spectra indicate hydrophilic triblock polymer (TBP, like Pluronic® F108) surfactant can boost the formation of stable solid-solution structure. With the TBP hydrophilic and block-length increase, the fabricated Irsbnd Sn oxides undergoing the rod-to-sphere transition obtain the relatively lower crystallization, decreased crystallite size, Ir-enriched surface and incremental available active sites, all of which can bolster the OER activity and stability. Meanwhile, it is observed that the coupled Ir oxidative etching takes a crucial role in determining the material structure and performance. Compared with commercial Ir black, half-cell tests confirm F108-assistant catalysts with over 40 wt% Ir loading reduction show 2-fold activity enhancement as well as significant stability improvement. The lowest cell voltage using 0.88 mg cm-2 Ir loading is only 1.621 V at 1000 mA cm-2 and 80 °C with a concomitant energy efficiency of 75.8% which is beyond the DOE 2017 efficiency target of 74%.

  15. Anisotropic magnetic interactions in 5d iridium oxides by many-body quantum chemistry calculations

    NASA Astrophysics Data System (ADS)

    Katukuri, Vamshi M.; Nishimoto, Satoshi; Yushankhai, Viktor; Rousochatzakis, Ioannis; Hozoi, Liviu; van den Brink, Jeroen

    2014-03-01

    Ir 5d5 oxides are being actively studied due to the realization of novel spin-orbit coupled jeff ~ 1/2 ground states. One remarkable feature in these compounds is the highly anisotropic magnetic interactions, orders of magnitude stronger than in 3d oxides. We address the nature of the anisotropic exchange in the 2D honeycomb (Na/Li)2IrO3 ((Na/Li)213) and square-lattice (Sr/Ba)2IrO4 ((Sr/Ba)213) iridates, by ab initio multireference configuration-interaction calculations on large embedded clusters. For Na213 we find that the Kitaev term is ferromagnetic and defines the dominant energy scale while the nearest-neighbor Heisenberg contribution is antiferromagnetic. Although Li213 is structurally similar, we predict quite different set of interaction parameters in Li213. We further analyze the magnetic order and the essential differences between these two materials by exact diagonalization and density-matrix renormalization-group calculations that additionally include 2nd and 3rd neighbor couplings. Sizable symmetric anisotropic interactions are also computed for Ba214. From the ab initio data, the relevant in-plane spin model for Ba214 turns out to be a Heisenberg-compass effective model. We finally discuss the Dzyaloshinskii-Moriya exchange in Sr214.

  16. The inhibition of iridium-promoted water oxidation catalysis (WOC) by cucurbit[n]urils.

    PubMed

    Iali, Wissam; Petrović, Predrag; Pfeffer, Michel; Grimme, Stefan; Djukic, Jean-Pierre

    2012-10-21

    A series of iridacycles bearing π-bonded moieties of variable electron-withdrawing capabilities were tested for their ability to promote water oxidation catalysis (WOC) in the presence of high loading in a sacrificial oxidant, under conditions chosen for optimal dioxygen production. This report shows that none of these complexes performs differently than monometallic iridacycles and that the π-bonded moiety does not affect the overall rate of O(2) production. Furthermore, it is shown that cucurbituril macrocycles significantly inhibit the production of dioxygen independently of the nature of the Cp*Ir(III)-based catalyst used to perform WOC. Theoretical first-principles based DFT-D3 investigations including a complete treatment of solvation with COSMO and COSMO-RS treatments supported by ITC analyses suggest that concealment of the catalyst by curcurbit[7]uril could occur by non-covalent interaction of the Cp*Ir moiety in the hydrophobic pocket of the cavitand. For other cavitands of smaller inner cavity diameter, inclusion may not be the main mode of inhibition. Assuming the intervention of the putative Ir(IV)-oxyl biradical of a Cp*Ir(IV)(O)(H(2)O)(2) species like suggested by many authors, inhibition of WOC by inclusion would probably result from unfavourable coulombic interactions between water and the inclusion complex. PMID:22930285

  17. Water oxidation with molecularly defined iridium complexes: insights into homogeneous versus heterogeneous catalysis.

    PubMed

    Junge, Henrik; Marquet, Nicolas; Kammer, Anja; Denurra, Stefania; Bauer, Matthias; Wohlrab, Sebastian; Gärtner, Felix; Pohl, Marga-Martina; Spannenberg, Anke; Gladiali, Serafino; Beller, Matthias

    2012-10-01

    Molecularly defined Ir complexes and different samples of supported IrO(2) nanoparticles have been tested and compared in the catalytic water oxidation with cerium ammonium nitrate (CAN) as the oxidant. By comparing the activity of nano-scaled supported IrO(2) particles to the one of organometallic complexes it is shown that the overall activity of the homogeneous Ir precursors is defined by both the formation of the homogeneous active species and its conversion to Ir(IV)-oxo nanoparticles. In the first phase of the reaction the activity is dominated by the homogeneous active species. With increasing reaction time, the influence of nano-sized Ir-oxo particles becomes more evident. Notably, the different conversion rates of the homogeneous precursor into the active species as well as the conversion into Ir-oxo nanoparticles and the different particle sizes have a significant influence on the overall activity. In addition to the homogeneous systems, IrO(2)@MCM-41 has also been synthesized, which contains stabilized nanoparticles of between 1 and 3 nm in size. This latter system shows a similar activity to IrCl(3)⋅xH(2)O and complexes 4 and 5. Mechanistic insights were obtained by in situ X-ray absorption spectroscopy and scanning transmission electron microscopy.

  18. Fabrication of two-layer poly(dimethyl siloxane) devices for hydrodynamic cell trapping and exocytosis measurement with integrated indium tin oxide microelectrodes arrays

    PubMed Central

    Gao, Changlu; Sun, Xiuhua; Gillis, Kevin D.

    2016-01-01

    The design, fabrication and test of a microfluidic cell trapping device to measure single cell exocytosis were reported. Research on the patterning of double layer template based on repetitive standard photolithography of AZ photoresist was investigated. The replicated poly(dimethyl siloxane) devices with 2.5 μm deep channels were proved to be efficient for stopping cells. Quantal exocytosis measurement can be achieved by targeting single or small clumps of chromaffin cells on top of the 10 μm ×10 μm indium tin oxide microelectrodes arrays with the developed microdevice. And about 72% of the trapping sites can be occupied by cells with hydrodynamic trapping method and the recorded amperometric signals are comparable to the results with traditional carbon fiber microelectrodes. The method of manufacturing the microdevices is simple, low-cost and easy to perform. The manufactured device offers a platform for the high throughput detection of quantal catecholamine exocytosis from chromaffin cells with sufficient sensitivity and broad application. PMID:23329291

  19. Magnetic field perturbation of neural recording and stimulating microelectrodes

    NASA Astrophysics Data System (ADS)

    Martinez-Santiesteban, Francisco M.; Swanson, Scott D.; Noll, Douglas C.; Anderson, David J.

    2007-04-01

    To improve the overall temporal and spatial resolution of brain mapping techniques, in animal models, some attempts have been reported to join electrophysiological methods with functional magnetic resonance imaging (fMRI). However, little attention has been paid to the image artefacts produced by the microelectrodes that compromise the anatomical or functional information of those studies. This work presents a group of simulations and MR images that show the limitations of wire microelectrodes and the potential advantages of silicon technology, in terms of image quality, in MRI environments. Magnetic field perturbations are calculated using a Fourier-based method for platinum (Pt) and tungsten (W) microwires as well as two different silicon technologies. We conclude that image artefacts produced by microelectrodes are highly dependent not only on the magnetic susceptibility of the materials used but also on the size, shape and orientation of the electrodes with respect to the main magnetic field. In addition silicon microelectrodes present better MRI characteristics than metallic microelectrodes. However, metallization layers added to silicon materials can adversely affect the quality of MR images. Therefore only those silicon microelectrodes that minimize the amount of metallic material can be considered MR-compatible and therefore suitable for possible simultaneous fMRI and electrophysiological studies. High resolution gradient echo images acquired at 2 T (TR/TE = 100/15 ms, voxel size = 100 × 100 × 100 µm3) of platinum-iridium (Pt-Ir, 90%-10%) and tungsten microwires show a complete signal loss that covers a volume significantly larger than the actual volume occupied by the microelectrodes: roughly 400 times larger for Pt-Ir and 180 for W, at the tip of the microelectrodes. Similar MR images of a single-shank silicon microelectrode only produce a partial volume effect on the voxels occupied by the probe with less than 50% of signal loss.

  20. Composite wire microelectrode and method of making same

    DOEpatents

    Isaacs, Hugh S.; Aldykiewicz, Jr., Antonio J.

    1996-12-03

    A composite wire microelectrode for making electro-chemical measurements, and method of making same. The microelectrode includes an inner conductive sensing wire and an outer tube that is oxidized to form a dielectric, self-healing oxide layer around the sensing wire.

  1. Composite wire microelectrode and method of making same

    DOEpatents

    Isaacs, H.S.; Aldykiewicz, A.J. Jr.

    1996-12-03

    A composite wire microelectrode for making electro-chemical measurements, and method of making same, are disclosed. The microelectrode includes an inner conductive sensing wire and an outer tube that is oxidized to form a dielectric, self-healing oxide layer around the sensing wire. 4 figs.

  2. Processing of Iridium and Iridium Alloys

    SciTech Connect

    Ohriner, Evan Keith

    2008-01-01

    Iridium and its alloys have been considered to be difficult to fabricate due to their high melting temperatures, limited ductility, sensitivity to impurity content, and chemical properties. The variety of processing methods used for iridium and its alloys are reviewed, including purification, melting, forming, joining, and powder metallurgy techniques. Also included are coating and forming by the methods of electroplating, chemical and physical vapor deposition, and melt particle deposition.

  3. Kinetics of the chemical oxidation of (5,10,15,20-tetraphenyl-21H,23H-porphinato)(chloro)(aqua)iridium(III)

    NASA Astrophysics Data System (ADS)

    Tyulyaeva, E. Yu.; Bichan, N. G.; Mozhzhukhina, E. G.; Lomova, T. N.

    2016-01-01

    The oxidation of (Cl)(H2O)IrTPP with atmospheric oxygen in the presence of concentrated H2SO4 accompanied by coordination of molecular O2 and substitution of axial ligands was studied spectrophotometrically. In 16.785-18.09 MH2SO4 at 298-318 K, (Cl)(H2O)IrTPP experienced two single-electron oxidations in sequence: with an increase in the oxidation state of the iridium cation and with formation of the π-radical cation form (HSO4)IrIVTPP•+ oxidized at the aromatic ligand ( k 298 = 7.2 × 10-6 mol-1 L s-1). Referring to the literature data on the oxidation of (Cl)(H2O)IrTPP in AcOH and CF3COOH, it was shown that the medium acidity and the nature of the axial ligands affect the electron removal site in the chemical oxidation of (Cl)(H2O)IrTPP with atmospheric oxygen in proton-donor solvents.

  4. Iridium-mediated Bond Activation and Water Oxidation as an Exemplary Case of CARISMA, A European Network for the Development of Catalytic Routines for Small Molecule Activation.

    PubMed

    Licini, Giulia; Albrecht, Martin

    2015-01-01

    CARISMA is a currently running COST Action that pools leading European experts in computational and experimental chemistry to foster synergies for developing new catalytic processes for the transformation of abundant small molecules such as water, carbon dioxide, or ammonia into high-value chemicals and energy-relevant products. CARISMA promotes new collaborations, exchange of knowledge and skills, frontier training to young as well as established researchers, and a platform for the advancement of theoretical and experimental research in an iterative process, comprised of expertise in various connate domains including synthesis, catalysis, spectroscopy, kinetics, and computational chemistry. These interactions stimulate the discovery of new and efficient catalytic processes, illustrated in the second part of this contribution with the collaborative development of powerful iridium-based complexes for bond activation and water oxidation catalysis.

  5. Hierarchical nanostructured noble metal/metal oxide/graphene-coated carbon fiber: in situ electrochemical synthesis and use as microelectrode for real-time molecular detection of cancer cells.

    PubMed

    Abdurhman, Abduraouf Alamer Mohamed; Zhang, Yan; Zhang, Guoan; Wang, Shuai

    2015-10-01

    We report the design and fabrication of a new type of nanohybrid microelectrode based on a hierarchical nanostructured Au/MnO2/graphene-modified carbon fiber (CF) via in situ electrochemical synthesis, which leads to better structural integration of different building blocks into the CF microelectrode. Our finding demonstrates that wrapping CF with graphene nanosheets has dramatically increased the surface area and electrical conductivity of the CF microelectrode. The subsequent template-free electrodeposition of MnO2 on graphene-wrapped CF gives rise to a porous nanonest architecture built up from twisted and intersectant MnO2 nanowires, which serves as an ideal substrate for the direct growth of Au nanoparticles. Owing to the structural merit and synergy effect between different components, the hierarchical nanostructured noble metal/metal oxide/graphene-coated CF demonstrates dramatically enhanced electrocatalytic activity. When used for nonenzymatic H2O2 sensing, the resultant modified microelectrode exhibits acceptable sensitivity, reproducibility, stability, and selectivity, which enable it to be used for real-time tracking H2O2 secretion in human cervical cancer cells. Graphical abstract A schematic illustration of preparation of hierarchical Au/MnO2/ERGO/CF nanohybrid electrode for real-time molecular detection of cancer cells.

  6. Iridium ultrasmall nanoparticles, worm-like chain nanowires, and porous nanodendrites: One-pot solvothermal synthesis and catalytic CO oxidation activity

    NASA Astrophysics Data System (ADS)

    Zhang, Tao; Li, Shuai-Chen; Zhu, Wei; Ke, Jun; Yu, Jing-Wen; Zhang, Zhi-Ping; Dai, Lin-Xiu; Gu, Jun; Zhang, Ya-Wen

    2016-06-01

    We report a facile one-pot solvothermal synthesis of monodisperse iridium (Ir) ultrasmall (1.5-2.5 nm in diameter) nanoparticles (NPs), worm-like chain nanowires (NWs), and porous nanodendrites (NDs), for which CO oxidation reaction has been employed as a probe reaction to investigate the effects of nanoparticle size and surface-capping organics on the catalytic activities. Time-dependent experiments revealed that an oriented attachment mechanism induced by the strong adsorption of halide anions (Br- and I-) on specific facet of Ir nanoclusters or by decreasing the reduction rate of Ir precursors with changing their concentrations during the synthesis was responsible for the formation of Ir NWs and NDs. Annealing tests indicated that an O2-H2 atmosphere treatment turned out to be an effective measure to clean up the surface-capping organics of Ir NPs supported on commercial SiO2. Catalytic CO oxidation reaction illustrated that a significant improvement in the catalytic activity of CO oxidation reaction was achieved together with the changing of activation energies after such atmosphere treatment for the supported catalysts of the ultrasmall Ir NPs. It is noteworthy that this enhancement in catalytic activity could be ascribed to the changes in the surface status (including populations of Ir species in metallic and oxidized states, removal of surface capping organics, the variety of active sites, and total effective active site number) for the supported nanocatalysts during the atmosphere treatment.

  7. Structure, electrochemical properties and capacitance performance of polypyrrole electrodeposited onto 1-D crystals of iridium complex

    NASA Astrophysics Data System (ADS)

    Wysocka-Żołopa, Monika; Winkler, Krzysztof

    2015-12-01

    Composites of polypyrrole and one-dimensional iridium complex crystals [(C2H5)4N]0.55[IrCl2(CO)2] were prepared by in situ two-step electrodeposition. Initially, iridium complex crystals were formed during [IrCl2(CO)2]- complex oxidation. Next, pyrrole was electropolymerized on the surface of the iridium needles. The morphology of the composite was investigated by scanning and transmission electron microscopy. At positive potentials, the iridium complex crystals and the polypyrrole were oxidized. In aprotic solvents, oxidation of the iridium complex crystals resulted in their dissolution. In water containing tetra(n-butyl)ammonium chlorides, the 1-D iridium complex crystals were reversibly oxidized. The product of the iridium complex oxidation remained on the electrode surface in crystalline form. The iridium complex needles significantly influenced the redox properties of the polymer. The polypyrrole involved electrode processes become more reversible in presence of crystals of iridium complex. The current of polypyrrole oxidation was higher compared to that of pure polypyrrole and the capacitance properties of the polymer were significantly enhanced. A specific capacitance as high as 590 F g-1 was obtained for a composite of polypyrrole and 1-D crystals of the iridium complex in water containing tetra(n-butyl)ammonium chloride. This value is approximately twice as high as the capacitance of the pure polymer deposited onto the electrode surface.

  8. Refining Radchem Detectors: Iridium

    NASA Astrophysics Data System (ADS)

    Arnold, C. W.; Bredeweg, T. A.; Vieira, D. J.; Bond, E. M.; Jandel, M.; Rusev, G.; Moody, W. A.; Ullmann, J. L.; Couture, A. J.; Mosby, S.; O'Donnell, J. M.; Haight, R. C.

    2013-10-01

    Accurate determination of neutron fluence is an important diagnostic of nuclear device performance, whether the device is a commercial reactor, a critical assembly or an explosive device. One important method for neutron fluence determination, generally referred to as dosimetry, is based on exploiting various threshold reactions of elements such as iridium. It is possible to infer details about the integrated neutron energy spectrum to which the dosimetry sample or ``radiochemical detector'' was exposed by measuring specific activation products post-irradiation. The ability of radchem detectors like iridium to give accurate neutron fluence measurements is limited by the precision of the cross-sections in the production/destruction network (189Ir-193Ir). The Detector for Advanced Neutron Capture Experiments (DANCE) located at LANSCE is ideal for refining neutron capture cross sections of iridium isotopes. Recent results from a measurement of neutron capture on 193-Ir are promising. Plans to measure other iridium isotopes are underway.

  9. Iridium Interfacial Stack (IRIS)

    NASA Technical Reports Server (NTRS)

    Spry, David James (Inventor)

    2015-01-01

    An iridium interfacial stack ("IrIS") and a method for producing the same are provided. The IrIS may include ordered layers of TaSi.sub.2, platinum, iridium, and platinum, and may be placed on top of a titanium layer and a silicon carbide layer. The IrIS may prevent, reduce, or mitigate against diffusion of elements such as oxygen, platinum, and gold through at least some of its layers.

  10. Direct electrochemistry of hemoglobin and myoglobin at didodecyldimethylammonium bromide-modified powder microelectrode and application for electrochemical detection of nitric oxide.

    PubMed

    Guo, Zhimou; Chen, Jian; Liu, Huan; Cha, Chuansin

    2008-01-21

    Hemoglobin (Hb) and myoglobin (Mb) were immobilized at the didodecyldimethylammonium bromide (DDAB)-modified powder microelectrode (PME) to fabricate Hb-DDAB-PME and Mb-DDAB-PME. Direct electrochemistry of Hb and Mb were achieved on the DDAB-modified PME. The formal potential was -0.224 V for Hb and -0.212 V for Mb (vs. SCE). The apparent surface concentration of Hb and Mb at the electrode surface was 2.83 x 10(-8) and 9.94 x 10(-8) mol cm(-2). The Hb-DDAB-PME and Mb-DDAB-PME were successfully applied for measurement of NO in vitro. The anodic current peaks for NO oxidation at +0.7 V and the cathodic current peaks for NO reduction at -0.85 V on the CV curves were obtained on the modified electrodes. For detection of NO at +0.7 V, the sensitivity is 3.31 mA microM(-1) cm(-2) for Hb-DDAB-PME and 0.6 mA microM(-1) cm(-2) for Mb-DDAB-PME. The detection limit is 5 nM for Hb-DDAB-PME and 9 nM for Mb-DDAB-PME. The linear response range is 9-100 and 28-330 nM for Hb- and Mb-modified PME, respectively. For the electrochemical detection of NO at -0.85 V by using Hb-DDAB-PME, the detection sensitivity is 39.56 microA microM(-1) cm(-2); the detection limit is as low as 0.2 microM; and the linear response range is 1.90-28.08 microM.

  11. Iridium wire grid polarizer fabricated using atomic layer deposition.

    PubMed

    Weber, Thomas; Käsebier, Thomas; Szeghalmi, Adriana; Knez, Mato; Kley, Ernst-Bernhard; Tünnermann, Andreas

    2011-10-25

    In this work, an effective multistep process toward fabrication of an iridium wire grid polarizer for UV applications involving a frequency doubling process based on ultrafast electron beam lithography and atomic layer deposition is presented. The choice of iridium as grating material is based on its good optical properties and a superior oxidation resistance. Furthermore, atomic layer deposition of iridium allows a precise adjustment of the structural parameters of the grating much better than other deposition techniques like sputtering for example. At the target wavelength of 250 nm, a transmission of about 45% and an extinction ratio of 87 are achieved.

  12. Dual-Enzyme Characteristics of Polyvinylpyrrolidone-Capped Iridium Nanoparticles and Their Cellular Protective Effect against H2O2-Induced Oxidative Damage.

    PubMed

    Su, Hua; Liu, Dan-Dan; Zhao, Meng; Hu, Wei-Liang; Xue, Shan-Shan; Cao, Qian; Le, Xue-Yi; Ji, Liang-Nian; Mao, Zong-Wan

    2015-04-22

    Polyvinylpyrrolidone-stabilized iridium nanoparticles (PVP-IrNPs), synthesized by the facile alcoholic reduction method using abundantly available PVP as protecting agents, were first reported as enzyme mimics showing intrinsic catalase- and peroxidase-like activities. The preparation procedure was much easier and more importantly, kinetic studies found that the catalytic activity of PVP-IrNPs was comparable to previously reported platinum nanoparticles. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) characterization indicated that PVP-IrNPs had the average size of approximately 1.5 nm and mainly consisted of Ir(0) chemical state. The mechanism of PVP-IrNPs' dual-enzyme activities was investigated using XPS, Electron spin resonance (ESR) and cytochrome C-based electron transfer methods. The catalase-like activity was related to the formation of oxidized species Ir(0)@IrO2 upon reaction with H2O2. The peroxidase-like activity originated from their ability acting as electron transfer mediators during the catalysis cycle, without the production of hydroxyl radicals. Interestingly, the protective effect of PVP-IrNPs against H2O2-induced cellular oxidative damage was investigated in an A549 lung cancer cell model and PVP-IrNPs displayed excellent biocompatibility and antioxidant activity. Upon pretreatment of cells with PVP-IrNPs, the intracellular reactive oxygen species (ROS) level in response to H2O2 was decreased and the cell viability increased. This work will facilitate studies on the mechanism and biomedical application of nanomaterials-based enzyme mimic.

  13. Iridium: failures & successes

    NASA Astrophysics Data System (ADS)

    Christensen, CarissaBryce; Beard, Suzette

    2001-03-01

    This paper will provide an overview of the Iridium business venture in terms of the challenges faced, the successes achieved, and the causes of the ultimate failure of the venture — bankruptcy and system de-orbit. The paper will address technical, business, and policy issues. The intent of the paper is to provide a balanced and accurate overview of the Iridium experience, to aid future decision-making by policy makers, the business community, and technical experts. Key topics will include the history of the program, the objectives and decision-making of Motorola, the market research and analysis conducted, partnering strategies and their impact, consumer equipment availability, and technical issues — target performance, performance achieved, technical accomplishments, and expected and unexpected technical challenges. The paper will use as sources trade media and business articles on the Iridium program, technical papers and conference presentations, Wall Street analyst's reports, and, where possible, interviews with participants and close observers.

  14. Multi-component nanoporous platinum-ruthenium-copper-osmium-iridium alloy with enhanced electrocatalytic activity towards methanol oxidation and oxygen reduction

    NASA Astrophysics Data System (ADS)

    Chen, Xiaoting; Si, Conghui; Gao, Yulai; Frenzel, Jan; Sun, Junzhe; Eggeler, Gunther; Zhang, Zhonghua

    2015-01-01

    Multi-component nanoporous platinum-ruthenium-copper-osmium-iridium (np-PtRuCuOsIr) electrocatalyst has been facilely fabricated by chemical dealloying of mechanically alloyed AlCuPtRuOsIr precursor. The np-PtRuCuOsIr catalyst exhibits a typical three-dimensional bi-continuous interpenetrating ligament/channel structure with a length scale of ∼2.5 nm. The np-PtRuCuOsIr catalyst reaches a higher level in the mass activity (857.5 mA mgPt-1) and specific activity (3.0 mA cm-2) towards methanol oxidation compared to the commercial PtC catalyst (229.5 mA mgPt-1 and 0.5 mA cm-2 respectively). Moreover, the CO stripping peak of np-PtRuCuOsIr is 0.54 V (vs. SCE), 130 mV negative shift in comparison with the commercial PtC (0.67 V vs. SCE). The half-wave potential of np-PtRuCuOsIr is 0.900 V vs. RHE, 36 mV positive compared with that of the commercial PtC (0.864 V vs. RHE). The np-PtRuCuOsIr catalyst also shows 1.8 and 3.8 times enhancement in the mass and specific activity towards oxygen reduction than the commercial PtC. Moreover, the np-PtRuCuOsIr alloy exhibits superior oxygen reduction activities even after 15 K cycles, indicating its excellent long-term stability. The present np-PtRuCuOsIr can act as a promising candidate for the electrocatalyst in direct methanol fuel cells (DMFCs).

  15. Cp* Iridium Precatalysts for Selective C-H Oxidation via Direct Insertion. A Joint Experimental/Computational Study

    SciTech Connect

    Zhou, Meng; Balcells, David; Parent, Alexander R.; Crabtree, Robert H; Eisenstein, Odile

    2012-01-01

    A series of Cp*Ir complexes are active precatalysts in C–H oxidation of cis-decalin, cyclooctane, 1-acetylpyrrolidine, tetrahydrofurans, and γ-lactones. Moderate to high yields were achieved, and surprisingly, high selectivity for mono-oxidation of cyclooctane to cyclooctanone was observed. Kinetic isotope effect experiments in the C–H oxidation of ethylbenezene to acetophenone yield kH/kD = 15.4 ± 0.8 at 23 °C and 17.8 ± 1.2 at 0 °C, which are consistent with C–H oxidation being the rate-limiting step with a significant tunneling contribution. The nature of the active species was investigated by TEM, UV–vis, microfiltration, and control experiments. DFT calculations showed that the C–H oxidation of cis-decalin by Cp*Ir(ppy)(Cl) (ppy = o-phenylpyridine) follows a direct oxygen insertion mechanism on the singlet potential energy surface, rather than the radical rebound route that would be seen for the triplet, in good agreement with the retention of stereochemistry observed in this reaction.

  16. Iridium-coated rhenium thrusters by CVD

    NASA Technical Reports Server (NTRS)

    Harding, J. T.; Kazaroff, J. M.; Appel, M. A.

    1989-01-01

    Operation of spacecraft thrusters at increased temperature reduces propellant requirements. Inasmuch as propellant comprises the bulk of a satellite's mass, even a small percentage reduction makes possible a significant enhancement of the mission in terms of increased payload. Because of its excellent high temperature strength, rhenium is often the structural material of choice. It can be fabricated into free-standing shapes by chemical vapor deposition (CVD) onto an expendable mandrel. What rhenium lacks is oxidation resistance, but this can be provided by a coating of iridium, also by CVD. This paper describes the process used by Ultramet to fabricate 22-N (5-lbf) and, more recently, 445-N (100-lbf) Ir/Re thrusters; characterizes the CVD-deposited materials; and summarizes the materials effects of firing these thrusters. Optimal propellant mixture ratios can be employed because the materials withstand an oxidizing environment up to the melting temperature of iridium, 2400 C (4350 F).

  17. Iridium-coated rhenium thrusters by CVD

    NASA Technical Reports Server (NTRS)

    Harding, John T.; Kazaroff, John M.; Appel, Marshall A.

    1988-01-01

    Operation of spacecraft thrusters at increased temperature reduces propellant requirements. Inasmuch as propellant comprises the bulk of a satellite's mass, even a small percentage reduction makes possible a significant enhancement of the mission in terms of increased payload. Because of its excellent high temperature strength, rhenium is often the structural material of choice. It can be fabricated into free-standing shapes by chemical vapor deposition (CVD) onto an expendable mandrel. What rhenium lacks is oxidation resistance, but this can be provided by a coating of iridium, also by CVD. This paper describes the process used by Ultramet to fabricate 22-N (5-lbf) and, more recently, 445-N (100-lbf) Ir/Re thrusters; characterizes the CVD-deposited materials; and summarizes the materials effects of firing these thrusters. Optimal propellant mixture ratios can be employed because the materials withstand an oxidizing environment up to the meltimg temperature of iridium, 2400 C (4350 F).

  18. Low energy cyclotron production and cyclometalation chemistry of iridium-192.

    PubMed

    Langille, G; Yang, H; Zeisler, S K; Hoehr, C; Storr, T; Andreoiu, C; Schaffer, P

    2016-09-01

    This work demonstrates the labelling of a novel class of iridium lumophore with radioiridium, as proof-of-feasibility for producing and using the medically useful isotope iridium-192. Natural osmium was electroplated onto silver target backings in basic media and irradiated for up to two hours with ≤20μA of 12.8MeV protons. A range of iridium isotopes were generated, characterized and quantified using γ-spectroscopy methods. The target material was removed from the backings via oxidative dissolution with hydrogen peroxide, and the iridium radioisotopes isolated using an anion exchange resin. Both no-carrier-added as well as carrier-added formulations were then used in subsequent cyclometalation reactions. PMID:27344003

  19. Longitudinally-vibrating surgical microelectrode

    NASA Technical Reports Server (NTRS)

    Feldstein, C.; Crawford, D.; Kawabus, E. W.

    1977-01-01

    Microelectrode attached to cone of loudspeaker imparting longitudinal vibrations, penetrates relatively tough tissue of arterial walls easier and with more precise depth control because dimpling is eliminated. Vibrating microelectrode has been successfully used to make accurate oxygen-content measurements in arterial walls.

  20. Effect of iridium(IV) oxides on the decay of zinc tetrakis(N-methylpyridinium-4-yl)porphyrin. pi. -radical cation in the presence of poly(styrenesulfonate)

    SciTech Connect

    Nahor, G.S. )

    1989-07-27

    The {pi}-radical cation of zinc tetrakis(N-methylpyridinium-4-yl)porphyrin(ZnTMPyP{sup 5+}) has been produced by pulse radiolysis and its decay reactions have been followed in the presence of oxoiridium(IV) hydrate species and a negatively charged polyelectrolyte, poly(styrenesulfonate) (PSS). The iridium oxide species were produced from hexachloroiridate, and the nature of the product strongly depended on the pH during preparation. A hexahydroxoiridate species that was produced at high pH was found to be very reactive, and its reactions account for most decay processes observed. {gamma}-Radiolysis experiments suggest that this decay involves oxidation of the iridium species in a catalytic process. PSS-stabilized IrO{sub x} hydrosols did not react with the radical cation fast enough to compete with its disproportionation, although such hydrosols were highly reactive when stabilized with neutral or positively charged polymers. The lack of reactivity is attributed to the low mobility of the positively charged porphyrin in the domain of the negatively charged polyelectrolyte as well as to the absence of interpolymer processes. However, under {gamma}-radiolysis conditions, a redox reaction between the hydrosols and the radical becomes feasible.

  1. Iridium Aluminide Coats For Protection Against Ox idation

    NASA Technical Reports Server (NTRS)

    Kaplan, Richard B.; Tuffias, Robert H.; La Ferla, Raffaele; Jang, Qin

    1996-01-01

    Iridium aluminide coats investigated for use in protecting some metallic substrates against oxidation at high temperatures. Investigation prompted by need for cost-effective anti-oxidation coats for walls of combustion chambers in rocket engines. Also useful in special terrestrial applications like laboratory combustion chambers and some chemical-processing chambers.

  2. Method for refining contaminated iridium

    DOEpatents

    Heshmatpour, B.; Heestand, R.L.

    1982-08-31

    Contaminated iridium is refined by alloying it with an alloying agent selected from the group consisting of manganese and an alloy of manganese and copper, and then dissolving the alloying agent from the formed alloy to provide a purified iridium powder.

  3. Method for refining contaminated iridium

    DOEpatents

    Heshmatpour, Bahman; Heestand, Richard L.

    1983-01-01

    Contaminated iridium is refined by alloying it with an alloying agent selected from the group consisting of manganese and an alloy of manganese and copper, and then dissolving the alloying agent from the formed alloy to provide a purified iridium powder.

  4. Electrodeposition of platinum-iridium coatings and nanowires for neurostimulating applications: Fabrication, characterization and in-vivo retinal stimulation/recording. EIS studies of hexavalent and trivalent chromium based military coating systems

    NASA Astrophysics Data System (ADS)

    Petrossians, Artin

    The studies presented in this thesis are composed of two different projects demonstrated in two different parts. The first part of this thesis represents an electrochemical approach to possible improvements of the interface between an implantable device and biological tissue. The second part of this thesis represents electrochemical impedance spectroscopy (EIS) studies on the corrosion resistance behavior of different types of polymer coated Al2024 alloys. In the first part of this thesis, a broad range of investigations on the development of an efficient and reproducible electrochemical deposition method for fabrication of thin-film platinum-iridium alloys were performed. The developed method for production of dense films was then modified to produce very high surface area coatings with ultra-low electrochemical impedance characteristics. The high-surface area platinum-iridium coating was applied on microelectrode arrays for chronic in-vitro stimulation. Using the same method of producing dense films, platinum-iridium nanowires were fabricated using Anodized Aluminum Oxide (AAO) templates for hermetic packaging applications to be used in implantable microelectronics. The implantable microelectronics will be used to perform data reception and transmission management, power recovery, digital processing and analog output of stimulus current. Finally, in-vivo electrical stimulation tests were performed on an animal retina using high surface-area platinum-iridium coated single microelectrodes to verify the charge transfer characteristics of the coatings. In the second part of this thesis, three different sets of samples with different combinations of pretreatments, primers with the same type of topcoat were tested in 0.5 N NaCl for period of 30 days. The surface changes measured by EIS as a function of time were then analyzed. The analysis of the fit parameters of the impedance spectra showed that the different primers had the most effect on the corrosion protection

  5. In Vivo Validation of Custom-Designed Silicon-Based Microelectrode Arrays for Long-Term Neural Recording and Stimulation

    PubMed Central

    Manoonkitiwongsa, Panya S.; Wang, Cindy X.; McCreery, Douglas B.

    2012-01-01

    We developed and validated silicon-based neural probes for neural stimulating and recording in long-term implantation in the brain. The probes combine the deep reactive ion etching process and mechanical shaping of their tip region, yielding a mechanically sturdy shank with a sharpened tip to reduce insertion force into the brain and spinal cord, particularly, with multiple shanks in the same array. The arrays’ insertion forces have been quantified in vitro. Five consecutive chronically-implanted devices were fully functional from 3 to 18 months. The microelectrode sites were electroplated with iridium oxide, and the charge injection capacity measurements were performed both in vitro and after implantation in the adult feline brain. The functionality of the chronic array was validated by stimulating in the cochlear nucleus and recording the evoked neuronal activity in the central nucleus of the inferior colliculus. The arrays’ recording quality has also been quantified in vivo with neuronal spike activity recorded up to 566 days after implantation. Histopathology evaluation of neurons and astrocytes using immunohistochemical stains indicated minimal alterations of tissue architecture after chronic implantation. PMID:22020666

  6. Iridium/Rhenium Parts For Rocket Engines

    NASA Technical Reports Server (NTRS)

    Schneider, Steven J.; Harding, John T.; Wooten, John R.

    1991-01-01

    Oxidation/corrosion of metals at high temperatures primary life-limiting mechanism of parts in rocket engines. Combination of metals greatly increases operating temperature and longevity of these parts. Consists of two transition-element metals - iridium and rhenium - that melt at extremely high temperatures. Maximum operating temperature increased to 2,200 degrees C from 1,400 degrees C. Increases operating lifetimes of small rocket engines by more than factor of 10. Possible to make hotter-operating, longer-lasting components for turbines and other heat engines.

  7. Validation of EXAFS Analysis of Iridium Compounds

    NASA Astrophysics Data System (ADS)

    Feiters, M. C.; Longo, A.; Banerjee, D.; van der Ham, C. J. M.; Hetterscheid, D. G. H.

    2016-05-01

    Results of iridium L3 edge EXAFS measurements of compounds relevant for water oxidation catalysis are compared to those of other structural techniques. The structural results from EXAFS for the Ir compounds investigated here compare well to those of other structural techniques. Multiple scattering contributions are important in the coordinated Cp* and NHC ligands as well as in the IrCl6 unit and the IrO2 rutile structure. NHC is relatively weak compared to Ir, Cl, and even Cp* and O, and often out of phase with the other contributions.

  8. Solar abundance of iridium

    PubMed Central

    Drake, Stephen; Aller, Lawrence H.

    1976-01-01

    By a method of spectrum synthesis, which yields log gfA, where g is the statistical weight of the lower level, f is the oscillator strength, and A is the abundance, an attempt is made to deduce the solar iridium abundance from one relatively unblended, but fairly weak IrI line, λ 3220.78 Å. If the Corliss-Bozman f-value for this line is adopted, we find log A(Ir) = 0.82 on the scale log A(H) = 12.00. The discordance with the value found from carbonaceous chondrites may arise from faulty f-values or from difficulties arising from line blending in this far ultraviolet domain of the solar spectrum. PMID:16578735

  9. Characterization of Platinum and Iridium Oxyhydrate Surface Layers from Platinum and Iridium Foils.

    PubMed

    Johnson, Benjamin; Ranjan, Chinmoy; Greiner, Mark; Arrigo, Rosa; Schuster, Manfred Erwin; Höpfner, Britta; Gorgoi, Mihaela; Lauermann, Iver; Willinger, Marc; Knop-Gericke, Axel; Schlögl, Robert

    2016-07-01

    Platinum and iridium polycrystalline foils were oxidized electrochemically through anodization to create thin platinum and iridium hydrous oxide layers, which were analyzed through laboratory photoelectron spectroscopy during heating and time series (temperature-programmed spectroscopy). The films contain oxygen in the form of bound oxides, water, and hydroxides and were investigated by depth profiling with high-energy photoelectron spectroscopy. The Pt films are unstable and begin to degrade immediately after removal from the electrolyte to form core-shell structures with a metallic inner core and a hydrous oxide outer shell almost devoid of Pt. However, evidence was found for metastable intermediate states of degradation; therefore, it may be possible to manufacture PtOx phases with increased stability. Heating the film to even 100 °C causes accelerated degradation, which shows that stoichiometric oxides such as PtO2 or PtO are not the active species in the electrolyte. The Ir films exhibit increased stability and higher surface Ir content, and gentle heating at low temperatures leads to a decrease in defect density. Although both layers are based on noble metals, their surface structures are markedly different. The complexity of such hydrous oxide systems is discussed in detail with the goal of identifying the film composition more precisely. PMID:27226255

  10. Hydridomethyl iridium complex

    DOEpatents

    Bergman, Robert G.; Buchanan, J. Michael; Stryker, Jeffrey M.; Wax, Michael J.

    1989-01-01

    A process for functionalizing methane comprising: (a) reacting methane with a hydridoalkyl metal complex of the formula: CpIr[P(R.sub.1).sub.3 ]H(R.sub.2) wherein Cp represents a cyclopentadienyl or alkylcyclopentadienyl radical having from 1 to 5 carbon atoms; Ir represents an iridium atom; P represents a phosphorus atom; R.sub.1 represents an alkyl group; R.sub.2 represents an alkyl group having at least two carbon atoms; and H represents a hydrogen atom, in the presence of a liquid alkane R.sub.3 H having at least three carbon atoms to form a hydridomethyl complex of the formula: CpIr[P(R.sub.1).sub.3 ]HMe where Me represents a methyl radical. (b) reacting said hydridomethyl complex with an organic halogenating agent such as a tetrahalomethane or a haloform of the formulas: CX'X"X'"X"" or CHX'X"X'"; wherein X', X", X"', and X"" represent halogens selected from bromine, iodine and chlorine, to halomethyl complex of step (a) having the formula: CpIr[P(R.sub.1).sub.3 ]MeX: (c) reacting said halomethyl complex with a mercuric halide of the formula HgX.sub.2 to form a methyl mercuric halide of the formula HgMeX; and (d) reacting said methyl mercuric halide with a molecular halogen of the formula X.sub.2 to form methyl halide.

  11. Processing and properties of iridium alloys for space power applications

    SciTech Connect

    Ohriner, E.K.

    1994-12-31

    Iridium alloys are used as fuel cladding in radioisotope thermoelectric generators due to their high-melting point, high- temperature strength, and oxidation and corrosion resistance. Although iridium has a face-centered cubic crystal structure, it undergoes a distinct ductile-to-brittle transition characteristic of many body-centered cubic metals. Improved ductility in the alloys is achieved through material purification and controlled alloy additions at the parts per million (ppm) level. A vacuum arc remelt operation produces a nearly defect-free casting, which is further processed to sheet products. A change in processing from drop castings of small arc-melted buttons to large arc-remelted ingots has substantially improved product yields. The effects of processing changes on alloy microstructure, sheet textures, oxidation effects, high-strain-rate ductility, and fabricability are discussed.

  12. Iridium-catalyst-based autonomous bubble-propelled graphene micromotors with ultralow catalyst loading.

    PubMed

    Wang, Hong; Sofer, Zdeněk; Eng, Alex Yong Sheng; Pumera, Martin

    2014-11-10

    A novel concept of an iridium-based bubble-propelled Janus-particle-type graphene micromotor with very high surface area and with very low catalyst loading is described. The low loading of Ir catalyst (0.54 at %) allows for fast motion of graphene microparticles with high surface area of 316.2 m(2)  g(-1). The micromotor was prepared with a simple and scalable method by thermal exfoliation of iridium-doped graphite oxide precursor composite in hydrogen atmosphere. Oxygen bubbles generated from the decomposition of hydrogen peroxide at the iridium catalytic sites provide robust propulsion thrust for the graphene micromotor. The high surface area and low iridium catalyst loading of the bubble-propelled graphene motors offer great possibilities for dramatically enhanced cargo delivery. PMID:25293511

  13. Electrochemical Oxidation of Cysteine at a Film Gold Modified Carbon Fiber Microelectrode Its Application in a Flow—Through Voltammetric Sensor

    PubMed Central

    Wang, Lai-Hao; Huang, Wen-Shiuan

    2012-01-01

    A flow-electrolytical cell containing a strand of micro Au modified carbon fiber electrodes (CFE) has been designedand characterized for use in a voltammatric detector for detecting cysteine using high-performance liquid chromatography. Cysteine is more efficiently electrochemical oxidized on a Au /CFE than a bare gold and carbon fiber electrode. The possible reaction mechanism of the oxidation process is described from the relations to scan rate, peak potentials and currents. For the pulse mode, and measurements with suitable experimental parameters, a linear concentration from 0.5 to 5.0 mg·L−1 was found. The limit of quantification for cysteine was below 60 ng·mL−1. PMID:22737024

  14. Revealing neuronal function through microelectrode array recordings

    PubMed Central

    Obien, Marie Engelene J.; Deligkaris, Kosmas; Bullmann, Torsten; Bakkum, Douglas J.; Frey, Urs

    2015-01-01

    Microelectrode arrays and microprobes have been widely utilized to measure neuronal activity, both in vitro and in vivo. The key advantage is the capability to record and stimulate neurons at multiple sites simultaneously. However, unlike the single-cell or single-channel resolution of intracellular recording, microelectrodes detect signals from all possible sources around every sensor. Here, we review the current understanding of microelectrode signals and the techniques for analyzing them. We introduce the ongoing advancements in microelectrode technology, with focus on achieving higher resolution and quality of recordings by means of monolithic integration with on-chip circuitry. We show how recent advanced microelectrode array measurement methods facilitate the understanding of single neurons as well as network function. PMID:25610364

  15. Stretchable Micro-Electrode Array

    SciTech Connect

    Maghribi, M; Hamilton, J; Polla, D; Rose, K; Wilson, T; Krulevitch, P

    2002-03-08

    This paper focuses on the design consideration, fabrication processes and preliminary testing of the stretchable micro-electrode array. We are developing an implantable, stretchable micro-electrode array using polymer-based microfabrication techniques. The device will serve as the interface between an electronic imaging system and the human eye, directly stimulating retinal neurons via thin film conducting traces and electroplated electrodes. The metal features are embedded within a thin ({approx}50 micron) substrate fabricated using poly (dimethylsiloxane) (PDMS), a biocompatible elastomeric material that has very low water permeability. The conformable nature of PDMS is critical for ensuring uniform contact with the curved surface of the retina. To fabricate the device, we developed unique processes for metalizing PDMS to produce robust traces capable of maintaining conductivity when stretched (5%, SD 1.5), and for selectively passivating the conductive elements. An in situ measurement of residual strain in the PDMS during curing reveals a tensile strain of 10%, explaining the stretchable nature of the thin metalized devices.

  16. Toward the Digital Electrochemical Recognition of Cobalt, Iridium, Nickel, and Iron Ion Collisions by Catalytic Amplification.

    PubMed

    Dick, Jeffrey E; Bard, Allen J

    2016-07-13

    We report the electrochemical detection of femtomolar amounts of cobalt, iridium, nickel, and iron ions in solution by electrocatalyst formation and amplification. The metal oxides of these ions can be formed electrochemically and can catalyze the oxidation of water. Alternatively, the reduction of metal ions to metals, such as the reduction of IrCl6(3-) to iridium, is capable of electrocatalytically reducing protons to molecular hydrogen, as shown previously with Pt. These events, which manifest themselves in amperometry, correspond to the formation of electrocatalytic nuclei on the electrode surface, capable of electrocatalytically oxidizing water or reducing protons. An analysis of the frequency of anodic blips compared to theory implies that the requirement for water oxidation is 10 ± 1 ions of cobalt, 13 ± 4 ions of iridium, and 11 ± 3 ions of nickel. A similar analysis for iridium reduction and the corresponding catalytic reduction of protons implies that 6 ± 2 ions of iridium are required for proton reduction. These numbers are confirmed in an analysis of the time of first nucleation event, i.e. the time at which the first blip on the amperometric i-t experiment occurs. We further show that the anodic blips in detecting nickel increase in intensity upon increasing amounts of iron ions in solution to a ratio of Ni/Fe of ∼5, surprisingly close to that for bulk electrocatalysts of Ni-Fe. PMID:27295309

  17. Conducting Polymer 3D Microelectrodes

    PubMed Central

    Sasso, Luigi; Vazquez, Patricia; Vedarethinam, Indumathi; Castillo-León, Jaime; Emnéus, Jenny; Svendsen, Winnie E.

    2010-01-01

    Conducting polymer 3D microelectrodes have been fabricated for possible future neurological applications. A combination of micro-fabrication techniques and chemical polymerization methods has been used to create pillar electrodes in polyaniline and polypyrrole. The thin polymer films obtained showed uniformity and good adhesion to both horizontal and vertical surfaces. Electrodes in combination with metal/conducting polymer materials have been characterized by cyclic voltammetry and the presence of the conducting polymer film has shown to increase the electrochemical activity when compared with electrodes coated with only metal. An electrochemical characterization of gold/polypyrrole electrodes showed exceptional electrochemical behavior and activity. PC12 cells were finally cultured on the investigated materials as a preliminary biocompatibility assessment. These results show that the described electrodes are possibly suitable for future in-vitro neurological measurements. PMID:22163508

  18. Excursion of vibrating microelectrodes in tissue

    NASA Technical Reports Server (NTRS)

    Kanabus, E. W.; Feldstein, C.; Crawford, D. W.

    1980-01-01

    The paper deals with a vibrating microelectrode holder consisting of a support rod attached to the cone of a miniature loudspeaker. This holder facilitates a microelectrode penetration into arterial wall tissue, eliminates surface dimpling, and relieves polarographic artifacts believed to be due to tissue compression. The paper presents construction and performance details of the electrode holder, and evaluates the extent of possible damage incurred during such vibration by measuring electrode motion relative to surrounding tissue in an excised segment of femoral artery in the rabbit. It is concluded that under proper vibratory conditions microelectrodes can be easily inserted into the arterial wall with minimum tissue disturbance.

  19. Electronic Structure of Iridium Clusters on Graphene

    NASA Astrophysics Data System (ADS)

    Barker, Bradford A.; Bradley, Aaron J.; Ugeda, Miguel M.; Coh, Sinisa; Zettl, Alex; Crommie, Michael F.; Cohen, Marvin L.; Louie, Steven G.

    2015-03-01

    Graphene was predicted to exhibit non-trivial Z2 topology, but its exceedingly weak spin-orbit coupling prevented this from being observed. Previous theoretical work has proposed enhancing the spin-orbit coupling strength by depositing individual adatoms adsorbed onto the surface of graphene. We show experimental evidence that the iridium adatoms cluster, with a cluster size of at least two atoms. We investigate through theoretical calculations the orientation of the iridium dimers on graphene, contrast the electronic structure of iridium dimers with iridium monomers, and compare the theoretical iridium dimer electronic structure calculations with the experimental results determined via scanning tunneling spectroscopy. This work was supported by NSF Grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at LBNL's NERSC facility.

  20. Development and application of microelectrodes in biofilms

    NASA Astrophysics Data System (ADS)

    Nguyen, Hung Duc

    The objective of this dissertation was to develop novel microelectrode techniques and to use microelectrodes for microscale chemistry characterization in biofilms. The first part of the dissertation focused on the development of microelectrodes operated in biofilms respiring on electrodes. The novel improvement required that microelectrodes be compatible within a three-electrode electrochemical cell. Redox potential, pH and hydrogen peroxide microelectrodes were successfully constructed with built-in silver/silver chloride reference electrodes that allowed for such measurements. By using these novel redox potential and pH microelectrodes we found that the decreasing redox potential in Shewanella oneidensis MR-1 biofilms from the bulk phase was not due to pH changes. Shewanella oneidensis MR-1 biofilms were not redox-controlled when they respired on electrodes. The second part of the dissertation focused on the development of a flavin microelectrode to detect flavins, known chemicals playing a role as electron mediators in Shewanella oneidensis MR-1. We successfully developed the novel microelectrode and operated it using a unique voltammetric technique, square wave voltammetry. It was found that the flavin concentration reached 0.7 µM, increasing near the bottom of the Shewanella oneidensis MR-1 biofilm, where no oxygen was present. The third part of the dissertation focused on microelectrode mapping techniques to quantify microscale geochemical gradients in Hanford 300A subsurface sediment biofilms. We found that there were significant differences in geochemical parameters across the sediment biofilm/water interface in the presence and absence of U(VI) under oxic and anoxic conditions. The results also revealed the presence of geochemical hotspots, i.e., microenvironments with relatively high or low biogeochemical activities in sediment biofilms, which had important practical implications for

  1. Study of degradation intermediates formed during electrochemical oxidation of pesticide residue 2,6-dichlorobenzamide (BAM) at boron doped diamond (BDD) and platinum-iridium anodes.

    PubMed

    Madsen, Henrik Tækker; Søgaard, Erik Gydesen; Muff, Jens

    2014-08-01

    Electrochemical oxidation is a promising technique for degradation of otherwise recalcitrant organic micropollutants in waters. In this study, the applicability of electrochemical oxidation was investigated concerning the degradation of the groundwater pollutant 2,6-dichlorobenzamide (BAM) through the electrochemical oxygen transfer process with two anode materials: Ti/Pt90-Ir10 and boron doped diamond (Si/BDD). Besides the efficiency of the degradation of the main pollutant, it is also of outmost importance to control the formation and fate of stable degradation intermediates. These were investigated quantitatively with HPLC-MS and TOC measurements and qualitatively with a combined HPLC-UV and HPLC-MS protocol. 2,6-Dichlorobenzamide was found to be degraded most efficiently by the BDD cell, which also resulted in significantly lower amounts of intermediates formed during the process. The anodic degradation pathway was found to occur via substitution of hydroxyl groups until ring cleavage leading to carboxylic acids. For the BDD cell, there was a parallel cathodic degradation pathway that occurred via dechlorination. The combination of TOC with the combined HPLC-UV/MS was found to be a powerful method for determining the amount and nature of degradation intermediates.

  2. Study of degradation intermediates formed during electrochemical oxidation of pesticide residue 2,6-dichlorobenzamide (BAM) at boron doped diamond (BDD) and platinum-iridium anodes.

    PubMed

    Madsen, Henrik Tækker; Søgaard, Erik Gydesen; Muff, Jens

    2014-08-01

    Electrochemical oxidation is a promising technique for degradation of otherwise recalcitrant organic micropollutants in waters. In this study, the applicability of electrochemical oxidation was investigated concerning the degradation of the groundwater pollutant 2,6-dichlorobenzamide (BAM) through the electrochemical oxygen transfer process with two anode materials: Ti/Pt90-Ir10 and boron doped diamond (Si/BDD). Besides the efficiency of the degradation of the main pollutant, it is also of outmost importance to control the formation and fate of stable degradation intermediates. These were investigated quantitatively with HPLC-MS and TOC measurements and qualitatively with a combined HPLC-UV and HPLC-MS protocol. 2,6-Dichlorobenzamide was found to be degraded most efficiently by the BDD cell, which also resulted in significantly lower amounts of intermediates formed during the process. The anodic degradation pathway was found to occur via substitution of hydroxyl groups until ring cleavage leading to carboxylic acids. For the BDD cell, there was a parallel cathodic degradation pathway that occurred via dechlorination. The combination of TOC with the combined HPLC-UV/MS was found to be a powerful method for determining the amount and nature of degradation intermediates. PMID:24873711

  3. On the dissolution of iridium by aluminum.

    SciTech Connect

    Hewson, John C.

    2009-08-01

    The potential for liquid aluminum to dissolve an iridium solid is examined. Substantial uncertainties exist in material properties, and the available data for the iridium solubility and iridium diffusivity are discussed. The dissolution rate is expressed in terms of the regression velocity of the solid iridium when exposed to the solvent (aluminum). The temperature has the strongest influence in the dissolution rate. This dependence comes primarily from the solubility of iridium in aluminum and secondarily from the temperature dependence of the diffusion coefficient. This dissolution mass flux is geometry dependent and results are provided for simplified geometries at constant temperatures. For situations where there is negligible convective flow, simple time-dependent diffusion solutions are provided. Correlations for mass transfer are also given for natural convection and forced convection. These estimates suggest that dissolution of iridium can be significant for temperatures well below the melting temperature of iridium, but the uncertainties in actual rates are large because of uncertainties in the physical parameters and in the details of the relevant geometries.

  4. Carbon Nanotube-based microelectrodes for enhanced detection of neurotransmitters

    NASA Astrophysics Data System (ADS)

    Jacobs, Christopher B.

    Fast-scan cyclic voltammetry (FSCV) is one of the common techniques used for rapid measurement of neurotransmitters in vivo. Carbon-fiber microelectrodes (CFMEs) are typically used for neurotransmitter detection because of sub-second measurement capabilities, ability to measure changes in neurotransmitter concentration during neurotransmission, and the small size electrode diameter, which limits the amount of damage caused to tissue. Cylinder CFMEs, typically 50 -- 100 microm long, are commonly used for in vivo experiments because the electrode sensitivity is directly related to the electrode surface area. However the length of the electrode can limit the spatial resolution of neurotransmitter detection, which can restrict experiments in Drosophila and other small model systems. In addition, the electrode sensitivity toward dopamine and serotonin detection drops significantly for measurements at rates faster than 10 Hz, limiting the temporal resolution of CFMEs. While the use of FSCV at carbon-fiber microelectrodes has led to substantial strides in our understanding of neurotransmission, techniques that expand the capabilities of CFMEs are crucial to fully maximize the potential uses of FSCV. This dissertation introduces new methods to integrate carbon nanotubes (CNT) into microelectrodes and discusses the electrochemical enhancements of these CNT-microelectrodes. The electrodes are specifically designed with simple fabrication procedures so that highly specialized equipment is not necessary, and they utilize commercially available materials so that the electrodes could be easily integrated into existing systems. The electrochemical properties of CNT modified CFMEs are characterized using FSCV and the effect of CNT functionalization on these properties is explored in Chapter 2. For example, CFME modification using carboxylic acid functionalized CNTs yield about a 6-fold increase in dopamine oxidation current, but modification with octadecylamine CNTs results in a

  5. Selective DNA purine base photooxidation by bis-terdentate iridium(III) polypyridyl and cyclometalated complexes.

    PubMed

    Jacques, Alexandre; Kirsch-De Mesmaeker, Andrée; Elias, Benjamin

    2014-02-01

    Two bis-terdentate iridium(III) complexes with polypyridyl and cyclometalated ligands have been prepared and characterized. Their spectroscopic and electrochemical properties have been studied, and a photophysical scheme addressing their properties is proposed. Different types of excited states have been considered to account for the deactivation processes in each complex. Interestingly, in the presence of mono- or polynucleotides, a photoinduced electron-transfer process from a DNA purine base (i.e., guanine or adenine) to the excited complex is shown through luminescence quenching experiments. For the first time, this work reports evidence for selective DNA purine bases oxidation by excited iridium(III) bis-terdentate complexes.

  6. Band-type microelectrodes for amperometric immunoassays.

    PubMed

    Lee, Ga-Yeon; Chang, Young Wook; Ko, Hyuk; Kang, Min-Jung; Pyun, Jae-Chul

    2016-07-20

    A band-type microelectrode was made using a parylene-N film as a passivation layer. A circular-type, mm-scale electrode with the same diameter as the band-type microelectrode was also made with an electrode area that was 5000 times larger than the band-type microelectrode. By comparing the amperometric signals of 3,5,3',5'-tetramethylbenzidine (TMB) samples at different optical density (OD) values, the band-type microelectrode was determined to be 9 times more sensitive than the circular-type electrode. The properties of the circular-type and the band-type electrodes (e.g., the shape of their cyclic voltammograms, the type of diffusion layer used, and the diffusion layer thickness per unit electrode area) were characterized according to their electrode area using the COMSOL Multiphysics software. From these simulations, the band-type electrode was estimated to have the conventional microelectrode properties, even when the electrode area was 100 times larger than a conventional circular-type electrode. These results show that both the geometry and the area of an electrode can influence the properties of the electrode. Finally, amperometric analysis based on a band-type electrode was applied to commercial ELISA kits to analyze human hepatitis B surface antigen (hHBsAg) and human immunodeficiency virus (HIV) antibodies. PMID:27251855

  7. Electrodeposition of platinum-iridium alloy nanowires for hermetic packaging of microelectronics.

    PubMed

    Petrossians, Artin; Whalen, John J; Weiland, James D; Mansfeld, Florian

    2012-01-01

    An electrodeposition technique was applied for fabrication of dense platinum-iridium alloy nanowires as interconnect structures in hermetic microelectronic packaging to be used in implantable devices. Vertically aligned arrays of platinum-iridium alloy nanowires with controllable length and a diameter of about 200 nm were fabricated using a cyclic potential technique from a novel electrodeposition bath in nanoporous aluminum oxide templates. Ti/Au thin films were sputter deposited on one side of the alumina membranes to form a base material for electrodeposition. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were used to characterize the morphology and the chemical composition of the nanowires, respectively. SEM micrographs revealed that the electrodeposited nanowires have dense and compact structures. EDS analysis showed a 60:40% platinum-iridium nanowire composition. Deposition rates were estimated by determining nanowire length as a function of deposition time. High Resolution Transmission Electron Microscopy (HRTEM) images revealed that the nanowires have a nanocrystalline structure with grain sizes ranging from 3 nm to 5 nm. Helium leak tests performed using a helium leak detector showed leak rates as low as 1 × 10(-11) mbar L s(-1) indicating that dense nanowires were electrodeposited inside the nanoporous membranes. Comparison of electrical measurements on platinum and platinum-iridium nanowires revealed that platinum-iridium nanowires have improved electrical conductivity.

  8. Grain-boundary cavitation and weld-underbead cracking in DOP-26 iridium alloy

    SciTech Connect

    Mosley, W.C. Jr.

    1983-01-01

    Plutonium-238 oxide fuel pellets for the General Purpose Heat Source Radioisotopic thermoelectric generators to be used on the NASA Galileo Mission to Jupiter and the International Solar Polar Mission are produced and encapsulated in DOP-26 iridium alloy at the Savannah River Plant. DOP-26 iridium alloy was developed at the Oak Ridge National Laboratory and contains nominally 0.3 weight-percent tungsten, 60-ppM thorium and 50-ppM aluminum. Underbead cracks occasionally occur in the girth weld on the iridium alloy cladding in the area where the gas tungsten arc is quenched. A variety of electron beam techniques have been used to determine the cause of cracking. Results are discussed. (WHK)

  9. The effect of resveratrol on neurodegeneration and blood brain barrier stability surrounding intracortical microelectrodes.

    PubMed

    Potter, Kelsey A; Buck, Amy C; Self, Wade K; Callanan, Megan E; Sunil, Smrithi; Capadona, Jeffrey R

    2013-09-01

    The current study seeks to elucidate a biological mechanism which may mediate neuroinflammation, and decreases in both blood-brain barrier stability and neuron viability at the intracortical microelectrode-tissue interface. Here, we have focused on the role of pro-inflammatory reactive oxygen species. Specifically, adult rats implanted within intracortical microelectrodes were systemically administered the anti-oxidant, resveratrol, both the day before and the day of surgery. Animals were sacrificed at two or four weeks post-implantation for histological analysis of the neuroinflammatory and neurodegenerative responses to the microelectrode. At two weeks post-implantation, we found animals treated with resveratrol demonstrated suppression of reactive oxygen species accumulation and blood-brain barrier instability, accompanied with increased density of neurons at the intracortical microelectrode-tissue interface. Four weeks post-implantation, animals treated with resveratrol exhibited indistinguishable levels of markers for reactive oxygen species and neuronal nuclei density in comparison to untreated control animals. However, of the neurons that remained, resveratrol treated animals were seen to display reductions in the density of degenerative neurons compared to control animals at both two and four weeks post-implantation. Initial mechanistic evaluation suggested the roles of both anti-oxidative enzymes and toll-like receptor 4 expression in facilitating microglia activation and the propagation of neurodegenerative inflammatory pathways. Collectively, our data suggests that short-term attenuation of reactive oxygen species accumulation and blood-brain barrier instability can result in prolonged improvements in neuronal viability around implanted intracortical microelectrodes, while also identifying potential therapeutic targets to reduce chronic intracortical microelectrode-mediated neurodegeneration.

  10. The Effect of Residual Endotoxin Contamination on the Neuroinflammatory Response to Sterilized Intracortical Microelectrodes.

    PubMed

    Ravikumar, Madhumitha; Hageman, Daniel J; Tomaszewski, William H; Chandra, Gabriella M; Skousen, John L; Capadona, Jeffrey R

    2014-05-01

    A major limitation to the use of microelectrode technologies in both research and clinical applications is our inability to consistently record high quality neural signals. There is increasing evidence that recording instability is linked, in part, to neuroinflammation. A number of factors including extravasated blood products and macrophage released soluble factors are believed to mediate neuroinflammation and the resulting recording instability. However, the roles of other inflammatory stimuli, such as residual endotoxin contamination, are poorly understood. Therefore, to determine the effect of endotoxin contamination we examined the brain tissue response of C57/BL6 mice to non-functional microelectrodes with a range of endotoxin levels. Endotoxin contamination on the sterilized microelectrodes was measured using a limulus amebocyte lysate test following FDA guidelines. Microelectrodes sterilized by autoclave, dry heat, or ethylene oxide gas, resulted in variable levels of residual endotoxins of 0.55 EU/mL, 0.22 EU/mL, and 0.11 EU/mL, respectively. Histological evaluation at two weeks showed a direct correlation between microglia/macrophage activation and endotoxin levels. Interestingly, astrogliosis, neuronal loss, and blood brain barrier dysfunction demonstrated a threshold-dependent response to bacterial endotoxins. However, at sixteen weeks, no histological differences were detected, regardless of initial endotoxin levels. Therefore, our results demonstrate that endotoxin contamination, within the range examined, contributes to initial but not chronic microelectrode associated neuroinflammation. Our results suggest that minimizing residual endotoxins may impact early recording quality. To this end, endotoxins should be considered as a potent stimulant to the neuroinflammatory response to implanted intracortical microelectrodes.

  11. Salt passivation during anodic iridium dissolution in chloride melts

    SciTech Connect

    Saltykova, N.A.; Pechorskaya, L.S.; Baraboshkin, A.N.; Kotovskii, S.N.; Kosikhin, L.T.

    1986-11-01

    Anodic iridium dissolution in chloride melts at 500-700/sup 0/C was studied by potentiostatic, potentiodynamic, and galvanostatic techniques. It was found that an iridium anode is passivated by hexachloroiridates, first by the iridium (III) salt and at more positive potentials by the iridium (IV) salt. Values for anode resistance during passivation by salt films were calculated. It was shown that the morphology of the dissolving anode surface is determined by the value of polarization.

  12. Fabrication of microelectrode arrays for neural measurements from retinal tissue

    NASA Astrophysics Data System (ADS)

    Cunningham, W.; Mathieson, K.; McEwan, F. A.; Blue, A.; McGeachy, R.; McLeod, J. A.; Morris-Ellis, C.; O'Shea, V.; Smith, K. M.; Litke, A.; Rahman, M.

    2001-09-01

    The production of high-density, large-area microelectrode arrays for neurophysiology studies requires a combination of electron beam lithography and photolithography, together with dry etch pattern transfer. The retina is one of the few parts of the animal nervous system to which the input (image) and output (ganglion) signals are accessible. To read out the signals from the ganglion cells, we have made microelectrode arrays in the transparent conductor indium tin oxide (ITO) by CH4/H2 reactive ion etching (RIE) using a novel masking technique that avoids the usual problem of resist cross-linking. An electron beam lithography process has also been developed exploiting multiple plasma steps. The ITO layer lies on a glass substrate to allow the retinal cells and the electrode positions to be photographed using a CCD camera. SF6 RIE of vias through a thick protective silicon nitride coating deposited by plasma onto the ITO/glass permits the platinization of the electrodes. Both CH4/H2 and SF6 RIE require low electrical damage to the ITO, which we verify.

  13. Nanostructured gold microelectrodes for extracellular recording from electrogenic cells

    NASA Astrophysics Data System (ADS)

    Brüggemann, D.; Wolfrum, B.; Maybeck, V.; Mourzina, Y.; Jansen, M.; Offenhäusser, A.

    2011-07-01

    We present a new biocompatible nanostructured microelectrode array for extracellular signal recording from electrogenic cells. Microfabrication techniques were combined with a template-assisted approach using nanoporous aluminum oxide to develop gold nanopillar electrodes. The nanopillars were approximately 300-400 nm high and had a diameter of 60 nm. Thus, they yielded a higher surface area of the electrodes resulting in a decreased impedance compared to planar electrodes. The interaction between the large-scale gold nanopillar arrays and cardiac muscle cells (HL-1) was investigated via focused ion beam milling. In the resulting cross-sections we observed a tight coupling between the HL-1 cells and the gold nanostructures. However, the cell membranes did not bend into the cleft between adjacent nanopillars due to the high pillar density. We performed extracellular potential recordings from HL-1 cells with the nanostructured microelectrode arrays. The maximal amplitudes recorded with the nanopillar electrodes were up to 100% higher than those recorded with planar gold electrodes. Increasing the aspect ratio of the gold nanopillars and changing the geometrical layout can further enhance the signal quality in the future.

  14. IRIDIUM (R): A Lockheed transition to commercial space

    NASA Technical Reports Server (NTRS)

    Tadano, Thomas N.

    1995-01-01

    At Lockheed Missiles & Space Company, the IRIDIUM commercial space program is dramatically revolutionizing spacecraft development and manufacturing processes to reduce cost while maintaining quality and reliability. This report includes the following sections: an overview of the IRIDIUM system, the Lockheed IRIDIUM project and challenges; cycle-time reduction through production reorganization; and design for manufacturing and quality.

  15. Laser spectroscopy of iridium monoboride

    NASA Astrophysics Data System (ADS)

    Ye, Jianjun; Pang, H. F.; Wong, A. M.-Y.; Leung, J. W.-H.; Cheung, A. S.-C.

    2008-04-01

    High resolution laser induced fluorescence spectrum of IrB in the spectral region between 545 and 610nm has been recorded and analyzed. Reacting laser-ablated iridium atoms with 1% B2H6 seeded in argon produced the IrB molecule. This is the first experimental observation of the IrB molecule. Four vibronic transition bands, (v,0) with v =0-3 of an electronic transition system, have been observed. Spectra of all four isotopic molecules, Ir191B10, Ir193B10, Ir191B11, and Ir193B11, were recorded. Isotopic relationships confirmed the carrier of the spectra and the vibrational quantum number assignment. Preliminary analysis of rotational lines showed that these vibronic bands are with Ω'=2 and Ω″=3. The electronic transition identified is assigned as the [16.5]Π23-XΔ33 system. Partially resolved hyperfine structure which conforms to the Hund's case aβ coupling scheme has been observed and analyzed. The bond length r0 of the lower XΔ33 state of IrB was determined to be 1.7675Å.

  16. Laser Spectroscopy of Iridium Monochloride

    NASA Astrophysics Data System (ADS)

    Linton, Colan; Adam, Allan G.; Foran, Samantha; Ma, Tongmei; Steimle, Timothy

    2016-06-01

    Iridium monochloride (IrCl) molecules have been produced in the gas phase using laser ablation sources at the University of New Brunswick (UNB) and Arizona State University (ASU). Low resolution laser induced fluorescence (LIF) spectra, obtained at UNB using a pulsed dye laser, showed three bands at 557, 545 and 534 nm which appeared to form an upper state vibrational progression. Dispersed fluorescence (DF) spectra, obtained by exciting each band at its band head frequency, showed a ground state vibrational progression extending from v=0 to 6. High resolution spectra (FWHM=0.006 wn), taken using a cw ring dye laser, showed resolved rotational lines, broadened by unresolved Ir (I=3/2) hyperfine structure, in both the 193Ir35Cl and 191Ir35Cl isotopologues. Vibrational assignments of 0-0, 1-0 and 2-0 for the three bands were determined from the isotope structure and the rotational analysis showed the transition to be ^3Φ_4 - ^3Φ_4, similar to that previously observed in IrF. Higher resolution spectra (FWHM=0.001 wn) of the 1-0 band, obtained at ASU, showed resolved hyperfine structure from which the magnetic and quadrupole hyperfine parameters in the ground and excited states were determined. The interpretation of the hyperfine parameters in terms of the electron configurations will be presented along with a comparison of the properties of IrCl and IrF.

  17. Electrochemical and chemical routes to hydride loss from an iridium dihydride.

    PubMed

    Walden, A G; Kumar, A; Lease, N; Goldman, A S; Miller, A J M

    2016-06-14

    With a view towards replacing sacrificial hydrogen acceptors in alkane dehydrogenation catalysis, electrochemical methods for oxidative activation of a pincer-ligated iridium hydride intermediate were explored. A 1H(+)/2e(-) oxidation process was observed in THF solvent, with net hydride loss leading to a reactive cationic intermediate that can be trapped by chloride. Analogous reactivity was observed with the concerted hydride transfer reagent Ph3C(+), connecting chemical and electrochemical hydride loss pathways. PMID:26979786

  18. Iridium emissions from Hawaiian volcanoes

    NASA Technical Reports Server (NTRS)

    Finnegan, D. L.; Zoller, W. H.; Miller, T. M.

    1988-01-01

    Particle and gas samples were collected at Mauna Loa volcano during and after its eruption in March and April, 1984 and at Kilauea volcano in 1983, 1984, and 1985 during various phases of its ongoing activity. In the last two Kilauea sampling missions, samples were collected during eruptive activity. The samples were collected using a filterpack system consisting of a Teflon particle filter followed by a series of 4 base-treated Whatman filters. The samples were analyzed by INAA for over 40 elements. As previously reported in the literature, Ir was first detected on particle filters at the Mauna Loa Observatory and later from non-erupting high temperature vents at Kilauea. Since that time Ir was found in samples collected at Kilauea and Mauna Loa during fountaining activity as well as after eruptive activity. Enrichment factors for Ir in the volcanic fumes range from 10,000 to 100,000 relative to BHVO. Charcoal impregnated filters following a particle filter were collected to see if a significant amount of the Ir was in the gas phase during sample collection. Iridium was found on charcoal filters collected close to the vent, no Ir was found on the charcoal filters. This indicates that all of the Ir is in particulate form very soon after its release. Ratios of Ir to F and Cl were calculated for the samples from Mauna Loa and Kilauea collected during fountaining activity. The implications for the KT Ir anomaly are still unclear though as Ir was not found at volcanoes other than those at Hawaii. Further investigations are needed at other volcanoes to ascertain if basaltic volcanoes other than hot spots have Ir enrichments in their fumes.

  19. Electrostatic Microactuators for Precise Positioning of Neural Microelectrodes

    PubMed Central

    Muthuswamy, Jit; Okandan, Murat; Jain, Tilak; Gilletti, Aaron

    2006-01-01

    Microelectrode arrays used for monitoring single and multineuronal action potentials often fail to record from the same population of neurons over a period of time likely due to micromotion of neurons away from the microelectrode, gliosis around the recording site and also brain movement due to behavior. We report here novel electrostatic microactuated microelectrodes that will enable precise repositioning of the microelectrodes within the brain tissue. Electrostatic comb-drive microactuators and associated microelectrodes are fabricated using the SUMMiT V™ (Sandia's Ultraplanar Multilevel MEMS Technology) process, a five-layer polysilicon micromachining technology of the Sandia National labs, NM. The microfabricated microactuators enable precise bidirectional positioning of the microelectrodes in the brain with accuracy in the order of 1 μm. The microactuators allow for a linear translation of the microelectrodes of up to 5 mm in either direction making it suitable for positioning microelectrodes in deep structures of a rodent brain. The overall translation was reduced to approximately 2 mm after insulation of the microelectrodes with epoxy for monitoring multiunit activity. The microactuators are capable of driving the microelectrodes in the brain tissue with forces in the order of several micro-Newtons. Single unit recordings were obtained from the somatosensory cortex of adult rats in acute experiments demonstrating the feasibility of this technology. Further optimization of the insulation, packaging and interconnect issues will be necessary before this technology can be validated in long-term experiments. PMID:16235660

  20. Carbon nanospikes grown on metal wires as microelectrode sensors for dopamine

    DOE PAGES

    Zestos, Alexander G.; Yang, Cheng; Jacobs, Christopher B.; Hensley, Dale; Venton, B. Jill

    2015-09-14

    Carbon nanomaterials are advantageous as electrodes for neurotransmitter detection, but the difficulty of nanomaterials deposition on electrode substrates limits the reproducibility and future applications. In our study, we used plasma enhanced chemical vapor deposition (PECVD) to directly grow a thin layer of carbon nanospikes (CNS) on cylindrical metal substrates. No catalyst is required and the CNS surface coverage is uniform over the cylindrical metal substrate. We characterized the CNS growth on several metallic substrates including tantalum, niobium, palladium, and nickel wires. Using fast-scan cyclic voltammetry (FSCV), bare metal wires could not detect 1 mu M dopamine while carbon nanospike coatedmore » wires could. Moreover, the highest sensitivity and optimized S/N ratio was recorded from carbon nanospike-tantalum (CNS-Ta) microwires grown for 7.5 minutes, which had a LOD of 8 +/- 2 nM for dopamine with FSCV. CNS-Ta microelectrodes were more reversible and had a smaller Delta E-p for dopamine than carbon-fiber microelectrodes, suggesting faster electron transfer kinetics. The kinetics of dopamine redox were adsorption controlled at CNS-Ta microelectrodes and repeated electrochemical measurements displayed stability for up to ten hours in vitro and over a ten day period as well. The oxidation potential was significantly different for ascorbic acid and uric acid compared to dopamine. Finally, growing carbon nanospikes on metal wires is a promising method to produce uniformly-coated, carbon nanostructured cylindrical microelectrodes for sensitive dopamine detection.« less

  1. Carbon nanospikes grown on metal wires as microelectrode sensors for dopamine

    SciTech Connect

    Zestos, Alexander G.; Yang, Cheng; Jacobs, Christopher B.; Hensley, Dale; Venton, B. Jill

    2015-09-14

    Carbon nanomaterials are advantageous as electrodes for neurotransmitter detection, but the difficulty of nanomaterials deposition on electrode substrates limits the reproducibility and future applications. In our study, we used plasma enhanced chemical vapor deposition (PECVD) to directly grow a thin layer of carbon nanospikes (CNS) on cylindrical metal substrates. No catalyst is required and the CNS surface coverage is uniform over the cylindrical metal substrate. We characterized the CNS growth on several metallic substrates including tantalum, niobium, palladium, and nickel wires. Using fast-scan cyclic voltammetry (FSCV), bare metal wires could not detect 1 mu M dopamine while carbon nanospike coated wires could. Moreover, the highest sensitivity and optimized S/N ratio was recorded from carbon nanospike-tantalum (CNS-Ta) microwires grown for 7.5 minutes, which had a LOD of 8 +/- 2 nM for dopamine with FSCV. CNS-Ta microelectrodes were more reversible and had a smaller Delta E-p for dopamine than carbon-fiber microelectrodes, suggesting faster electron transfer kinetics. The kinetics of dopamine redox were adsorption controlled at CNS-Ta microelectrodes and repeated electrochemical measurements displayed stability for up to ten hours in vitro and over a ten day period as well. The oxidation potential was significantly different for ascorbic acid and uric acid compared to dopamine. Finally, growing carbon nanospikes on metal wires is a promising method to produce uniformly-coated, carbon nanostructured cylindrical microelectrodes for sensitive dopamine detection.

  2. Carbon nanospikes grown on metal wires as microelectrode sensors for dopamine.

    PubMed

    Zestos, Alexander G; Yang, Cheng; Jacobs, Christopher B; Hensley, Dale; Venton, B Jill

    2015-11-01

    Carbon nanomaterials are advantageous as electrodes for neurotransmitter detection, but the difficulty of nanomaterials deposition on electrode substrates limits the reproducibility and future applications. In this study, we used plasma enhanced chemical vapor deposition (PECVD) to directly grow a thin layer of carbon nanospikes (CNS) on cylindrical metal substrates. No catalyst is required and the CNS surface coverage is uniform over the cylindrical metal substrate. The CNS growth was characterized on several metallic substrates including tantalum, niobium, palladium, and nickel wires. Using fast-scan cyclic voltammetry (FSCV), bare metal wires could not detect 1 μM dopamine while carbon nanospike coated wires could. The highest sensitivity and optimized S/N ratio was recorded from carbon nanospike-tantalum (CNS-Ta) microwires grown for 7.5 minutes, which had a LOD of 8 ± 2 nM for dopamine with FSCV. CNS-Ta microelectrodes were more reversible and had a smaller ΔE(p) for dopamine than carbon-fiber microelectrodes, suggesting faster electron transfer kinetics. The kinetics of dopamine redox were adsorption controlled at CNS-Ta microelectrodes and repeated electrochemical measurements displayed stability for up to ten hours in vitro and over a ten day period as well. The oxidation potential was significantly different for ascorbic acid and uric acid compared to dopamine. Growing carbon nanospikes on metal wires is a promising method to produce uniformly-coated, carbon nanostructured cylindrical microelectrodes for sensitive dopamine detection. PMID:26389138

  3. Iridium-catalyzed enantioselective polyene cyclization.

    PubMed

    Schafroth, Michael A; Sarlah, David; Krautwald, Simon; Carreira, Erick M

    2012-12-19

    A highly enantioselective polycyclization method has been developed using the combination of Lewis acid activation with iridium-catalyzed allylic substitution. This strategy relies on direct use of branched, racemic allylic alcohols and furnishes a diverse and unique set of carbo- and heteropolycyclic ring systems in good yields and ≥99% ee. PMID:23193947

  4. Note: electrochemical etching of sharp iridium tips.

    PubMed

    Lalanne, Jean-Benoît; Paul, William; Oliver, David; Grütter, Peter H

    2011-11-01

    We describe an etching procedure for the production of sharp iridium tips with apex radii of 15-70 nm, as determined by scanning electron microscopy, field ion microscopy, and field emission measurements. A coarse electrochemical etch followed by zone electropolishing is performed in a relatively harmless calcium chloride solution with high success rate.

  5. Osmium-191/iridium-191m radionuclide

    DOEpatents

    Knapp, Jr., Furn F.; Butler, Thomas A.; Brihaye, Claude

    1987-01-01

    A generator system to provide iridium-191m for clinical imaging applications comprises an activated carbon adsorbent loaded with a compound containing the parent nuclide, osmium-191. The generator, which has a shelf-life in excess of two weeks and does not require a scavenger column, can be eluted with physiologically compatible saline.

  6. Iridium-192 Production for Cancer Treatment

    SciTech Connect

    Rostelato, M.E.C.M.; Silva, C.P.G.; Rela, P.R.; Zeituni, C.A.; Lepki, V.; Feher, A.

    2004-10-05

    The purpose of this work is to settle a laboratory for Iridium -192 sources production, that is, to determine a wire activation method and to build a hot cell for the wires manipulation, quality control and packaging. The paper relates, mainly, the wire activation method and its quality control. The wire activation is carried out in our nuclear reactor, IEA- R1m.

  7. Iridium-catalyzed enantioselective polyene cyclization.

    PubMed

    Schafroth, Michael A; Sarlah, David; Krautwald, Simon; Carreira, Erick M

    2012-12-19

    A highly enantioselective polycyclization method has been developed using the combination of Lewis acid activation with iridium-catalyzed allylic substitution. This strategy relies on direct use of branched, racemic allylic alcohols and furnishes a diverse and unique set of carbo- and heteropolycyclic ring systems in good yields and ≥99% ee.

  8. Osmium-191/iridium-191m radionuclide

    DOEpatents

    Knapp, F.F. Jr.; Butler, T.A.; Brihaye, C.

    1985-08-26

    A generator system to provide iridium-191m for clinical imaging applications comprises an activated carbon adsorbent loaded with a compound containing the parent nuclide, osmium-191. The generator, which has a shelf-life in excess of two weeks and does not require a scavenger column, can be eluted with physiologically compatible saline. 4 figs. 3 tabs.

  9. Iridium-Coated Rhenium Combustion Chamber

    NASA Technical Reports Server (NTRS)

    Schneider, Steven J.; Tuffias, Robert H.; Rosenberg, Sanders D.

    1994-01-01

    Iridium-coated rhenium combustion chamber withstands operating temperatures up to 2,200 degrees C. Chamber designed to replace older silicide-coated combustion chamber in small rocket engine. Modified versions of newer chamber could be designed for use on Earth in gas turbines, ramjets, and scramjets.

  10. A simple circuit for automatic continuous recording of microelectrode resitance.

    PubMed

    Naylor, G R

    1978-12-28

    Microelectrodes with tip diameters less than or equal to 0.5 micron used for intracellular recording sometimes give artefactual readings due to tip potentials. These appear to be caused by a change in the tip of the microelectrode upon impalement with a corresponding change in microelectrode resistance. A circuit is described which enables the resistance of the microelectrode to be continuously monitored throughout an experiment. The electrode is used as one half of a potential divider for an a.c. signal at 20 Hz with an amplitude of 20 mV. The other half of the potential divider is a 1000 Momega resistor. The a.c. signal across the microelectrode is approximately proportional to the microelectrode resistance in the range 0 --50 Momega. This signal is amplified, rectified and smoothed and then displayed on a chart recorder or other convenient meter.

  11. Localized electron transfer rates and microelectrode-based enrichment of microbial communities within a phototrophic microbial mat

    SciTech Connect

    Babauta, Jerome T.; Atci, Erhan; Ha, Phuc T.; Lindemann, Stephen R.; Ewing, Timothy; Call, Douglas R.; Fredrickson, James K.; Beyenal, Haluk

    2014-01-01

    Phototrophic microbial mats frequently exhibit sharp, light-dependent redox gradients that regulate microbial respiration on specific electron acceptors as a function of depth. In this work, a benthic phototrophic microbial mat from Hot Lake, a hypersaline, epsomitic lake located near Oroville in north-central Washington, was used to develop a microscale electrochemical method to study local electron transfer processes within the mat. To characterize the physicochemical variables influencing electron transfer, we initially quantified redox potential, pH, and dissolved oxygen gradients by depth in the mat under photic and aphotic conditions. We further demonstrated that power output of a mat fuel cell was light-dependent. To study local electron transfer processes, we deployed a microscale electrode (microelectrode) with tip size ~20 μm. To enrich a subset of microorganisms capable of interacting with the microelectrode, we anodically polarized the microelectrode at depth in the mat. Subsequently, to characterize the microelectrode- associated community and compare it to the neighboring mat community, we performed amplicon sequencing of the V1-V3 region of the 16S gene. Differences in Bray-Curtis beta diversity, illustrated by large changes in relative abundance at the phylum level, suggested successful enrichment of specific mat community members on the microelectrode surface. The microelectrode-associated community exhibited substantially reduced alpha diversity and elevated relative abundances of Prosthecochloris, Loktanella, Catellibacterium, other unclassified members of Rhodobacteraceae, Thiomicrospira, and Limnobacter, compared with the community at an equivalent depth in the mat. Our results suggest that local electron transfer to an anodically polarized microelectrode selected for a specific microbial population, with substantially more abundance and diversity of sulfur-oxidizing phylotypes compared with the neighboring mat community.

  12. Localized electron transfer rates and microelectrode-based enrichment of microbial communities within a phototrophic microbial mat

    PubMed Central

    Babauta, Jerome T.; Atci, Erhan; Ha, Phuc T.; Lindemann, Stephen R.; Ewing, Timothy; Call, Douglas R.; Fredrickson, James K.; Beyenal, Haluk

    2014-01-01

    Phototrophic microbial mats frequently exhibit sharp, light-dependent redox gradients that regulate microbial respiration on specific electron acceptors as a function of depth. In this work, a benthic phototrophic microbial mat from Hot Lake, a hypersaline, epsomitic lake located near Oroville in north-central Washington, was used to develop a microscale electrochemical method to study local electron transfer processes within the mat. To characterize the physicochemical variables influencing electron transfer, we initially quantified redox potential, pH, and dissolved oxygen gradients by depth in the mat under photic and aphotic conditions. We further demonstrated that power output of a mat fuel cell was light-dependent. To study local electron transfer processes, we deployed a microscale electrode (microelectrode) with tip size ~20 μm. To enrich a subset of microorganisms capable of interacting with the microelectrode, we anodically polarized the microelectrode at depth in the mat. Subsequently, to characterize the microelectrode-associated community and compare it to the neighboring mat community, we performed amplicon sequencing of the V1–V3 region of the 16S gene. Differences in Bray-Curtis beta diversity, illustrated by large changes in relative abundance at the phylum level, suggested successful enrichment of specific mat community members on the microelectrode surface. The microelectrode-associated community exhibited substantially reduced alpha diversity and elevated relative abundances of Prosthecochloris, Loktanella, Catellibacterium, other unclassified members of Rhodobacteraceae, Thiomicrospira, and Limnobacter, compared with the community at an equivalent depth in the mat. Our results suggest that local electron transfer to an anodically polarized microelectrode selected for a specific microbial population, with substantially more abundance and diversity of sulfur-oxidizing phylotypes compared with the neighboring mat community. PMID:24478768

  13. Application of the Iridium Satellite System to Aeronautical Communications

    NASA Technical Reports Server (NTRS)

    Kerczewski, Robert J.; Meza, Mike; Gupta, Om

    2008-01-01

    The next generation air transportation system will require greater air-ground communications capacity to accommodate more air traffic with increased safety and efficiency. Communications will remain primarily terrestrially based, but satellite communications will have an increased role. Inmarsat s aeronautical services have been approved and are in use for aeronautical safety communications provided by geostationary satellites. More recently the approval process for the Iridium low earth orbit constellation is nearing completion. The current Iridium system will be able to provide basic air traffic services communications suitable for oceanic, remote and polar regions. The planned second generation of the Iridium system, called Iridium NEXT, will provide enhanced capabilities and enable a greater role in the future of aeronautical communications. This paper will review the potential role of satellite communications in the future of air transportation, the Iridium approval process and relevant system testing, and the potential role of Iridium NEXT.

  14. Handling System for Iridium-192 Seeds

    NASA Technical Reports Server (NTRS)

    Carpenter, W.; Wodicka, D.

    1973-01-01

    A complete system is proposed for safe handling of iridium-192 seeds used to internally irradiate malignant growths. A vibratory hopper feeds the seeds onto a transport system for deposit in a magazine or storage area. A circular magazine consisting of segmented plastic tubing with holes in the walls to accommodate the seeds seems feasible. The magazine is indexed to stop and release a seed for calibration and deposition.

  15. Iridium isotope ratio measurements by negative thermal ionization mass spectrometry and atomic weight of iridium

    NASA Astrophysics Data System (ADS)

    Walczyk, Thomas; Heumann, Klaus G.

    1993-02-01

    A technique of negative thermal ionization mass spectrometry (NTI-MS) for the precise iridium isotope ratio determination is presented. IrO-2 and IrO-3 ions are formed in a double-filament (Pt) ion source using (NH4)2IrCl6 as a sample compound. The IrO-2 ion current always exceeds the IrO-3 current by a factor of about 50-300 depending on the filament temperature and the oxygen gas introduced into the ion source. IrO-3 ion currents of more than 10-11 A can be obtained at the detector side from 100 ng iridium samples. The relative standard deviation of the 191Ir/193 ratio determination is 0.06%, which is much better than the data quoted in past literature. From such data the atomic weight of iridium could be calculated to be 192.21661 ± 0.00029. This value is a great improvement when compared with the iridium atomic weight of 192.22 ± 0.03 recommended by IUPAC. Additionally, an NTI-MS technique has been developed which allows the simultaneous measurement of iridium and osmium isotope ratio from osmiridium samples without any chemical separation. The iridium isotope ratios of three osmiridium samples agree well with the ratios determined from the hexachloroiridate compound. The direct 187Os/186OS determination from osmiridium samples opens the possibility of studying the evolution of osmium in the Earth's mantle due to the radioactive decay of 187Re into 187Os.

  16. Surface studies of iridium-alloy grain boundaries associated with weld cracking

    SciTech Connect

    Mosley, W.C.

    1982-01-01

    Plutonium-238 oxide fuel pellets for the General Purpose Heat Source (GPHS) Radioisotopic Thermoelectric Generators to be used on the NASA Galileo Mission to Jupiter and the International Solar Polar Mission are produced and encapsulated in iridium alloy at the Savannah River Plant (SRP). Underbead cracks occasionally occur in the girth weld on the iridium-alloy-clad vent sets in the region where the gas tungsten arc is quenched. Grain-boundary structures and compositions were characterized by scanning electron microscopy/x-ray energy spectroscopy, electron microprobe analysis and scanning Auger microprobe analysis to determine the cause of weld quench area cracking. Results suggest that weld quench area cracking may be caused by gas porosity or liquation in the grain boundaries.

  17. Apparatus and method of inserting a microelectrode in body tissue or the like using vibration means

    NASA Technical Reports Server (NTRS)

    Feldstein, C.; Crawford, D. W.; Kanabus, E. W. (Inventor)

    1979-01-01

    An arrangement for and method of inserting a glass microelectrode having a tip in the micron range into body tissue is presented. The arrangement includes a microelectrode. The top of the microelectrode is attached to the diaphragm center of a first speaker. The microelectrode tip is brought into contact with the tissue by controlling a micromanipulator. Thereafter, an audio signal is applied to the speaker to cause the microelectrode to vibrate and thereby pierce the tissue surface without breaking the microelectrode tip. Thereafter, the tip is inserted into the tissue to the desired depth by operating the micromanipulator with the microelectrode in a vibratory or non-vibratory state.

  18. Boron-doped diamond nano/microelectrodes for bio-sensing and in vitro measurements

    PubMed Central

    Dong, Hua; Wang, Shihua; Galligan, James J.; Swain, Greg M.

    2015-01-01

    Since the fabrication of the first diamond electrode in the mid 1980s, repid progress has been made on the development and application of this new type of electrode material. Boron-doped diamond (BDD) electrodes exhibit outstanding properties compared to oxygen-containing sp2 carbon electrodes. These properties make BDD electrodes an ideal choice for use in complex samples. In recent years, BDD microelectrodes have been applied to in vitro and in vivo measurements of biological molecules in animals, tissues and cells. This review will summarize recent progress in the development and applications of BDD electrodes in bio-sensing and in vitro measurements of biomolecules. In the first section, the methods for BDD nanocrystalline diamond film deposition and BDD microelectrodes preparation are described. This is followed by a description and discussion of several approaches for characterization of the BDD electrode surface structure, morphology, and electrochemical activity. Further, application of BDD microelectrodes for use in the in vitro analysis of norepinephrine (NE), serotonin (5-HT), nitric oxide (NO), histamine, and adenosine from tissues are summarized and finally some of the remaining challenges are discussed. PMID:21196394

  19. Iridium Abundances across the Ordovician-Silurian Stratotype

    NASA Astrophysics Data System (ADS)

    Wilde, Pat; Berry, William B. N.; Quinby-Hunt, Mary S.; Orth, Charles J.; Quintana, Leonard R.; Gilmore, James S.

    1986-07-01

    Chemostratigraphic analyses in the Ordovician-Silurian boundary stratotype section, bracketing a major extinction event in the graptolitic shale section at Dob's Linn, Scotland, show persistently high iridium concentrations of 0.050 to 0.250 parts per billion. There is no iridium concentration spike in the boundary interval or elsewhere in the 13 graptolite zones examined encompassing about 20 million years. Iridium correlated with chromium, both elements showing a gradual decrease with time into the middle part of the Lower Silurian. The chromium-iridium ratio averages about 106. Paleogeographic and geologic reconstructions coupled with the occurrence of ophiolites and other deep crustal rocks in the source area suggest that the high iridium and chromium concentrations observed in the shales result from terrestrial erosion of exposed upper mantle ultramafic rocks rather than from a cataclysmic extraterrestrial event.

  20. Vesicular exocytosis and microdevices - microelectrode arrays.

    PubMed

    Amatore, Christian; Delacotte, Jérôme; Guille-Collignon, Manon; Lemaître, Frédéric

    2015-06-01

    Among all the analytical techniques capable of monitoring exocytosis in real time at the single cell level, electrochemistry (particularly amperometry at a constant potential) using ultramicroelectrodes has been demonstrated to be an important and convenient tool for more than two decades. Indeed, because the electrochemical sensor is located in the close vicinity of the emitting cell ("artificial synapse" configuration), much data can be gathered from the whole cell activity (secretion frequency) to the individual vesicular release (duration, fluxes or amount of molecules released) with an excellent sensitivity. However, such a single cell analysis and its intrinsic benefits are at the expense of the spatial resolution and/or the number of experiments. The quite recent development of microdevices/microsystems (and mainly the microelectrode arrays (MEAs)) offers in some way a complementary approach either by combining spectroscopy-microscopy or by implementing a multianalysis. Such developments are described and discussed in the present review over the 2005-2014 period. PMID:25803190

  1. Synthesis and Electroluminescent Property of New Orange Iridium Compounds for Flexible White Organic Light Emitting Diodes.

    PubMed

    Lee, Ho Won; Jeong, Hyunjin; Kim, Young Kwan; Ha, Yunkyoung

    2015-10-01

    Recently, white organic light-emitting diodes (OLEDs) have aroused considerable attention because they have the potential of next-generation flexible displays and white illuminated applications. White OLED applications are particularly heading to the industry but they have still many problems both materials and manufacturing. Therefore, we proposed that the new iridium compounds of orange emitters could be demonstrated and also applied to flexible white OLEDs for verification of potential. First, we demonstrated the chemical properties of new orange iridium compounds. Secondly, conventional two kinds of white phosphorescent OLEDs were fabricated by following devices; indium-tin oxide coated glass substrate/4,4'-bis[N-(napthyl)-N-phenylamino]biphenyl/N,N'-dicarbazolyl-3,5-benzene doped with blue and new iridium compounds for orange emitting 8 wt%/1,3,5-tris[N-phenylbenzimidazole-2-yl]benzene/lithium quinolate/aluminum. In addition, we fabricated white OLEDs using these emitters to verify the potential on flexible substrate. Therefore, this work could be proposed that white light applications can be applied and could be extended to additional research on flexible applications. PMID:26726407

  2. Sonochemically Fabricated Microelectrode Arrays for Use as Sensing Platforms

    PubMed Central

    Collyer, Stuart D.; Davis, Frank; Higson, Séamus P.J.

    2010-01-01

    The development, manufacture, modification and subsequent utilisation of sonochemically-formed microelectrode arrays is described for a range of applications. Initial fabrication of the sensing platform utilises ultrasonic ablation of electrochemically insulating polymers deposited upon conductive carbon substrates, forming an array of up to 70,000 microelectrode pores cm−2. Electrochemical and optical analyses using these arrays, their enhanced signal response and stir-independence area are all discussed. The growth of conducting polymeric “mushroom” protrusion arrays with entrapped biological entities, thereby forming biosensors is detailed. The simplicity and inexpensiveness of this approach, lending itself ideally to mass fabrication coupled with unrivalled sensitivity and stir independence makes commercial viability of this process a reality. Application of microelectrode arrays as functional components within sensors include devices for detection of chlorine, glucose, ethanol and pesticides. Immunosensors based on microelectrode arrays are described within this monograph for antigens associated with prostate cancer and transient ischemic attacks (strokes). PMID:22399926

  3. Quasi-simultaneous Measurements of Ionic Currents by Vibrating Probe and pH Distribution by Ion-selective Microelectrode

    SciTech Connect

    Isaacs, H.S.; Lamaka, S.V.; Taryba, M.; Montemor, M.F.; Ferreira, M.G.S.

    2011-01-01

    This work reports a new methodology to measure quasi-simultaneously the local electric fields and the distribution of specific ions in a solution via selective microelectrodes. The field produced by the net electric current was detected using the scanning vibrating electrode technique (SVET) with quasi-simultaneous measurements of pH with an ion-selective microelectrode (pH-SME). The measurements were performed in a validation cell providing a 48 ?m diameter Pt wire cross section as a source of electric current. A time lag between acquiring each current density and pH data-point was 1.5 s due to the response time of pH-SME. The quasi-simultaneous SVET-pH measurements that correlate electrochemical oxidation-reduction processes with acid-base chemical equilibria are reported for the first time. No cross-talk between the vibrating microelectrode and the ion-selective microelectrode could be detected under given experimental conditions.

  4. Graphene microelectrode arrays for neural activity detection.

    PubMed

    Du, Xiaowei; Wu, Lei; Cheng, Ji; Huang, Shanluo; Cai, Qi; Jin, Qinghui; Zhao, Jianlong

    2015-09-01

    We demonstrate a method to fabricate graphene microelectrode arrays (MEAs) using a simple and inexpensive method to solve the problem of opaque electrode positions in traditional MEAs, while keeping good biocompatibility. To study the interface differences between graphene-electrolyte and gold-electrolyte, graphene and gold electrodes with a large area were fabricated. According to the simulation results of electrochemical impedances, the gold-electrolyte interface can be described as a classical double-layer structure, while the graphene-electrolyte interface can be explained by a modified double-layer theory. Furthermore, using graphene MEAs, we detected the neural activities of neurons dissociated from Wistar rats (embryonic day 18). The signal-to-noise ratio of the detected signal was 10.31 ± 1.2, which is comparable to those of MEAs made with other materials. The long-term stability of the MEAs is demonstrated by comparing differences in Bode diagrams taken before and after cell culturing. PMID:25712492

  5. Superconductivity in Ca10(Ir4As8)(Fe2As2)5 with Square-Planar Coordination of Iridium

    PubMed Central

    Kudo, Kazutaka; Mitsuoka, Daisuke; Takasuga, Masaya; Sugiyama, Yuki; Sugawara, Kento; Katayama, Naoyuki; Sawa, Hiroshi; Kubo, Hiroaki S.; Takamori, Kenta; Ichioka, Masanori; Fujii, Tatsuo; Mizokawa, Takashi; Nohara, Minoru

    2013-01-01

    We report the unprecedented square-planar coordination of iridium in the iron iridium arsenide Ca10(Ir4As8)(Fe2As2)5. This material experiences superconductivity at 16 K. X-ray photoemission spectroscopy and first-principles band calculation suggest Ir(II) oxidation state, which yields electrically conductive Ir4As8 layers. Such metallic spacer layers are thought to enhance the interlayer coupling of Fe2As2, in which superconductivity emerges, thus offering a way to control the superconducting transition temperature. PMID:24173038

  6. Iridium anomaly approximately synchronous with terminal eocene extinctions

    SciTech Connect

    Alvarez, W.; Asaro, F.; Michel, H.V.; Alvarez, L.W.

    1982-05-21

    An iridium anomaly has been found in coincidence with the known microtektite level in cores from Deep Sea Drilling Project site 149 in the Caribbean Sea. The iridium was probably not in the microtektites but deposited simultaneously with them; this could occur if the iridium was deposited from a dust cloud resulting from a bolide impact, as suggested for the anomaly associated with the Cretaceous-Tertiary boundary. Other workers have deduced that the microtektites are part of the North American strewn tektite field, which is dated at about 34 million years before present, and that the microtektite horizon in deep-sea cores is synchronous with the extinction of five radiolarian species. Mass extinctions also occur in terrestrial mammals within 4 million years of this time. The iridium anomaly and the tektites and microtektites are supportive of a major bolide impact about 34 million years ago.

  7. Iridium anomaly approximately synchronous with terminal eocene extinctions.

    PubMed

    Alvarez, W; Asaro, F; Michel, H V; Alvarez, L W

    1982-05-21

    An iridium anomaly has been found in coincidence with the known microtektite level in cores from Deep Sea Drilling Project site 149 in the Caribbean Sea. The iridium was probably not in the microtektites but deposited simultaneously with them; this could occur if the iridium was deposited from a dust cloud resulting from a bolide impact, as suggested for the anomaly associated with the Cretaceous-Tertiary boundary. Other workers have deduced that the microtektites are part of the North American strewn tektite field, which is dated at about 34 million years before present, and that the microtektite horizon in deep-sea cores is synchronous with the extinction of five radiolarian species. Mass extinctions also occur in terrestrial mammals within 4 million years of this time. The iridium anomaly and the tektites and microtektites are supportive of a major bolide impact about 34 million years ago.

  8. Acute radiodermatitis from occupational exposure to iridium 192

    SciTech Connect

    Becker, J.; Rosen, T. )

    1989-12-01

    Industrial radiography using the man-made radioisotope iridium 192 is commonplace in the southern states. Despite established procedures and safeguards, accidental exposure may result in typical acute radiodermatitis. We have presented a clinical example of this phenomenon.9 references.

  9. Membrane-disrupting iridium(iii) oligocationic organometallopeptides.

    PubMed

    Salvadó, Iria; Gamba, Ilaria; Montenegro, Javier; Martínez-Costas, José; Brea, Jose Manuel; Loza, María Isabel; Vázquez López, Miguel; Vázquez, M Eugenio

    2016-09-21

    A series of oligoarginine peptide derivatives containing cyclometallated iridium(iii) units display remarkable cytotoxicity, comparable to that of cisplatin. In vitro studies with unilamellar vesicles support a membrane-disrupting mechanism of action.

  10. Scattering effects on the dosimetry of iridium-192

    SciTech Connect

    Serago, C.F. Department of Radiation Oncology, University of Miami, Miami, Florida ); Houdek, P.V. ); Pisciotta, V. ); Schwade, J.G. ); Abitbol, A.A.; Lewin, A.A. Department of Radiation Oncology, University of Miami, Miami, Florida ); Poole, D.O. ); Marcial-Vega, V. )

    1991-11-01

    Dosimetry calculations for iridium-192 sources generally assume that a sufficient medium surrounds both the iridium source(s) and the point of calculation so that full scattering conditions exist. In several clinical applications the iridium sources may be anatomically located so that the full scattering requirement is not satisfied. To assess the magnitude of this problem, relative measurements were made with a small ionization chamber in phantoms near air and lung-equivalent interfaces. Dose reduction caused by decreasing the volume of scattering material near these interfaces was then evaluated for a few clinical applications. The results show that reductions on the order of 8% may be expected at the interface with minimal dose reduction within the volume of the implant itself. In addition, the results indicate the verification of source strength of iridium sources in phantom require phantom dimensions determined by the source-chamber separation distance.

  11. Iridium anomaly approximately synchronous with terminal eocene extinctions.

    PubMed

    Alvarez, W; Asaro, F; Michel, H V; Alvarez, L W

    1982-05-21

    An iridium anomaly has been found in coincidence with the known microtektite level in cores from Deep Sea Drilling Project site 149 in the Caribbean Sea. The iridium was probably not in the microtektites but deposited simultaneously with them; this could occur if the iridium was deposited from a dust cloud resulting from a bolide impact, as suggested for the anomaly associated with the Cretaceous-Tertiary boundary. Other workers have deduced that the microtektites are part of the North American strewn tektite field, which is dated at about 34 million years before present, and that the microtektite horizon in deep-sea cores is synchronous with the extinction of five radiolarian species. Mass extinctions also occur in terrestrial mammals within 4 million years of this time. The iridium anomaly and the tektites and microtektites are supportive of a major bolide impact about 34 million years ago. PMID:17819180

  12. GPS/GNSS Interference from Iridium Data Transmitters

    NASA Astrophysics Data System (ADS)

    Berglund, H. T.; Blume, F.; Estey, L.; White, S.

    2011-12-01

    The Iridium satellite communication system broadcasts in the 1610 to 1626.5 MHz band. The L1 frequencies broadcast by GPS, Galileo and GLONASS satellites are 1575.42 MHz, 1575.42 MHz and 1602 MHz + n × 0.5625 MHz, respectively (each GLONASS satellite uses a unique frequency). The proximity of the Iridium frequency band with the L1 frequencies of the GPS, Galileo and GLONASS systems leaves GNSS receivers susceptible to interference from Iridium data transmissions. Interference from Iridium transmissions can cause cycle slips and loss of lock on the carrier and code phases, thereby degrading the quality of GNSS observations and position estimates. In 2008, UNAVCO staff members observed that the percent of slips vs. the number of observations increased as the distance between a GPS choke ring antenna (TRM29659.00) and an Iridium antenna decreased. From those observations they suggested that Iridium antennas and GPS antennas should be separated by >30 m to minimize cycle slips caused by the interference from Iridium data transmissions. A second test conducted in 2009 using a newer Trimble GNSS choke ring antenna (TRM59800.00) showed similar results to the previous test despite the wider frequency range of the newer antenna. More recent testing conducted to investigate the response of new receiver models to iridium transmissions has shown that many GNSS enabled models, when combined with GNSS enabled antennas, have increased sensitivity to interference when compared to older GPS-only models. The broader frequency spectrum of the Low Noise Amplifiers (LNA) installed in many newer GNSS antennas can increase the impact of near-band RF interference on tracking performance. Our testing has shown that the quality of data collected at sites collocated with iridium communications is highly degraded for antenna separations exceeding 100m. Using older GPS antenna models (e.g. TRM29659.00) with newer GNSS enabled receivers can reduce this effect. To mitigate the effects that

  13. Improvements in manufacture of iridium alloy materials

    NASA Astrophysics Data System (ADS)

    Ohriner, E. K.

    1992-10-01

    Iridium alloys are used as fuel-cladding material in radioisotope thermoelectric generators (RTG's). Hardware produced at the Oak Ridge National Laboratory (ORNL) has been used in Voyager 1 and 2, Galileo, and Ulysses spacecraft. This hardware was fabricated from small, 500-g drop-cast ingots. Porosity in these ingots and the resulting defects in the rolled sheets caused rejection of about 30 percent of the product. An improved manufacturing process was developed with the goal of substantially reducing the level of defects in the rolled sheets. The ingot size is increased to 10 kg and is produced by vacuum arc remelting. In addition, the ingot is hot extruded prior to rolling. Since implementation of the process in 1989, the average rate of rejection of the product has been reduced to below 10 percent.

  14. Improvements in manufacture of iridium alloy materials

    SciTech Connect

    Ohriner, E.K.

    1992-08-01

    Iridium alloys are used as fuel-cladding material in radioisotope thermoelectric generators (RTGs). Hardware produced at the Oak Ridge National Laboratory (ORNL) has been used in Voyager 1 and 2, Galileo, and Ulysses spacecraft. This hardware was fabricated from small, 500-g drop-cast ingots. Porosity in these ingots and the resulting defects in the rolled sheets caused rejection of about 30% of the product. An improved manufacturing process was developed with the goal of substantially reducing the level of defects in the rolled sheets. The ingot size is increased to 10 kg and is produced by vacuum arc remelting. In addition, the ingot is hot extruded prior to rolling. Since implementation of the process in 1989, the average rate of rejection of the product has been reduced to below 10%.

  15. Improvements in manufacture of iridium alloy materials

    SciTech Connect

    Ohriner, E.K.

    1992-01-01

    Iridium alloys are used as fuel-cladding material in radioisotope thermoelectric generators (RTGs). Hardware produced at the Oak Ridge National Laboratory (ORNL) has been used in Voyager 1 and 2, Galileo, and Ulysses spacecraft. This hardware was fabricated from small, 500-g drop-cast ingots. Porosity in these ingots and the resulting defects in the rolled sheets caused rejection of about 30% of the product. An improved manufacturing process was developed with the goal of substantially reducing the level of defects in the rolled sheets. The ingot size is increased to 10 kg and is produced by vacuum arc remelting. In addition, the ingot is hot extruded prior to rolling. Since implementation of the process in 1989, the average rate of rejection of the product has been reduced to below 10%.

  16. Iridium{reg_sign} worldwide personal communication system

    SciTech Connect

    Helm, J.

    1997-01-01

    The IRIDIUM system is a personal worldwide communication system designed to support portable, low power subscriber units through the use of a constellation of satellites in low earth polar orbit. The satellites are networked together to form a system which provides continuous line-of-sight communications between the IRIDIUM system and any point within 30 km of the earth{close_quote}s surface. The system architecture and operation are described. {copyright} {ital 1997 American Institute of Physics.}

  17. PURIFICATION OF IRIDIUM BY ELECTRON BEAM MELTING

    SciTech Connect

    Ohriner, Evan Keith

    2008-01-01

    The purification of iridium metal by electron beam melting has been characterized for 48 impurity elements. Chemical analysis was performed by glow discharge mass spectrographic (GDMS) analysis for all elements except carbon, which was analyzed by combustion. The average levels of individual elemental impurities in the starting powder varied from 37 g/g to 0.02 g/g. The impurity elements Li, Na, Mg, P, S, Cl, K, Ca, Mn, Co, Ni, Cu, Zn, As, Pd, Ag, Cd, Sn, Sb, Te, Ba, Ce, Tl, Pb, and Bi were not detectable following the purification. No significant change in concentration of the elements Ti, V, Zr, Nb, Mo, and Re was found. The elements B, C, Al, Si, Cr, Fe, Ru, Rh, and Pt were partially removed by vaporization during electron beam melting. Langmuir's equation for ideal vaporization into a vacuum was used to calculate for each impurity element the expected ratio of impurity content after melting to that before melting. Equilibrium vapor pressures were calculated using Henry's law, with activity coefficients obtained from published data for the elements Fe, Ti, and Pt. Activity coefficients were estimated from enthalpy data for Al, Si, V, Cr, Mn, Co, Ni, Zr, Nb, Mo, and Hf and an ideal solution model was used for the remaining elements. The melt temperature was determined from measured iridium weight loss. Excellent agreement was found between measured and calculated impurity ratios for all impurity elements. The results are consistent with some localized heating of the melt pool due to rastering of the electron beam, with an average vaporization temperature of 3100 K as compared to a temperature of 2965 K calculated for uniform heating of the melt pool. The results are also consistent with ideal mixing in the melt pool.

  18. Surface properties of pulsed laser deposited Ir, Rh, and Ir 0.9Rh 0.1 thin films for use as microelectrode arrays in electroanalytical heavy metal trace sensors

    NASA Astrophysics Data System (ADS)

    Le Drogoff, B.; El Khakani, M. A.; Silva, P. R. M.; Chaker, M.; Ross, G. G.

    1999-11-01

    Pulsed laser deposition (PLD) of iridium, rhodium, and Ir 0.9Rh 0.1 thin films onto a-SiC:H-coated silicon substrates for use in heavy metal sensors has been achieved by ablating iridium and/or rhodium targets with a KrF excimer laser. The deposited films are polycrystalline and exhibited very smooth surfaces with an average roughness value ( Ra) of ˜1 nm. The wettability by mercury of their surface was investigated by means of the contact angle measurement technique, and compared to that of Ag and Pt films. The PLD films (whether Ir, Rh, or Ir 0.9Rh 0.1) were found to present an almost identical Hg-wetting behavior, which is characterized by a high static contact angle of 132±2°. Moreover, in contrast to the cases of Pt or Ag films, where amalgamation with Hg rapidly occurs during the contact angle measurements, no evident interaction of Hg with the surface of the PLD films was observed. Microelectrode arrays of each of the three films (Ir, Rh and Ir 0.9Rh 0.1) were fabricated and used as a conducting base onto which Hg microdrops are electroplated. Reproducible and uniform Hg deposits on the microelectrode arrays were obtained. The electroanalytical performance of these Hg-electroplated microelectrode arrays based sensors was then evaluated by means of Square Wave Anodic Stripping Voltammetry (SWASV), in synthetic solutions containing Zn, Cd and Pb ion traces. Over a concentration range as wide as 0.2-20 ppb, the detected signals are found to exhibit a strong linear correlation with ion concentration. For a preconcentration time of only 5 min, detection limits as low as 0.2 ppb for both Cd and Pb, and 0.5 ppb for Zn were achieved.

  19. A new moving-coil microelectrode puller.

    PubMed

    Ensor, D R

    1979-03-01

    This paper describes an improved electrode puller for the manufacture of glass microelectrodes or micropipettes. The instrument resembles a conventional horizontal two-stage, solenoid-powered electrode puller but the pull is now developed by a light moving-coil and a fixed permanent magnet, using the principle of the moving-coil loudspeaker. In a conventional puller the force is generated by a solenoid with a massive moving-iron core. In this new puller the moving-coil solenoid responds much more rapidly to changing currents because of its greatly reduced inductance, and a substantial reduction in mass to 25 g, gives more acceleration from a comparable force. The sudden discharge of a capacitor bank through the coil accelerates the glass quickly during the last stage of the pull. This rapid acceleration is of importance in the formation of good electrodes with fine tips. For the prototype, an electronic control unit was constructed which allows the parameters necessary for the manufacture of electrodes to be set and regulated accurately and repeatedly, so that series of electrodes of constant shapes can be made. The length of the electrode shank may be predetermined over a wide range and tip diameters down to 0.08 micron have already been measured. The angle of the taper that supports the tip may be varied from less than 1 to over 6 degrees. The mechanical design of the instrument is comparatively simple, as it has only one moving part, while the relative complexity of the electronic control section should not present any manufacturing difficulties. Although this puller has been used mainly to make single-barrel fine electrodes from borosilicate glass, it is adaptable for other purposes. The extent of the control over the shape of the shank of the electrode renders it particularly suitable for the manufacture of composite, ion-sensitive electrodes. PMID:544958

  20. Enabling long term monitoring of dopamine using dimensionally stable ultrananocrystalline diamond microelectrodes

    NASA Astrophysics Data System (ADS)

    Dutta, Gaurab; Tan, Chao; Siddiqui, Shabnam; Arumugam, Prabhu U.

    2016-09-01

    Chronic dopamine (DA) monitoring is a critical enabling technology to identify the neural basis of human behavior. Carbon fiber microelectrodes (CFM), the current gold standard electrode for in vivo fast scan cyclic voltammetry (FSCV), rapidly loses sensitivity due to surface fouling during chronic neural testing. Periodic voltage excursions at elevated anodic potentials regenerate fouled CFM surfaces but they also chemically degrade the CFM surfaces. Here, we compare the dimensional stability of 150 μm boron-doped ultrananocrystalline diamond (BDUNCD) microelectrodes in 1X PBS during ‘electrochemical cleaning’ with a similar-sized CFM. Scanning electron microscopy and Raman spectroscopy confirm the exceptional dimensional stability of BDUNCD after 40 h of FSCV cycling (∼8 million cycles). The fitting of electrochemical impedance spectroscopy data to an appropriate circuit model shows a 2x increase in charge transfer resistance and an additional RC element, which suggests oxidation of BDUNCD electrode surface. This could have likely increased the DA oxidation potential by ∼34% to +308 mV. A 2x increase in BDUNCD grain capacitance and a negligible change in grain boundary impedance suggests regeneration of grains and the exposure of new grain boundaries, respectively. Overall, DA voltammogram signals were reduced by only ∼20%. In contrast, the CFM is completely etched with a ∼90% reduction in the DA signal using the same cleaning conditions. Thus, BDUNCD provides a robust electrode surface that is amenable to repeated and aggressive cleaning which could be used for chronic DA sensing.

  1. Double Potential Pulse Chronocoulometry for Detection of Plasma Membrane Cholesterol Efflux at Disk Platinum Microelectrodes

    PubMed Central

    West, Richard H.; Lu, Hui; Shaw, Kendrick; Chiel, Hillel J.; Kelley, Thomas J.; Burgess, James D.

    2016-01-01

    A double potential pulse scheme is reported for observation of cholesterol efflux from the plasma membrane of a single neuron cell. Capillary Pt disk microelectrodes having a thin glass insulator allow the 10 μm diameter electrode and cell to be viewed under optical magnification. The electrode, covalently functionalized with cholesterol oxidase, is positioned in contact with the cell surface resulting in enzyme catalyzed cholesterol oxidation and efflux of cholesterol from the plasma membrane at the electrode contact site. Enzymatically generated hydrogen peroxide accumulates at the electrode/cell interface during a 5 s hold-time and is oxidized during application of a potential pulse. A second, replicate potential pulse is applied 0.5 s after the first potential pulse to gauge background charge prior to significant accumulation of hydrogen peroxide. The difference in charge passed between the first and second potential pulse provides a measure of hydrogen peroxide generated by the enzyme and is an indication of the cholesterol efflux. Control experiments for bare Pt microelectrodes in contact with the cell plasma membrane show difference charge signals in the range of about 7–10 pC. Enzyme-modified electrodes in contact with the plasma membrane show signals in the range of 16–26 pC. PMID:27330196

  2. Characterization and Application of a Chlorine Microelectrode for Measuring Monochloramine within a Biofilm

    EPA Science Inventory

    Chlorine microelectrodes with tip sizes of 5-15 μm were developed and used to measure biofilm monochloramine penetration profiles. The chlorine microelectrode showed response to total chlorine, including free chlorine, monochloramine, and dichloramine under various conditions. ...

  3. Monochloramine Microelectrode for In-Situ Application Within Chloraminated Distribution System Biofilm

    EPA Science Inventory

    A monochloramine microelectrode with a tip size between 5 and 15 μm and using platinum wire was successfully designed, fabricated and characterized for in-situ monochloramine measurement within chloraminated distribution system biofilm. The monochloramine microelectrode showed s...

  4. Iridium NEXT: A Global access for your sensor needs

    NASA Astrophysics Data System (ADS)

    Gupta, O. P.; Fish, C. S.

    2010-12-01

    The operational Iridium constellation is comprised of 66 satellites, used to primarily provide worldwide voice and data coverage to satellite phones, pagers and integrated transceivers. The satellites are in low Earth orbit at 781 km and inclination of 86.4 deg, resulting in unprecedented 24/7 coverage and real-time visibility of the entire globe. Recently, through funding from the National Science Foundation (NSF), Iridium has been utilized by the Johns Hopkins University Applied Physics Laboratory (APL), with help from The Boeing Company, as an infrastructure for a comprehensive network for space environment measurements. Known as the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), the Iridium-based system provides real-time magnetic field measurements using the satellites as part of a new observation network to forecast weather in space. In February 2007, Iridium announced Iridium NEXT, a novel design for a second-generation satellite constellation. Anticipated to begin launching in 2015, Iridium NEXT will maintain the existing Iridium constellation architecture of 66 cross-linked satellite LEO covering 100 percent of the globe. In the spirit of AMPERE, for commercial, government, and scientific organizations Iridium NEXT also plans to offer new earth and space observation opportunities through hosted hosted payloads on the 66 Iridium NEXT satellite network. To provide seamless support and access to this latest innovation in payload transportation, Iridium NEXT has teamed with Space Dynamics Laboratory - Utah State University which has delivered thousands of successful sensors and subsystems for over 400 space borne and aircraf based payloads. One such innovation called SensorPOD will offer unique benefits such as unprecedented spatial and temporal coverage, real-time relay of data to and from up to 5 Kg payloads in space, and access to space at a fraction of the cost of a dedicated missions such as 3U or larger Cubesats. In this

  5. Modeling and Simulation of Microelectrode-Retina Interactions

    SciTech Connect

    Beckerman, M

    2002-11-30

    The goal of the retinal prosthesis project is the development of an implantable microelectrode array that can be used to supply visually-driven electrical input to cells in the retina, bypassing nonfunctional rod and cone cells, thereby restoring vision to blind individuals. This goal will be achieved through the study of the fundamentals of electrical engineering, vision research, and biomedical engineering with the aim of acquiring the knowledge needed to engineer a high-density microelectrode-tissue hybrid sensor that will restore vision to millions of blind persons. The modeling and simulation task within this project is intended to address the question how best to stimulate, and communicate with, cells in the retina using implanted microelectrodes.

  6. A novel implantable multichannel silicon-based microelectrode

    NASA Astrophysics Data System (ADS)

    Sui, Xiao-Hong; Zhang, Ruo-Xin; Pei, Wei-Hua; Chen, Hong-Da

    2007-07-01

    Silicon-based microelectrodes have been confirmed to be helpful in neural prostheses. The fabricated 7-channel silicon-based microelectrode was feasible to be implanted into the brain cortex. The manufacturing process by microelectromechanical system (MEMS) technology was detailed with four photolithographic masks. The microscopic photographs and SEM images indicated that the probe shank was 3 mm long, 100 μm wide and 20 μm thick with the recording sites spaced 120 μm apart for good signal isolation. To facilitate the insertion and minimize the trauma, the microelectrode is narrowed down gradually near the tip with the tip taper angle of 6 degrees. Curve of the single recording site impedance versus frequency was shown by test in vitro and the impedance declined from 150.5kΩ to 6.0 kΩ with frequency changing from 10 k to 10 MHz.

  7. Microelectrode measurements of the activity distribution in nitrifying bacterial aggregates

    SciTech Connect

    Beer, D. de; Heuval, J.C. van den; Ottengraf, S.P.P. )

    1993-02-01

    Environmental problems caused by strongly increased ammonium emission by intensive agricultural and industrial activities, wastewater and waste gas purification plants are being redesigned. Since the growth rates and biomass yields of nitrifying organisms are low, their application in continuous-flow processes requires efficient retention of biomass, and development of bacterial aggregates with good settling properties is needed. In this study microelectrodes were used to study the activity distribution of bacterial aggregates in a biological fluidized-bed nitrification reactor with an external aerator. Measurements of ammonium, oxygen, nitrate, and pH were made. Results included the following: biomass yield was close to expected; the active nitrifying zone was limited to the outer 100 to 120 [mu]m of the aggregates; distribution of activity was determined by the penetration depth of oxygen during aggregate development; measurements of activity required the use of ammonium or nitrate microelectrodes, not oxygen microelectrodes alone. 32 refs., 5 figs., 2 tabs.

  8. Signal distortion from microelectrodes in clinical EEG acquisition systems

    NASA Astrophysics Data System (ADS)

    Stacey, William C.; Kellis, Spencer; Patel, Paras R.; Greger, Bradley; Butson, Christopher R.

    2012-10-01

    Many centers are now using high-density microelectrodes during traditional intracranial electroencephalography (iEEG) both for research and clinical purposes. These microelectrodes are FDA-approved and integrate into clinical EEG acquisition systems. However, the electrical characteristics of these electrodes are poorly described and clinical systems were not designed to use them; thus, it is possible that this shift into clinical practice could have unintended consequences. In this study, we characterized the impedance of over 100 commercial macro- and microelectrodes using electrochemical impedance spectroscopy (EIS) to determine how electrode properties could affect signal acquisition and interpretation. The EIS data were combined with the published specifications of several commercial EEG systems to design digital filters that mimic the behavior of the electrodes and amplifiers. These filters were used to analyze simulated brain signals that contain a mixture of characteristic features commonly observed in iEEG. Each output was then processed with several common quantitative EEG measurements. Our results show that traditional macroelectrodes had low impedances and produced negligible distortion of the original signal. Brain tissue and electrical wiring also had negligible filtering effects. However, microelectrode impedances were much higher and more variable than the macroelectrodes. When connected to clinical amplifiers, higher impedance electrodes produced considerable distortion of the signal at low frequencies (<60 Hz), which caused significant changes in amplitude, phase, variance and spectral band power. In contrast, there were only minimal changes to the signal content for frequencies above 100 Hz. In order to minimize distortion with microelectrodes, we determined that an acquisition system should have an input impedance of at least 1 GΩ, which is much higher than most clinical systems. These results show that it is critical to account for variations

  9. Mobility of iridium in terrestrial environments: Implications for the interpretation of impact-related mass-extinctions

    NASA Astrophysics Data System (ADS)

    Martín-Peinado, F. J.; Rodríguez-Tovar, F. J.

    2010-08-01

    Traditionally, iridium has been considered an element of low mobility, but its behavior is still debated. Ir concentration in a soil affected by a catastrophic mining spill in 1998 that covered the soil with a layer of tailings offers the opportunity to analyse an exceptional Ir-bearing horizon 10 years after deposition. This has enabled comparisons with the values of past Ir-bearing horizons associated to impact-related mass-extinction events. Iridium concentration in the tailings (0.349 ppm) was 5-fold higher than the anomaly in the K-Pg at The Moody Creek Mine section (the highest values obtained from terrestrial sections). The oxidative weathering of the tailings caused the release of Ir and infiltration into the soil. Iridium distribution in depth indicates redistribution throughout the profile in relation to the change in the physico-chemical properties of the soil. With regard to the background concentration in the soil (0.056 ppm), anomalous values of Ir (0.129 ppm) can be detected to 11 cm below the layer of tailings. The correlation analysis between the Ir concentration and the main properties and constituents of the soils indicated a significant correlation with sulfur, iron, clay content, and pH. Selective extractions were made to study the forms in which Ir can be mobilized in the soil. The residual/insoluble fraction was >90% of the total Ir concentration in soil. Soluble-in-water concentration of Ir (1.5% of total) was detected in the uppermost 2-3 cm of the soil, which were directly affected by the leaching of acidic waters coming from the oxidation of the pyrite tailings. Iridium retention in the affected part of the soil reached 9% of the total Ir concentration; this retention could be related to the amorphous iron forms dissolved by the oxalic-oxalate extraction. However, according to our research, original Ir abundance could be secondarily modified, and then a direct analysis of the iridium values recorded in sediments could induce

  10. Iridium complexes demonstrating broadband emission through controlled geometric distortion and applications thereof

    DOEpatents

    Li, Jian; Turner, Eric

    2016-04-12

    Iridium compounds and their uses are disclosed herein. For example, carbazole containing iridium compounds are disclosed. The compounds are useful in many devices, including, but not limited to, electroluminescent devices.

  11. DETERMINATION OF HETEROGENEOUS ELECTRON TRANSFER RATE CONSTANTS AT MICROFABRICATED IRIDIUM ELECTRODES. (R825511C022)

    EPA Science Inventory

    There has been an increasing use of both solid metal and microfabricated iridium electrodes as substrates for various types of electroanalysis. However, investigations to determine heterogeneous electron transfer rate constants on iridium, especially at an electron beam evapor...

  12. Iridium complexes containing mesoionic C donors: selective C(sp3)-H versus C(sp2)-H bond activation, reactivity towards acids and bases, and catalytic oxidation of silanes and water.

    PubMed

    Petronilho, Ana; Woods, James A; Mueller-Bunz, Helge; Bernhard, Stefan; Albrecht, Martin

    2014-11-24

    Metalation of a C2-methylated pyridylimidazolium salt with [IrCp*Cl2]2 affords either an ylidic complex, resulting from C(sp(3))-H bond activation of the C2-bound CH3 group if the metalation is performed in the presence of a base, such as AgO2 or Na2CO3, or a mesoionic complex via cyclometalation and thermally induced heterocyclic C(sp(2))-H bond activation, if the reaction is performed in the absence of a base. Similar cyclometalation and complex formation via C(sp(2))-H bond activation is observed when the heterocyclic ligand precursor consists of the analogous pyridyltriazolium salt, that is, when the metal bonding at the C2 position is blocked by a nitrogen rather than a methyl substituent. Despite the strongly mesoionic character of both the imidazolylidene and the triazolylidene, the former reacts rapidly with D(+) and undergoes isotope exchange at the heterocyclic C5 position, whereas the triazolylidene ligand is stable and only undergoes H/D exchange under basic conditions, where the imidazolylidene is essentially unreactive. The high stability of the Ir-C bond in aqueous solution over a broad pH range was exploited in catalytic water oxidation and silane oxidation. The catalytic hydrosilylation of ketones proceeds with turnover frequencies as high as 6,000 h(-1) with both the imidazolylidene and the triazolylidene system, whereas water oxidation is enhanced by the stronger donor properties of the imidazol-4-ylidene ligands and is more than three times faster than with the triazolylidene analogue. PMID:25302630

  13. Iridium complexes containing mesoionic C donors: selective C(sp3)-H versus C(sp2)-H bond activation, reactivity towards acids and bases, and catalytic oxidation of silanes and water.

    PubMed

    Petronilho, Ana; Woods, James A; Mueller-Bunz, Helge; Bernhard, Stefan; Albrecht, Martin

    2014-11-24

    Metalation of a C2-methylated pyridylimidazolium salt with [IrCp*Cl2]2 affords either an ylidic complex, resulting from C(sp(3))-H bond activation of the C2-bound CH3 group if the metalation is performed in the presence of a base, such as AgO2 or Na2CO3, or a mesoionic complex via cyclometalation and thermally induced heterocyclic C(sp(2))-H bond activation, if the reaction is performed in the absence of a base. Similar cyclometalation and complex formation via C(sp(2))-H bond activation is observed when the heterocyclic ligand precursor consists of the analogous pyridyltriazolium salt, that is, when the metal bonding at the C2 position is blocked by a nitrogen rather than a methyl substituent. Despite the strongly mesoionic character of both the imidazolylidene and the triazolylidene, the former reacts rapidly with D(+) and undergoes isotope exchange at the heterocyclic C5 position, whereas the triazolylidene ligand is stable and only undergoes H/D exchange under basic conditions, where the imidazolylidene is essentially unreactive. The high stability of the Ir-C bond in aqueous solution over a broad pH range was exploited in catalytic water oxidation and silane oxidation. The catalytic hydrosilylation of ketones proceeds with turnover frequencies as high as 6,000 h(-1) with both the imidazolylidene and the triazolylidene system, whereas water oxidation is enhanced by the stronger donor properties of the imidazol-4-ylidene ligands and is more than three times faster than with the triazolylidene analogue.

  14. Highly Sensitive and Long Term Stable Electrochemical Microelectrodes for Implantable Glucose Monitoring Devices

    NASA Astrophysics Data System (ADS)

    Qiang, Liangliang

    A miniature wireless implantable electrochemical glucose system for continuous glucose monitoring with good selectivity, sensitivity, linearity and long term stability was developed. First, highly sensitive, long-term stable and reusable planar H2O2 microelectrodes have been fabricated by microlithography. These electrodes composed of a 300 nm Pt black layer situated on a 5 um thick Au layer, provide effective protection to the underlying chromium adhesion layer. Using repeated cyclic voltammetric sweeps in flowing buffer solution, highly sensitive Pt black working electrodes were realized with five-decade linear dynamic range and low detection limit (10 nM) for H2O2 at low oxidation potentials. Second, a highly sensitive, low cost and flexible microwire biosensor was described using 25-mum thick gold wire as working electrode together with 125-mum thick Pt/Ir and Ag wires as counter and reference electrode, embedded within a PDMS-filled polyethylene tube. Surface area and activity of sensor was enhanced by converting gold electrode to nanoporous configuration followed by electrodeposition of platinum black. Glucose oxidase based biosensors by electrodeposition of poly(o-phenylenediamine) and glucose oxidase on the working electrode, displayed a higher glucose sensitivity (1.2 mA mM-1 cm-2) than highest literature reported. In addition it exhibits wide detection range (up to 20 mM) and selectivity (>95%). Third, novel miniaturized and flexible microelectrode arrays with 8 of 25 mum electrodes displayed the much needed 3D diffusion profiles similar to a single 25 mum microelectrode, but with one order increase in current levels. These microelectrode arrays displayed a H2O2 sensitivity of 13 mA mM-1 cm-2, a wide dynamic range of 100 nM to 10 mM, limit of detection of 10 nM. These microwire based edge plane microsensors incorporated flexibility, miniaturization and low operation potential are an promising approach for continuous in vivo metabolic monitoring. Fourth

  15. Testing of electroformed deposited iridium/powder metallurgy rhenium rockets

    NASA Technical Reports Server (NTRS)

    Reed, Brian D.; Dickerson, Robert

    1996-01-01

    High-temperature, oxidation-resistant chamber materials offer the thermal margin for high performance and extended lifetimes for radiation-cooled rockets. Rhenium (Re) coated with iridium (Ir) allow hours of operation at 2200 C on Earth-storable propellants. One process for manufacturing Ir/Re rocket chambers is the fabrication of Re substrates by powder metallurgy (PM) and the application of Ir coatings by using electroformed deposition (ED). ED Ir coatings, however, have been found to be porous and poorly adherent. The integrity of ED Ir coatings could be improved by densification after the electroforming process. This report summarizes the testing of two 22-N, ED Ir/PM Re rocket chambers that were subjected to post-deposition treatments in an effort to densify the Ir coating. One chamber was vacuum annealed, while the other chamber was subjected to hot isostatic pressure (HIP). The chambers were tested on gaseous oxygen/gaseous hydrogen propellants, at mixture ratios that simulated the oxidizing environments of Earth-storable propellants. ne annealed ED Ir/PM Re chamber was tested for a total of 24 firings and 4.58 hr at a mixture ratio of 4.2. After only 9 firings, the annealed ED Ir coating began to blister and spall upstream of the throat. The blistering and spalling were similar to what had been experienced with unannealed, as-deposited ED Ir coatings. The HIP ED Ir/PM Re chamber was tested for a total of 91 firings and 11.45 hr at mixture ratios of 3.2 and 4.2. The HIP ED Ir coating remained adherent to the Re substrate throughout testing; there were no visible signs of coating degradation. Metallography revealed, however, thinning of the HIP Ir coating and occasional pores in the Re layer upstream of the throat. Pinholes in the Ir coating may have provided a path for oxidation of the Re substrate at these locations. The HIP ED Ir coating proved to be more effective than vacuum annealed and as-deposited ED Ir. Further densification is still required to

  16. In vivo microelectrode track reconstruction using magnetic resonance imaging

    PubMed Central

    Fung, S.H.; Burstein, D.; Born, R.T.

    2010-01-01

    To obtain more precise anatomical information about cortical sites of microelectrode recording and microstimulation experiments in alert animals, we have developed a non-invasive, magnetic resonance imaging (MRI) technique for reconstructing microelectrode tracks. We made microelectrode penetrations in the brains of anesthetized rats and marked sites along them by depositing metal, presumably iron, with anodic monophasic or biphasic current from the tip of a stainless steel microelectrode. The metal deposits were clearly visible in the living animal as approximately 200 μm wide hypointense punctate marks using gradient echo sequences in a 4.7T MRI scanner. We confirmed the MRI findings by comparing them directly to the postmortem histology in which the iron in the deposits could be rendered visible with a Prussian blue reaction. MRI-visible marks could be created using currents as low as 1 μA (anodic) for 5 s, and they remained stable in the brains of living rats for up to nine months. We were able to make marks using either direct current or biphasic current pulses. Biphasic pulses caused less tissue damage and were similar to those used by many laboratories for functional microstimulation studies in the brains of alert monkeys. PMID:9667395

  17. Neurotoxicity testing using Microelectrode Arrays (MEAs): a growing trend

    EPA Science Inventory

    Microelectrode arrays (MEAs) are groups of extracellular electrodes that are 10-30 microns in diameter and can be utilized in vivo or in vitro. For in vitro uses, an MEA typically contains up to 64 electrodes and can be utilized to measure the activity of cells and tissues that a...

  18. Fabrication of PMMA nanofluidic electrochemical chips with integrated microelectrodes.

    PubMed

    Liu, Junshan; Wang, Liang; Ouyang, Wei; Wang, Wei; Qin, Jun; Xu, Zheng; Xu, Shenbo; Ge, Dan; Wang, Longchang; Liu, Chong; Wang, Liding

    2015-10-15

    A novel method based on plasma etching was proposed for monolithically integrating planar nanochannels and microelectrodes on a poly (methyl methacrylate) (PMMA) plate, and complete PMMA nanofluidic electrochemical chips with integrated microelectrodes were constructed by bonding with another PMMA plate containing microchannels. The fabrication sequences of nanochannels and microelectrodes were optimized. The oxygen plasma etching rate of PMMA nanochannels was studied, and the average rate was 15 nm/min under optimal conditions. An UV-ozone assisted thermal bonding method was developed to realize a low-temperature chip bonding, and the variations in width and depth of nanochannels before and after bonding were 2% and 5%, respectively. As a demonstration, a nanoparticle crystal (NPC)-based nanofluidic biosensor with integrated Ag microelectrodes was designed and fabricated. Sub-microchannel arrays with a depth of 400 nm and a width of 30 μm on the biosensor functioned as filters, and trapped 540 nm silica nanoparticles modified with streptavidin inside the connected microchannel to assemble the NPC. The interspaces in the NPC formed a three-dimensional nanochannel network with an equivalent diameter of 81 nm. By measuring the conductance across the NPC, a high quality nanofluidic sensing of biotin was achieved. The limit of detection was 1 aM, and the detection range was from 1 aM to 0.1 nM.

  19. Progress towards biocompatible intracortical microelectrodes for neural interfacing applications

    NASA Astrophysics Data System (ADS)

    Jorfi, Mehdi; Skousen, John L.; Weder, Christoph; Capadona, Jeffrey R.

    2015-02-01

    To ensure long-term consistent neural recordings, next-generation intracortical microelectrodes are being developed with an increased emphasis on reducing the neuro-inflammatory response. The increased emphasis stems from the improved understanding of the multifaceted role that inflammation may play in disrupting both biologic and abiologic components of the overall neural interface circuit. To combat neuro-inflammation and improve recording quality, the field is actively progressing from traditional inorganic materials towards approaches that either minimizes the microelectrode footprint or that incorporate compliant materials, bioactive molecules, conducting polymers or nanomaterials. However, the immune-privileged cortical tissue introduces an added complexity compared to other biomedical applications that remains to be fully understood. This review provides a comprehensive reflection on the current understanding of the key failure modes that may impact intracortical microelectrode performance. In addition, a detailed overview of the current status of various materials-based approaches that have gained interest for neural interfacing applications is presented, and key challenges that remain to be overcome are discussed. Finally, we present our vision on the future directions of materials-based treatments to improve intracortical microelectrodes for neural interfacing.

  20. Microelectrode array biosensor for studying carbohydrate-mediated interactions

    PubMed Central

    Chamberlain, Jeffrey W.; Maurer, Karl; Cooper, John; Lyon, Wanda J.; Danley, David L.; Ratner, Daniel M.

    2013-01-01

    Carbohydrate-mediated host-pathogen interactions are essential to bacterial and viral pathogenesis, and represent an attractive target for the development of antiadhesives to prevent infection. We present a versatile microelectrode array-based platform to investigate carbohydrate-mediated protein and bacterial binding, with the objective of developing a generalizable method for screening inhibitors of host-microbe interactions. Microelectrode arrays are well suited for interrogating biological binding events, including proteins and whole-cells, and are amenable to electrochemical derivitization, facilitating rapid deposition of biomolecules. In this study, we achieve microelectrode functionalization with carbohydrates via controlled polymerization of pyrrole to individual microelectrodes, followed by physisorption of neoglycoconjugates to the polypyrrole-coated electrodes. Bioactivity of the immobilized carbohydrates was confirmed with carbohydrate-binding proteins (lectins) detected by both fluorescent and electrochemical means. The platform’s ability to analyze whole-cell binding was demonstrated using strains of Escherichia coli and Salmonella enterica, and the dose-dependent inhibition of S. enterica by a soluble carbohydrate antiadhesive. PMID:22405843

  1. Progress Towards Biocompatible Intracortical Microelectrodes for Neural Interfacing Applications

    PubMed Central

    Jorfi, Mehdi; Skousen, John L.; Weder, Christoph; Capadona, Jeffrey R.

    2015-01-01

    To ensure long-term consistent neural recordings, next-generation intracortical microelectrodes are being developed with an increased emphasis on reducing the neuro-inflammatory response. The increased emphasis stems from the improved understanding of the multifaceted role that inflammation may play in disrupting both biologic and abiologic components of the overall neural interface circuit. To combat neuro-inflammation and improve recording quality, the field is actively progressing from traditional inorganic materials towards approaches that either minimizes the microelectrode footprint or that incorporate compliant materials, bioactive molecules, conducting polymers or nanomaterials. However, the immune-privileged cortical tissue introduces an added complexity compared to other biomedical applications that remains to be fully understood. This review provides a comprehensive reflection on the current understanding of the key failure modes that may impact intracortical microelectrode performance. In addition, a detailed overview of the current status of various materials-based approaches that have gained interest for neural interfacing applications is presented, and key challenges that remain to be overcome are discussed. Finally, we present our vision on the future directions of materials-based treatments to improve intracortical microelectrodes for neural interfacing. PMID:25460808

  2. IR-doped ruthenium oxide catalyst for oxygen evolution

    NASA Technical Reports Server (NTRS)

    Valdez, Thomas I. (Inventor); Narayanan, Sekharipuram R. (Inventor)

    2012-01-01

    A method for preparing a metal-doped ruthenium oxide material by heating a mixture of a doping metal and a source of ruthenium under an inert atmosphere. In some embodiments, the doping metal is in the form of iridium black or lead powder, and the source of ruthenium is a powdered ruthenium oxide. An iridium-doped or lead-doped ruthenium oxide material can perform as an oxygen evolution catalyst and can be fabricated into electrodes for electrolysis cells.

  3. Oxidation of Ruthenium and Iridium Metal by XeF2 and Crystal Structure Determination of [Xe2F3][RuF6]·XeF2 and [Xe2F3][MF6] (M = Ru, Ir).

    PubMed

    Tramšek, Melita; Goreshnik, Evgeny; Tavčar, Gašper

    2016-01-01

    Salts containing [Xe2F3]+ cations and [MF6]- anions (M = Ru, Ir) were synthesized by the oxidation of metal with excess of XeF2 in anhydrous hydrogen fluoride (aHF) as a solvent. Single crystals of [Xe2F3][RuF6]·XeF2, [Xe2F3][RuF6] and [Xe2F3][IrF6] were grown by slow evaporation of the solvent. [Xe2F3][RuF6]·XeF2 crystallizes in a triclinic P-1 space group (a = 8.3362(1) Å, b = 8.8197(2) Å, c = 9.3026(4) Å; α = 68.27(1)°, β = 63.45(1)°, γ = 82.02°, V = 568.09(9) Å3 (Z = 2)). Discrete [Xe2F3]+, XeF2 and [RuF6]- units are found in the asymmetric unit. [Xe2F3][RuF6] and [Xe2F3][IrF6] compounds are isostructural and crystallize in a monoclinic Cc space group (a = 14.481(3) Å (Ru); 14.544(3) Å (Ir); b = 8.0837(8) Å (Ru), 8.0808(7) Å (Ir), c = 10.952(2) Å (Ru), 11.014(2) Å (Ir); β = 136.825(6)° (Ru), 139.954(7)°, V = 877.2(3) Å3 (Ru), 883.6(3) Å3 (Ir); Z = 4). The asymmetric unit in the [Xe2F3][MF6] (M = Ru, Ir) consists of one [Xe2F3]+ and one [MF6]- unit. PMID:27333561

  4. Electrogenerated chemiluminescence from heteroleptic iridium(III) complexes with multicolor emission.

    PubMed

    Zhou, Yuyang; Gao, Hongfang; Wang, Xiaomei; Qi, Honglan

    2015-02-16

    Electrogenerated chemiluminescence (ECL) with different emission colors is important in the development of multichannel analytical techniques. In this report, five new heteroleptic iridium(III) complexes were synthesized, and their photophysical, electrochemical, and ECL properties were studied. Here, 2-(2,4-difluorophenyl)pyridine (dfppy, complex 1), 2-phenylbenzo[d]thiazole (bt, complex 2), and 2-phenylpyridine (ppy, complex 3) were used as the main ligands to tune the emission color, while avobenzone (avo) was used as the ancillary ligand. For comparison, complexes 4 and 5 with 2-phenylpyridine and 2-phenylbenzo[d]thiazole as the main ligand, respectively, and acetyl acetone (acac) as the ancillary ligand were also synthesized. All five iridium(III) complexes had strong intraligand absorption bands (π–π*) in the UV region (below 350 nm) and a featureless MLCT (d−π*) transition in the visible 400–500 nm range. Multicolored emissions were observed for these five iridium(III) complexes, including green, orange, and red for complexes 4, 5, 2, 1, 3, respectively. Density functional theory calculations indicate that the electronic density of the highest occupied molecular orbital is entirely located on the C^N ligands and the iridium atom, while the formation of the lowest unoccupied molecular orbital (LUMO) is complicated. The LUMO is mainly assigned to the ancillary ligand for complexes 1 and 3 but to the C^N ligand for complexes 2, 4, and 5. Cyclic voltammetry studies showed that all these complexes have a reversible oxidation wave, but no reduction waves were found in the electrochemical windows of CH2Cl2. The E1/2(ox) values of these complexes ranged from 0.642 to 0.978 V for complexes 3, 4, 2, 5, 1, (in increasing order) and are all lower than that of Ru(bpy)3(2+). Most importantly, when using tripropylamine as a coreactant, complexes 1–5 exhibited intense ECL signals with an emission wavelength centered at 616, 580, 663, 536, and 569 nm, respectively

  5. Experimental determination of the solubility of iridium in silicate melts: Preliminary results

    NASA Technical Reports Server (NTRS)

    Borisov, Alexander; Dingwell, Donald B.; Oneill, Hugh ST.C.; Palme, Herbert

    1992-01-01

    Little is known of the geochemical behavior of iridium. Normally this element is taken to be chalcophile and/or siderophile so that during planetary differentiation processes, e.g., core formation, iridium is extracted from silicate phases into metallic phases. Experimental determination of the metal/silicate partition coefficient of iridium is difficult simply because it is so large. Also there are no data on the solubility behavior of iridium in silicate melts. With information on the solubility of iridium in silicate melts it is possible, in combination with experimental data for Fe-Ir alloys, to calculate the partition coefficient between a metallic phase and a silicate melt.

  6. Synthesis of new heteroscorpionate iridium(I) and iridium(III) complexes.

    PubMed

    Roa, A E; Campos, J; Paneque, M; Salazar, V; Otero, A; Lara-Sánchez, A; Rodríguez, A M; López-Solera, I; Gómez, M V

    2015-04-21

    The reactivity of different heteroscorpionate ligands based on bis(pyrazol-1-yl)methane, with different iridium-(i) and -(iii) precursors is reported. The reaction of the heteroscorpionate lithium salts "Li(bdmpza)", [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate], "Li(bdmpzdta)" [bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate] and "Li(S)-mbpam" [(S)-mbpam = (S)-(-)-N-α-methylbenzyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamidate] with 1 equivalent of [IrCl3(THF)3] in THF for 18 h affords high yields of neutral and anionic heteroscorpionate chloride iridium complexes [IrCl2(bdmpza)(THF)] (), [Li(THF)4][IrCl3(bdmpzdta)] () and [IrCl2{(S)-mbpam})(THF)] (). Solution of complex in acetonitrile at room temperature leads to complex [IrCl2{(S)-mbpam})(NCCH3)] (). Complexes and were isolated as enantiopure compounds. The reaction of the lithium salt "Li(bdmpza)" with [IrCl(η(4)-CH2[double bond, length as m-dash]C(Me)C(Me)[double bond, length as m-dash]CH2)]2 in THF for 18 h gave the Ir(i) complex [Ir(bdmpza)(η(4)-CH2[double bond, length as m-dash]C(Me)C(Me)[double bond, length as m-dash]CH2)] (). The reaction of complex with CO (2 atm) at room temperature leads to a new complex of Ir(iii), [Ir(bdmpza)(k(2)-CH2C(Me)[double bond, length as m-dash]C(Me)CH2)(CO)] (). Treatment of heteroscorpionate ligand precursors "Li(bdmpza)" and "Li(bdmpzdta)" with [IrCp*Cl2]2 in THF yielded the iridium(iii) complexes [Ir2Cp*2Cl2(bdmpzx)] (x = a , x = dta ). These complexes have helical chirality due to the demands of the fixed pyrazole rings. The stereoisomerism and the self-assembly processes of these helicates have been studied in some detail in solution by NMR spectroscopy and in the solid state by X-ray diffraction. Mixtures of M- and P-handed enantiomers were obtained. Complex undergoes a decarboxylation process initiated by the HCl generated in the previous step leading to the known ionic complex [IrClCp*(bdmpm)][IrCl3Cp*] [bdmpm = bis(3,5-dimethylpyrazol-1-yl)methane] (). The

  7. Synthesis of new heteroscorpionate iridium(I) and iridium(III) complexes.

    PubMed

    Roa, A E; Campos, J; Paneque, M; Salazar, V; Otero, A; Lara-Sánchez, A; Rodríguez, A M; López-Solera, I; Gómez, M V

    2015-04-21

    The reactivity of different heteroscorpionate ligands based on bis(pyrazol-1-yl)methane, with different iridium-(i) and -(iii) precursors is reported. The reaction of the heteroscorpionate lithium salts "Li(bdmpza)", [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate], "Li(bdmpzdta)" [bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate] and "Li(S)-mbpam" [(S)-mbpam = (S)-(-)-N-α-methylbenzyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamidate] with 1 equivalent of [IrCl3(THF)3] in THF for 18 h affords high yields of neutral and anionic heteroscorpionate chloride iridium complexes [IrCl2(bdmpza)(THF)] (), [Li(THF)4][IrCl3(bdmpzdta)] () and [IrCl2{(S)-mbpam})(THF)] (). Solution of complex in acetonitrile at room temperature leads to complex [IrCl2{(S)-mbpam})(NCCH3)] (). Complexes and were isolated as enantiopure compounds. The reaction of the lithium salt "Li(bdmpza)" with [IrCl(η(4)-CH2[double bond, length as m-dash]C(Me)C(Me)[double bond, length as m-dash]CH2)]2 in THF for 18 h gave the Ir(i) complex [Ir(bdmpza)(η(4)-CH2[double bond, length as m-dash]C(Me)C(Me)[double bond, length as m-dash]CH2)] (). The reaction of complex with CO (2 atm) at room temperature leads to a new complex of Ir(iii), [Ir(bdmpza)(k(2)-CH2C(Me)[double bond, length as m-dash]C(Me)CH2)(CO)] (). Treatment of heteroscorpionate ligand precursors "Li(bdmpza)" and "Li(bdmpzdta)" with [IrCp*Cl2]2 in THF yielded the iridium(iii) complexes [Ir2Cp*2Cl2(bdmpzx)] (x = a , x = dta ). These complexes have helical chirality due to the demands of the fixed pyrazole rings. The stereoisomerism and the self-assembly processes of these helicates have been studied in some detail in solution by NMR spectroscopy and in the solid state by X-ray diffraction. Mixtures of M- and P-handed enantiomers were obtained. Complex undergoes a decarboxylation process initiated by the HCl generated in the previous step leading to the known ionic complex [IrClCp*(bdmpm)][IrCl3Cp*] [bdmpm = bis(3,5-dimethylpyrazol-1-yl)methane] (). The

  8. Method of making a cathode from tungsten and iridium powders using a strontium peroxide containing material as the impregnant

    SciTech Connect

    Branovich, L.E.; Freeman, G.L.; Smith, B.

    1988-11-25

    This invention relates in general to a method of making a long-life high-current-density cathode and in particular, to a method of making such a cathode from a mixture of tungsten and iridium powders using a strontium peroxide containing material as the impregnant. The general object of this invention is to provide an improved method of making a long life high current density cathode. A more specific object of the invention is to provide such a method in which lower temperatures can be used than were used in S.N. 204,327 for the impregnation of the tungsten-iridium billet. It has now been found that the aforementioned objects can be attained by a method that uses a strontium peroxide-containing material as the impregnant. More particularly, according to the invention, a suitable porous billet of tungsten, or tungsten-iridium, or tungsten-osmium or tungsten-rhodium is impregnated with a strontium peroxide containing material in a hydrogen atmosphere and slowly heated to above 215 C to decompose the strontium peroxide, SrO/sub 2/ to form strontium oxide, SrO, and oxygen, O/sub 2/.

  9. Tuning electrode impedance for the electrical recording of biopotentials.

    PubMed

    Fontes, M A; de Beeck, M; Van Hoof, C; Neves, H P

    2010-01-01

    Tuning the electrode impedance through the DC biasing of iridium oxide is presented. Impedance reduction of up to two orders of magnitude was reproducibly observed in 20 microm diameter microelectrodes at a biasing of 1V.

  10. A VOLTAMMETRIC FLAVIN MICROELECTRODE FOR USE IN BIOFILMS

    PubMed Central

    Nguyen, Hung Duc; Renslow, Ryan; Babauta, Jerome; Ahmed, Bulbul; Beyenal, Haluk

    2011-01-01

    Biofilms used in bioelectrochemical systems are expected to transfer electrons using electron transfer mediators. One mediator type, flavins, which includes flavin mononucleotide, riboflavin, and flavin adenine dinucleotide, has been found to be endogenously produced by Shewanella oneidensis MR-1. However, the presence and concentration of flavins inside a S. oneidensis MR-1 biofilm have never been reported. The goal of this study was to develop a flavin microelectrode capable of measuring flavins inside a living biofilm and apply it to a biofilm which produces flavins. Because flavins are electrochemically active molecules, the flavin microelectrode was based on detection via square-wave voltammetry. The microelectrode consisted of a carbon working electrode with a 10–30 μm tip diameter, a built-in platinum counter electrode, and a Ag/AgCl reference electrode, all enclosed in a glass outer case. The microelectrode was calibrated between 0.1 μM and 10 μM flavins and showed a linear correlation between flavin concentration and peak currents located at −424 mVAg/AgCl on a square-wave voltammogram. We also developed a model to explain the electrochemical mechanism of flavin detection, and to determine the effective surface area of the microelectrode, the standard reduction potential, and the transfer coefficient. We found that the effective surface area of the microelectrode was close to 100 times the projected surface area. The model predicted a standard reduction potential for RF/RFH2 of −419 mVAg/AgCl at 20 °C and a transfer coefficient of 0.45. Lastly, we measured flavin concentration inside a S. oneidensis MR-1 biofilm grown on a glass surface using oxygen as the electron acceptor. The flavin concentration reached 0.7 μM, increasing near the bottom of the biofilm, where no oxygen was present. This shows the possibility that flavins are produced in the anaerobic zone to act as intermediate electron acceptors in the deeper parts of the biofilm, where

  11. Iridium-catalyzed enantioselective hydrogenation of unsaturated heterocyclic acids.

    PubMed

    Song, Song; Zhu, Shou-Fei; Pu, Liu-Yang; Zhou, Qi-Lin

    2013-06-01

    Spiral binding: A highly enantioselective hydrogenation of unsaturated heterocyclic acids has been developed by using chiral iridium/spirophosphino oxazoline catalysts (see scheme; BArF(-) =tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, Boc=tert-butoxycarbonyl). This reaction provided an efficient method for the preparation of optically active heterocyclic acids with excellent enantioselectivities. PMID:23610004

  12. The Iridium (tm) system: Personal communications anytime, anyplace

    NASA Technical Reports Server (NTRS)

    Hatlelid, John E.; Casey, Larry

    1993-01-01

    The Iridium system is designed to provide handheld personal communications between diverse locations around the world at any time and without prior knowledge of the location of the personal units. This paper provides an overview of the system, the services it provides, its operation, and an overview of the commercial practices and relatively high volume satellite production techniques which will make the system cost effective. A constellation of 66 satellites will provide an orbiting, spherical-shell, infrastructure for this global calling capability. The satellites act as tall cellular towers and allow convenient operation for portable handheld telephones. The system will provide a full range of services including voice, paging, data, geolocation, and fax capabilities. Motorola is a world leader in the production of high volume, high quality, reliable telecommunications hardware. One of Iridium's goals is to apply these production techniques to high reliability space hardware. Concurrent engineering, high performance work teams, advanced manufacturing technologies, and improved assembly and test methods are some of the techniques that will keep the Iridium system cost effective. Mobile, global, flexible personal communications are coming that will allow anyone to call or receive a call from/to anyplace at anytime. The Iridium system will provide communications where none exist today. This connectivity will allow increased information transfer, open new markets for various business endeavors, and in general increase productivity and development.

  13. The Iridium (tm) system: Personal communications anytime, anyplace

    NASA Astrophysics Data System (ADS)

    Hatlelid, John E.; Casey, Larry

    The Iridium system is designed to provide handheld personal communications between diverse locations around the world at any time and without prior knowledge of the location of the personal units. This paper provides an overview of the system, the services it provides, its operation, and an overview of the commercial practices and relatively high volume satellite production techniques which will make the system cost effective. A constellation of 66 satellites will provide an orbiting, spherical-shell, infrastructure for this global calling capability. The satellites act as tall cellular towers and allow convenient operation for portable handheld telephones. The system will provide a full range of services including voice, paging, data, geolocation, and fax capabilities. Motorola is a world leader in the production of high volume, high quality, reliable telecommunications hardware. One of Iridium's goals is to apply these production techniques to high reliability space hardware. Concurrent engineering, high performance work teams, advanced manufacturing technologies, and improved assembly and test methods are some of the techniques that will keep the Iridium system cost effective. Mobile, global, flexible personal communications are coming that will allow anyone to call or receive a call from/to anyplace at anytime. The Iridium system will provide communications where none exist today. This connectivity will allow increased information transfer, open new markets for various business endeavors, and in general increase productivity and development.

  14. Discovery of tantalum, rhenium, osmium, and iridium isotopes

    SciTech Connect

    Robinson, R.; Thoennessen, M.

    2012-09-15

    Currently, thirty-eight tantalum, thirty-eight rhenium, thirty-nine osmium, and thirty-eight iridium isotopes have been observed and the discovery of these isotopes is described here. For each isotope a brief synopsis of the first refereed publication, including the production and identification method, is presented.

  15. Mononuclear iridium dinitrogen complexes bonded to zeolite HY

    SciTech Connect

    Yang, Dong; Chen, Mingyang; Martinez-Macias, Claudia; Dixon, David A.; Gates, Bruce C.

    2014-11-07

    In this study, the adsorption of N2 on structurally well-defined dealuminated HY zeolite-supported iridium diethylene complexes was investigated. Iridium dinitrogen complexes formed when the sample was exposed to N2 in H2 at 298 K, as shown by infrared spectra recorded with isotopically labeled N2. Four supported species formed in various flowing gases: Ir(N2), Ir(N2)(N2), Ir(C2H5)(N2), and Ir(H)(N2). Their interconversions are summarized in a reaction network, showing, for example, that, in the presence of N2, Ir(N2) was the predominant dinitrogen species at temperatures of 273-373 K. Ir(CO)(N2) formed transiently in flowing CO, and in the presence of H2, rather stable iridium hydride complexes formed. Here, four structural models of each iridium complex bonded at the acidic sites of the zeolite were employed in a computational investigation, showing that the calculated vibrational frequencies agree well with experiment when full calculations are done at the level of density functional theory, independent of the size of the model of the zeolite.

  16. Achieving Zero Stress in Iridium, Chromium, and Nickle Thin Films

    NASA Technical Reports Server (NTRS)

    Broadway, David M.; Weimer, Jeffrey; Gurgew, Danielle; Lis, Tomasz; Ramsey, Brian D.; O'Dell, Stephen L.; Ames, A.; Bruni, R.

    2015-01-01

    We examine a method for achieving zero intrinsic stress in thin films of iridium, chromium, and nickel deposited by magnetron sputter deposition. The examination of the stress in these materials is motivated by efforts to advance the optical performance of light-weight x-ray space telescopes into the regime of sub-arc second resolution that rely on control of the film stress to values within 10-100 MPa. A characteristic feature of the intrinsic stress behavior in chromium and nickel is their sensitivity to the magnitude and sign of the intrinsic stress with argon gas pressure, including the existence of a critical pressure that results in zero film stress. This critical pressure scales linearly with the film's density. While the effect of stress reversal with argon pressure has been previously reported by Hoffman and others for nickel and chromium, we have discovered a similar behavior for iridium. Additionally, we have identified zero stress in iridium shortly after island coalescence. This feature of film growth is used for achieving a total internal stress of -2.89 MPa for a 15.8 nm thick iridium film. The surface roughness of this low-stress film was examined using scanning probe microscopy (SPM) and x-ray reflectivity (XRR) at CuKa and these results presented and discussed.

  17. Magnetostratigraphy, Late devonian iridium anomaly, and impact hypotheses

    SciTech Connect

    Hurley, N.F.; Van der Voo, R. )

    1990-04-01

    Paleomagnetism, sedimentology, and fine-scale stratigraphy have been integrated to explain the origin of an iridium anomaly in the Late Devonian of Western Australia. Thermal demagnetization experiments were carried out on 93 specimens of marginal-slope limestone form the northern Canning Basin. Samples are from a condensed sequence of deep-water (> 100 m) Frutexites microstromatolites. Frutexites is a shrublike cyanobacterial organism that probably precipitated hematite, or a metastable precursor, from sea water. When plotted within the microstratigraphic framework for the study area, the observed characteristic directions from the sampled interval (14.5 cm thick) are in five discrete, layer-parallel, normal- and reversed-polarity zones. The measured northeast-southwest declinations and shallow inclinations probably record Late Devonian magnetostratigraphy on a centimetre scale. The Frutexites bed studied there occurs close to the Frasnian/Famennian (Late Devonian) boundary, a time of mass extinction of a wide variety of marine organisms throughout the world. Anomalously high iridium concentrations observed in the Frutexites bed have suggested to some authors that the mass extinction was caused by meteorite impact. This study concludes that iridium, which is present over the span of five layer-parallel magnetic reversals, was concentrated over a long period of time by biologic processes. Thus, the Canning Basin iridium anomaly may be unrelated to meteorite impact.

  18. Photoconducting properties of a unit nanostructure of ZnO assembled between microelectrodes.

    PubMed

    Kulkarni, Atul; Wahab, Rizwan; Ansari, S G; Kim, Tae-Sung; Al-Deyab, Salem S; Ansari, Z A

    2012-03-01

    The photoconducting properties of a unit microflower of zinc oxide are investigated as a function of wavelength from UV to IR region at constant illumination intensity. Synthesized flowers were trapped in 2 microm gap, between pre-prepared gold microelectrodes, using AC dielectrophoresis. Photocurrent drastically increases upon illumination in the UV region, whereas it gradually reduces when irradiated in visible and IR region. Higher photoconductivity in UV region is correlated to band to band transition upon illumination. In visible region, deep level transitions are expected which intern exhibits comparatively low photocurrent. Photoconduction in IR region is only due to the adsorbed surface oxygen species. This investigation suggests the potential application of ZnO nanostructures for various optoelectronic device applications.

  19. Electrochemical measurements on a droplet using gold microelectrodes

    NASA Astrophysics Data System (ADS)

    Jenabi, Amin; Souri, Asma; Rastkhadiv, Ali

    2016-03-01

    Facile methods of ion recognition are important for the fabrication of electronic tongue systems. In this work, we demonstrate performing pulsed conductometry on microliter electrolyte droplets dropped on gold microelectrodes vapor deposited on soda lime glass slides. A droplet is dropped between two microelectrodes when a voltage waveform from a preprogramed power supply is applied on them. The temporal variation of the electric current passing through the droplet is recorded, digitized and stored. The obtained data are compared with the database formed out of the previous experiences for the classification of the sample electrolytes. It is shown that the shape of the voltage waveform is the important parameter of the process. We devised a method for the optimization of the voltage waveform profile for obtaining the maximum of discriminating information from the recorded current variations.

  20. Utilization of Low Bandwidth Iridium Modems for Polar Seismology

    NASA Astrophysics Data System (ADS)

    Parker, T.

    2012-12-01

    Transmission of realtime seismic data is a desirable goal when a rapid response is needed. However, for many science applications sample waveform data, system state of health, and the ability to command and control the seismic station are operationally adequate. Determining the optimal telemetry requirements for a remote polar seismic experiment requires balancing science objective against the expensive, over-subscribed support available in the polar environments? For example there is a significant difference in the resources needed for a permanent "monitoring" effort versus a short-term experiment. We will describe IRIS/PASSCAL's successful approach to utilizing Iridium telemetry for short-term seismic experiments and suggest viable use of an Iridium RUDICs system for higher data-rate, permanent seismic stations such as a monitoring scenario. Most seismic stations are configured to record at a rate that exceeds twice the data rate of a single Iridium Internet modem. The power requirement to run continuous Iridium telemetry better than doubles that of a standalone seismic station. Doubling station power roughly doubles station logistics by requiring an increased number of support flights for installation and service. The tradeoffs between desirable and adequate telemetry requirements and the ramifications these requirements have on support services must be considered for a successful seismic station. We describe two Iridium telemetry systems, developed by the IRIS/PASSCAL Polar Program, for use with seismic stations in Antarctica and the Arctic. The first system uses an inexpensive Iridium 9602 modem based device and short burst data (SBD) transmission to monitor station performance, provide some command and control, and return a small amount of representative seismic data. Power requirements for this SBD system are approximately 10Ah per year for a daily message. The second system uses an Iridium 9522b modem based device the DOD RUDICs system for a 2400 Baud

  1. In vivo deployment of mechanically adaptive nanocomposites for intracortical microelectrodes

    PubMed Central

    Harris, J P; Hess, A E; Rowan, S J; Weder, C; Zorman, C A; Tyler, D J; Capadona, J R

    2012-01-01

    We recently introduced a series of stimuli-responsive, mechanically-adaptive polymer nanocomposites. Here, we report the first application of these bio-inspired materials as substrates for intracortical microelectrodes. Our hypothesis is that the ideal electrode should be initially stiff to facilitate minimal trauma during insertion into the cortex, yet becomes mechanically compliant to match the stiffness of the brain tissue and minimize forces exerted on the tissue, attenuating inflammation. Microprobes created from mechanically reinforced nanocomposites demonstrated a significant advantage compared to model microprobes composed of neat polymer only. The nanocomposite microprobes exhibit a higher storage modulus (E’ = ~5 GPa) than the neat polymer microprobes (E’ = ~2 GPa) and could sustain higher loads (~17 mN), facilitating penetration through the pia mater and insertion into the cerebral cortex of a rat. In contrast, the neat polymer microprobes mechanically failed under lower loads (~7 mN) before they were capable of inserting into cortical tissue. Further, we demonstrated the material’s ability to morph while in the rat cortex to more closely match the mechanical properties of the cortical tissue. Nanocomposite microprobes that were implanted into the rat cortex for up to 8 weeks demonstrated increased cell density at the microelectrode-tissue interface and a lack of tissue necrosis or excessive gliosis. This body of work introduces our nanocomposite-based microprobes as adaptive substrates for intracortical microelectrodes and potentially other biomedical applications. PMID:21654037

  2. Electrochemical properties and myocyte interaction of carbon nanotube microelectrodes.

    PubMed

    Fung, Andrew O; Tsiokos, Christos; Paydar, Omeed; Chen, Li Han; Jin, Sungho; Wang, Yibin; Judy, Jack W

    2010-11-10

    Arrays of carbon nanotube (CNT) microelectrodes (nominal geometric surface areas 20-200 μm(2)) were fabricated by photolithography with chemical vapor deposition of randomly oriented CNTs. Raman spectroscopy showed strong peak intensities in both G and D bands (G/D = 0.86), indicative of significant disorder in the graphitic layers of the randomly oriented CNTs. The impedance spectra of gold and CNT microelectrodes were compared using equivalent circuit models. Compared to planar gold surfaces, pristine nanotubes lowered the overall electrode impedance at 1 kHz by 75%, while nanotubes treated in O(2) plasma reduced the impedance by 95%. Cyclic voltammetry in potassium ferricyanide showed potential peak separations of 133 and 198 mV for gold and carbon nanotube electrodes, respectively. The interaction of cultured cardiac myocytes with randomly oriented and vertically aligned CNTs was investigated by the sectioning of myocytes using focused-ion-beam milling. Vertically aligned nanotubes deposited by plasma-enhanced chemical vapor deposition (PECVD) were observed to penetrate the membrane of neonatal-rat ventricular myocytes, while randomly oriented CNTs remained external to the cells. These results demonstrated that CNT electrodes can be leveraged to reduce impedance and enhance biological interfaces for microelectrodes of subcellular size. PMID:20954739

  3. In vivo deployment of mechanically adaptive nanocomposites for intracortical microelectrodes.

    PubMed

    Harris, J P; Hess, A E; Rowan, S J; Weder, C; Zorman, C A; Tyler, D J; Capadona, J R

    2011-08-01

    We recently introduced a series of stimuli-responsive, mechanically adaptive polymer nanocomposites. Here, we report the first application of these bio-inspired materials as substrates for intracortical microelectrodes. Our hypothesis is that the ideal electrode should be initially stiff to facilitate minimal trauma during insertion into the cortex, yet become mechanically compliant to match the stiffness of the brain tissue and minimize forces exerted on the tissue, attenuating inflammation. Microprobes created from mechanically reinforced nanocomposites demonstrated a significant advantage compared to model microprobes composed of neat polymer only. The nanocomposite microprobes exhibit a higher storage modulus (E' = ~5 GPa) than the neat polymer microprobes (E' = ~2 GPa) and can sustain higher loads (~12 mN), facilitating penetration through the pia mater and insertion into the cerebral cortex of a rat. In contrast, the neat polymer microprobes mechanically failed under lower loads (~7 mN) before they were capable of insertion into cortical tissue. Further, we demonstrated the material's ability to morph while in the rat cortex to more closely match the mechanical properties of the cortical tissue. Nanocomposite microprobes that were implanted into the rat cortex for up to eight weeks demonstrated increased cell density at the microelectrode-tissue interface and a lack of tissue necrosis or excessive gliosis. This body of work introduces our nanocomposite-based microprobes as adaptive substrates for intracortical microelectrodes and potentially for other biomedical applications.

  4. A tapered aluminium microelectrode array for improvement of dielectrophoresis-based particle manipulation.

    PubMed

    Buyong, Muhamad Ramdzan; Larki, Farhad; Faiz, Mohd Syafiq; Hamzah, Azrul Azlan; Yunas, Jumrail; Majlis, Burhanuddin Yeop

    2015-01-01

    In this work, the dielectrophoretic force (F(DEP)) response of Aluminium Microelectrode Arrays with tapered profile is investigated through experimental measurements and numerical simulations. A standard CMOS processing technique with a step for the formation of a tapered profile resist is implemented in the fabrication of Tapered Aluminium Microelectrode Arrays (TAMA). The F(DEP) is investigated through analysis of the Clausius-Mossotti factor (CMF) and cross-over frequency (f(xo)). The performance of TAMA with various side wall angles is compared to that of microelectrodes with a straight cut sidewall profile over a wide range of frequencies through FEM numerical simulations. Additionally, electric field measurement (EFM) is performed through scanning probe microscopy (SPM) in order to obtain the region of force focus in both platforms. Results showed that the tapered profile microelectrodes with angles between 60° and 70° produce the highest electric field gradient on the particles. Also, the region of the strongest electric field in TAMA is located at the bottom and top edge of microelectrode while the strongest electric field in microelectrodes with straight cut profile is found at the top corner of the microelectrode. The latter property of microelectrodes improves the probability of capturing/repelling the particles at the microelectrode's side wall. PMID:25970255

  5. Formation of C-C Bonds via Iridium-Catalyzed Hydrogenation and Transfer Hydrogenation.

    PubMed

    Bower, John F; Krische, Michael J

    2011-01-01

    The formation of C-C bonds via catalytic hydrogenation and transfer hydrogenation enables carbonyl and imine addition in the absence of stoichiometric organometallic reagents. In this review, iridium-catalyzed C-C bond-forming hydrogenations and transfer hydrogenations are surveyed. These processes encompass selective, atom-economic methods for the vinylation and allylation of carbonyl compounds and imines. Notably, under transfer hydrogenation conditions, alcohol dehydrogenation drives reductive generation of organoiridium nucleophiles, enabling carbonyl addition from the aldehyde or alcohol oxidation level. In the latter case, hydrogen exchange between alcohols and π-unsaturated reactants generates electrophile-nucleophile pairs en route to products of hydro-hydroxyalkylation, representing a direct method for the functionalization of carbinol C-H bonds. PMID:21822399

  6. Iridium-Catalyzed, Hydrosilyl-Directed Borylation of Unactivated Alkyl C-H Bonds.

    PubMed

    Larsen, Matthew A; Cho, Seung Hwan; Hartwig, John

    2016-01-27

    We report the iridium-catalyzed borylation of primary and secondary alkyl C-H bonds directed by a Si-H group to form alkylboronate esters site selectively. The reactions occur with high selectivity at primary C-H bonds γ to the hydrosilyl group to form primary alkyl bisboronate esters. In the absence of such primary C-H bonds, the borylation occurs selectively at a secondary C-H bond γ to the hydrosilyl group, and these reactions of secondary C-H bonds occur with high diastereoselectivity. The hydrosilyl-containing alkyl boronate esters formed by this method undergo transformations selectively at the carbon-boron or carbon-silicon bonds of these products under distinct conditions to give the products of amination, oxidation, and arylation.

  7. Formation of C–C Bonds via Iridium-Catalyzed Hydrogenation and Transfer Hydrogenation

    PubMed Central

    Bower, John F.; Krische, Michael J.

    2011-01-01

    The formation of C–C bonds via catalytic hydrogenation and transfer hydrogenation enables carbonyl and imine addition in the absence of stoichiometric organometallic reagents. In this review, iridium-catalyzed C–C bond-forming hydrogenations and transfer hydrogenations are surveyed. These processes encompass selective, atom-economic methods for the vinylation and allylation of carbonyl compounds and imines. Notably, under transfer hydrogenation conditions, alcohol dehydrogenation drives reductive generation of organoiridium nucleophiles, enabling carbonyl addition from the aldehyde or alcohol oxidation level. In the latter case, hydrogen exchange between alcohols and π-unsaturated reactants generates electrophile–nucleophile pairs en route to products of hydro-hydroxyalkylation, representing a direct method for the functionalization of carbinol C–H bonds. PMID:21822399

  8. Simulation of dose distribution for iridium-192 brachytherapy source type-H01 using MCNPX

    NASA Astrophysics Data System (ADS)

    Purwaningsih, Anik

    2014-09-01

    Dosimetric data for a brachytherapy source should be known before it used for clinical treatment. Iridium-192 source type H01 was manufactured by PRR-BATAN aimed to brachytherapy is not yet known its dosimetric data. Radial dose function and anisotropic dose distribution are some primary keys in brachytherapy source. Dose distribution for Iridium-192 source type H01 was obtained from the dose calculation formalism recommended in the AAPM TG-43U1 report using MCNPX 2.6.0 Monte Carlo simulation code. To know the effect of cavity on Iridium-192 type H01 caused by manufacturing process, also calculated on Iridium-192 type H01 if without cavity. The result of calculation of radial dose function and anisotropic dose distribution for Iridium-192 source type H01 were compared with another model of Iridium-192 source.

  9. Simulation of dose distribution for iridium-192 brachytherapy source type-H01 using MCNPX

    SciTech Connect

    Purwaningsih, Anik

    2014-09-30

    Dosimetric data for a brachytherapy source should be known before it used for clinical treatment. Iridium-192 source type H01 was manufactured by PRR-BATAN aimed to brachytherapy is not yet known its dosimetric data. Radial dose function and anisotropic dose distribution are some primary keys in brachytherapy source. Dose distribution for Iridium-192 source type H01 was obtained from the dose calculation formalism recommended in the AAPM TG-43U1 report using MCNPX 2.6.0 Monte Carlo simulation code. To know the effect of cavity on Iridium-192 type H01 caused by manufacturing process, also calculated on Iridium-192 type H01 if without cavity. The result of calculation of radial dose function and anisotropic dose distribution for Iridium-192 source type H01 were compared with another model of Iridium-192 source.

  10. A comparison of electrochemically pre-treated and spark-platinized carbon fiber microelectrode. Measurement of 8-oxo-7,8-dihydro-2'-deoxyguanosine in human urine and plasma.

    PubMed

    Bartosova, Z; Riman, D; Halouzka, V; Vostalova, J; Simanek, V; Hrbac, J; Jirovsky, D

    2016-09-01

    A novel method of carbon fiber microelectrode activation using spark discharge was demonstrated and compared to conventional electrochemical pretreatment by potential cycling. The spark discharge was performed at 800 V between the microelectrode connected to positive pole of the power supply and platinum counter electrode. Spark discharge led both to trimming of the fiber tip into conical shape and to the modification of carbon fiber microelectrode with platinum, as proven by scanning electron microscopy and electron dispersive X-ray spectroscopy. After the characterization of electrochemical properties using ferricyanide voltammetry, the activated electrodes were used for electrochemical analysis of 8-oxo-7,8-dihydro-2'-deoxyguanosine, an oxidative stress marker. Subnanomolar detection limits (0.55 nmol L(-1)) in high-performance liquid chromatography were achieved for spark platinized electrodes incorporated into the flow detection cell. PMID:27543016

  11. Rapid, sensitive detection of neurotransmitters at microelectrodes modified with self-assembled SWCNT forests

    PubMed Central

    Xiao, Ning; Venton, B. Jill

    2012-01-01

    Carbon nanotube (CNT) modification of microelectrodes can result in increased sensitivity without compromising time response. However, dip coating CNTs is not very reproducible and the CNTs tend to lay flat on the electrode surface which limits access to the electroactive sites on the ends. In this study, aligned CNT forests were formed using a chemical self-assembly method, which resulted in more exposed CNT ends to the analyte. Shortened, carboxylic acid functionalized single-walled CNTs were assembled from a DMF suspension onto a carbon-fiber disk microelectrode modified with a thin iron hydroxide-decorated Nafion film. The modified electrodes were highly sensitive, with 36-fold higher oxidation currents for dopamine using fast-scan cyclic voltammetry than bare electrodes and 34-fold more current than electrodes dipped in CNTs. The limit of detection for dopamine was 17 ± 3 nM at a 10 Hz repetition rate and 65 ± 7 nM at 90 Hz. The LOD at 90 Hz was the same as a bare electrode at 10 Hz, allowing a 9-fold increase in temporal resolution without a decrease in sensitivity. Similar increases were observed for other cationic catecholamine neurotransmitters and the increases in current were greater than for anionic interferents such as ascorbic acid and 3,4-dihydroxyphenylacetic acid (DOPAC). The CNT forest electrodes had high sensitivity at 90 Hz repetition rate when stimulated dopamine release was measured in Drosophila. The sensitivity, temporal resolution, and spatial resolution of these CNT forest modified disk electrodes facilitate enhanced electrochemical measurements of neurotransmitters release in vivo. PMID:22823497

  12. Circularly polarised phosphorescent photoluminescence and electroluminescence of iridium complexes

    PubMed Central

    Li, Tian-Yi; Jing, Yi-Ming; Liu, Xuan; Zhao, Yue; Shi, Lin; Tang, Zhiyong; Zheng, You-Xuan; Zuo, Jing-Lin

    2015-01-01

    Nearly all the neutral iridium complexes widely used as dopants in PhOLEDs are racemic mixtures; however, this study observed that these complexes can be separated into stable optically active Λ and ∆ isomers and that their chirality is an intrinsic property. The circularly polarised phosphorescent photoluminescence (CPPPL) signals of Λ/Δ isomers are perfect mirror images with opposite polarisation and equal intensity exhibiting a “handedness” for the polarisation. For the first time, we applied the Λ/Δ iridium isomers as emitters in OLEDs, and the circularly polarised phosphorescent electroluminescence (CPPEL) spectra reveal completely positive or negative broad peaks consistent with the CPPPL spectra. The results demonstrate that the Λ/Δ isomers have potential application for 3D OLEDs because they can exhibit high efficiency and luminance, and 3D display technology based on circularly polarised light is the most comfortable for the eyes. PMID:26446521

  13. Olefin hydroaryloxylation catalyzed by pincer-iridium complexes.

    PubMed

    Haibach, Michael C; Guan, Changjian; Wang, David Y; Li, Bo; Lease, Nicholas; Steffens, Andrew M; Krogh-Jespersen, Karsten; Goldman, Alan S

    2013-10-01

    Aryl alkyl ethers, which are widely used throughout the chemical industry, are typically produced via the Williamson ether synthesis. Olefin hydroaryloxylation potentially offers a much more atom-economical alternative. Known acidic catalysts for hydroaryloxylation, however, afford very poor selectivity. We report the organometallic-catalyzed intermolecular hydroaryloxylation of unactivated olefins by iridium "pincer" complexes. These catalysts do not operate via the hidden Brønsted acid pathway common to previously developed transition-metal-based catalysts. The reaction is proposed to proceed via olefin insertion into an iridium-alkoxide bond, followed by rate-determining C-H reductive elimination to yield the ether product. The reaction is highly chemo- and regioselective and offers a new approach to the atom-economical synthesis of industrially important ethers and, potentially, a wide range of other oxygenates. PMID:24028199

  14. Iridium alloy clad vent set manufacturing qualification studies

    SciTech Connect

    Ulrich, G.B. )

    1991-01-10

    Qualification studies have been successfully conducted to demonstrate iridium alloy Clad Vent Set (CVS) manufacturing readiness for the General Purpose Heat Source (GPHS) program at the Oak Ridge Y-12 Plant. These studies were joint comparison evaluations of both the Y-12 Plant and EG G Mound Applied Technologies, Inc. (EG G-MAT) products. Note: EG G-MAT formerly manufactured the iridium alloy CVS. The comparison evaluations involved work in a number of areas; however, only the CVS cup metallurgical evalution will be presented here. The initial metallurgical comparisons in conjunction with follow-up metallurgical work showed the Y-12 Plant CVS product to be comparable to the fully qualified (for Galileo and Ulysses missions) EG G-MAT product. This allowed the Y-12 Plant to commence pilot production of CVS components for potential use in the CRAF and CASSINI missions.

  15. Photoswitchable azobenzene-appended iridium(iii) complexes.

    PubMed

    Pérez-Miqueo, J; Altube, A; García-Lecina, E; Tron, A; McClenaghan, N D; Freixa, Z

    2016-09-21

    Iridium(iii) cyclometalated complexes have been used as models to study the effect that extended conjugation and substitution pattern has on the photochromic behavior of azobenzene-appended 2-phenylpyridyl (ppy) ligands. For this purpose four azobenzene-containing ppy ligands were synthesized. With these ligands, nine iridium(iii) complexes containing up to three appended azobenzenes were synthesized. Analysis of their photochromic behaviour by means of UV-vis and (1)H-NMR spectroscopy permitted us to conclude that the light-induced trans-to-cis isomerization of the azobenzene was strongly inhibited upon coordination to the Ir(iii) cation when the electronic conjugation was extended along the whole ligand. The use of an aliphatic spacer unit (either -CH2- or -OCH2-) between the azobenzene and the ppy fragment of the ligand sufficed to disrupt the electronic communication, and obtain photochromic organometallic complexes. PMID:27460186

  16. A MULTIPLEXED ASSAY FOR DETERMINATION OF NEUROTOXICANT EFFECTS ON SPONTANEOUS NETWORK ACTIVITY AND CELL VIABILITY FROM MICROELECTRODE ARRAYS

    EPA Science Inventory

    AbstractTITLE: A MULTIPLEXED ASSAY FOR DETERMINATION OF NEUROTOXICANT EFFECTS ON SPONTANEOUS NETWORK ACTIVITY AND CELL VIABILITY FROM MICROELECTRODE ARRAYSABSTRACT BODY: Microelectrode array (MEA) recordings are increasingly being used as an in vitro method to detect and characte...

  17. Mononuclear iridium dinitrogen complexes bonded to zeolite HY

    DOE PAGES

    Yang, Dong; Chen, Mingyang; Martinez-Macias, Claudia; Dixon, David A.; Gates, Bruce C.

    2014-11-07

    In this study, the adsorption of N2 on structurally well-defined dealuminated HY zeolite-supported iridium diethylene complexes was investigated. Iridium dinitrogen complexes formed when the sample was exposed to N2 in H2 at 298 K, as shown by infrared spectra recorded with isotopically labeled N2. Four supported species formed in various flowing gases: Ir(N2), Ir(N2)(N2), Ir(C2H5)(N2), and Ir(H)(N2). Their interconversions are summarized in a reaction network, showing, for example, that, in the presence of N2, Ir(N2) was the predominant dinitrogen species at temperatures of 273-373 K. Ir(CO)(N2) formed transiently in flowing CO, and in the presence of H2, rather stable iridiummore » hydride complexes formed. Here, four structural models of each iridium complex bonded at the acidic sites of the zeolite were employed in a computational investigation, showing that the calculated vibrational frequencies agree well with experiment when full calculations are done at the level of density functional theory, independent of the size of the model of the zeolite.« less

  18. A Tapered Aluminium Microelectrode Array for Improvement of Dielectrophoresis-Based Particle Manipulation

    PubMed Central

    Buyong, Muhamad Ramdzan; Larki, Farhad; Faiz, Mohd Syafiq; Hamzah, Azrul Azlan; Yunas, Jumrail; Majlis, Burhanuddin Yeop

    2015-01-01

    In this work, the dielectrophoretic force (FDEP) response of Aluminium Microelectrode Arrays with tapered profile is investigated through experimental measurements and numerical simulations. A standard CMOS processing technique with a step for the formation of a tapered profile resist is implemented in the fabrication of Tapered Aluminium Microelectrode Arrays (TAMA). The FDEP is investigated through analysis of the Clausius-Mossotti factor (CMF) and cross-over frequency (fxo). The performance of TAMA with various side wall angles is compared to that of microelectrodes with a straight cut sidewall profile over a wide range of frequencies through FEM numerical simulations. Additionally, electric field measurement (EFM) is performed through scanning probe microscopy (SPM) in order to obtain the region of force focus in both platforms. Results showed that the tapered profile microelectrodes with angles between 60° and 70° produce the highest electric field gradient on the particles. Also, the region of the strongest electric field in TAMA is located at the bottom and top edge of microelectrode while the strongest electric field in microelectrodes with straight cut profile is found at the top corner of the microelectrode. The latter property of microelectrodes improves the probability of capturing/repelling the particles at the microelectrode’s side wall. PMID:25970255

  19. Semiconductor films on flexible iridium substrates

    DOEpatents

    Goyal, Amit

    2005-03-29

    A laminate semiconductor article includes a flexible substrate, an optional biaxially textured oxide buffer system on the flexible substrate, a biaxially textured Ir-based buffer layer on the substrate or the buffer system, and an epitaxial layer of a semiconductor. Ir can serve as a substrate with an epitaxial layer of a semiconductor thereon.

  20. Highly conductive and flexible silver nanowire-based microelectrodes on biocompatible hydrogel.

    PubMed

    Ahn, Yumi; Lee, Hyungjin; Lee, Donghwa; Lee, Youngu

    2014-01-01

    We successfully fabricated silver nanowire (AgNW)-based microelectrodes on various substrates such as a glass and polydimethylsiloxane by using a photolithographic process for the first time. The AgNW-based microelectrodes exhibited excellent electrical conductivity and mechanical flexibility. We also demonstrated the direct transfer process of AgNW-based microelectrodes from a glass to a biocompatible polyacrylamide-based hydrogel. The AgNW-based microelectrodes on the biocompatible hydrogel showed excellent electrical performance. Furthermore, they showed great mechanical flexibility as well as superior stability under wet conditions. We anticipate that the AgNW-based microelectrodes on biocompatible hydrogel substrates can be a promising platform for realization of practical bioelectronics devices.

  1. Highly conductive and flexible silver nanowire-based microelectrodes on biocompatible hydrogel.

    PubMed

    Ahn, Yumi; Lee, Hyungjin; Lee, Donghwa; Lee, Youngu

    2014-01-01

    We successfully fabricated silver nanowire (AgNW)-based microelectrodes on various substrates such as a glass and polydimethylsiloxane by using a photolithographic process for the first time. The AgNW-based microelectrodes exhibited excellent electrical conductivity and mechanical flexibility. We also demonstrated the direct transfer process of AgNW-based microelectrodes from a glass to a biocompatible polyacrylamide-based hydrogel. The AgNW-based microelectrodes on the biocompatible hydrogel showed excellent electrical performance. Furthermore, they showed great mechanical flexibility as well as superior stability under wet conditions. We anticipate that the AgNW-based microelectrodes on biocompatible hydrogel substrates can be a promising platform for realization of practical bioelectronics devices. PMID:25347028

  2. Electrocatalysis with vitamin B sub 12 in water-in-oil microemulsions at carbon-fiber microelectrodes

    SciTech Connect

    Owlia, A.

    1989-01-01

    Microemulsions are clear, thermodynamically stable dispersions containing oil, surfactant and water. They are crude models of biological membranes and can be used to investigate some of the organizational influence of membranes in lipid and protein synthesis, energy transduction, ion and group transport, etc. This thesis concerns the investigation of microemulsion properties as media in which catalytic reduction of vicinal dibromides can take place with the electrochemically generated Co(I) form of Vitamin B{sub 12}. Methods to study fundamental properties of resistive w/o AOT/H{sub 2}O/isoctane were developed. Microelectrodes of approximate radius of 6 {mu}m were prepared and characterized. Nonlinear regression was applied to the analysis of steady state voltammograms obtained at carbon-fiber microelectrodes. Reversible regression models were used to analyze data for oxidation of ferrocene in acetonitrile with and without added electrolyte. An estimate of cell resistance in highly resistive media was obtained by including ohmic drop in the model for reversible electron transfer. The electrocatalytic reduction of 1,2-dibromoethane (EDB), 1,2-dibromobutane (DBB), and trans-1,2-dibromocyclohexane (DBCH) with Vitamin B{sub 12} in pH {le} 3 water MeCN and w/o microemulsions of AOT/H{sub 2}O/isoctane at carbon fiber microelectrode was investigated. The microviscosity of w/o microemulsions were estimated from the Stokes-Einstein equation using ferrocene as a probe. Results show that the diffusion of molecules in the microemulsions are similar to their diffusion in organic phase (isoctane). Nonlinear regression analysis of the data for AOT w/o microemulsions describing the dependence of D{prime} on C{sub x} enables an estimate of micelle diffusion coefficients.

  3. Rockot Launch Vehicle Commercial Operations for Grace and Iridium Program

    NASA Astrophysics Data System (ADS)

    Viertel, Y.; Kinnersley, M.; Schumacher, I.

    2002-01-01

    The GRACE mission and the IRIDIUM mission on ROCKOT launch vehicle are presented. Two identical GRACE satellites to measure in tandem the gravitational field of the earth with previously unattainable accuracy - it's called the Gravity Research and Climate Experiment, or and is a joint project of the U.S. space agency, NASA and the German Centre for Aeronautics and Space Flight, DLR. In order to send the GRACE twins into a 500x500 km , 89deg. orbit, the Rockot launch vehicle was selected. A dual launch of two Iridium satellites was scheduled for June 2002 using the ROCKOT launch vehicle from Plesetsk Cosmodrome in Northern Russia. This launch will inject two replacement satellites into a low earth orbit (LEO) to support the maintenance of the Iridium constellation. In September 2001, Eurockot successfully carried out a "Pathfinder Campaign" to simulate the entire Iridium mission cycle at Plesetsk. The campaign comprised the transport of simulators and related equipment to the Russian port-of-entry and launch site and also included the integration and encapsulation of the simulators with the actual Rockot launch vehicle at Eurockot's dedicated launch facilities at Plesetsk Cosmodrome. The pathfinder campaign lasted four weeks and was carried out by a joint team that also included Khrunichev, Russian Space Forces and Eurockot personnel on the contractors' side. The pathfinder mission confirmed the capability of Eurockot Launch Services to perform the Iridium launch on cost and on schedule at Plesetsk following Eurockot's major investment in international standard preparation, integration and launch facilities including customer facilities and a new hotel. In 2003, Eurockot will also launch the Japanese SERVI'S-1 satellite for USEF. The ROCKOT launch vehicle is a 3 stage liquid fuel rocket whose first 2 stages have been adapted from the Russian SS-19. A third stage, called "Breeze", can be repeatedly ignited and is extraordinarily capable of manoeuvre. Rockot can place

  4. Evaluation of Molybdenum as a Surrogate for Iridium in the GPHS Weld Development

    SciTech Connect

    Stine, Andrew Martin; Pierce, Stanley W.; Moniz, Paul F.

    2015-10-17

    The welding equipment used for welding iridium containers (clads) at Los Alamos National Laboratory is twenty five years old and is undergoing an upgrade. With the upgrade, there is a requirement for requalification of the welding process, and the opportunity for process improvement. Testing of the new system and requalification will require several welds on iridium test parts and clads, and any efforts to improve the process will add to the need for iridium parts. The extreme high cost of iridium imposes a severe limitation on the extent of test welding that can be done. The 2 inch diameter, 0.027 inch thick, iridium blank disc that the clad cup is formed from, is useful for initial weld trials, but it costs $5000. The development clad sets needed for final tests and requalification cost $15,000 per set. A solution to iridium cost issue would be to do the majority of the weld development on a less expensive surrogate metal with similar weld characteristics. One such metal is molybdenum. Since its melting index (melting temperature x thermal conductivity) is closest to iridium, welds on molybdenum should be similar in size for a given weld power level. Molybdenum is inexpensive; a single 2 inch molybdenum disc costs only $9. In order to evaluate molybdenum as a surrogate for iridium, GTA welds were first developed to provide full penetration on 0.030 inch thick molybdenum discs at speeds of 20, 25, and 30 inches per minute (ipm). These weld parameters were then repeated on the standard 0.027 inch thick iridium blanks. The top surface and bottom surface (root) width and grain structure of the molybdenum and iridium welds were compared, and similarities were evident between the two metals. Due to material and thickness differences, the iridium welds were approximately 35% wider than the molybdenum welds. A reduction in iridium weld current of 35% produce welds slightly smaller than the molybdenum welds yet showed that current could be scaled according to molybdenum/iridium

  5. Cationic iridium(III) complexes with two carbene-based cyclometalating ligands: cis versus trans isomers.

    PubMed

    Monti, Filippo; La Placa, Maria Grazia I; Armaroli, Nicola; Scopelliti, Rosario; Grätzel, Michael; Nazeeruddin, Mohammad Khaja; Kessler, Florian

    2015-03-16

    A series of cationic iridium(III) complexes with two carbene-based cyclometalating ligands and five different N^N bipyridine and 1,10-phenanthroline ancillary ligands is presented. For the first time--in the frame of a rarely studied class of bis(heteroleptic) iridium complexes with two carbene-based cyclometalating ligands--a pair of cis and trans isomers has been isolated. All complexes (trans-1-5 and cis-3) were characterized by (1)H NMR, (13)C NMR, (31)P NMR, and HRMS (ESI-TOF); in addition, crystal structures of cis-3 and trans-4 are reported and discussed. Cyclic voltammetric studies show that the whole series exhibits highly reversible oxidation and reduction processes, suggesting promising potential for optoelectronic applications. Ground-state DFT and TD-DFT calculations nicely predict the blue shift experimentally observed in the room-temperature absorption and emission spectra of cis-3, compared to the trans complexes. In CH3CN, cis-3 displays a 4-fold increase in photoluminescence quantum yield (PLQY) with respect to trans-3, as a consequence of drastically slower nonradiative rate constant. By contrast, at 77 K, the emission properties of all the compounds, including the cis isomer, are much more similar, with a pronounced hypsochromic shift for the trans complexes. A similar behavior is found in solid state (1% w/w poly(methyl methacrylate) matrix), with all complexes displaying PLQY of ∼70-80%, comparable emission lifetimes (τ ≈ 1.3 μs), and a remarkable rigidochromic shift. To rationalize the more pronounced nonradiative deactivation (and smaller PLQY) observed for photoexcited trans complexes, comparative temperature-dependent emission studies in the range of 77-450 K for cis-3 and trans-3 were made in propylene glycol, showing that solvation effects are primarily responsible for the observed behavior.

  6. Fabrication of oxocuprate superconductor microelectrodes for sub-{Tc} use

    SciTech Connect

    Green, S.J.; Rosseinsky, D.R.; Toohey, M.J.

    1995-07-01

    The technique of partial resin encapsulation is described for the direct fabrication of cryorobust oxocuprate microelectrodes from bulk ceramic samples, here Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8{minus}{delta}}, Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10{minus}{delta}}. Cyclic voltammetry is used in tests of the electrochemical response at 295 K (ferrocene in acetonitrile/NBu{sub 4}BF{sub 4}), affording approximated disk radii 2.9, 37.0, and 32.5 {micro}m, and at 123 and at 103 K (ferrocene in chloroethane/tetrahydrofuran/LiBF{sub 4}). Some nonideality in the 295 K responses results from electrode porosity and, at the smallest electrodes, defects in the HTSC/resin seal. Acceptable sub-T{sub c} responses show these problems to be irrelevant in the high viscosity of the electrolytes at low temperature. These microelectrodes usefully advance the emerging study of electrochemistry on superconducting electrodes by responding to free-solute electroactives at <{Tc}.

  7. Interdigitated array microelectrode capacitive sensor for detection of paraffinophilic mycobacteria

    NASA Astrophysics Data System (ADS)

    Sampson, Andrew M.; Peterson, Erik T. K.; Papautsky, Ian

    2008-02-01

    Mycobacterium Avium Complex (MAC) is an opportunistic pathogen that threatens public health and has high clinical relevance. While culture-based and molecular biology techniques for identification are available, these methods are prone to error and require weeks to perform. There is a critical need for improved portable lab-on-a-chip sensor technology which will enable accurate and rapid point-of-care detection of these microorganisms. In this work, a new capacitive sensing strategy is explored utilizing interdigitated array (IDA) microelectrodes and exploiting the paraffinophilic nature of MAC. In this approach, paraffin wax is deposited over IDA microelectrodes to selectively extract these microorganisms from samples. As bacteria consume the dielectric paraffin layer, the charging current of the IDA capacitor changes to facilitate detection. Several IDA geometries were designed and simulated using CFD-ACE+ modeling software and compared with mathematical models. Capacitance of fabricated devices was determined using a charge-based capacitance measurement (CBCM) technique. Modeling and experimental results were in good agreement. Detection of femto-Farad changes in capacitance is possible, making this a feasible technique for sensing small changes in the paraffin for detection of paraffinophilic MAC.

  8. Characterization of Iridium Coated Rhenium Used in High-Temperature, Radiation-Cooled Rocket Thrusters

    NASA Technical Reports Server (NTRS)

    Stulen, R. H.; Boehme, D. R.; Clift, W. M.; McCarty, K. F.

    1990-01-01

    Materials used for radiation-cooled rocket thrusters must be capable of surviving under extreme conditions of high-temperatures and oxidizing environments. While combustion efficiency is optimized at high temperatures, many refractory metals are unsuitable for thruster applications due to rapid material loss from the formation of volatile oxides. This process occurs during thruster operation by reaction of the combustion products with the material surface. Aerojet Technical Systems has developed a thruster cone chamber constructed of Re coated with Ir on the inside surface where exposure to the rocket exhaust occurs. Re maintains its structural integrity at high temperature and the Ir coating is applied as an oxidation barrier. Ir also forms volatile oxide species (IrO2 and IrO3) but at a considerably slower rate than Re. In order to understand the performance limits of Ir-coated Re thrusters, we are investigating the interdiffusion and oxidation kinetics of Ir/Re. The formation of iridium and rhenium oxides has been monitored in situ by Raman spectroscopy during high temperature exposure to oxygen. For pure Ir, the growth of oxide films as thin as approximately 200 A could be easily detected and the formation of IrO2 was observed at temperatures as low as 600 C. Ir/Re diffusion test specimens were prepared by magnetron sputtering of Ir on Re substrates. Concentration profiles were determined by sputter Auger depth profiles of the heat treated specimens. Significant interdiffusion was observed at temperatures as low as 1000 C. Measurements of the activation energy suggest that below 1350 C, the dominant diffusion path is along defects, most likely grain boundaries, rather than bulk diffusion through the grains. The phases that form during interdiffusion have been examined by x ray diffraction. Analysis of heated test specimens indicates that the Ir-Re reaction produces a solid solution phase of Ir dissolved in the HCP structure of Re.

  9. Effects of hydroxylamine on microbial community structure and function of autotrophic nitrifying biofilms determined by in situ hybridization and the use of microelectrodes.

    PubMed

    Kindaichi, T; Okabe, S; Satoh, H; Watanabe, Y

    2004-01-01

    Effects of hydroxylamine (NH2OH), an intermediate of NH4+ oxidation, on microbial community structure and function of two autotrophic nitrifying biofilms fed with and without NH2OH were analyzed by a 16S rRNA approach and the use of microelectrodes. In the NH2OH-added biofilm, partial oxidation of NH4+ to NO2- was observed, whereas complete oxidation of NH4+ to NO3- was achieved in the control biofilm. In situ hybridization results revealed that no nitrite-oxidizing bacteria (NOB) hybridized with any specific probes were detected in the NH2OH-added biofilm. Thus, the addition of low concentrations of NH2OH (250 microM) completely inhibited the growth of NOB. Phylogenetic analysis of 16S rDNA indicated that the ammonia-oxidizing bacteria (AOB) detected in both biofilms were closely related to Nitrosomonas europaea, and that the clone sequences from both biofilm libraries have more than 99% similarity to each other. However, in situ hybridization results revealed that the addition of NH2OH changed the form of growth pattern of the dominant Nitrosomonas spp. from dense clusters mode to single scattered cells mode. Microelectrode measurements revealed that the average NH4+ consumption rate calculated in the NH2OH-added biofilm was two times higher than that in the control biofilm. This clearly demonstrated that the oxidation of NH4+ was stimulated by NH2OH addition.

  10. Delivery of molecules into cells using localized single cell electroporation on ITO micro-electrode based transparent chip.

    PubMed

    Chen, Sheng-Chiech; Santra, Tuhin Subhra; Chang, Chia-Jung; Chen, Tsung-Ju; Wang, Pen-Cheng; Tseng, Fan-Gang

    2012-10-01

    Single cell electroporation is one of the nonviral method which successfully allows transfection of exogenous macromolecules into individual living cell. We present localized cell membrane electroporation at single-cell level by using indium tin oxide (ITO) based transparent micro-electrodes chip with inverted microscope. A focused ion beam (FIB) technique has been successfully deployed to fabricate transparent ITO micro-electrodes with submicron gaps, which can generate more intense electric field to produce very localized cell membrane electroporation. In our approach, we have successfully achieved 0.93 μm or smaller electroporation region on the cell surface to inject PI (Propidium Iodide) dye into the cell with 60 % cell viability. This experiments successfully demonstrate the cell self-recover process from the injected PI dye intensity variation. Our localized cell membrane electroporation technique (LSCMEP) not only generates reversible electroporation process but also it provides a clear optical path for potentially monitoring/tracking of drugs to deliver in single cell level.

  11. Sensitized near-infrared emission from ytterbium(III) via direct energy transfer from iridium(III) in a heterometallic neutral complex.

    PubMed

    Mehlstäubl, Marita; Kottas, Gregg S; Colella, Silvia; De Cola, Luisa

    2008-05-14

    A tetrametallic iridium-ytterbium complex has been synthesised that shows sensitized near-infrared emission (lambda(max) = 976 nm) upon excitation of the iridium unit in the visible region (400 nm) due to efficient energy transfer from the iridium units to the Yb(III) ion. The iridium phosphorescence is quenched nearly quantitatively while the ytterbium ion emits brightly in the NIR.

  12. Iridium: Global OTH data communications for high altitude scientific ballooning

    NASA Astrophysics Data System (ADS)

    Denney, A.

    beneficial points provided by the Iridium platform include pure global accessibility (as well as polar), cost effectiveness because it is available as a COTS (Commercially Off The Shelf) technology, reliability in that the equipment must operate in extreme conditions (near space), integration and development time into current systems must be minimized. As a bonus Motorola and NAL Research Corporation are developing SBD (Short Burst Data) into the Iridium network. This may lead the way to a global IP (Internet Protocol) node based ballooning platform. The Iridium satellite data modems employ the Iridium Low-Earth Orbit (LEO) satellite network. The scope of this paper is to introduce an OTH communications alternative, albeit not necessarily a primary one, to existing ballooning platforms using COTS based emerging technologies. Design aspects, characteristics, actual flight testing statistics, principles of the Iridium modems and communication paths are described including payload and support instrumentation interfacing. Not limited to high altitude ballooning, the Iridium communications platform opens a new era in remote commanding and data retrieval.

  13. The solubility of hydrogen in rhodium, ruthenium, iridium and nickel.

    NASA Technical Reports Server (NTRS)

    Mclellan, R. B.; Oates, W. A.

    1973-01-01

    The temperature variation of the solubility of hydrogen in rhodium, ruthenium, iridium, and nickel in equilibrium with H2 gas at 1 atm pressure has been measured by a technique involving saturating the solvent metal with hydrogen, quenching, and analyzing in resultant solid solutions. The solubilities determined are small (atom fraction of H is in the range from 0.0005 to 0.00001, and the results are consistent with the simple quasi-regular model for dilute interstitial solid solutions. The relative partial enthalpy and excess entropy of the dissolved hydrogen atoms have been calculated from the solubility data and compared with well-known correlations between these quantities.

  14. Levitation of iridium and liquid mercury by ultrasound.

    PubMed

    Xie, W J; Cao, C D; Lü, Y J; Wei, B

    2002-09-01

    Single-axis acoustic levitation of the heaviest solid (iridium, rho=22.6 g cm(-3)) and liquid (mercury, rho=13.6 g cm(-3) on the Earth is achieved by greatly enhancing both the levitation force and stability through optimizing the geometric parameters of the levitator. The acoustically levitated Pb-Sn eutectic alloy melt (rho=8.5 g cm(-3)) is highly undercooled by up to 38 K, which results in a microstructural transition of "lamellae-broken lamellae-dendrites." The drastic enhancement of levitation capability indicates a broader application range of single-axis acoustic levitation. PMID:12225198

  15. Determination of iridium in mafic rocks by atomic absorption

    USGS Publications Warehouse

    Grimaldi, F.S.; Schnepfe, M.M.

    1970-01-01

    Iridium is determined in mineralized mafic rocks by atomic absorption after fire-assay concentration into a gold bead. Interelement interferences in the atomic-absorption determination are removed and Ir sensitivity is increased by buffering the solutions with a mixture of copper and sodium sulphates. Substantial amounts of Ag, Al, Au, Bi, Ca, Cd, Co, Cr, Fe, Ho, Hg, K, La, Mg, Mn, Mo, Ni, Pb, Te, Ti, V, Y, Zn and platinum metals can be tolerated in the atomic-absorption determination. The sensitivity and detection limits are 3.2 and 0.25 ppm of Ir, respectively. ?? 1970.

  16. Intercalation of graphene on iridium with sodium atoms

    NASA Astrophysics Data System (ADS)

    Rut'kov, E. V.; Gall', N. R.

    2015-06-01

    It has been shown that sodium atoms deposited on the surface of graphene atop iridium at T ≤ 850 K diffuse under the graphene layer into an intercalated state and accumulate there in significant concentrations ˜(2-3) × 1014 atoms cm-2. The release of the atoms from under the graphene "carpet" takes place upon destruction of the layer at T ≥ 1800 K. The physical nature of the differences in the processes of release of atoms of different alkali metals from under graphene has been discussed.

  17. Luminescent cyclometallated iridium(III) complexes having acetylide ligands

    SciTech Connect

    Thompson, Mark E.; Bossi, Alberto; Djurovich, Peter Ivan

    2014-09-02

    The present invention relates to phosphorescent (triplet-emitting) organometallic materials. The phosphorescent materials of the present invention comprise Ir(III)cyclometallated alkynyl complexes for use as triplet light-emitting materials. The Ir(III)cyclometallated alkynyl complexes comprise at least one cyclometallating ligand and at least one alkynyl ligand bonded to the iridium. Also provided is an organic light emitting device comprising an anode, a cathode and an emissive layer between the anode and the cathode, wherein the emissive layer comprises a Ir(III)cyclometallated alkynyl complex as a triplet emitting material.

  18. Measurements of the hard-x-ray reflectivity of iridium

    SciTech Connect

    Romaine, S.; Bruni, R.; Gorenstein, P.; Zhong, Z

    2007-01-10

    In connection with the design of a hard-x-ray telescope for the Constellation X-Ray Observatory we measured the reflectivity of an iridium-coated zerodur substrate as a function of angle at 55, 60, 70, and 80 keV at the National Synchrotron Light Source of Brookhaven National Laboratory. The optical constants were derived from the reflectivity data. The real component of the index of refraction is in excellent agreement with theoretical values at all four energies. However, the imaginary component, which is related to the mass attenuation coefficient, is 50% to 70% larger at 55, 60, and 70 keV than theoretical values.

  19. Biocompatibility of Intracortical Microelectrodes: Current Status and Future Prospects

    PubMed Central

    Marin, Cristina; Fernández, Eduardo

    2010-01-01

    Rehabilitation of sensory and/or motor functions in patients with neurological diseases is more and more dealing with artificial electrical stimulation and recording from populations of neurons using biocompatible chronic implants. As more and more patients have benefited from these approaches, the interest in neural interfaces has grown significantly. However an important problem reported with all available microelectrodes to date is long-term viability and biocompatibility. Therefore it is essential to understand the signals that lead to neuroglial activation and create a targeted intervention to control the response, reduce the adverse nature of the reactions and maintain an ideal environment for the brain-electrode interface. We discuss some of the exciting opportunities and challenges that lie in this intersection of neuroscience research, bioengineering, neurology and biomaterials. PMID:20577634

  20. Deposition studies of lithium and bismuth at tungsten microelectrodes in LiCl:KCl eutectic

    NASA Astrophysics Data System (ADS)

    Carlin, Richard T.; Osteryoung, Robert A.

    1989-05-01

    Tungsten microelectrodes (diam = 25 microns) have been used to study the deposition and stripping behavior of Li/Li(+) and Bi/Bi(3+) in the LiCl:KCl eutectic at 400 C. The Li deposition current can be simulated assuming the growth of a single hemisphere of liquid metal on the microelectrode. High stripping current densities were observed and quantitated using standard electrochemical equipment. An inverted microscope assembly was employed for in situ observation of the Li/Li(+) deposition and stripping processes at the microelectrode. A precipitate appears to form in the melt surrounding the electrode during Li deposition.

  1. The robo-pigeon based on the multiple brain regions synchronization implanted microelectrodes.

    PubMed

    Huai, Rui-Tuo; Yang, Jun-Qing; Wang, Hui

    2016-07-01

    Almost all multichannel microelectrodes are only applied to the same nucleus. The multiple brain regions synchronization implanted microelectrodes can be implanted in the several brain regions at the same time, when used in the robo-animal, which can reduce the operation process, shorten animals operation time. Due to electrode position relatively fixed, errors caused by each separately implanted electrode were reduced and the animal control effect was greatly increased compared to the original electrodes. The electrode fixed time was also extended. This microelectrode provided beneficial reference function for the study of the free state of small animals in different brain regions. PMID:27459594

  2. Local structure of Iridium organometallic catalysts covalently bonded to carbon nanotubes.

    NASA Astrophysics Data System (ADS)

    Blasco, J.; Cuartero, V.; Subías, G.; Jiménez, M. V.; Pérez-Torrente, J. J.; Oro, L. A.; Blanco, M.; Álvarez, P.; Blanco, C.; Menéndez, R.

    2016-05-01

    Hybrid catalysts based on Iridium N-heterocyclic carbenes anchored to carbon nanotubes (CNT) have been studied by XAFS spectroscopy. Oxidation of CNT yields a large amount of functional groups, mainly hydroxyl groups at the walls and carboxylic groups at the tips, defects and edges. Different kinds of esterification reactions were performed to functionalize oxidized CNT with imidazolium salts. Then, the resulting products were reacted with an Ir organometallic compound to form hybrid catalysts efficient in hydrogen transfer processes. XANES spectroscopy agree with the presence of Ir(I) in these catalysts and the EXAFS spectra detected differences in the local structure of Ir atoms between the initial Ir organometallic compound and the Ir complexes anchored to the CNT. Our results confirm that the halide atom, present in the Ir precursor, was replaced by oxygen from -OH groups at the CNT wall in the first coordination shell of Ir. The lability of this group accounts for the good recyclability and the good efficiency shown by these hybrid catalysts.

  3. Dynamic high-temperature characterization of an iridium alloy in tension

    SciTech Connect

    Song, Bo; Nelson, Kevin; Jin, Helena; Lipinski, Ronald J.; Bignell, John; Ulrich, G. B.; George, E. P.

    2015-09-01

    Iridium alloys have been utilized as structural materials for certain high-temperature applications, due to their superior strength and ductility at elevated temperatures. The mechanical properties, including failure response at high strain rates and elevated temperatures of the iridium alloys need to be characterized to better understand high-speed impacts at elevated temperatures. A DOP-26 iridium alloy has been dynamically characterized in compression at elevated temperatures with high-temperature Kolsky compression bar techniques. However, the dynamic high-temperature compression tests were not able to provide sufficient dynamic high-temperature failure information of the iridium alloy. In this study, we modified current room-temperature Kolsky tension bar techniques for obtaining dynamic tensile stress-strain curves of the DOP-26 iridium alloy at two different strain rates (~1000 and ~3000 s-1) and temperatures (~750°C and ~1030°C). The effects of strain rate and temperature on the tensile stress-strain response of the iridium alloy were determined. The DOP-26 iridium alloy exhibited high ductility in stress-strain response that strongly depended on both strain rate and temperature.

  4. Analysis and Consequences of the Iridium 33-Cosmos 2251 Collision

    NASA Technical Reports Server (NTRS)

    Anz-Meador, P. D.; Liou, Jer-Chi

    2010-01-01

    The collision of Iridium 33 and Cosmos 2251, on 10 February 2009, was the first known unintentional hypervelocity collision in space of intact satellites. Iridium 33 was an active commercial telecommunications satellite, while Cosmos 2251 was a derelict communication satellite of the Strela-2M class. The collision occurred at a relative velocity of 11.6 km/s at an altitude of approximately 790 km over the Great Siberian Plain and near the northern apex of Cosmos 2251 s orbit. This paper describes the physical and orbital characteristics of the relevant spacecraft classes and reports upon our analysis of the resulting debris clouds size, mass, area-to-mass ratio, and relative velocity/directionality distributions. We compare these distributions to those predicted by the NASA breakup model and notable recent fragmentation events; in particular, we compare the area-to-mass ratio distribution for each spacecraft to that exhibited by the FY-1C debris cloud for the purpose of assessing the relative contribution of modern aerospace materials to debris clouds resulting from energetic collisions. In addition, we examine the long-term consequences of this event for the low Earth orbit (LEO) environment. Finally, we discuss "lessons learned", which may be incorporated into NASA s environmental models.

  5. Analysis of Abrasive Blasting of DOP-26 Iridium Alloy

    SciTech Connect

    Ohriner, Evan Keith; Zhang, Wei; Ulrich, George B

    2012-01-01

    The effects of abrasive blasting on the surface geometry and microstructure of DOP-26 iridium alloy (Ir-0.3% W-0.006% Th 0.005% Al) have been investigated. Abrasive blasting has been used to control emissivity of components operating at elevated temperature. The effects of abrasive blasting conditions on surface morphology were investigated both experimentally and by numerical modeling. The simplified model, based on finite element analysis of a single angular particle impacting on Ir alloy disk, calculates the surface deformation and residual strain distribution. The experimental results and modeling results both indicate that the surface geometry is not sensitive to the abrasive blast process conditions of nozzle pressure and standoff distance considered in this study. On the other hand, the modeling results suggest that the angularity of the abrasive particle has an important role in determining surface geometry, which in turn, affects the emissivity. Abrasive blasting causes localized surface strains and localized recrystallization, but it does not affect grain size following extended exposure at elevated temperature. The dependence of emissivity of the DOP-26 alloy on mean surface slope follows a similar trend to that reported for pure iridium.

  6. Evaluation of a Microelectrode Arrays for Neurotoxicity Testing Using a Chemical Training Set

    EPA Science Inventory

    Microelectrode array (MEA) approaches have been proposed as a tool for detecting functional changes in electrically active cells, including neurons, exposed to drugs, chemicals, or particles. However, conventional single well MEA systems lack the throughput necessary for screenin...

  7. Evaluation of Multi-Well Microelectrode Arrays for Neurotoxicity Screening Using a Chemical Training Set

    EPA Science Inventory

    Microelectrode array (MEA) approaches have been proposed as a tool for detecting functional changes in electrically-excitable cells, including neurons, exposed to drugs, chemical or particles. However, conventional single well-MEA systems lack the throughput necessary for screen...

  8. Low Frequency Activity of Cortical Networks on Microelectrode Arrays is Differentially Altered by Bicuculline and Carbaryl

    EPA Science Inventory

    Thousands of chemicals need to be characterized for their neurotoxicity potential. Neurons grown on microelectrode arrays (MEAs) are an in vitro model used to screen chemicals for functional effects on neuronal networks. Typically, after removal of low frequency components, effec...

  9. Microelectrode Arrays: A Physiologically-based Neurotoxicity Testing Platform for the 21st Century

    EPA Science Inventory

    Microelectrode Arrays (MEAs) have been in use over the past decade and a half to study multiple aspects ofelectrically excitable cells. Inparticular, MEAs have been applied to explore the pharmacological and toxicological effects ofnumerous compounds on spontaneous activity ofneu...

  10. Microelectrode miRNA sensors enabled by enzymeless electrochemical signal amplification.

    PubMed

    Wang, Tanyu; Viennois, Emilie; Merlin, Didier; Wang, Gangli

    2015-08-18

    Better detections of circulating microRNAs (miRNAs) as disease biomarkers could advance diseases diagnosis and treatment. Current analysis methods or sensors for research and applications are challenged by the low concentrations and wide dynamic range (from aM to nM) of miRNAs in a physiological sample. Here, we report a one-step label-free electrochemical sensor comprising a triple-stem DNA-redox probe structure on a gold microelectrode. A new signal amplification mechanism without the need of a redox enzyme is introduced. The novel strategy overcomes the fundamental limitations of microelectrode DNA sensors that fail to generate detectable current, which is primarily due to the limited amount of redox probes in response to the target analyte binding. By employing a reductant, tris(2-carboxyethyl) phosphine hydrochloride (TCEP) in the detection buffer solution, each redox molecule on the detection probe is cyclically oxidized at the electrode and reduced by the reductant; thus, the signal is amplified in situ during the detection period. The combined merits in the diagnosis power of cyclic voltammetry and the high sensitivity of pulse voltammetry enable parallel analysis for method validation and optimization previously inaccessible. As such, the detection limit of miRNA-122 was 0.1 fM via direct readout, with a wide detection range from sub fM to nM. The detection time is within minutes, which is a significant improvement over other macroscopic sensors and other relevant techniques such as quantitative reverse transcription polymerase chain reaction (qRT-PCR). The high selectivity of the developed sensors is demonstrated by the discrimination against two most similar family sequences: miR-122-3p present in serum and 2-mismatch synthetic RNA sequence. Interference such as nonspecific adsorption, a common concern in sensor development, is reduced to a negligible amount by adopting a multistep surface modification strategy. Importantly, unlike qRT-PCR, the

  11. Iridium anomaly in the Cretaceous section of the Eastern Kamchatka

    NASA Astrophysics Data System (ADS)

    Savelyev, Dmitry; Savelyeva, Olga

    2010-05-01

    The origin of iridium anomalies is widely discussed with regard to massive fauna and flora extinction at several geologic boundaries. Two hypotheses are most popular, cosmogenic and volcanogenic. Anomalies of iridium are known at many stratigraphic levels, both at the geologic series borders and within geologic series. Our studies revealed increased content of iridium in a section of Cretaceous oceanic deposits on the Kamchatsky Mys Peninsula (Eastern Kamchatka, Russia). The investigated section (56°03.353´N, 163°00.376´E) includes interbedded jaspers and siliceous limestones overlaying pillow-basalts. These deposits belong to the Smagin Formation of the Albian-Cenomanian age. In the middle and upper parts of the section two beds of black carbonaceous rocks with sapropelic organic matter were observed. Their formation marked likely episodes of oxygen depletion of oceanic intermediate water (oceanic anoxic events). Our geochemical studies revealed an enrichment of the carbonaceous beds in a number of major and trace elements (Al2O3, TiO2, FeO, MgO, K2O, P2O5, Cu, Zn, Ni, Cr, V, Mo, Ba, Y, Zr, Nb, REE, U, Au, Pt etc.) in comparison with associating jaspers and limestones. There are likely different sources which contributed to the enrichment. It is possible however to correlate the excess of Al, Ti, Zr, Nb with volcanogenic admixture, which is absent in limestones and jaspers. A possible source of the volcanogenic material was local volcanism as suggested by the close association of the investigated section with volcanic rocks (basaltic lavas and hyaloclastites). The basalts of the Smagin Formation were previously proposed to originate during Cretaceous activity of the Hawaiian mantle plume (Portnyagin et al., Geology, 2008). Neutron activation analysis indicated increased up to 9 ppb concentration of Ir at the bottom of the lower carbonaceous bed (inorganic part of the sample was analyzed comprising 46% of the bulk rock). In other samples Ir content was below

  12. Highly Doped Polycrystalline Silicon Microelectrodes Reduce Noise in Neuronal Recordings In Vivo

    PubMed Central

    Saha, Rajarshi; Jackson, Nathan; Patel, Chetan; Muthuswamy, Jit

    2013-01-01

    The aims of this study are to 1) experimentally validate for the first time the nonlinear current-potential characteristics of bulk doped polycrystalline silicon in the small amplitude voltage regimes (0–200 μV) and 2) test if noise amplitudes (0–15 μV) from single neuronal electrical recordings get selectively attenuated in doped polycrystalline silicon microelectrodes due to the above property. In highly doped polycrystalline silicon, bulk resistances of several hundred kilo-ohms were experimentally measured for voltages typical of noise amplitudes and 9–10 kΩ for voltages typical of neural signal amplitudes (>150–200 μV). Acute multiunit measurements and noise measurements were made in n = 6 and n = 8 anesthetized adult rats, respectively, using polycrystalline silicon and tungsten microelectrodes. There was no significant difference in the peak-to-peak amplitudes of action potentials recorded from either microelectrode (p > 0.10). However, noise power in the recordings from tungsten microelectrodes (26.36 ± 10.13 pW) was significantly higher (p < 0.001) than the corresponding value in polycrystalline silicon microelectrodes (7.49 ± 2.66 pW). We conclude that polycrystalline silicon microelectrodes result in selective attenuation of noise power in electrical recordings compared to tungsten microelectrodes. This reduction in noise compared to tungsten microelectrodes is likely due to the exponentially higher bulk resistances offered by highly doped bulk polycrystalline silicon in the range of voltages corresponding to noise in multiunit measurements. PMID:20667815

  13. Measurement of extracellular ion fluxes using the ion-selective self-referencing microelectrode technique.

    PubMed

    Luxardi, Guillaume; Reid, Brian; Ferreira, Fernando; Maillard, Pauline; Zhao, Min

    2015-05-03

    Cells from animals, plants and single cells are enclosed by a barrier called the cell membrane that separates the cytoplasm from the outside. Cell layers such as epithelia also form a barrier that separates the inside from the outside or different compartments of multicellular organisms. A key feature of these barriers is the differential distribution of ions across cell membranes or cell layers. Two properties allow this distribution: 1) membranes and epithelia display selective permeability to specific ions; 2) ions are transported through pumps across cell membranes and cell layers. These properties play crucial roles in maintaining tissue physiology and act as signaling cues after damage, during repair, or under pathological condition. The ion-selective self-referencing microelectrode allows measurements of specific fluxes of ions such as calcium, potassium or sodium at single cell and tissue levels. The microelectrode contains an ionophore cocktail which is selectively permeable to a specific ion. The internal filling solution contains a set concentration of the ion of interest. The electric potential of the microelectrode is determined by the outside concentration of the ion. As the ion concentration varies, the potential of the microelectrode changes as a function of the log of the ion activity. When moved back and forth near a source or sink of the ion (i.e. in a concentration gradient due to ion flux) the microelectrode potential fluctuates at an amplitude proportional to the ion flux/gradient. The amplifier amplifies the microelectrode signal and the output is recorded on computer. The ion flux can then be calculated by Fick's law of diffusion using the electrode potential fluctuation, the excursion of microelectrode, and other parameters such as the specific ion mobility. In this paper, we describe in detail the methodology to measure extracellular ion fluxes using the ion-selective self-referencing microelectrode and present some representative results.

  14. Reduction of sample volume and waste generation in acid/base titrations using microelectrodes

    SciTech Connect

    Ekechukwu, A.A.

    1996-03-22

    The Analytical Development Section (ADS) has developed microelectrode methods for use with pH titrations and pH determinations. These microelectrode methods offer increased sensitivity and enable analyses to be done with smaller sample and buffer volumes than are used with standard size electrodes. This report establishes the technical validity of the methods and describes the application of these methods to decreased detection limits, decreased waste generation, and decreased radiation exposure.

  15. Carbon nanotubes grown on metal microelectrodes for the detection of dopamine

    DOE PAGES

    Yang, Cheng; Jacobs, Christopher B.; Nguyen, Michael; Ganesana, Mallikarjunarao; Zestos, Alexander; Ivanov, Ilia N.; Puretzky, Alexander A.; Rouleau, Christopher M.; Geohegan, David B.; Venton, B. Jill

    2015-12-07

    Microelectrodes modified with carbon nanotubes (CNTs) are useful for the detection of neurotransmitters because the CNTs enhance sensitivity and have electrocatalytic effects. CNTs can be grown on carbon fiber microelectrodes (CFMEs) but the intrinsic electrochemical activity of carbon fibers makes evaluating the effect of CNT enhancement difficult. Metal wires are highly conductive and many metals have no intrinsic electrochemical activity for dopamine, so we investigated CNTs grown on metal wires as microelectrodes for neurotransmitter detection. In this work, we successfully grew CNTs on niobium substrates for the first time. Instead of planar metal surfaces, metal wires with a diameter ofmore » only 25 μm were used as CNT substrates; these have potential in tissue applications due to their minimal tissue damage and high spatial resolution. Scanning electron microscopy shows that aligned CNTs are grown on metal wires after chemical vapor deposition. By use of fast-scan cyclic voltammetry, CNT-coated niobium (CNT-Nb) microelectrodes exhibit higher sensitivity and lower ΔEp value compared to CNTs grown on carbon fibers or other metal wires. The limit of detection for dopamine at CNT-Nb microelectrodes is 11 ± 1 nM, which is approximately 2-fold lower than that of bare CFMEs. Adsorption processes were modeled with a Langmuir isotherm, and detection of other neurochemicals was also characterized, including ascorbic acid, 3,4-dihydroxyphenylacetic acid, serotonin, adenosine, and histamine. CNT-Nb microelectrodes were used to monitor stimulated dopamine release in anesthetized rats with high sensitivity. This research demonstrates that CNT-grown metal microelectrodes, especially CNTs grown on Nb microelectrodes, are useful for monitoring neurotransmitters.« less

  16. Carbon nanotubes grown on metal microelectrodes for the detection of dopamine

    SciTech Connect

    Yang, Cheng; Jacobs, Christopher B.; Nguyen, Michael; Ganesana, Mallikarjunarao; Zestos, Alexander; Ivanov, Ilia N.; Puretzky, Alexander A.; Rouleau, Christopher M.; Geohegan, David B.; Venton, B. Jill

    2015-12-07

    Microelectrodes modified with carbon nanotubes (CNTs) are useful for the detection of neurotransmitters because the CNTs enhance sensitivity and have electrocatalytic effects. CNTs can be grown on carbon fiber microelectrodes (CFMEs) but the intrinsic electrochemical activity of carbon fibers makes evaluating the effect of CNT enhancement difficult. Metal wires are highly conductive and many metals have no intrinsic electrochemical activity for dopamine, so we investigated CNTs grown on metal wires as microelectrodes for neurotransmitter detection. In this work, we successfully grew CNTs on niobium substrates for the first time. Instead of planar metal surfaces, metal wires with a diameter of only 25 μm were used as CNT substrates; these have potential in tissue applications due to their minimal tissue damage and high spatial resolution. Scanning electron microscopy shows that aligned CNTs are grown on metal wires after chemical vapor deposition. By use of fast-scan cyclic voltammetry, CNT-coated niobium (CNT-Nb) microelectrodes exhibit higher sensitivity and lower ΔEp value compared to CNTs grown on carbon fibers or other metal wires. The limit of detection for dopamine at CNT-Nb microelectrodes is 11 ± 1 nM, which is approximately 2-fold lower than that of bare CFMEs. Adsorption processes were modeled with a Langmuir isotherm, and detection of other neurochemicals was also characterized, including ascorbic acid, 3,4-dihydroxyphenylacetic acid, serotonin, adenosine, and histamine. CNT-Nb microelectrodes were used to monitor stimulated dopamine release in anesthetized rats with high sensitivity. This research demonstrates that CNT-grown metal microelectrodes, especially CNTs grown on Nb microelectrodes, are useful for monitoring neurotransmitters.

  17. Carbon Nanotubes Grown on Metal Microelectrodes for the Detection of Dopamine.

    PubMed

    Yang, Cheng; Jacobs, Christopher B; Nguyen, Michael D; Ganesana, Mallikarjunarao; Zestos, Alexander G; Ivanov, Ilia N; Puretzky, Alexander A; Rouleau, Christopher M; Geohegan, David B; Venton, B Jill

    2016-01-01

    Microelectrodes modified with carbon nanotubes (CNTs) are useful for the detection of neurotransmitters because the CNTs enhance sensitivity and have electrocatalytic effects. CNTs can be grown on carbon fiber microelectrodes (CFMEs) but the intrinsic electrochemical activity of carbon fibers makes evaluating the effect of CNT enhancement difficult. Metal wires are highly conductive and many metals have no intrinsic electrochemical activity for dopamine, so we investigated CNTs grown on metal wires as microelectrodes for neurotransmitter detection. In this work, we successfully grew CNTs on niobium substrates for the first time. Instead of planar metal surfaces, metal wires with a diameter of only 25 μm were used as CNT substrates; these have potential in tissue applications due to their minimal tissue damage and high spatial resolution. Scanning electron microscopy shows that aligned CNTs are grown on metal wires after chemical vapor deposition. By use of fast-scan cyclic voltammetry, CNT-coated niobium (CNT-Nb) microelectrodes exhibit higher sensitivity and lower ΔEp value compared to CNTs grown on carbon fibers or other metal wires. The limit of detection for dopamine at CNT-Nb microelectrodes is 11 ± 1 nM, which is approximately 2-fold lower than that of bare CFMEs. Adsorption processes were modeled with a Langmuir isotherm, and detection of other neurochemicals was also characterized, including ascorbic acid, 3,4-dihydroxyphenylacetic acid, serotonin, adenosine, and histamine. CNT-Nb microelectrodes were used to monitor stimulated dopamine release in anesthetized rats with high sensitivity. This study demonstrates that CNT-grown metal microelectrodes, especially CNTs grown on Nb microelectrodes, are useful for monitoring neurotransmitters. PMID:26639609

  18. Formylated chloro-bridged iridium(III) dimers as OLED materials: opening up new possibilities.

    PubMed

    Wong, Michael Y; Xie, Guohua; Tourbillon, Clarisse; Sandroni, Martina; Cordes, David B; Slawin, Alexandra M Z; Samuel, Ifor D W; Zysman-Colman, Eli

    2015-05-14

    In this study, a series of four formyl-substituted chloro-bridged iridium(iii) dimers were prepared. Their absorption, photophysical and electrochemical properties were studied in dichloromethane solution. It was found that as the formyl content increased on the cyclometalating ligands, emission unexpectedly became brighter. Organic light-emitting diodes (OLEDs) were fabricated using each of these iridium dimers as the emitter. The OLED fabricated using the brightest of the series, 2b, as the dopant afforded a decent external quantum efficiency (EQE) of 2.6%. This suggests that chloro-bridged iridium dimers are potential candidates as solid-state emitters.

  19. A flexible and implantable microelectrode arrays using high-temperature grown vertical carbon nanotubes and a biocompatible polymer substrate

    NASA Astrophysics Data System (ADS)

    Yi, Wenwen; Chen, Chaoyang; Feng, Zhaoying; Xu, Yong; Zhou, Chengpeng; Masurkar, Nirul; Cavanaugh, John; Ming-Cheng Cheng, Mark

    2015-03-01

    This paper presents a novel microelectrode arrays using high-temperature grown vertically aligned carbon nanotubes (CNTs) integrated on a flexible and biocompatible parylene substrate. A simple microfabrication process is proposed to unite the high quality vertical CNTs grown at high temperature with the heat sensitive parylene substrate in a highly controllable manner. Briefly, the CNTs electrode is encapsulated by two layers of parylene and the device is released using xenon difluoride (XeF2). The process is compatible with wafer-scale post complementary metal oxide semiconductor integration. Lower impedance and larger interfacial capacitance have been demonstrated using CNTs compared to a Pt electrode. The flexible CNT electrodes have been utilized for extracellular neuronal recording and stimulation in rats. The signal-to-noise ratio of the device is about 12.5. The threshold voltage for initiating action potential is about 0.5 V.

  20. Carbon-Ring Microelectrode Arrays for Electrochemical Imaging of Single Cell Exocytosis: Fabrication and Characterization

    PubMed Central

    Lin, Yuqing; Trouillon, Raphaël; Svensson, Maria I.; Keighron, Jacqueline D.; Cans, Ann-Sofie; Ewing, Andrew G.

    2012-01-01

    Fabrication of carbon microelectrode arrays, with up to 15 electrodes in total tips as small as 10 to 50 μm, is presented. The support structures of microelectrodes were obtained by pulling multiple quartz capillaries together to form hollow capillary arrays before carbon deposition. Carbon ring microelectrodes were deposited by pyrolysis of acetylene in the lumen of these quartz capillary arrays. Each carbon deposited array tip was filled with epoxy, followed by beveling of the tip of the array to form a deposited carbon-ring microelectrode array (CRMA). Both the number of the microelectrodes in the array and the tip size are independently tunable. These CRMAs have been characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, and electrogenerated chemiluminescence. Additionally, the electrochemical properties were investigated with steady-state voltammetry. In order to demonstrate the utility of these fabricated microelectrodes in neurochemistry, CRMAs containing eight microring electrodes were used for electrochemical monitoring of exocytotic events from single PC12 cells. Subcellular temporal heterogeneities in exocytosis (ie. cold spots vs. hot spots) were successfully detected with the CRMAs. PMID:22339586

  1. Enhanced Flexible Tubular Microelectrode with Conducting Polymer for Multi-Functional Implantable Tissue-Machine Interface.

    PubMed

    Tian, Hong-Chang; Liu, Jing-Quan; Kang, Xiao-Yang; Tang, Long-Jun; Wang, Ming-Hao; Ji, Bo-Wen; Yang, Bin; Wang, Xiao-Lin; Chen, Xiang; Yang, Chun-Sheng

    2016-01-01

    Implantable biomedical microdevices enable the restoration of body function and improvement of health condition. As the interface between artificial machines and natural tissue, various kinds of microelectrodes with high density and tiny size were developed to undertake precise and complex medical tasks through electrical stimulation and electrophysiological recording. However, if only the electrical interaction existed between electrodes and muscle or nerve tissue without nutrition factor delivery, it would eventually lead to a significant symptom of denervation-induced skeletal muscle atrophy. In this paper, we developed a novel flexible tubular microelectrode integrated with fluidic drug delivery channel for dynamic tissue implant. First, the whole microelectrode was made of biocompatible polymers, which could avoid the drawbacks of the stiff microelectrodes that are easy to be broken and damage tissue. Moreover, the microelectrode sites were circumferentially distributed on the surface of polymer microtube in three dimensions, which would be beneficial to the spatial selectivity. Finally, the in vivo results confirmed that our implantable tubular microelectrodes were suitable for dynamic electrophysiological recording and simultaneous fluidic drug delivery, and the electrode performance was further enhanced by the conducting polymer modification. PMID:27229174

  2. Enhanced Flexible Tubular Microelectrode with Conducting Polymer for Multi-Functional Implantable Tissue-Machine Interface

    NASA Astrophysics Data System (ADS)

    Tian, Hong-Chang; Liu, Jing-Quan; Kang, Xiao-Yang; Tang, Long-Jun; Wang, Ming-Hao; Ji, Bo-Wen; Yang, Bin; Wang, Xiao-Lin; Chen, Xiang; Yang, Chun-Sheng

    2016-05-01

    Implantable biomedical microdevices enable the restoration of body function and improvement of health condition. As the interface between artificial machines and natural tissue, various kinds of microelectrodes with high density and tiny size were developed to undertake precise and complex medical tasks through electrical stimulation and electrophysiological recording. However, if only the electrical interaction existed between electrodes and muscle or nerve tissue without nutrition factor delivery, it would eventually lead to a significant symptom of denervation-induced skeletal muscle atrophy. In this paper, we developed a novel flexible tubular microelectrode integrated with fluidic drug delivery channel for dynamic tissue implant. First, the whole microelectrode was made of biocompatible polymers, which could avoid the drawbacks of the stiff microelectrodes that are easy to be broken and damage tissue. Moreover, the microelectrode sites were circumferentially distributed on the surface of polymer microtube in three dimensions, which would be beneficial to the spatial selectivity. Finally, the in vivo results confirmed that our implantable tubular microelectrodes were suitable for dynamic electrophysiological recording and simultaneous fluidic drug delivery, and the electrode performance was further enhanced by the conducting polymer modification.

  3. Direct-growth carbon nanotubes on 3D structural microelectrodes for electrophysiological recording.

    PubMed

    Pan, Alice Ian; Lin, Min-Hsuan; Chung, Hui-Wen; Chen, Hsin; Yeh, Shih-Rung; Chuang, Yung-Jen; Chang, Yen-Chung; Yew, Tri-Rung

    2016-01-01

    A novel 3D carbon nanotube (CNT) microelectrode was developed through direct growth of CNTs on a gold pin-shaped 3D microelectrode at a low temperature (400 °C) for applications in neural and cardiac recording. With an electroplated Ni catalyst layer covering the entire surface of the pin-shaped structure, CNTs were synthesized on a 3D microelectrode by catalytic thermal chemical vapor deposition (CVD). According to the analyses by electrochemical impedance spectroscopy, the impedance of 3D microelectrodes after CNT growth and UV/O3 treatment decreased from 9.3 Ω mm(-2) to 1.2 Ω mm(-2) and the capacitance increased largely from 2.2 mF cm(-2) to 73.3 mF cm(-2). The existence of UVO3-treated CNT led to a large improvement of interfacial capacitance, contributing to the decrease of impedance. The electrophysiological detection capability of this 3D CNT microelectrode was demonstrated by the distinguished P waves, QRS complex and T waves in the electrocardiogram of the zebrafish heart and the action potential recorded from individual rat hippocampal neurons. The compatibility of integration with ICs, high resolution in space, electrophysiological signals, and non-invasive long-term recording suggest that the 3D CNT microelectrode exhibits promising potential for applications in electrophysiological research and clinical trials.

  4. Enhanced Flexible Tubular Microelectrode with Conducting Polymer for Multi-Functional Implantable Tissue-Machine Interface

    PubMed Central

    Tian, Hong-Chang; Liu, Jing-Quan; Kang, Xiao-Yang; Tang, Long-Jun; Wang, Ming-Hao; Ji, Bo-Wen; Yang, Bin; Wang, Xiao-Lin; Chen, Xiang; Yang, Chun-Sheng

    2016-01-01

    Implantable biomedical microdevices enable the restoration of body function and improvement of health condition. As the interface between artificial machines and natural tissue, various kinds of microelectrodes with high density and tiny size were developed to undertake precise and complex medical tasks through electrical stimulation and electrophysiological recording. However, if only the electrical interaction existed between electrodes and muscle or nerve tissue without nutrition factor delivery, it would eventually lead to a significant symptom of denervation-induced skeletal muscle atrophy. In this paper, we developed a novel flexible tubular microelectrode integrated with fluidic drug delivery channel for dynamic tissue implant. First, the whole microelectrode was made of biocompatible polymers, which could avoid the drawbacks of the stiff microelectrodes that are easy to be broken and damage tissue. Moreover, the microelectrode sites were circumferentially distributed on the surface of polymer microtube in three dimensions, which would be beneficial to the spatial selectivity. Finally, the in vivo results confirmed that our implantable tubular microelectrodes were suitable for dynamic electrophysiological recording and simultaneous fluidic drug delivery, and the electrode performance was further enhanced by the conducting polymer modification. PMID:27229174

  5. Direct-growth carbon nanotubes on 3D structural microelectrodes for electrophysiological recording.

    PubMed

    Pan, Alice Ian; Lin, Min-Hsuan; Chung, Hui-Wen; Chen, Hsin; Yeh, Shih-Rung; Chuang, Yung-Jen; Chang, Yen-Chung; Yew, Tri-Rung

    2016-01-01

    A novel 3D carbon nanotube (CNT) microelectrode was developed through direct growth of CNTs on a gold pin-shaped 3D microelectrode at a low temperature (400 °C) for applications in neural and cardiac recording. With an electroplated Ni catalyst layer covering the entire surface of the pin-shaped structure, CNTs were synthesized on a 3D microelectrode by catalytic thermal chemical vapor deposition (CVD). According to the analyses by electrochemical impedance spectroscopy, the impedance of 3D microelectrodes after CNT growth and UV/O3 treatment decreased from 9.3 Ω mm(-2) to 1.2 Ω mm(-2) and the capacitance increased largely from 2.2 mF cm(-2) to 73.3 mF cm(-2). The existence of UVO3-treated CNT led to a large improvement of interfacial capacitance, contributing to the decrease of impedance. The electrophysiological detection capability of this 3D CNT microelectrode was demonstrated by the distinguished P waves, QRS complex and T waves in the electrocardiogram of the zebrafish heart and the action potential recorded from individual rat hippocampal neurons. The compatibility of integration with ICs, high resolution in space, electrophysiological signals, and non-invasive long-term recording suggest that the 3D CNT microelectrode exhibits promising potential for applications in electrophysiological research and clinical trials. PMID:26588673

  6. Sub-Chronic Oral Exposure to Iridium (III) Chloride Hydrate in Female Wistar Rats: Distribution and Excretion of the Metal

    PubMed Central

    Iavicoli, Ivo; Fontana, Luca; Bergamaschi, Antonio; Conti, Marcelo Enrique; Pino, Anna; Mattei, Daniela; Bocca, Beatrice; Alimonti, Alessandro

    2012-01-01

    Iridium tissue distribution and excretion in female Wistar rats following oral exposure to iridium (III) chloride hydrate in drinking water (from 1 to 1000 ng/ml) in a sub-chronic oral study were determined. Samples of urine, feces, blood and organs (kidneys, liver, lung, spleen and brain) were collected at the end of exposure. The most prominent fractions of iridium were retained in kidney and spleen; smaller amounts were found in lungs, liver and brain. Iridium brain levels were lower than those observed in other tissues but this finding can support the hypothesis of iridium capability to cross the blood brain barrier. The iridium kidney levels rose significantly with the administered dose. At the highest dose, important amounts of the metal were found in serum, urine and feces. Iridium was predominantly excreted via feces with a significant linear correlation with the ingested dose, which is likely due to low intestinal absorption of the metal. However, at the higher doses iridium was also eliminated through urine. These findings may be useful to help in the understanding of the adverse health effects, particularly on the immune system, of iridium dispersed in the environment as well as in identifying appropriate biological indices of iridium exposure. PMID:22942873

  7. Analysis and Implications of the Iridium 33-Cosmos 2251 Collision

    NASA Astrophysics Data System (ADS)

    Kelso, T. S.

    On 2009 February 10, Iridium 33--an operational US communications satellite in low-Earth orbit--was struck and destroyed by Cosmos 2251--a long-defunct Russian communications satellite. This is the first time since the dawn of the Space Age that two satellites have collided in orbit. To better understand the circumstances of this event and the ramifications for avoiding similar events in the future, this paper provides a detailed analysis of the predictions leading up to the collision, using various data sources, and looks in detail at the collision, the evolution of the debris clouds, and the long-term implications for satellite operations. The only publicly available system available to satellite operators for screening for close approaches, SOCRATES, did predict this close approach, but it certainly wasn't the closest approach predicted for the week of February 10. In fact, at the time of the collision, SOCRATES ranked this close approach 152 of the 11,428 within 5 km of any payload. A detailed breakdown is provided to help understand the limitations of screening for close approaches using the two-line orbital element sets. Information is also provided specifically for the Iridium constellation to provide an understanding of how these limitations affect decision making for satellite operators. Post-event analysis using high-accuracy orbital data sources will be presented to show how that information might have been used to prevent this collision, had it been available and used. Analysis of the collision event, along with the distribution of the debris relative to the original orbits, will be presented to help develop an understanding of the geometry of the collision and the near-term evolution of the resulting debris clouds. Additional analysis will be presented to show the long-term evolution of the debris clouds, including orbital lifetimes, and estimate the increased risk for operations conducted by Iridium and other satellite operators in the low-Earth orbit

  8. Iridium-Catalyzed Selective Isomerization of Primary Allylic Alcohols.

    PubMed

    Li, Houhua; Mazet, Clément

    2016-06-21

    This Account presents the development of the iridium-catalyzed isomerization of primary allylic alcohols in our laboratory over the past 8 years. Our initial interest was driven by the long-standing challenge associated with the development of a general catalyst even for the nonasymmetric version of this seemingly simple chemical transformation. The added value of the aldehyde products and the possibility to rapidly generate molecular complexity from readily accessible allylic alcohols upon a redox-economical isomerization reaction were additional sources of motivation. Certainly influenced by the success story of the related isomerization of allylic amines, most catalysts developed for the selective isomerization of allylic alcohols were focused on rhodium as a transition metal of choice. Our approach has been based on the commonly accepted precept that hydrogenation and isomerization are often competing processes, with the latter being usually suppressed in favor of the former. The cationic iridium complexes [(Cy3P)(pyridine)Ir(cod)]X developed by Crabtree (X = PF6) and Pfaltz (X = BArF) are usually considered as the most versatile catalysts for the hydrogenation of allylic alcohols. Using molecular hydrogen to generate controlled amounts of the active form of these complexes but performing the reaction in the absence of molecular hydrogen enabled deviation from the typical hydrogenation manifold and favored exclusively the isomerization of allylic alcohols into aldehydes. Isotopic labeling and crossover experiments revealed the intermolecular nature of the process. Systematic variation of the ligand on the iridium center allowed us to identify the structural features beneficial for catalytic activity. Subsequently, three generations of chiral catalysts have been investigated and enabled us to reach excellent levels of enantioselectivity for a wide range of 3,3-disubstituted aryl/alkyl and alkyl/alkyl primary allylic alcohols leading to β-chiral aldehydes. The

  9. Photochemistry of Dihydrido(hydrotris(3,5-dimethylpyrazolyl)borato)(Z-cyclooctene)iridium. Synthetic Intermediates and Mechanism of the Photochemical Formation of Hydridophenyl(hydrotris(3,5-dimethylpyrazolyl)borato)(trimethyl phosphite)iridium.

    PubMed

    Ferrari, Arlen; Polo, Eleonora; Rüegger, Heinz; Sostero, Silvana; Venanzi, Luigi M.

    1996-03-13

    The photolysis of a benzene solution of [Tp(Me2)IrH(2)(COE)], 1 (Tp(Me2) = hydrotris(3,5-dimethylpyrazolyl)borate, COE = Z-cyclooctene), in the presence of P(OMe)(3), gives the stable novel complex [Tp(Me2)IrH(C(6)H(5))(P(OMe)(3))], 3a. The photochemical syntheses of [Tp(Me2)IrH(2)(P(OMe)(3))], from 1 and P(OMe)(3) in diethyl ether, and [Tp(Me2)IrH(2)(CH(2)=CHCOO(t)Bu)], from 1 in tert-butyl acrylate, are also reported. The above reactions and several experiments using C(6)D(6) and P(OCD(3))(3) show that, in all cases, the primary photoproduct is the 16-electron, five-coordinate iridium(III) intermediate {Tp(Me2)IrH(2)}, 6a, produced by loss of COE from 1. The above experiments also allow the postulation of a mechanistic pathway for the formation of 3a which involves the oxidative addition of an aromatic C-H bond by 6a. Furthemore, the photochemical reaction of 1 in the presence of P(OCD(3))(3) shows that, under the reaction conditions used, oxidative addition of C-H bonds of P(OMe)(3) and of coordinated Tp(Me2)-ligands, presumably, to the intermediates 6a and {Tp(Me2)IrH(C(6)H(5))}, also occurs. Thus, coordinatively unsaturated iridium(III) species readily activate C-H bonds.

  10. Neural sensing of electrical activity with stretchable microelectrode arrays.

    PubMed

    Yu, Zhe; Graudejus, Oliver; Lacour, Stéphanie P; Wagner, Sigurd; Morrison, Barclay

    2009-01-01

    Sensing neural activity within mechanically active tissues poses particular hurdles because most electrodes are much stiffer than biological tissues. As the tissue deforms, the rigid electrodes may damage the surrounding tissue. The problem is exacerbated when sensing neural activity in experimental models of traumatic brain injury (TBI) which is caused by the rapid and large deformation of brain tissue. We have developed a stretchable microelectrode array (SMEA) that can withstand large elastic deformations (>5% biaxial strain) while continuing to function. The SMEA were fabricated from thin metal conductors patterned on polydimethylsiloxane (PDMS) and encapsulated with a photo-patternable silicone. SMEA were used to record spontaneous activity from brain slice cultures, as well as evoked activity after stimulating through SMEA electrodes. Slices of brain tissue were grown on SMEA in long-term culture and then mechanically injured with our well-characterized in vitro injury model by stretching the SMEA and the adherent culture, which was confirmed by image analysis. Because brain tissue was grown on the substrate-integrated SMEA, post-injury changes in electrophysiological function were normalized to pre-injury function since the SMEA deformed with the tissue and remained in place during mechanical stimulation. The combination of our injury model and SMEA could help elucidate mechanisms responsible for post-traumatic neuronal dysfunction in the quest for TBI therapies. The SMEA may have additional sensing applications in other mechanically active tissues such as peripheral nerve and heart. PMID:19964344

  11. An active, flexible carbon nanotube microelectrode array for recording electrocorticograms

    NASA Astrophysics Data System (ADS)

    Chen, Yung-Chan; Hsu, Hui-Lin; Lee, Yu-Tao; Su, Huan-Chieh; Yen, Shiang-Jie; Chen, Chang-Hsiao; Hsu, Wei-Lun; Yew, Tri-Rung; Yeh, Shih-Rung; Yao, Da-Jeng; Chang, Yen-Chung; Chen, Hsin

    2011-06-01

    A variety of microelectrode arrays (MEAs) has been developed for monitoring intra-cortical neural activity at a high spatio-temporal resolution, opening a promising future for brain research and neural prostheses. However, most MEAs are based on metal electrodes on rigid substrates, and the intra-cortical implantation normally causes neural damage and immune responses that impede long-term recordings. This communication presents a flexible, carbon-nanotube MEA (CMEA) with integrated circuitry. The flexibility allows the electrodes to fit on the irregular surface of the brain to record electrocorticograms in a less invasive way. Carbon nanotubes (CNTs) further improve both the electrode impedance and the charge-transfer capacity by more than six times. Moreover, the CNTs are grown on the polyimide substrate directly to improve the adhesion to the substrate. With the integrated recording circuitry, the flexible CMEA is proved capable of recording the neural activity of crayfish in vitro, as well as the electrocorticogram of a rat cortex in vivo, with an improved signal-to-noise ratio. Therefore, the proposed CMEA can be employed as a less-invasive, biocompatible and reliable neuro-electronic interface for long-term usage.

  12. Dynamics of Single Hydrogen Bubbles at a Platinum Microelectrode.

    PubMed

    Yang, Xuegeng; Karnbach, Franziska; Uhlemann, Margitta; Odenbach, Stefan; Eckert, Kerstin

    2015-07-28

    Bubble dynamics, including the formation, growth, and detachment, of single H2 bubbles was studied at a platinum microelectrode during the electrolysis of 1 M H2SO4 electrolyte. The bubbles were visualized through a microscope by a high-speed camera. Electrochemical measurements were conducted in parallel to measure the transient current. The periodic current oscillations, resulting from the periodic formation and detachment of single bubbles, allow the bubble lifetime and size to be predicted from the transient current. A comparison of the bubble volume calculated from the current and from the recorded bubble image shows a gas evolution efficiency increasing continuously with the growth of the bubble until it reaches 100%. Two different substrates, glass and epoxy, were used to embed the Pt wire. While nearly no difference was found with respect to the growth law for the bubble radius, the contact angle differs strongly for the two types of cell. Data provided for the contact point evolution further complete the image of single hydrogen bubble growth. Finally, the velocity field driven by the detached bubble was measured by means of PIV, and the effects of the convection on the subsequent bubble were evaluated.

  13. Polycrystalline-Diamond MEMS Biosensors Including Neural Microelectrode-Arrays

    PubMed Central

    Varney, Michael W.; Aslam, Dean M.; Janoudi, Abed; Chan, Ho-Yin; Wang, Donna H.

    2011-01-01

    Diamond is a material of interest due to its unique combination of properties, including its chemical inertness and biocompatibility. Polycrystalline diamond (poly-C) has been used in experimental biosensors that utilize electrochemical methods and antigen-antibody binding for the detection of biological molecules. Boron-doped poly-C electrodes have been found to be very advantageous for electrochemical applications due to their large potential window, low background current and noise, and low detection limits (as low as 500 fM). The biocompatibility of poly-C is found to be comparable, or superior to, other materials commonly used for implants, such as titanium and 316 stainless steel. We have developed a diamond-based, neural microelectrode-array (MEA), due to the desirability of poly-C as a biosensor. These diamond probes have been used for in vivo electrical recording and in vitro electrochemical detection. Poly-C electrodes have been used for electrical recording of neural activity. In vitro studies indicate that the diamond probe can detect norepinephrine at a 5 nM level. We propose a combination of diamond micro-machining and surface functionalization for manufacturing diamond pathogen-microsensors. PMID:25586924

  14. Polycrystalline-Diamond MEMS Biosensors Including Neural Microelectrode-Arrays.

    PubMed

    Varney, Michael W; Aslam, Dean M; Janoudi, Abed; Chan, Ho-Yin; Wang, Donna H

    2011-01-01

    Diamond is a material of interest due to its unique combination of properties, including its chemical inertness and biocompatibility. Polycrystalline diamond (poly-C) has been used in experimental biosensors that utilize electrochemical methods and antigen-antibody binding for the detection of biological molecules. Boron-doped poly-C electrodes have been found to be very advantageous for electrochemical applications due to their large potential window, low background current and noise, and low detection limits (as low as 500 fM). The biocompatibility of poly-C is found to be comparable, or superior to, other materials commonly used for implants, such as titanium and 316 stainless steel. We have developed a diamond-based, neural microelectrode-array (MEA), due to the desirability of poly-C as a biosensor. These diamond probes have been used for in vivo electrical recording and in vitro electrochemical detection. Poly-C electrodes have been used for electrical recording of neural activity. In vitro studies indicate that the diamond probe can detect norepinephrine at a 5 nM level. We propose a combination of diamond micro-machining and surface functionalization for manufacturing diamond pathogen-microsensors. PMID:25586924

  15. Dynamics of Single Hydrogen Bubbles at a Platinum Microelectrode.

    PubMed

    Yang, Xuegeng; Karnbach, Franziska; Uhlemann, Margitta; Odenbach, Stefan; Eckert, Kerstin

    2015-07-28

    Bubble dynamics, including the formation, growth, and detachment, of single H2 bubbles was studied at a platinum microelectrode during the electrolysis of 1 M H2SO4 electrolyte. The bubbles were visualized through a microscope by a high-speed camera. Electrochemical measurements were conducted in parallel to measure the transient current. The periodic current oscillations, resulting from the periodic formation and detachment of single bubbles, allow the bubble lifetime and size to be predicted from the transient current. A comparison of the bubble volume calculated from the current and from the recorded bubble image shows a gas evolution efficiency increasing continuously with the growth of the bubble until it reaches 100%. Two different substrates, glass and epoxy, were used to embed the Pt wire. While nearly no difference was found with respect to the growth law for the bubble radius, the contact angle differs strongly for the two types of cell. Data provided for the contact point evolution further complete the image of single hydrogen bubble growth. Finally, the velocity field driven by the detached bubble was measured by means of PIV, and the effects of the convection on the subsequent bubble were evaluated. PMID:26133052

  16. Piezo-Driven Vibrating Insertion Device for Microelectrode Array

    NASA Astrophysics Data System (ADS)

    Noda, Takahiro; Kanzaki, Ryohei; Takahashi, Hirokazu

    Microelectrode arrays are commonly used to measure neural activities in the brain, and arrays with some 100 electrodes are commercially available to date. However, insertion of a dense grid array deforms the brain, resulting in deterioration of the measurements. In order to overcome this problem, we propose a piezo-driven vibrating insertion device to reduce the insertion-induced deformation of the brain. We attempted under various conditions to insert the array into an agarose substrate, whose hardness was adjusted to that of the cerebral cortex of rats. Our experiments demonstrated that inverse-sawtooth vibration reduced the insertion-induced deformation of the substrate in proportion to the logarithm of an upstroke velocity when the velocity was higher than 10 mm/s, and vibrating insertion of the maximum velocity at 36.7 mm/s reduced the deformation by up to 40% as compared to insertion without vibration. In addition, we tested the vibrating insertion device in an electrophysiological experiment in the rat auditory cortex in vivo, and successfully measured tone-evoked neuronal activities.

  17. Iridium-mediated C-S bond activation and transformation: organoiridium(III) thioether, thiolato, sulfinato and thiyl radical compounds. Synthesis, mechanistic, spectral, electrochemical and theoretical aspects.

    PubMed

    Das, Ujjwal; Ghorui, Tapas; Adhikari, Basab; Roy, Sima; Pramanik, Shuvam; Pramanik, Kausikisankar

    2015-05-14

    An attractive methodology, single-electron transfer (SET) reductive cleavage of the C-S bond mediated by a metal in the presence of the external stimuli PPh3, has been applied to the kinetically inert IrCl3 in order to synthesize the thiolato complex [Ir(III)(L(S))Cl(PPh3)2] 3 from precursor thioether complexes [Ir(III)(L(SR))Cl2(PPh3)] (R = alkyl) 2. The aforesaid cleavage process in association with (arene)C-H activation furnishes a new class of organosulfur compounds of iridium(III). The thiolato chelate 3 displays a reversible oxidative wave at 0.75 V vs. Ag/AgCl signifying its remarkable nucleophilic character. The high electron density on the thiolato-S vis-à-vis superior nucleophilicity can be envisaged through the formation of a number of S-centered derivatives. This observation has been corroborated with the nature of HOMO in 3, which assumes 49% of S(3p). Notably, the facile oxidative nature of 3 makes it an apposite precursor for metal-stabilized thiyl radical species. Indeed, iridium(III)-stabilized 3˙(+) can be generated by chemical/electrochemical means. The axial EPR spectra with g ∼ 2.0 along with theoretical analysis of SOMO (S(3p) 24% + Ph(π) 43% + d(yz) 15%) and spin density (ρ(S) = +0.543, ρ(Ph) = +0.315, ρ(Ir) = +0.151) of one-electron oxidized 3˙(+) validate the iridium-stabilized thiyl radical description. This observation suggests that the CNS coordination mode in thiophenolato complex 3 is redox-active. Complex 3 is very prone to S-centered oxidation under normal aerobic conditions to yield metallosulfoxide [Ir(III)(L(SO2))Cl(PPh3)2] 4. The enhanced nucleophilicity of thiolato-S can also be manifested via the smooth S-C bond making process with alkyl halides (R'X, R' = Me and allyl; X = Br, I) and subsequent formation of thioether complexes of type [Ir(III)(L(SR'))ClX(PPh3)] 5. The organosulfur compounds of iridium(III) exhibit rich spectral properties including luminescence and the origin of these transitions is scrutinized with

  18. The use of organolithium reagents for the synthesis of 4-aryl-2-phenylpyridines and their corresponding iridium(iii) complexes.

    PubMed

    Davidson, Ross; Hsu, Yu-Ting; Batchelor, Thomas; Yufit, Dmitry; Beeby, Andrew

    2016-07-28

    A versatile palladium-free route for the synthesis of 4-aryl-substituted phenylpyridines (ppy), starting from tert-butyl 4-oxopiperidine-1-carboxylate, is reported. Reaction with an aryllithium, followed by trifluoroacetic acid dehydration/deprotection and oxidation with 2-iodoylbenzoic acid and finally phenylation, gave 4 ligands (L(1-4)H): 2,4-diphenylpyridine, 4-(4-methoxyphenyl)-2-phenylpyridine, 2-phenyl-4-(o-tolyl)pyridine and 4-mesityl-2-phenylpyridine. These ligands were coordinated to iridium to give the corresponding Ir(L)2(A) complexes (Ir1-7), where A = ancillary ligand acetylacetate or 2-picolinate. This was used to demonstrate that, through a combination of ancillary ligand choice and torsional twisting between the 4-aryl substituents of the ppy ligands, it is possible to tune the phosphorescent emission of the complexes in the range 502-560 nm. PMID:27346376

  19. Iridium-alloy processing experience in FY 1990

    SciTech Connect

    Ohriner, E.K.

    1991-11-01

    Iridium-alloy blanks and foil are produced at the Oak Ridge National Laboratory for use as fuel cladding material in radioisotope thermoelectric generators for space power sources. Until 1984, the material was produced from small, 500-g drop castings. A new process has been developed in which consumable electrodes of about 10 kg are melted, extruded, and then rolled to produce the sheet products. The work performed during FY 1990 included the consumable-electrode arc melting of four ingots and the extruding and rolling to sheet of four billets. Significant improvements made in the extruding and arc-melting processes during FY 1989 have been demonstrated to dramatically increase the rate of blank acceptance in nondestructive evaluations. Efforts to improve the rolling practice and to better characterize intermetallic particle distributions in the sheet are also described.

  20. Iridium-alloy processing experience in FY 1989

    SciTech Connect

    Ohriner, E.K.

    1990-11-01

    Iridium-alloy blanks and foil are produced at the Oak Ridge National Laboratory for use as fuel cladding material in radioisotope thermoelectric generators for space power sources. Until 1984, the material was produced from small 500-g drop castings. A new process has been developed in which consumable electrodes of about 10 kg are arc melted, extruded, and then rolled to produce the sheet products. The work performed during FY 1989 included the arc melting of three electrodes and the extruding and rolling to sheet of three billets. Significant improvements have been made in the extruding and arc-melting processes. Preliminary results show that these improvements have had an important effect in increasing the rate of blank acceptance in nondestructive evaluations. 4 refs., 33 figs., 11 tabs.

  1. Comparative modelling of chemical ordering in palladium-iridium nanoalloys

    SciTech Connect

    Davis, Jack B. A.; Johnston, Roy L.; Rubinovich, Leonid; Polak, Micha

    2014-12-14

    Chemical ordering in “magic-number” palladium-iridium nanoalloys has been studied by means of density functional theory (DFT) computations, and compared to those obtained by the Free Energy Concentration Expansion Method (FCEM) using derived coordination dependent bond energy variations (CBEV), and by the Birmingham Cluster Genetic Algorithm using the Gupta potential. Several compositions have been studied for 38- and 79-atom particles as well as the site preference for a single Ir dopant atom in the 201-atom truncated octahedron (TO). The 79- and 38-atom nanoalloy homotops predicted for the TO by the FCEM/CBEV are shown to be, respectively, the global minima and competitive low energy minima. Significant reordering of minima predicted by the Gupta potential is seen after reoptimisation at the DFT level.

  2. Iridium abundance maxima in the Upper Cenomanian extinction interval

    NASA Astrophysics Data System (ADS)

    Orth, C. J.; Attrep, M., Jr.; Mao, X. Y.; Kauffman, E. G.; Diner, R.

    1988-04-01

    Two iridium abundance peaks, both 0.11 ppb (whole-rock basis) over a local background of 0.017 ppb, have been found in Middle Cretaceous marine rocks near Pueblo, Colorado. They occur just below the 92-million-year-old Cenomanian-Turonian (C-T) stage boundary. No other peaks were found in 45 meters of strata (about 2.5 million years of deposition) above and below the boundary interval. The broad lower peak straddles the first in a series of extinctions of benthic and nektonic macrobiota which comprise the C-T extinction event. The sharp upper peak occurs stratigraphically about 1.2 meters above the lower peak. The excess Ir might be from meteoroid impacts.

  3. Iridium abundance maxima in the Upper Cenomanian extinction interval

    NASA Technical Reports Server (NTRS)

    Orth, C. J.; Attrep, M., Jr.; Mao, X. Y.; Kauffman, E. G.; Diner, R.

    1988-01-01

    Two iridium abundance peaks, both 0.11 ppb (whole-rock basis) over a local background of 0.017 ppb, have been found in Middle Cretaceous marine rocks near Pueblo, Colorado. They occur just below the 92-million-year-old Cenomanian-Turonian (C-T) stage boundary. No other peaks were found in 45 meters of strata (about 2.5 million years of deposition) above and below the boundary interval. The broad lower peak straddles the first in a series of extinctions of benthic and nektonic macrobiota which comprise the C-T extinction event. The sharp upper peak occurs stratigraphically about 1.2 meters above the lower peak. The excess Ir might be from meteoroid impacts.

  4. Intercalation of graphene on iridium with samarium atoms

    NASA Astrophysics Data System (ADS)

    Afanas'eva, E. Yu.; Rut'kov, E. V.; Gall, N. R.

    2016-07-01

    Intercalation of graphene on Ir (111) with Sm atoms is studied by methods of thermal desorption spectroscopy and thermionic emission. It is shown that adsorption of samarium at T = 300 K on graphene to concentrations of N ≤ 6 × 1014 atoms cm-2 followed by heating of the substrate leads to practically complete escape of adsorbate underneath the graphene layer. At N > 6 × 1014 atoms cm-2 and increasing temperature, a fraction of adsorbate remains on graphene in the form of two-dimensional "gas" and samarium islands and are desorbed in the range of temperatures of 1000-1200 K. Samarium remaining under the graphene is desorbed from the surface in the temperature range 1200-2150 K. Model conceptions for the samarium-graphene-iridium system in a wide temperature range are developed.

  5. Laminar iridium coating produced by pulse current electrodeposition from chloride molten salt

    NASA Astrophysics Data System (ADS)

    Zhu, Li'an; Bai, Shuxin; Zhang, Hong; Ye, Yicong

    2013-10-01

    Due to the unique physical and chemical properties, Iridium (Ir) is one of the most promising oxidation-resistant coatings for refractory materials above 1800 °C in aerospace field. However, the Ir coatings prepared by traditional methods are composed of columnar grains throughout the coating thickness. The columnar structure of the coating is considered to do harm to its oxidation resistance. The laminar Ir coating is expected to have a better high-temperature oxidation resistance than the columnar Ir coating does. The pulse current electrodeposition, with three independent parameters: average current density (Jm), duty cycle (R) and pulse frequency (f), is considered to be a promising method to fabricate layered Ir coating. In this study, laminar Ir coatings were prepared by pulse current electrodeposition in chloride molten salt. The morphology, roughness and texture of the coatings were determined by scanning electron microscope (SEM), profilometer and X-ray diffraction (XRD), respectively. The results showed that the laminar Ir coatings were composed of a nucleation layer with columnar structure and a growth layer with laminar structure. The top surfaces of the laminar Ir coatings consisted of cauliflower-like aggregates containing many fine grains, which were separated by deep grooves. The laminar Ir coating produced at the deposition condition of 20 mA/cm2 (Jm), 10% (R) and 6 Hz (f) was quite smooth (Ra 1.01 ± 0.09 μm) with extremely high degree of preferred orientation of <1 1 1>, and its laminar structure was well developed with clear boundaries and uniform thickness of sub-layers.

  6. Inhibition of Beta-Amyloid Fibrillation by Luminescent Iridium(III) Complex Probes

    PubMed Central

    Lu, Lihua; Zhong, Hai-Jing; Wang, Modi; Ho, See-Lok; Li, Hung-Wing; Leung, Chung-Hang; Ma, Dik-Lung

    2015-01-01

    We report herein the application of kinetically inert luminescent iridium(III) complexes as dual inhibitors and probes of beta-amyloid fibrillogenesis. These iridium(III) complexes inhibited Aβ1–40 peptide aggregation in vitro, and protected against Aβ-induced cytotoxicity in neuronal cells. Furthermore, the complexes differentiated between the aggregated and unaggregated forms of Aβ1–40 peptide on the basis of their emission response. PMID:26419607

  7. Synthesis of a chloro protected iridium nitrido complex.

    PubMed

    Sieh, Daniel; Schöffel, Julia; Burger, Peter

    2011-10-01

    Intramolecular activation processes of vulnerable ligand C-H bonds frequently limit the thermal stability and accessibility of late transition metal complexes with terminal metal nitrido units. In this study chloro substitution of the 2,6-ketimine N-aryl substituents (2,6-C(6)H(3)R(2), R = Cl) of the pyridine, diimine ligand is probed to increase the stability of square-planar iridium nitrido compounds. The thermal stability of iridium azido precursor and nitrido compounds was studied by a combination of thermoanalytical methods (DTG/MS and DSC) and were compared to the results for the related complexes with 2,6-dialkyl substituted N-aryl groups (R = Me, iPr). The investigations were complemented by DFT calculations, which allowed us to unravel details of the thermal decomposition pathways and provided mechanistic insights of further conversion steps and fluctional processes. The DTG/MS and DSC measurements revealed two different types of thermolysis pathways for the azido compounds. For the complexes with R = Cl and iPr substituents, two well-separated exothermic processes were observed. The first moderately exothermic loss of N(2) is followed by a second, strongly exothermic transformation. This contrasts the experimental results for the compound with 2,6-dimethyl substituents (R = Me), where both steps proceed concurrently in the same temperature range. The separation of the two thermal steps in the 2,6-dichloro substituted derivative allowed us to develop a protocol for the isolation of the highly insoluble nitrido complex, which was characterized by UV/vis, IR-spectroscopy and elemental analysis. Its constitution was further confirmed by reaction with silanes, which gave the corresponding silyl amido complexes.

  8. Evaluation of adsorption capacities of humic acids extracted from Algerian soil on polyaniline for application to remove pollutants such as Cd(II), Zn(II) and Ni(II) and characterization with cavity microelectrode.

    PubMed

    Terbouche, Achour; Ramdane-Terbouche, Chafia Ait; Hauchard, Didier; Djebbar, Safia

    2011-01-01

    The adsorption capacities of new humic acids isolated from Yakouren forest (YHA) and Sahara (Tamenrasset: THA) soils (Algeria) and commercial humic acid (PFHA) on polyaniline emeraldine base (PEB) were studied at pH 6.6. Also the adsorption of heavy metals such as Cd2+, Zn2+ and Ni2+ on humic acid-polyaniline systems (HA-PEB) was investigated at the same conditions. HA-PEB compounds were characterized by scanning electron microscopy (SEM), infrared spectrometry and cavity microelectrode. In addition, batch adsorption and cavity microelectrode were used in the adsorption study of Cd2+, Zn2+ and Ni2+ on HA-PEB. To develop biocaptors of polluting metals using a cavity microelectrode modified by HA-PEB systems, the adsorption kinetic and adsorption capacity were investigated. The SEM analysis showed that the presence of humic acid affected the PEB surface and caused the formation of a granular morphology. The maximum adsorption capacities (q(max)) of PFHA, THA and YHA determined by adsorption isotherms were 91.31, 132.1 and 151.0 mg/g, respectively. Batch adsorption results showed that q(max) of Cd2+, Zn2+ and Ni2+ on HA-PEB followed the order: THA-PEB > YHA-PEB > PFHA-PEB. The voltammograms obtained with HA-PEB modified cavity microelectrode showed the appearance of new redox couples reflecting the adsorption of HA on PEB. Metal-humic acid-polyaniline voltammograms were characterized by appearance of oxidation-reduction couples or reduction wave corresponding to metal. Finally, the result may be exploited to develop a biocaptor based on the cavity microelectrode amended by THA-PEB and YHA-PEB.

  9. Dynamic High-Temperature Characterization of an Iridium Alloy in Compression at High Strain Rates

    SciTech Connect

    Song, Bo; Nelson, Kevin; Lipinski, Ronald J.; Bignell, John L.; Ulrich, G. B.; George, E. P.

    2014-06-01

    Iridium alloys have superior strength and ductility at elevated temperatures, making them useful as structural materials for certain high-temperature applications. However, experimental data on their high-temperature high-strain-rate performance are needed for understanding high-speed impacts in severe elevated-temperature environments. Kolsky bars (also called split Hopkinson bars) have been extensively employed for high-strain-rate characterization of materials at room temperature, but it has been challenging to adapt them for the measurement of dynamic properties at high temperatures. Current high-temperature Kolsky compression bar techniques are not capable of obtaining satisfactory high-temperature high-strain-rate stress-strain response of thin iridium specimens investigated in this study. We analyzed the difficulties encountered in high-temperature Kolsky compression bar testing of thin iridium alloy specimens. Appropriate modifications were made to the current high-temperature Kolsky compression bar technique to obtain reliable compressive stress-strain response of an iridium alloy at high strain rates (300 – 10000 s-1) and temperatures (750°C and 1030°C). Uncertainties in such high-temperature high-strain-rate experiments on thin iridium specimens were also analyzed. The compressive stress-strain response of the iridium alloy showed significant sensitivity to strain rate and temperature.

  10. Acute human brain responses to intracortical microelectrode arrays: challenges and future prospects.

    PubMed

    Fernández, Eduardo; Greger, Bradley; House, Paul A; Aranda, Ignacio; Botella, Carlos; Albisua, Julio; Soto-Sánchez, Cristina; Alfaro, Arantxa; Normann, Richard A

    2014-01-01

    The emerging field of neuroprosthetics is focused on the development of new therapeutic interventions that will be able to restore some lost neural function by selective electrical stimulation or by harnessing activity recorded from populations of neurons. As more and more patients benefit from these approaches, the interest in neural interfaces has grown significantly and a new generation of penetrating microelectrode arrays are providing unprecedented access to the neurons of the central nervous system (CNS). These microelectrodes have active tip dimensions that are similar in size to neurons and because they penetrate the nervous system, they provide selective access to these cells (within a few microns). However, the very long-term viability of chronically implanted microelectrodes and the capability of recording the same spiking activity over long time periods still remain to be established and confirmed in human studies. Here we review the main responses to acute implantation of microelectrode arrays, and emphasize that it will become essential to control the neural tissue damage induced by these intracortical microelectrodes in order to achieve the high clinical potentials accompanying this technology.

  11. Brain machine interfaces combining microelectrode arrays with nanostructured optical biochemical sensors

    NASA Astrophysics Data System (ADS)

    Hajj-Hassan, Mohamad; Gonzalez, Timothy; Ghafer-Zadeh, Ebrahim; Chodavarapu, Vamsy; Musallam, Sam; Andrews, Mark

    2009-02-01

    Neural microelectrodes are an important component of neural prosthetic systems which assist paralyzed patients by allowing them to operate computers or robots using their neural activity. These microelectrodes are also used in clinical settings to localize the locus of seizure initiation in epilepsy or to stimulate sub-cortical structures in patients with Parkinson's disease. In neural prosthetic systems, implanted microelectrodes record the electrical potential generated by specific thoughts and relay the signals to algorithms trained to interpret these thoughts. In this paper, we describe novel elongated multi-site neural electrodes that can record electrical signals and specific neural biomarkers and that can reach depths greater than 8mm in the sulcus of non-human primates (monkeys). We hypothesize that additional signals recorded by the multimodal probes will increase the information yield when compared to standard probes that record just electropotentials. We describe integration of optical biochemical sensors with neural microelectrodes. The sensors are made using sol-gel derived xerogel thin films that encapsulate specific biomarker responsive luminophores in their nanostructured pores. The desired neural biomarkers are O2, pH, K+, and Na+ ions. As a prototype, we demonstrate direct-write patterning to create oxygen-responsive xerogel waveguide structures on the neural microelectrodes. The recording of neural biomarkers along with electrical activity could help the development of intelligent and more userfriendly neural prosthesis/brain machine interfaces as well as aid in providing answers to complex brain diseases and disorders.

  12. Chitosan coated carbon fiber microelectrode for selective in vivo detection of neurotransmitters in live zebrafish embryos.

    PubMed

    Ozel, Rıfat Emrah; Wallace, Kenneth N; Andreescu, Silvana

    2011-06-10

    We report the development of a chitosan modified carbon fiber microelectrode for in vivo detection of serotonin. We find that chitosan has the ability to reject physiological levels of ascorbic acid interferences and facilitate selective and sensitive detection of in vivo levels of serotonin, a common catecholamine neurotransmitter. Presence of chitosan on the microelectrode surface was investigated using scanning electron microscopy (SEM) and cyclic voltammetry (CV). The electrode was characterized using differential pulse voltammetry (DPV). A detection limit of 1.6 nM serotonin with a sensitivity of 5.12 nA/μM, a linear range from 2 to 100 nM and a reproducibility of 6.5% for n=6 electrodes were obtained. Chitosan modified microelectrodes selectively measure serotonin in presence of physiological levels of ascorbic acid. In vivo measurements were performed to measure concentration of serotonin in the live embryonic zebrafish intestine. The sensor quantifies in vivo intestinal levels of serotonin while successfully rejecting ascorbic acid interferences. We demonstrate that chitosan can be used as an effective coating to reject ascorbic acid interferences at carbon fiber microelectrodes, as an alternative to Nafion, and that chitosan modified microelectrodes are reliable tools for in vivo monitoring of changes in neurotransmitter levels. PMID:21601035

  13. Chitosan coated carbon fiber microelectrode for selective in vivo detection of neurotransmitters in live zebrafish embryos

    PubMed Central

    Özel, Rıfat Emrah; Wallace, Kenneth N.; Andreescu, Silvana

    2011-01-01

    We report the development of a chitosan modified carbon fiber microelectrode for in vivo detection of serotonin. We find that chitosan has the ability to reject physiological levels of ascorbic acid interferences and facilitate selective and sensitive detection of in vivo levels of serotonin, a common catecholamine neurotransmitter. Presence of chitosan on the microelectrode surface was investigated using scanning electron microscopy (SEM) and cyclic voltammetry (CV). The electrode was characterized using differential pulse voltammetry (DPV). A detection limit of 1.6 nM serotonin with a sensitivity of 5.12 nA/µM, a linear range from 2 to 100 nM and a reproducibility of 6.5 % for n=6 electrodes were obtained. Chitosan modified microelectrodes selectively measure serotonin in presence of physiological levels of ascorbic acid. In vivo measurements were performed to measure concentration of serotonin in the live embryonic zebrafish intestine. The sensor quantifies in vivo intestinal levels of serotonin while successfully rejecting ascorbic acid interferences. We demonstrate that chitosan can be used as an effective coating to reject ascorbic acid interferences at carbon fiber microelectrodes, as an alternative to Nafion, and that chitosan modified microelectrodes are reliable tools for in vivo monitoring of changes in neurotransmitter levels. PMID:21601035

  14. Acute human brain responses to intracortical microelectrode arrays: challenges and future prospects

    PubMed Central

    Fernández, Eduardo; Greger, Bradley; House, Paul A.; Aranda, Ignacio; Botella, Carlos; Albisua, Julio; Soto-Sánchez, Cristina; Alfaro, Arantxa; Normann, Richard A.

    2014-01-01

    The emerging field of neuroprosthetics is focused on the development of new therapeutic interventions that will be able to restore some lost neural function by selective electrical stimulation or by harnessing activity recorded from populations of neurons. As more and more patients benefit from these approaches, the interest in neural interfaces has grown significantly and a new generation of penetrating microelectrode arrays are providing unprecedented access to the neurons of the central nervous system (CNS). These microelectrodes have active tip dimensions that are similar in size to neurons and because they penetrate the nervous system, they provide selective access to these cells (within a few microns). However, the very long-term viability of chronically implanted microelectrodes and the capability of recording the same spiking activity over long time periods still remain to be established and confirmed in human studies. Here we review the main responses to acute implantation of microelectrode arrays, and emphasize that it will become essential to control the neural tissue damage induced by these intracortical microelectrodes in order to achieve the high clinical potentials accompanying this technology. PMID:25100989

  15. Hygroscopic particle behavior studied by interdigitated array microelectrode impedance sensors.

    PubMed

    Schindelholz, Eric; Tsui, Lok-kun; Kelly, Robert G

    2014-01-01

    The hygroscopic behavior of soluble salts bears importance in many research fields including atmospheric sciences, corrosion, porous building materials, and pharmaceuticals. Several methods have been used to study deliquescence (solid to liquid) and efflorescence (liquid to solid) phase transitions of these salts. In this study, we measured the deliquescence and efflorescence RH values of single salt microparticles deposited on an interdigitated microelectrode sensor via electrical impedance. The salts examined were NaCl, LiCl, NaBr, KCl, and MgCl2. Measured values were in agreement with in situ optical microscopic observations and, with the exception of MgCl2, literature values. In the case of MgCl2, deliquescence occurred at 33% RH and 12-15% RH, with the latter range being previously unreported. The depressed deliquescence RH was hypothesized to be a result of the formation of a metastable MgCl2 hydrate. Incomplete efflorescence of MgCl2 was also observed after exposure to <1.5% RH for up to 22 h due to formation of solid shells which trapped fluid. The phenomena elucidated by these results provide an explanation for the anomalous water retention and uptake behavior of MgCl2 below 33% RH reported elsewhere in the literature. The results presented in this study validate the use of this method as an alternative or complementary method for study of bulk-phase transitions of substrate-deposited particles across a broad RH range. These findings also demonstrate the utility of this method for detection of fluid trapping which cannot be directly ascertained by gravimetric and line-of-sight techniques commonly used in the study of hygroscopic particles.

  16. Micro-profiles of activated sludge floc determined using microelectrodes.

    PubMed

    Li, Baikun; Bishop, Paul L

    2004-03-01

    The microbial activity within activated sludge floc is a key factor in the performance of the activated sludge process. In this study, the microenvironment of activated sludge flocs from two wastewater treatment plants (Mill Creek Wastewater Treatment Plant and Muddy Creek Wastewater Treatment Plant, with aeration tank influent CODs of 60-120 and 15-35 mg/L, respectively) were studied by using microelectrodes. Due to microbial oxygen utilization, the aerobic region in the activated sludge floc was limited to the surface layer (0.1-0.2mm) of the sludge aggregate at the Mill Creek plant. The presence of an anoxic zone inside the sludge floc under aerobic conditions was confirmed in this study. When the dissolved oxygen (DO) in the bulk liquid was higher than 4.0mg/L, the anoxic zone inside the activated sludge floc disappeared, which is helpful for biodegradation. At the Muddy Creek plant, with its lower wastewater pollutant concentrations, the redox potential and DO inside the sludge aggregates were higher than those at the Mill Creek plant. The contaminant concentration in the bulk wastewater correlates with the oxygen utilization rate, which directly influences the oxygen penetration inside the activated sludge floc, and results in redox potential changes within the floc. The measured microprofiles revealed the continuous decrease of nitrate concentration inside the activated sludge floc, even though significant nitrification was observed in the bulk wastewater. The oxygen consumption and nitrification rate analyses reveal that the increase of ammonia flux under aerobic conditions correlates with nitrification. Due to the metabolic mechanisms of the microorganisms in activated sludge floc, which varies from one treatment plant to another, the oxygen flux inside the sludge floc changes accordingly.

  17. Process for catalytically oxidizing cycloolefins, particularly cyclohexene

    DOEpatents

    Mizuno, Noritaka; Lyon, David K.; Finke, Richard G.

    1993-01-01

    This invention is a process for catalytically oxidizing cycloolefins, particularly cyclohexenes, to form a variety of oxygenates. The catalyst used in the process is a covalently bonded iridium-heteropolyanion species. The process uses the catalyst in conjunction with a gaseous oxygen containing gas to form 2-cyclohexen-1-ol and also 2-cyclohexen-1-one.

  18. Simulation of an ac electro-osmotic pump with step microelectrodes

    NASA Astrophysics Data System (ADS)

    Kim, Byoung Jae; Lee, Seung-Hyun; Rezazadeh, Soghra; Sung, Hyung Jin

    2011-05-01

    Pumps with step microelectrodes subjected to an ac voltage are known to have faster pumping rates than those with planar asymmetric microelectrodes. The driving force for pumping in these systems is ac electro-osmosis. This paper aims to understand the flow behaviors of pumps with step microelectrodes by using a realistic model applicable to high external voltages. This model takes the steric effect due to the finite sizes of ions into account and copes with the exponential sensitivity of the counterion concentration to voltage. The effects on the pumping flow rate of varying the pump parameters were investigated. The geometrical parameters were optimized, and the effects of varying the ac frequency and amplitude were examined. The electrical potential of the fluid and the electrical charge at the electrode surface were solved simultaneously, and the Stokes equation was used to describe the fluid flow.

  19. Microelectrode Arrays with Overlapped Diffusion Layers as Electroanalytical Detectors: Theory and Basic Applications

    PubMed Central

    Tomčík, Peter

    2013-01-01

    This contribution contains a survey of basic literature dealing with arrays of microelectrodes with overlapping diffusion layers as prospective tools in contemporary electrochemistry. Photolithographic thin layer technology allows the fabrication of sensors of micrometric dimensions separated with a very small gap. This fact allows the diffusion layers of single microelectrodes to overlap as members of the array. Various basic types of microelectrode arrays with interacting diffusion layers are described and their analytical abilities are accented. Theoretical approaches to diffusion layer overlapping and the consequences of close constitution effects such as collection efficiency and redox cycling are discussed. Examples of basis applications in electroanalytical chemistry such as amperometric detectors in HPLC and substitutional stripping voltammetry are also given. PMID:24152927

  20. Electrodeposition of anchored polypyrrole film on microelectrodes and stimulation of cultured cardiac myocytes.

    PubMed

    Nishizawa, Matsuhiko; Nozaki, Hyuma; Kaji, Hirokazu; Kitazume, Takahiro; Kobayashi, Noriyuki; Ishibashi, Takeshi; Abe, Takashi

    2007-03-01

    The electrically conducting polymer polypyrrole (PPy) was electrochemically deposited onto Pt microelectrodes on a polyimide (PI) substrate. Pre-modification of the PI surface with a self-assembled monolayer of octadecyltrichlorosilane-induced anisotropic lateral growth of PPy along the PI surface and enhanced adhesive strength of the PPy film. The lateral growth of PPy film around the electrode anchored the whole film to the substrate. External stimulation of cultured cardiac myocytes was carried out using the PPy-coated microelectrode. The myocytes on the microelectrode substrate were electrically conjugated to form a sheet, and showed synchronized beating upon stimulation. The threshold charge for effective stimulation of a 0.8 cm(2) sheet of myocytes was around 0.2 microC, roughly corresponding to a membrane depolarization of 250 mV.

  1. Microelectrode arrays with overlapped diffusion layers as electroanalytical detectors: theory and basic applications.

    PubMed

    Tomčík, Peter

    2013-10-11

    This contribution contains a survey of basic literature dealing with arrays of microelectrodes with overlapping diffusion layers as prospective tools in contemporary electrochemistry. Photolithographic thin layer technology allows the fabrication of sensors of micrometric dimensions separated with a very small gap. This fact allows the diffusion layers of single microelectrodes to overlap as members of the array. Various basic types of microelectrode arrays with interacting diffusion layers are described and their analytical abilities are accented. Theoretical approaches to diffusion layer overlapping and the consequences of close constitution effects such as collection efficiency and redox cycling are discussed. Examples of basis applications in electroanalytical chemistry such as amperometric detectors in HPLC and substitutional stripping voltammetry are also given.

  2. In Vivo Monitoring of H2O2 with Polydopamine and Prussian Blue-coated Microelectrode.

    PubMed

    Li, Ruixin; Liu, Xiaomeng; Qiu, Wanling; Zhang, Meining

    2016-08-01

    In vivo monitoring of hydrogen peroxide (H2O2) in the brain is of importance for understanding the function of both reactive oxygen species (ROS) and signal transmission. Producing a robust microelectrode for in vivo measurement of H2O2 is challenging due to the complex brain environment and the instability of electrocatalysts employed for the reduction of H2O2. Here, we develop a new kind of microelectrode for in vivo monitoring of H2O2, which is prepared by, first, electrodeposition of Prussian blue (PB) onto carbon nanotube (CNT) assembled carbon fiber microelectrodes (CFEs) and then overcoating of the CFEs with a thin membrane of polydopamine (PDA) through self-polymerization. Scanning electron microscopic and X-ray proton spectroscopic results confirm the formation of PDA/PB/CNT/CFEs. The PDA membrane enables PB-based electrodes to show high stability in both in vitro and in vivo studies and to stably catalyze the electrochemical reduction of H2O2. The microelectrode is selective for in vivo measurements of H2O2, interference-free from O2 and other electroactive species coexisting in the brain. These properties, along with good linearity, high biocompatibility, and stability toward H2O2, substantially enable the microelectrode to track H2O2 changes in vivo during electrical stimulation and microinfusion of H2O2 and drug, which demonstrates that the microelectrode could be well suited for in vivo monitoring of dynamic changes of H2O2 in rat brain.

  3. Correlations between histology and neuronal activity recorded by microelectrodes implanted chronically in the cerebral cortex

    NASA Astrophysics Data System (ADS)

    McCreery, Douglas; Cogan, Stuart; Kane, Sheryl; Pikov, Victor

    2016-06-01

    Objective. To quantify relations between the neuronal activity recorded with chronically-implanted intracortical microelectrodes and the histology of the surrounding tissue, using radial distance from the tip sites and time after array implantation as parameters. Approach. ‘Utah’-type intracortical microelectrode arrays were implanted into cats’ sensorimotor cortex for 275-364 days. The brain tissue around the implants was immuno-stained for the neuronal marker NeuN and for the astrocyte marker GFAP. Pearson’s product-moment correlations were used to quantify the relations between these markers and the amplitudes of the recorded neuronal action potentials (APs) and their signal-to-noise ratios (S/N). Main results. S/N was more stable over post-implant time than was AP amplitude, but its increased correlation with neuronal density after many months indicates ongoing loss of neurons around the microelectrodes. S/N was correlated with neuron density out to at least 140 μm from the microelectrodes, while AP amplitude was correlated with neuron density and GFAP density within ˜80 μm. Correlations between AP amplitude and histology markers (GFAP and NeuN density) were strongest immediately after implantation, while correlation between the neuron density and S/N was strongest near the time the animals were sacrificed. Unlike AP amplitude, there was no significant correlation between S/N and density of GFAP around the tip sites. Significance. Our findings indicate an evolving interaction between changes in the tissue surrounding the microelectrodes and the microelectrode’s electrical properties. Ongoing loss of neurons around recording microelectrodes, and the interactions between their delayed electrical deterioration and early tissue scarring around the tips appear to pose the greatest threats to the microelectrodes’ long-term functionality.

  4. In Vivo Monitoring of H2O2 with Polydopamine and Prussian Blue-coated Microelectrode.

    PubMed

    Li, Ruixin; Liu, Xiaomeng; Qiu, Wanling; Zhang, Meining

    2016-08-01

    In vivo monitoring of hydrogen peroxide (H2O2) in the brain is of importance for understanding the function of both reactive oxygen species (ROS) and signal transmission. Producing a robust microelectrode for in vivo measurement of H2O2 is challenging due to the complex brain environment and the instability of electrocatalysts employed for the reduction of H2O2. Here, we develop a new kind of microelectrode for in vivo monitoring of H2O2, which is prepared by, first, electrodeposition of Prussian blue (PB) onto carbon nanotube (CNT) assembled carbon fiber microelectrodes (CFEs) and then overcoating of the CFEs with a thin membrane of polydopamine (PDA) through self-polymerization. Scanning electron microscopic and X-ray proton spectroscopic results confirm the formation of PDA/PB/CNT/CFEs. The PDA membrane enables PB-based electrodes to show high stability in both in vitro and in vivo studies and to stably catalyze the electrochemical reduction of H2O2. The microelectrode is selective for in vivo measurements of H2O2, interference-free from O2 and other electroactive species coexisting in the brain. These properties, along with good linearity, high biocompatibility, and stability toward H2O2, substantially enable the microelectrode to track H2O2 changes in vivo during electrical stimulation and microinfusion of H2O2 and drug, which demonstrates that the microelectrode could be well suited for in vivo monitoring of dynamic changes of H2O2 in rat brain. PMID:27385361

  5. Correlations between histology and neuronal activity recorded by microelectrodes implanted chronically in the cerebral cortex

    NASA Astrophysics Data System (ADS)

    McCreery, Douglas; Cogan, Stuart; Kane, Sheryl; Pikov, Victor

    2016-06-01

    Objective. To quantify relations between the neuronal activity recorded with chronically-implanted intracortical microelectrodes and the histology of the surrounding tissue, using radial distance from the tip sites and time after array implantation as parameters. Approach. ‘Utah’-type intracortical microelectrode arrays were implanted into cats’ sensorimotor cortex for 275–364 days. The brain tissue around the implants was immuno-stained for the neuronal marker NeuN and for the astrocyte marker GFAP. Pearson’s product-moment correlations were used to quantify the relations between these markers and the amplitudes of the recorded neuronal action potentials (APs) and their signal-to-noise ratios (S/N). Main results. S/N was more stable over post-implant time than was AP amplitude, but its increased correlation with neuronal density after many months indicates ongoing loss of neurons around the microelectrodes. S/N was correlated with neuron density out to at least 140 μm from the microelectrodes, while AP amplitude was correlated with neuron density and GFAP density within ∼80 μm. Correlations between AP amplitude and histology markers (GFAP and NeuN density) were strongest immediately after implantation, while correlation between the neuron density and S/N was strongest near the time the animals were sacrificed. Unlike AP amplitude, there was no significant correlation between S/N and density of GFAP around the tip sites. Significance. Our findings indicate an evolving interaction between changes in the tissue surrounding the microelectrodes and the microelectrode’s electrical properties. Ongoing loss of neurons around recording microelectrodes, and the interactions between their delayed electrical deterioration and early tissue scarring around the tips appear to pose the greatest threats to the microelectrodes’ long-term functionality.

  6. Preparation and characterization of redox active molecular assemblies on microelectrode arrays

    NASA Astrophysics Data System (ADS)

    Frisbie, C. D.; Fritsch-Faules, I.; Wollman, E. W.; Wrighton, M. S.

    1992-02-01

    Microelectrode arrays, consisting of six or eight individually addressable Au or Pt microelectrodes about 2 microns wide, 50 um long, and 0.1 microns thick separated by about 2 microns on a Si3N4 substrate, can be modified by immersion into a solution containing molecules having thiol, dithiocarbamate, or disulfide functional groups. The functional groups yield selective modification of the gold or platinum, not the Si3N4, with about one monolayer of molecular reagents. Electrochemical and Auger electron spectroscopy (AES) data are summarized to illustrate that the dithiocarbamate functional group can be used to link redox active molecules to Au or Pt surfaces.

  7. Strain response of stretchable micro-electrodes: Controlling sensitivity with serpentine designs and encapsulation

    SciTech Connect

    Gutruf, Philipp; Walia, Sumeet; Nur Ali, Md; Sriram, Sharath E-mail: madhu.bhaskaran@gmail.com; Bhaskaran, Madhu E-mail: madhu.bhaskaran@gmail.com

    2014-01-13

    The functionality of flexible electronics relies on stable performance of thin film micro-electrodes. This letter investigates the behavior of gold thin films on polyimide, a prevalent combination in flexible devices. The dynamic behavior of gold micro-electrodes has been studied by subjecting them to stress while monitoring their resistance in situ. The shape of the electrodes was systematically varied to examine resistive strain sensitivity, while an additional encapsulation was applied to characterize multilayer behavior. The realized designs show remarkable tolerance to repetitive strain, demonstrating that curvature and encapsulation are excellent approaches for minimizing resistive strain sensitivity to enable durable flexible electronics.

  8. Sonochemically fabricated enzyme microelectrode arrays for the environmental monitoring of pesticides.

    PubMed

    Pritchard, Jeanette; Law, Karen; Vakurov, Alexander; Millner, Paul; Higson, Séamus P J

    2004-11-01

    This paper describes the development of a novel sonochemically fabricated microelectrode based acetylcholinesterase and polyaniline carbon/cobalt phthalocyanine biosensor for the ultra-sensitive determination of pesticides. Arrays of this type are fabricated using microelectrode templates with population densities of 2 x 10(5) cm(-2). The enzymatic response of the sensors is inhibited upon incubation with the pesticide and in this report it is shown that paraoxon may be determined down to concentrations of 1 x 10(-17) M. This sensitivity has thus far not been achieved and mechanisms accounting for the enhancement of the sensitivity reported here are discussed. PMID:15522591

  9. Microelectrode for energy and current control of nanotip field electron emitters

    SciTech Connect

    Lüneburg, S.; Müller, M. Paarmann, A. Ernstorfer, R.

    2013-11-18

    Emerging experiments and applications in electron microscopy, holography, and diffraction benefit from miniaturized electron guns for compact experimental setups. We present a highly compact microelectrode integrated field emitter that consists of a tungsten nanotip coated with a few micrometers thick polyimide film followed by a several nanometers thick gold film, both positioned behind the exposed emitter apex by approximately 10–30 μm. The control of the electric field strength at the nanometer scale tip apex allows suppression, extraction, and energy tuning of field-emitted electrons. The performance of the microelectrode is demonstrated experimentally and supported by numerical simulations.

  10. Microelectrode-based technology for the detection of low levels of bacteria

    NASA Technical Reports Server (NTRS)

    Rogers, Tom D.; Hitchens, G. D.; Mishra, S. K.; Pierson, D. L.

    1992-01-01

    A microelectrode-based electrochemical detection method was used for quantitation of bacteria in water samples. The redox mediator, benzoquinone, was used to accept electrons from the bacterial metabolic pathway to create a flow of electrons by reducing the mediator. Electrochemical monitoring electrodes detected the reduced mediator as it diffused out of the cells and produced a small electrical current. By using a combination of microelectrodes and monitoring instrumentation, the cumulative current generated by a particular bacterial population could be monitored. Using commercially available components, an electrochemical detection system was assembled and tested to evaluate its potential as an emerging technology for rapid detection and quantitation of bacteria in water samples.

  11. A molecular catalyst for water oxidation that binds to metal oxide surfaces

    PubMed Central

    Sheehan, Stafford W.; Thomsen, Julianne M.; Hintermair, Ulrich; Crabtree, Robert H.; Brudvig, Gary W.; Schmuttenmaer, Charles A.

    2015-01-01

    Molecular catalysts are known for their high activity and tunability, but their solubility and limited stability often restrict their use in practical applications. Here we describe how a molecular iridium catalyst for water oxidation directly and robustly binds to oxide surfaces without the need for any external stimulus or additional linking groups. On conductive electrode surfaces, this heterogenized molecular catalyst oxidizes water with low overpotential, high turnover frequency and minimal degradation. Spectroscopic and electrochemical studies show that it does not decompose into iridium oxide, thus preserving its molecular identity, and that it is capable of sustaining high activity towards water oxidation with stability comparable to state-of-the-art bulk metal oxide catalysts. PMID:25757425

  12. Wafer-scale fabrication of penetrating neural microelectrode arrays

    NASA Astrophysics Data System (ADS)

    Bhandari, Rajmohan

    In order to have an efficient neural interface, uniformity and predictability of electrodes electrical, and mechanical characteristics are desired. Furthermore, the electrodes should have small active sites to selectively record or stimulate neural signals. Also, there should be close geometrical match between the electrode array and the targeted tissue for long-term stability. Currently the Utah electrode array (UEA) is in either constant electrode length (UEA) or varying length configurations (Utah slant electrode array: USEA). The current processes used to fabricate the UEAs impose limitations in the tolerances of the electrode array geometry. Furthermore, the flat architecture of the UEA and convoluted geometry of the targeted tissue results in poor coupling between the two "mating" surfaces, leading in active electrode tips that are not in proximity to the neuronal tissue. Therefore, a robust, flexible and high precision fabrication technology is needed that can produce (a) uniformly shaped microelectrodes (b) small and uniformly exposed active tip sites and (c) convoluted electrode arrays for better geometrical match. This dissertation presents a wafer-scale fabrication process for both the UEA and the USEA. A wafer-scale etching method has been developed and optimum etching conditions are established to achieve uniform shape electrode arrays. Also, the etching rate of silicon columns, produced by dicing, is studied as a function of temperature, etching time and stirring rate in the acid solution. Furthermore, a novel photoresist based masking technique for procuring extremely small active area has been developed on wafer-scale. In this technique, the tip exposure is controlled by varying the spin speed during photoresist coating. The technique allows fabrication of uniformly exposed tip lengths, over a range of 30 to 350 microm in length. Lastly, a novel array fabrication technique is developed for building a variety of neural interface devices having

  13. Meteoric smoke fallout over the Holocene epoch revealed by iridium and platinum in Greenland ice.

    PubMed

    Gabrielli, Paolo; Barbante, Carlo; Plane, John M C; Varga, Anita; Hong, Sungmin; Cozzi, Giulio; Gaspari, Vania; Planchon, Frédéric A M; Cairns, Warren; Ferrari, Christophe; Crutzen, Paul; Cescon, Paolo; Boutron, Claude F

    2004-12-23

    An iridium anomaly at the Cretaceous/Tertiary boundary layer has been attributed to an extraterrestrial body that struck the Earth some 65 million years ago. It has been suggested that, during this event, the carrier of iridium was probably a micrometre-sized silicate-enclosed aggregate or the nanophase material of the vaporized impactor. But the fate of platinum-group elements (such as iridium) that regularly enter the atmosphere via ablating meteoroids remains largely unknown. Here we report a record of iridium and platinum fluxes on a climatic-cycle timescale, back to 128,000 years ago, from a Greenland ice core. We find that unexpectedly constant fallout of extraterrestrial matter to Greenland occurred during the Holocene, whereas a greatly enhanced input of terrestrial iridium and platinum masked the cosmic flux in the dust-laden atmosphere of the last glacial age. We suggest that nanometre-sized meteoric smoke particles, formed from the recondensation of ablated meteoroids in the atmosphere at altitudes >70 kilometres, are transported into the winter polar vortices by the mesospheric meridional circulation and are preferentially deposited in the polar ice caps. This implies an average global fallout of 14 +/- 5 kilotons per year of meteoric smoke during the Holocene.

  14. Earth's Radiation Imbalance from a Constellation of 66 Iridium Satellites

    NASA Astrophysics Data System (ADS)

    Chiu, J. C.; Wiscombe, W. J.

    2012-04-01

    The Earth Radiation Imbalance (ERI) at the top of the atmosphere is the primary driving force for climate change. If ERI is not zero, then Earth's temperature, both oceanic and atmospheric, will change gradually over time, tending toward a new steady state. The best estimates of current ERI from climate models range from 0.4 to 0.9 W/m2 (the imbalance being caused mainly by increasing CO2), but current satellite systems do not have the accuracy to measure ERI to even one significant digit. In this paper, we will describe a proposed constellation of 66 Earth radiation budget instruments, to be hosted on Iridium satellites. This system represents a quantum leap over current systems in several ways, in particular in providing ERI to at least one significant digit, thus enabling a crucial test of climate models. Because of its 24/7 coverage, the system will also provide ERI at three-hourly time scales without requiring extrapolations from narrowband geostationary instruments. This would allow studies of ERI's response to fast-evolving phenomena like dust storms and hurricanes. This offers a new, synoptic view of Earth radiation budget that will transform it from a monthly average into a dynamical variable alongside standard meteorological variables like temperature and pressure.

  15. High Strain Rate Tensile Testing of DOP-26 Iridium

    SciTech Connect

    Schneibel, Joachim H; Carmichael Jr, Cecil Albert; George, Easo P

    2007-11-01

    The iridium alloy DOP-26 was developed through the Radioisotope Power Systems Program in the Office of Nuclear Energy of the Department of Energy. It is used for clad vent set cups containing radioactive fuel in radioisotope thermoelectric generator (RTG) heat sources which provide electric power for spacecraft. This report describes mechanical testing results for DOP-26. Specimens were given a vacuum recrystallization anneal of 1 hour at 1375 C and tested in tension in orientations parallel and perpendicular to the rolling direction of the sheet from which they were fabricated. The tests were performed at temperatures ranging from room temperature to 1090 C and strain rates ranging from 1 x 10{sup -3} to 50 s{sup -1}. Room temperature testing was performed in air, while testing at elevated temperatures was performed in a vacuum better than 1 x 10{sup -4} Torr. The yield stress (YS) and the ultimate tensile stress (UTS) decreased with increasing temperature and increased with increasing strain rate. Between 600 and 1090 C, the ductility showed a slight increase with increasing temperature. Within the scatter of the data, the ductility did not depend on the strain rate. The reduction in area (RA), on the other hand, decreased with increasing strain rate. The YS and UTS values did not differ significantly for the longitudinal and transverse specimens. The ductility and RA values of the transverse specimens were marginally lower than those of the longitudinal specimens.

  16. Enhancing the Bipolar Redox Cycling Efficiency of Plane-Recessed Microelectrode Arrays by Adding a Chemically Irreversible Interferent.

    PubMed

    He, Dingwen; Yan, Jiawei; Zhu, Feng; Zhou, Yongliang; Mao, Bingwei; Oleinick, Alexander; Svir, Irina; Amatore, Christian

    2016-09-01

    The individual electrochemical anodic responses of dopamine (DA), epinephrine (EP), and pyrocatechol (CT) were investigated at arrays of recessed gold disk-microelectrodes arrays (MEAs) covered by a gold plane electrode and compared to those of their binary mixture (CT and EP) when the top-plane electrode was operated as a bipolar electrode or as a collector. The interferent species (EP) displays a chemically irreversible wave over the same potential range as the chemically reversible ones of DA or CT. As expected, in the generator-collector (GC) mode, EP did not contribute to the redox cycling amplification that occurred only for DA or CT. Conversely, in the bipolar mode, the presence of EP drastically increased the bipolar redox cycling efficiency of DA and CT. This evidenced that the chemically irreversible oxidation of EP at the anodic poles of the top plane floating electrode provided additional electron fluxes that were used to more efficiently reduce the oxidized DA or CT species at the cathodic poles. This suggests an easy experimental strategy for enhancing the bipolar efficiency of MEAs up to reach a performance identical to that achieved when the same MEAs are operated in a GC mode. PMID:27490270

  17. Permeability and partitioning of ferrocene ethylene oxide and propylene oxide oligomers into electropolymerized films from acetonitrile and polyether solutions

    SciTech Connect

    Pyati, R.; Murray, R.W. )

    1994-10-27

    We report the first electrochemically-based measurements of the rates of small polymer permeation into another polymer. The small polymer permeants are ferrocene ethylene oxide oligomers containing 2, 7, and 16 units and a propylene oxide oligomer containing 3 units. Their permeation into ultrathin microelectrode-supported films of the metal complex polymer poly[Ru(vbpy)[sub 3

  18. Identification of an iridium(III) complex with anti-bacterial and anti-cancer activity

    PubMed Central

    Lu, Lihua; Liu, Li-Juan; Chao, Wei-chieh; Zhong, Hai-Jing; Wang, Modi; Chen, Xiu-Ping; Lu, Jin-Jian; Li, Ruei-nian; Ma, Dik-Lung; Leung, Chung-Hang

    2015-01-01

    Group 9 transition metal complexes have been widely explored as therapeutic agents due to their unique geometry, their propensity to undergo ligand exchanges with biomolecules and their diverse steric and electronic properties. These metal complexes can offer distinct modes of action in living organisms compared to carbon-based molecules. In this study, we investigated the antimicrobial and anti-proliferative abilities of a series of cyclometallated iridium(III) complexes. The iridium(III) complex 1 inhibited the growth of S. aureus with MIC and MBC values of 3.60 and 7.19 μM, respectively, indicating its potent bactericidal activity. Moreover, complex 1 also exhibited cytotoxicity against a number of cancer cell lines, with particular potency against ovarian, cervical and melanoma cells. This cyclometallated iridium(III) complex is the first example of a substitutionally-inert, Group 9 organometallic compound utilized as a direct and selective inhibitor of S. aureus. PMID:26416333

  19. Near-Infrared Phosphorescent Iridium(III) Benzonorrole Complexes Possessing Pyridine-based Axial Ligands.

    PubMed

    Maurya, Yogesh Kumar; Ishikawa, Takahiro; Kawabe, Yasunori; Ishida, Masatoshi; Toganoh, Motoki; Mori, Shigeki; Yasutake, Yuhsuke; Fukatsu, Susumu; Furuta, Hiroyuki

    2016-06-20

    Novel near-infrared phosphorescent iridium(III) complexes based on benzo-annulated N-linked corrole analogue (termed as benzonorrole) were synthesized. The structures of the complexes revealed octahedral coordination geometries involving an organometallic iridium-carbon bond with two external axial ligands. Interestingly, the iridium(III) complex exhibits near-infrared phosphorescence at room temperature at wavelengths beyond 900 nm. The significant redshift of the emission, as compared to the corrole congener, is originated from the ligand-centered triplet character. The fine-tuning of the photophysical properties of the complexes was achieved by introducing electron-donating and electron-withdrawing substituents on the axial pyridine ligands. PMID:27249778

  20. Preparation of iridium targets by electrodeposition for neutron capture cross section measurements

    DOE PAGES

    Bond, Evelyn M.; Moody, W. Allen; Arnold, Charles; Bredeweg, Todd A.; Jandel, Marian; Rusev, Gencho Y.

    2016-03-01

    Here, the preparation of 191Ir and 193Ir electrodeposits for neutron capture cross-section measurements at the detector for advanced neutron capture experiments located at the at Los Alamos Neutron Science Center is described. The electrodeposition of iridium in the desired thickness of 0.4–1 mg/cm2 is challenging. Better yields and thicknesses were obtained using electrodeposition from isopropyl alcohol solutions than from ammonium sulfate solutions. 191Ir and 193Ir targets were initially prepared using the standard single-sided electrodeposition cell. Iridium electrodepositions using a double-sided electrodeposition cell were developed and were optimized, resulting in thick, uniform iridium deposits. LA UR 15-22475.

  1. Preparation of iridium targets by electrodeposition for neutron capture cross section measurements

    SciTech Connect

    Bond, Evelyn M.; Moody, W. Allen; Arnold, Charles; Bredeweg, Todd A.; Jandel, Marian; Rusev, Gencho Y.

    2015-11-18

    Here, the preparation of 191Ir and 193Ir electrodeposits for neutron capture cross-section measurements at the detector for advanced neutron capture experiments located at the at Los Alamos Neutron Science Center is described. The electrodeposition of iridium in the desired thickness of 0.4–1 mg/cm2 is challenging. Better yields and thicknesses were obtained using electrodeposition from isopropyl alcohol solutions than from ammonium sulfate solutions. 191Ir and 193Ir targets were initially prepared using the standard single-sided electrodeposition cell. Iridium electrodepositions using a double-sided electrodeposition cell were developed and were optimized, resulting in thick, uniform iridium deposits. LA UR 15-22475.

  2. Redox processes in silicon dioxide thin films using copper microelectrodes

    NASA Astrophysics Data System (ADS)

    Tappertzhofen, S.; Menzel, S.; Valov, I.; Waser, R.

    2011-11-01

    Although SiO2 is a typical insulator, we demonstrate an electrochemical characteristic of the Cu/Cu+ oxidation at the interface with 30 nm thick silicon dioxide thin films studied by cyclic voltammetry. This study reveals the process of anodic oxidation and subsequent reduction of oxidized Cu ions injected in the SiO2 layer with special attention to the kinetics of the redox process. We estimated the diffusion coefficient and the mobility of Cu ions in SiO2. The results gain deeper insight in the processes involved during resistive switching of Cu/SiO2 based nonvolatile memory devices.

  3. Fabrication of a flexible penetrating microelectrode array for use on curved surfaces of neural tissues

    NASA Astrophysics Data System (ADS)

    Byun, Donghak; Cho, Sung Joon; Kim, Sohee

    2013-12-01

    Conventionally, invasive neural microelectrodes for recording neuronal signals or stimulating the nervous system have been fabricated based on silicon substrate mainly due to well-established manufacturing processes. However, these silicon-based microelectrode devices have an issue of mechanical stability caused by the absence of flexibility when implanted onto curved surfaces of tissues. In this paper, a flexible and penetrating microelectrode array, a hybrid structure composed of silicon and elastomer, was devised and fabricated by bulk micromachining technologies. The structure uses individual silicon needles as independent electrodes in a square array and polydimethysiloxane (PDMS) as a base to support the needles. The dimensions of the electrode array and the needles are adjustable, depending on the number of needles, the pitch between the needles and the targeted penetration depth of the neural tissue. For mechanical characterization, the adhesion between PDMS and silicon was evaluated and the flexibility and integrity of the fabricated structure were investigated through flexural test and insertion test. Also, the electrochemical impedance spectroscopy of the electrodes was measured. The results suggest that the proposed microelectrode array is promising for use in neuronal recording and stimulation over curved surfaces such as cortical surface and peripheral nerves with larger curvatures.

  4. Direct-write assembly of microperiodic planar and spanning ITO microelectrodes

    SciTech Connect

    Ahn, Bok Y; Lorang, David J; Duoss, Eric B.; Lewis, Jennifer A

    2010-01-01

    Printed Sn-doped In{sub 2}O{sub 3} (ITO) microelectrodes are fabricated by direct-write assembly of sol–gel inks with varying concentration. This maskless, non-lithographic approach provides a facile route to patterning transparent conductive features in planar arrays and spanning architectures.

  5. Effects of Organophosphorus Flame Retardants on Spontaneous Activity in Neuronal Networks Grown on Microelectrode Arrays

    EPA Science Inventory

    EFFECTS OF ORGANOPHOSPHORUS FLAME RETARDANTS ON SPONTANEOUS ACTIVITY IN NEURONAL NETWORKS GROWN ON MICROELECTRODE ARRAYS TJ Shafer1, K Wallace1, WR Mundy1, M Behl2,. 1Integrated Systems Toxicology Division, NHEERL, USEPA, RTP, NC, USA, 2National Toxicology Program, NIEHS, RTP, NC...

  6. Electrochemical detection of single cancer and healthy cell collisions on a microelectrode.

    PubMed

    Dick, Jeffrey E

    2016-09-18

    The electrochemical detection of single cancer cells and healthy cells is reported. Detection was achieved by monitoring the consumption of a single cell's contents upon its collisions with a microelectrode in the presence of surfactant. The electrochemical response between acute lymphoblastic lymphoma T-cells and healthy thymocytes differed by two orders of magnitude.

  7. Invariance of exocytotic events detected by amperometry as a function of the carbon fiber microelectrode diameter.

    PubMed

    Amatore, Christian; Arbault, Stéphane; Bouret, Yann; Guille, Manon; Lemaître, Frédéric; Verchier, Yann

    2009-04-15

    Etched carbon fiber microelectrodes of different radii have been used for amperometric measurements of single exocytotic events occurring at adrenal chromaffin cells. Frequency, kinetic, and quantitative information on exocytosis provided by amperometric spikes were analyzed as a function of the surface area of the microelectrodes. Interestingly, the percentage of spikes with foot (as well as their own characteristics), a category revealing the existence of sufficient long-lasting fusion pores, was found to be constant whatever the microelectrode diameter was, whereas the probability of overlapping spikes decreased with the electrode size. This confirmed that the prespike foot could not feature accidental superimposition of separated events occurring at different places. Moreover, the features of amperometric spikes investigated here (charge, intensity and kinetics) were found constant for all microelectrode diameters. This demonstrated that the electrochemical measurement does not introduce significant bias onto the kinetics and thermodynamics of release during individual exocytotic events. All in all, this work evidences that information on exocytosis amperometrically recorded with the usual 7 microm diameter carbon fiber electrodes is biologically relevant, although the frequent overlap between spikes requires a censorship of the data during the analytical treatment. PMID:19290664

  8. Modeling of the cell-electrode interface noise for microelectrode arrays.

    PubMed

    Guo, Jing; Yuan, Jie; Chan, Mansun

    2012-12-01

    Microelectrodes are widely used in the physiological recording of cell field potentials. As microelectrode signals are generally in the μV range, characteristics of the cell-electrode interface are important to the recording accuracy. Although the impedance of the microelectrode-solution interface has been well studied and modeled in the past, no effective model has been experimentally verified to estimate the noise of the cell-electrode interface. Also in existing interface models, spectral information is largely disregarded. In this work, we developed a model for estimating the noise of the cell-electrode interface from interface impedances. This model improves over existing noise models by including the cell membrane capacitor and frequency dependent impedances. With low-noise experiment setups, this model is verified by microelectrode array (MEA) experiments with mouse muscle myoblast cells. Experiments show that the noise estimated from this model has <;10% error, which is much less than estimations from existing models. With this model, noise of the cell-electrode interface can be estimated by simply measuring interface impedances. This model also provides insights for micro- electrode design to achieve good recording signal-to-noise ratio.

  9. A comparison of neuroinflammation to implanted microelectrodes in rat and mouse models.

    PubMed

    Potter-Baker, Kelsey A; Ravikumar, Madhumitha; Burke, Alan A; Meador, William D; Householder, Kyle T; Buck, Amy C; Sunil, Smrithi; Stewart, Wade G; Anna, Jake P; Tomaszewski, William H; Capadona, Jeffrey R

    2014-07-01

    Rat models have emerged as a common tool to study neuroinflammation to intracortical microelectrodes. While a number of studies have attempted to understand the factors resulting in neuroinflammation using rat models, a complete understanding of key mechanistic pathways remains elusive. Transgenic mouse models, however, could facilitate a deeper understanding of mechanistic pathways due to an ease of genetic alteration. Therefore, the goal of the present study is to compare neuroinflammation following microelectrode implantation between the rat and the mouse model. Our study suggests that subtle differences in the classic neuroinflammatory markers exist between the animal models at both two and sixteen weeks post implantation. Most notably, neuronal densities surrounding microelectrodes were significantly lower in the rat model at two weeks, while similar densities were observed between the animal models at sixteen weeks. Physiological differences between the species and slight alterations in surgical methods are likely key contributors to the observed differences. Moving forward, we propose that differences in the time course of neuroinflammation between the animal models should be considered when trying to understand and prevent intracortical microelectrode failure.

  10. Effect of nitrite and nitrate on in situ sulfide production in an activated sludge immobilized agar gel film as determined by use of microelectrodes.

    PubMed

    Okabe, Satoshi; Santegoeds, Cecilia M; De Beer, Dirk

    2003-03-01

    Microelectrode, fluorescence in situ hybridization (FISH), and denaturing gradient gel electrophoresis (DGGE) analyses were used to investigate the effect of nitrite and nitrate on in situ sulfide production in an activated sludge immobilized agar gel film. Microelectrode measurements of O(2), H(2)S, NO(3)(-), NO(2)(-), and pH revealed that the addition of NO(2)(-) and NO(3)(-) forced sulfate reduction zones deeper in the agar gel and significantly reduced the in situ sulfide production levels. The sulfate reduction zone was consequently separated from O(2) and NO(2)(-) or NO(3)(-) respiration zones with increasing the concentrations of NO(2)(-) and NO(3)(-). These NO(2)(-) and NO(3)(-) treatments had only a transient effect on sulfide production. The in situ sulfide production quickly recovered to the previous levels when NO(2)(-) and NO(3)(-) were removed. The PCR-DGGE and FISH analyses revealed that 2-day-continuous addition of 500 microM NO(3)(-) did not change the metabolically active sulfate-reducing bacterial (SRB) community. On the basis of these data, it could be concluded that the addition of NO(2)(-) and NO(3)(-) did not kill SRB, but induced the interspecies competition for common carbon source (i.e., acetate) between nitrate-reducing heterotrophic bacteria and SRB and enhanced the oxidation of the produced sulfide, which were main possible causes of the suppression of in situ sulfide production in the agar gel.

  11. A magnetism-based approach to examining spin-orbit coupling effects in solid systems of isolated iridium octahedra

    NASA Astrophysics Data System (ADS)

    Phelan, Brendan F.

    This thesis explores the relative strengths of Spin-Orbit Coupling (SOC) in several perovskite-like systems that feature uninterrupted arrays of isolated IrO6 octahedra. Iridate compounds are particularly interesting to the community due to their relevance to emergent material properties such as insulating antiferromagnets, superconductors, and topological insulators. Recently literature has pointed to a complex interaction between SOC and crystal field splitting (CFS) in d5 metals. I utilize a straightforward, magnetic approach to determine the relative strengths of SOC vs CFS by chemically modifying structure and oxidation state. This contrasts with other work where advanced spectroscopic measurements are utilized to probe energy levels within a single compound. The focus of this study lies in two main methodologies: 1) Tracking the evolution of the Ir magnetic moment on progressing from 5 d5 Ir4+ to 5d 4 Ir5+ oxidation states that are clearly best described by a transition from a J=1/2 to a J=0 Ir magnetic state. In these cases, the evolution of the magnetic susceptibility shows the dominance of spin-orbit coupling in determining the magnetic properties of a material with highly isolated IrO6 octahedra. 2) Distorting J=0 Ir5+ systems where there is no emergence of an enhanced magnetic moment in the series on increasing the structural distortions, as would have been the case for significant crystal field splitting that reinforces the notion that spin-orbit coupling is the dominant force in determining the magnetism of iridium-oxygen octahedra in perovskite-like structures. The organization of this thesis is as follows: Chapter 1 presents a brief introduction to solid-state chemistry, iridates, and magnetism. Chapter 2 is an overview of experimental methodology and instrumentation. Chapter 3, presents a study of tuning the oxidation state of a new structure type: SrxLa11-xIr4O24. Chapter 4 presents a structural tuning of the Ir5+ system: Ba 2-xSrxYIrO6. Finally

  12. Design, Fabrication, Simulation and Characterization of a Novel Dual-Sided Microelectrode Array for Deep Brain Recording and Stimulation

    PubMed Central

    Zhao, Zongya; Gong, Ruxue; Huang, Hongen; Wang, Jue

    2016-01-01

    In this paper, a novel dual-sided microelectrode array is specially designed and fabricated for a rat Parkinson’s disease (PD) model to study the mechanisms of deep brain stimulation (DBS). The fabricated microelectrode array can stimulate the subthalamic nucleus and simultaneously record electrophysiological information from multiple nuclei of the basal ganglia system. The fabricated microelectrode array has a long shaft of 9 mm and each planar surface is equipped with three stimulating sites (diameter of 100 μm), seven electrophysiological recording sites (diameter of 20 μm) and four sites with diameter of 50 μm used for neurotransmitter measurements in future work. The performances of the fabricated microelectrode array were characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. In addition, the stimulating effects of the fabricated microelectrode were evaluated by finite element modeling (FEM). Preliminary animal experiments demonstrated that the designed microelectrode arrays can record spontaneous discharge signals from the striatum, the subthalamic nucleus and the globus pallidus interna. The designed and fabricated microelectrode arrays provide a powerful research tool for studying the mechanisms of DBS in rat PD models. PMID:27314356

  13. Magnetron sputtered diamond-like carbon microelectrodes for on-chip measurement of quantal catecholamine release from cells.

    PubMed

    Gao, Yuanfang; Chen, Xiaohui; Gupta, Sanju; Gillis, Kevin D; Gangopadhyay, Shubhra

    2008-10-01

    Carbon electrodes are widely used in electrochemistry due to their low cost, wide potential window, and low and stable background noise. Carbon-fiber electrodes (CFE) are commonly used to electrochemically measure "quantal" catecholamine release via exocytosis from individual cells, but it is difficult to integrate CFEs into lab-on-a-chip devices. Here we report the development of nitrogen doped diamond-like carbon (DLC:N) microelectrodes on a chip to monitor quantal release of catecholamines from cells. Advantages of DLC:N microelectrodes are that they are batch producible at low cost, and are harder and more durable than graphite films. The DLC:N microelectrodes were prepared by a magnetron sputtering process with nitrogen doping. The 30 microm by 40 microm DLC:N microelectrodes were patterned onto microscope glass slides by photolithography and lift-off technology. The properties of the DLC:N microelectrodes were characterized by AFM, Raman spectroscopy and cyclic voltammetry. Quantal catecholamine release was recorded amperometrically from bovine adrenal chromaffin cells on the DLC:N microelectrodes. Amperometric spikes due to quantal release of catecholamines were similar in amplitude and area as those recorded using CFEs and the background current and noise levels of microchip DLC:N electrodes were also comparable to CFEs. Therefore, DLC:N microelectrodes are suitable for microchip-based high-throughput measurement of quantal exocytosis with applications in basic research, drug discovery and cell-based biosensors.

  14. Magnetron sputtered diamond-like carbon microelectrodes for on-chip measurement of quantal catecholamine release from cells.

    PubMed

    Gao, Yuanfang; Chen, Xiaohui; Gupta, Sanju; Gillis, Kevin D; Gangopadhyay, Shubhra

    2008-10-01

    Carbon electrodes are widely used in electrochemistry due to their low cost, wide potential window, and low and stable background noise. Carbon-fiber electrodes (CFE) are commonly used to electrochemically measure "quantal" catecholamine release via exocytosis from individual cells, but it is difficult to integrate CFEs into lab-on-a-chip devices. Here we report the development of nitrogen doped diamond-like carbon (DLC:N) microelectrodes on a chip to monitor quantal release of catecholamines from cells. Advantages of DLC:N microelectrodes are that they are batch producible at low cost, and are harder and more durable than graphite films. The DLC:N microelectrodes were prepared by a magnetron sputtering process with nitrogen doping. The 30 microm by 40 microm DLC:N microelectrodes were patterned onto microscope glass slides by photolithography and lift-off technology. The properties of the DLC:N microelectrodes were characterized by AFM, Raman spectroscopy and cyclic voltammetry. Quantal catecholamine release was recorded amperometrically from bovine adrenal chromaffin cells on the DLC:N microelectrodes. Amperometric spikes due to quantal release of catecholamines were similar in amplitude and area as those recorded using CFEs and the background current and noise levels of microchip DLC:N electrodes were also comparable to CFEs. Therefore, DLC:N microelectrodes are suitable for microchip-based high-throughput measurement of quantal exocytosis with applications in basic research, drug discovery and cell-based biosensors. PMID:18493856

  15. The roles of blood-derived macrophages and resident microglia in the neuroinflammatory response to implanted Intracortical microelectrodes

    PubMed Central

    Ravikumar, Madhumitha; Sunil, Smrithi; Black, James; Barkauskas, Deborah S.; Haung, Alex Y.; Miller, Robert H.; Selkirk, Stephen M.; Capadona, Jeffrey R.

    2014-01-01

    Resident microglia and blood-borne macrophages have both been implicated to play a dominant role in mediating the neuroinflammatory response affecting implanted intracortical microelectrodes. However, the distinction between each cell type has not been demonstrated due to a lack of discriminating cellular markers. Understanding the subtle differences of each cell population in mediating neuroinflammation can aid in determining the appropriate therapeutic approaches to improve microelectrode performance. Therefore, the goal of this study is to characterize the role of infiltrating blood-derived cells, specifically macrophages, in mediating neuroinflammation following intracortical microelectrode implantation. Interestingly, we found no correlation between microglia and neuron populations at the microelectrode-tissue interface. On the other hand, blood-borne macrophages consistently dominated the infiltrating cell population following microelectrode implantation. Most importantly, we found a correlation between increased populations of blood-derived cells (including the total macrophage population) and neuron loss at the microelectrode-tissue interface. Specifically, the total macrophage population was greatest at two and sixteen weeks post implantation, at the same time points when we observed the lowest densities of neuronal survival in closest proximity to the implant. Together, our results suggest a dominant role of infiltrating macrophages, and not resident microglia, in mediating neurodegeneration following microelectrode implantation. PMID:24973296

  16. The roles of blood-derived macrophages and resident microglia in the neuroinflammatory response to implanted intracortical microelectrodes.

    PubMed

    Ravikumar, Madhumitha; Sunil, Smrithi; Black, James; Barkauskas, Deborah S; Haung, Alex Y; Miller, Robert H; Selkirk, Stephen M; Capadona, Jeffrey R

    2014-09-01

    Resident microglia and blood-borne macrophages have both been implicated to play a dominant role in mediating the neuroinflammatory response affecting implanted intracortical microelectrodes. However, the distinction between each cell type has not been demonstrated due to a lack of discriminating cellular markers. Understanding the subtle differences of each cell population in mediating neuroinflammation can aid in determining the appropriate therapeutic approaches to improve microelectrode performance. Therefore, the goal of this study is to characterize the role of infiltrating blood-derived cells, specifically macrophages, in mediating neuroinflammation following intracortical microelectrode implantation. Interestingly, we found no correlation between microglia and neuron populations at the microelectrode-tissue interface. On the other hand, blood-borne macrophages consistently dominated the infiltrating cell population following microelectrode implantation. Most importantly, we found a correlation between increased populations of blood-derived cells (including the total macrophage population) and neuron loss at the microelectrode-tissue interface. Specifically, the total macrophage population was greatest at two and sixteen weeks post implantation, at the same time points when we observed the lowest densities of neuronal survival in closest proximity to the implant. Together, our results suggest a dominant role of infiltrating macrophages, and not resident microglia, in mediating neurodegeneration following microelectrode implantation.

  17. High-strain-rate, high-temperature biaxial testing of DOP-26 iridium

    SciTech Connect

    George, T.G.

    1988-05-01

    High-strain-rate biaxial punch tests were performed on DOP-26 (Ir-0.3 wt.% tungsten) iridium-alloy disc given annealing and aging heat treatments. Test temperatures ranged between 600 and 1440/degree/C, and punch velocity was held constant at 45 m/s. Three types of samples were evaluated: Z-batch old-process discs, B-batch old-process discs, and B-batch new-process discs. The results indicate that batch-to-batch variations in ductility are significant and that new-process iridium is slightly more ductile than old-process material. 12 refs., 43 figs., 26 tabs.

  18. Thermocouples of molybdenum and iridium alloys for more stable vacuum-high temperature performance

    NASA Technical Reports Server (NTRS)

    Morris, J. F. (Inventor)

    1978-01-01

    Thermocouples providing stability and performance reliability in systems involving high temperatures and vacuums by employing a bimetallic thermocouple sensor are described. Each metal of the sensor is selected from a group of metals comprising molybdenum and iridium and alloys containing only those two metals. The molybdenum, iridium thermocouple sensor alloys provide bare metal thermocouple sensors having advantageous vapor pressure compatibility and performance characteristics. The compatibility and physical characteristics of the thermocouple sensor alloys result in improved emf, temperature properties and thermocouple hot junction performance.

  19. New Iridium Complex Coordinated with Tetrathiafulvalene Substituted Triazole-pyridine Ligand: Synthesis, Photophysical and Electrochemical Properties.

    PubMed

    Niu, Zhi-Gang; Xie, Hui; He, Li-Rong; Li, Kai-Xiu; Xia, Qing; Wu, Dong-Min; Li, Gao-Nan

    2016-01-01

    A new iridium(III) complex based on the triazole-pyridine ligand with tetrathiafulvalene unit, [Ir(ppy)2(L)]PF6 (1), has been synthesized and structurally characterized. The absorption spectra, luminescent spectra and electrochemical behaviors of L and 1 have been investigated. Complex 1 is found to be emissive at room temperature with maxima at 481 and 510 nm. The broad and structured emission bands are suggested a mixing of 3LC (3π-π*) and 3CT (3MLCT) excited states. The influence of iridium ion coordination on the redox properties of the TTF has also been investigated by cyclic voltammetry. PMID:27333555

  20. L-lactate measures in brain tissue with ceramic-based multisite microelectrodes.

    PubMed

    Burmeister, Jason J; Palmer, Michael; Gerhardt, Greg A

    2005-03-15

    A newly developed multisite array microelectrode for in vivo measurements of L-lactate is presented. The resulting microelectrode is composed of three functional layers. First, Nafion is used to repel interfering electroactive anions, such as ascorbate. Second, L-lactate oxidase immobilized onto the recording sites is used to convert L-lactate to hydrogen peroxide. The H2O2 produced is proportional to L-lactate concentrations and is quantified at the platinum recording sites. Third, a layer of polyurethane is coated over the L-lactate oxidase to adjust the linear range of the microelectrode to one that is compatible with in vivo measurements. This layer reduces the amount of L-lactate that diffuses to the enzyme while not significantly limiting oxygen diffusion. The resulting L-lactate microelectrodes were linear to 20 mM (R2 = 0.997 +/- 0.001) and beyond in some cases with detection limits of 0.078 +/- 0.013 mM (n = 12). The selectivity and response time of these electrodes make them suitable for in vivo measurements in brain tissue. Self-referencing recordings may be utilized to further improve the selectivity of the recordings. However this is not necessary for most applications in the brain, because the resting and stimulated levels of dopamine (DA), norepinephrine (NE), and other potentially interfering cations are two to three orders of magnitude lower than that of in vivo L-lactate, which is in the millimolar range. Preliminary in vivo measures of L-lactate in the brain of anesthetized rats support that the microelectrodes are capable of measuring rapid endogenous changes in vivo. PMID:15681193

  1. Experimental and theoretical characterization of implantable neural microelectrodes modified with conducting polymer nanotubes

    PubMed Central

    Abidian, Mohammad Reza; Martin, David C.

    2009-01-01

    Neural prostheses transduce bioelectric signals to electronic signals at the interface between neural tissue and neural microelectrodes. A low impedance electrode-tissue interface is important for the quality of signal during recording as well as quantity of applied charge density during stimulation. However, neural microelectrode sites exhibit high impedance because of their small geometric surface area. Here we analyze nanostructured-conducting polymers that can be used to significantly decrease the impedance of microelectrode typically by about two orders of magnitude and increase the charge transfer capacity of microelectrodes by three orders of magnitude. In this study poly(pyrrole) (PPy) and poly(3, 4- ethylenedioxythiophene) (PEDOT) nanotubes were electrochemically polymerized on the surface of neural microelectrode sites (1250 μm2). An equivalent circuit model comprising a coating capacitance in parallel with a pore resistance and interface impedance in series was developed and fitted to experimental results to characterize the physical and electrical properties of the interface. To confirm that the fitting parameters correlate with physical quantities of interface, theoretical equations were used to calculate the parameter values thereby validating the proposed model. Finally, an apparent diffusion coefficient was calculated for PPy film (29.2 ± 1.1 cm2/s), PPy nanotubes (72.4 ± 3.3 cm2/s), PEDOT film (7.4 ± 2.1 cm2/s), and PEDOT nanotubes (13.0 ± 1.8 cm2/s). The apparent diffusion coefficient of conducting polymer nanotubes was larger than the corresponding conducting polymer films. PMID:18093644

  2. Rhizosphere pH responses to simulated acid rain as measured with glass microelectrodes

    SciTech Connect

    Conkling, B.L.

    1988-01-01

    The objectives of this study were to develop a useful experimental system for studying the rhizosphere of growing roots, and to investigate the effects of bulk soil pH and foliar acid rain application on the rhizosphere pH of alfalfa, corn and soybeans. First, a study was done to compare soil pH measurements made with a standard glass pH electrode with those made using an antimony (Sb) microelectrode. Because of uncertainty with the Sb microelectrodes' response, glass pH-sensitive microelectrodes were made and tested for rhizosphere pH measurements. The influence of soil water pressure gradients in the range of {minus}10 to {minus}1500 kPa in the proximity of the pH and reference electrodes on pH measurements made with microelectrodes was studied. The effect of foliar acid rain application on the rhizosphere pH of alfalfa, corn, and soybean as a function of soil pH were studied. Alfalfa, corn, and soybean were grown into minirhizotrons containing reformed samples of both Seymour A and Bt soil horizons, and the rhizosphere pH measured. The measured in situ bulk soil pH ranged from 4.9 to 6.2 in the A horizon and from 4.0 to 5.7 in the Bt horizon. Plants received acid or non-acid foliar rain applications. Rhizosphere pH was measured using a glass pH-sensitive microelectrode. Acid rain applications caused foliar damage, but had little effect on the rhizosphere pH. The general trend was for the lateral root pH values to be slightly higher than the main root values.

  3. Iridium {mu}-imido/amido A-frame complexes

    SciTech Connect

    Ye, Changqing; Sharp, P.R.

    1995-01-04

    The reaction of Ir{sub 2}Cl{sub 2}(CO){sub 2}({mu}-dppm){sub 2}(dppm=bis(diphenylphosphino)methane) with 2 equiv of LiNHR yields Ir{sub 2}({mu}-NR)(CO){sub 2}({mu}-dppm){sub 2}, (1) (R=p-tolyl,Ph,p-BrC{sub 6}H{sub 4}), or its tautomer Ir{sub 2}({mu}-NHR)(CO){sub 2}({mu}-dppm)-({mu}-dppm-H), (2) (dppm-H = bis(diphenylphosphino)methanide; R= Et, Bu{sup 5}). NMR data suggest that (1) (R=p-tolyl, Ph, p-BrC{sub 6}H{sub 4}) are in equilibrium with small amounts of (2) in polar solvents. An X-ray structural determination of (1) (R = p-tolyl) shows that the imido nitrogen atom links two iridium atoms at the apex of an A-frame complex. A very short N-C distance in the imido group suggests extensive N-lone pair donation to the tolyl ring. Crystals of (1) (R = p-tolyl) from benzene are tetragonal (P4{sub 3}) with a = 21.337(1) {Angstrom},c = 14.478-(2) {Angstrom}, and Z = 4. With the exception of R=p-NO{sub 2}C{sub 6}H{sub 4}, p-BrC{sub 6}H{sub 4}, and Et, the complexes react with 1 equiv of CO at ambient temperature to form Ir{sub 2}(CO){sub 3}({mu}-dppm){sub 2} as the major metal containing product. For R = Et, the reaction generates the unstable isocyanate complex Ir{sub 2}(CO){sub 4}({mu}-dppm){sub 2} and amine except for the p-NO{sub 2}C{sub 6}H{sub 4} complex, which gives a complex mixture of products.

  4. Efficient Energy Transfer and Metal Coupling in Cyanide-Bridged Heterodinuclear Complexes Based on (Bipyridine)(terpyridine)ruthenium(II) and (Phenylpyridine)iridium(III) Complexes.

    PubMed

    Barthelmes, Kevin; Jäger, Michael; Kübel, Joachim; Friebe, Christian; Winter, Andreas; Wächtler, Maria; Dietzek, Benjamin; Schubert, Ulrich S

    2016-06-01

    We report a series of cyanide-bridged, heterodinuclear iridium(III)-ruthenium(II) complexes with the generalized formula [Ir((R2)2-ppy)2(CN)(μ-CN)Ru(bpy)(tpy-R1)]PF6 (ppy = 2-phenylpyridine, bpy = 2,2'-bipyridine, and tpy = 2,2':6',2″-terpyridine). The structural, spectroscopic, and electrochemical properties were analyzed in the context of variation of the electron-withdrawing (e.g., -F, -Br, -CHO) and -donating (e.g., -Me) and extended π-conjugated groups at several positions. In total, ten dinuclear complexes and the appropriate model complexes have been prepared. The iridium(III)-based emission is almost fully quenched in these complexes, and only the ruthenium(II)-based emission is observed, which indicates an efficient energy transfer toward the Ru center. Upon oxidation of the Ru center, the fluorinated complexes 2 exhibit a broad intervalence charge-transfer transition in the near-infrared region. The complexes are assigned to a weakly coupled class II system according to the Robin-Day classification. The electronic structure was evaluated by density functional theory (DFT) and time-dependent DFT calculations to corroborate the experimental data. PMID:27214264

  5. Electrochemical properties of silver-copper alloy microelectrodes for use in voltammetric field apparatus.

    PubMed

    Skogvold, Silje M; Mikkelsen, Oyvind; Billon, Gabriel; Garnier, Cedric; Lesven, Ludovic; Barthe, Jean-Francois

    2006-04-01

    Microelectrodes of silver-copper alloys have been evaluated for use in voltammetric analyses. Increased overpotential towards the hydrogen overvoltage reaction (HER) was found as a function of increased copper content in the silver. A study of oxidizing products by cyclic voltammetry (CV) in NaOH solution showed ten anodic and eight cathodic peaks which are described in the present paper. The behaviour of these alloy electrodes is somewhere between pure silver and pure copper electrodes. Differential pulse anodic stripping voltammetry (DPASV) was used to measure zinc, cadmium and lead in ultrapure water only (18 MOmegacm), and good linearity was found for all metals (r (2)=0.998) in the range of 0.5 to 5 ppb with a 600- to 1,200-s plating time. It was additionally found that cadmium and lead were better separated on the alloy electrodes compared to pure silver electrodes. Measurements of nickel were carried out on alloy electrodes by use of adsorptive differential pulse cathodic stripping voltammetry (Ad-DPCSV), and good linearity (r (2)=1.000) was found in the range from 0.5 to 5 ppb with an adsorption time of 120 s. The alloy electrodes were also found to be sensitive to nitrate, and good linearity (r (2)=0.997) was found in the range from 1 mg L(-1) to 100 mg L(-1) using differential pulse voltammetry (DPV) scanning from -450 mV to -1,500 mV. Addition of nitrate in ultrapure water afforded two different peaks related to the successive reductions of nitrate and nitrite. In ammonium buffer solution (pH 8.6) only one peak resulting from reduction of nitrate was observed. Furthermore, the use of alloy electrodes containing 17% Cu was tested in real samples, by installing it in a voltammetric system for monitoring of zinc and lead in a polluted river, the river Deûle, near the town of Douai in northern France. Results were found to be in agreement with parallel measurements carried out by ICP-MS. PMID:16550424

  6. Iridium(I) Compounds as Prospective Anticancer Agents: Solution Chemistry, Antiproliferative Profiles and Protein Interactions for a Series of Iridium(I) N-Heterocyclic Carbene Complexes.

    PubMed

    Gothe, Yvonne; Marzo, Tiziano; Messori, Luigi; Metzler-Nolte, Nils

    2016-08-22

    A series of structurally related mono- and bis-NHC-iridium(I) (NHC: N-heterocyclic carbene) complexes have been investigated for their suitability as potential anticancer drugs. Their spectral behaviour in aqueous buffers under physiological-like conditions and their cytotoxicity against the cancer cell lines MCF-7 and HT-29 are reported. Notably, almost all complexes exhibit significant cytotoxic effects towards both cancer cell lines. In general, the cationic bis-carbene complexes show higher stability and greater anticancer activity than their neutral mono-carbene analogues with IC50 values in the high nanomolar range. Furthermore, to gain initial mechanistic insight, the interactions of these iridium(I)-NHC complexes with two model proteins, namely lysozyme and cytochrome c, were explored by HR-ESI-MS analyses. The different protein metalation patterns of the complexes can be roughly classified into two distinct groups. Those interactions give us a first idea about the possible mechanism of action of this class of compounds. Overall, our findings show that iridium(I)-NHC complexes represent very interesting candidates for further development as new metal-based anticancer drugs.

  7. Iridium(I) Compounds as Prospective Anticancer Agents: Solution Chemistry, Antiproliferative Profiles and Protein Interactions for a Series of Iridium(I) N-Heterocyclic Carbene Complexes.

    PubMed

    Gothe, Yvonne; Marzo, Tiziano; Messori, Luigi; Metzler-Nolte, Nils

    2016-08-22

    A series of structurally related mono- and bis-NHC-iridium(I) (NHC: N-heterocyclic carbene) complexes have been investigated for their suitability as potential anticancer drugs. Their spectral behaviour in aqueous buffers under physiological-like conditions and their cytotoxicity against the cancer cell lines MCF-7 and HT-29 are reported. Notably, almost all complexes exhibit significant cytotoxic effects towards both cancer cell lines. In general, the cationic bis-carbene complexes show higher stability and greater anticancer activity than their neutral mono-carbene analogues with IC50 values in the high nanomolar range. Furthermore, to gain initial mechanistic insight, the interactions of these iridium(I)-NHC complexes with two model proteins, namely lysozyme and cytochrome c, were explored by HR-ESI-MS analyses. The different protein metalation patterns of the complexes can be roughly classified into two distinct groups. Those interactions give us a first idea about the possible mechanism of action of this class of compounds. Overall, our findings show that iridium(I)-NHC complexes represent very interesting candidates for further development as new metal-based anticancer drugs. PMID:27443984

  8. Oxidation State 10 Exists.

    PubMed

    Yu, Haoyu S; Truhlar, Donald G

    2016-07-25

    In a recent paper, Wang et al. found an iridium-containing compound with a formal oxidation state of 9. This is the highest oxidation state ever found in a stable compound. To learn if this is the highest chemical oxidation state possible, Kohn-Sham density functional theory was used to study various compounds, including PdO4 (2+) , PtO4 (2+) , PtO3 F2 (2+) , PtO4 OH(+) , PtO5 , and PtO4 SH(+) , in which the metal has an oxidation state of 10. It was found that PtO4 (2+) has a metastable state that is kinetically stable with a barrier height for decomposition of 31 kcal mol(-1) and a calculated lifetime of 0.9 years. All other compounds studied would readily decompose to lower oxidation states.

  9. Anion effects to deliver enhanced iridium catalysts for hydrogen isotope exchange processes.

    PubMed

    Kennedy, Alan R; Kerr, William J; Moir, Rory; Reid, Marc

    2014-10-28

    Synthesis of a series of iridium(I) complexes of the type [(COD)Ir(IMes)(PPh3)]X (X = BF4, OTf, and BArF) has been established. Application of these species in mild hydrogen isotope exchange processes revealed more efficient catalysis and, further, a wider solvent scope when employing larger, more weakly coordinating counterions. PMID:25208265

  10. The growth of graphite phase on an iridium field electron emitter

    NASA Astrophysics Data System (ADS)

    Bernatskii, D. P.; Pavlov, V. G.

    2016-06-01

    The growth of graphite on the surface of an iridium tip in pyrolysis of benzene to give a ribbed crystal has been found by the methods of field electron and desorption microscopy. The formation of a graphite crystal results in the electric field factor increasing. The adsorption of alkali metals on the surface of graphite is accompanied by the intercalation effect.

  11. Catalytic cleavage of ether C-O bonds by pincer iridium complexes.

    PubMed

    Haibach, Michael C; Lease, Nicholas; Goldman, Alan S

    2014-09-15

    The development of efficient catalytic methods to cleave the relatively unreactive C-O bonds of ethers remains an important challenge in catalysis. Building on our group's recent work, we report the dehydroaryloxylation of aryl alkyl ethers using pincer iridium catalysts. This method represents a rare fully atom-economical method for ether C-O bond cleavage. PMID:25060043

  12. Single orientation graphene synthesized on iridium thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Dangwal Pandey, A.; Krausert, K.; Franz, D.; Grânäs, E.; Shayduk, R.; Müller, P.; Keller, T. F.; Noei, H.; Vonk, V.; Stierle, A.

    2016-08-01

    Heteroepitaxial iridium thin films were deposited on (0001) sapphire substrates by means of molecular beam epitaxy, and subsequently, one monolayer of graphene was synthesized by chemical vapor deposition. The influence of the growth parameters on the quality of the Ir films, as well as of graphene, was investigated systematically by means of low energy electron diffraction, x-ray reflectivity, x-ray diffraction, Auger electron spectroscopy, scanning electron microscopy, and atomic force microscopy. Our study reveals (111) oriented iridium films with high crystalline quality and extremely low surface roughness, on which the formation of large-area epitaxial graphene is achieved. The presence of defects, like dislocations, twins, and 30° rotated domains in the iridium films is also discussed. The coverage of graphene was found to be influenced by the presence of 30° rotated domains in the Ir films. Low iridium deposition rates suppress these rotated domains and an almost complete coverage of graphene was obtained. This synthesis route yields inexpensive, air-stable, and large-area graphene with a well-defined orientation, making it accessible to a wider community of researchers for numerous experiments or applications, including those which use destructive analysis techniques or irreversible processes. Moreover, this approach can be used to tune the structural quality of graphene, allowing a systematic study of the influence of defects in various processes like intercalation below graphene.

  13. Potential contributions to space geodesy from the IridiumNEXT constellation

    NASA Astrophysics Data System (ADS)

    Gunter, B. C.; Encarnação, J.; Ditmar, P.; Klees, R.

    2012-12-01

    The IridiumNEXT constellation will soon replace the existing Iridium satellite telecommunication network, with initial launches set to start in 2015. In addition to the primary task of providing global telecommunication services, each IridiumNEXT satellite will also carry a hosted payload that will provide both private and public institutions the opportunity to place an instrument suite on one or all of constellation's satellites. This creates the possibility to gather continuous, global observations of Earth over the entire 15 year projected mission lifetime. Access to such a platform creates the potential to investigate many of Earth's highly dynamic processes at a spatiotemporal resolution that is simply not possible from single-satellite missions. Space geodesy is one the numerous fields that would benefit from such a mission. Precise orbits of the IridiumNEXT satellites derived through an on-board GNSS receiver (plus accelerometers and star cameras) have the potential to observe the large-scale, high-frequency variations in Earth's gravity field at time scales as short as one day. Additional positioning data from ground-based laser ranging stations would help improve the orbit determination, in addition to providing the necessary link to improve estimates of geocenter motion and reference frames. In this presentation, we will analyze the expected geodetic science returns from such a mission and will discuss the instrumental requirements needed to achieve these objectives.

  14. Luminescent Iridium Complexes Used in Light-Emitting Electrochemical Cells (LEECs).

    PubMed

    Henwood, Adam F; Zysman-Colman, Eli

    2016-08-01

    Cationic iridium(III) complexes represent the single largest class of emitters used in light emitting electrochemical cells (LEECs). In this chapter, we highlight the state-of-the-art emitters in terms of efficiency and stability in LEEC devices, highlighting blue, green, yellow/orange, red and white devices, and provide an outlook to the future of LEECs. PMID:27573388

  15. A neutron activation analysis of iridium concentration in Yamato carbonaceous chondrite

    NASA Astrophysics Data System (ADS)

    Yabushita, S.; Wada, K.; Moriyama, H.; Takeuchi, K.

    1988-09-01

    Iridium concentration in extra-terrestrial bodies is an important quantity in relation to Ir-rich geological layers. Ir concentration of a Yamato carbonaceous chondrite (Y-793321) has been measured by a neutron activation method. The measurement yields a value (0.57±0.06) μg per gramme for the chondrite.

  16. Iridium complexes of new NCP pincer ligands: catalytic alkane dehydrogenation and alkene isomerization.

    PubMed

    Jia, Xiangqing; Zhang, Lei; Qin, Chuan; Leng, Xuebing; Huang, Zheng

    2014-09-28

    Iridium complexes of novel NCP pincer ligands containing pyridine and phosphinite arms have been synthesized. One Ir complex shows good catalytic activity for alkane dehydrogenation, and all complexes are highly active for olefin isomerization. A combination of the Ir complex and a (PNN)Fe pincer complex catalyzes the formation of linear alkylboronates selectively from internal olefins via sequential olefin isomerization-hydroboration.

  17. Arctic Ocean Communications: Performance Of High-Data Transmission Over The Iridium System

    NASA Astrophysics Data System (ADS)

    Wilkinson, J.; Valcic, L.; Doble, M. J.; Maksym, T. L.; Robst, J.

    2014-12-01

    The Iridium satellite communications service was launched over 15 years ago, and it is presently the "go to" service for transmitting data and voice from the polar regions. However there is very little information available regarding the metrics associated with the throughput of data via this system. During a recent campaign we released over 30 "dial-up" iridium enabled drifting buoys in a relatively small region of the Arctic Ocean. Over the past 6 months relatively large amounts of data have now been routinely downloaded (every hour) from these systems. Each platform, as well as the base station in the UK, independently monitored the throughput of data and here we present an analysis of the metrics (download speed, drop outs, power consumption etc.) associated with the transmission of data through the Iridium system. As the role of autonomous platforms in the polar region increases there is a greater need to better understand the issues associated with data transfer. Iridium is a vital component of any autonomous system and therefore the information presented here will be of value to the technological, scientific and engineering communities.

  18. Report of Iridium/{sup 238}PuO{sub 2} Compatibility Test

    SciTech Connect

    Taylor, D.H.

    2001-08-09

    This study indicates that the chemical purity of the fuel used presently to fabricate fueled clad vent sets will not present any special problems to the performance of the fueled clad vent sets as intended. However, cation impurities in the fuel can have a deleterious effect on the iridium cladding and vents and should be minimized as much as practical.

  19. Template and catalytic effects of DNA in the construction of polypyrrole/DNA composite macro and microelectrodes.

    PubMed

    Tosar, Juan Pablo; Holmes, Joanne L; Collyer, Stuart D; Davis, Frank; Laíz, Justo; Higson, Séamus P J

    2013-03-15

    Electrochemical DNA hybridization-based sensors show great promise as portable and automated analytical devices for routine screening of pathogenic or foreign nucleic acid sequences in biological samples. However, current sensor technologies still exhibit some unresolved issues which hampers their direct application into everyday life. Conducting polymers, such as polypyrrole (PPy), are increasingly being adopted as suitable platforms for DNA probe immobilization and signal transduction. Immobilization of DNA probes during pyrrole electropolymerization is a simple and efficient strategy to build composite electrodes suitable for DNA sensing. However, the effects of the probe state and sequence on PPy growth kinetics have not been studied yet. Here, we show that growth of PPy is drastically affected by the presence of guanine in the DNA probes and whether DNA is present in its single-stranded or double-stranded form. We show that some immobilization protocols may provoke irreversible oxidation of guanine moieties in the probe and that this issue deserves careful investigation as it may interfere with hybridization processes. We have also explored new procedures to build microelectrode arrays bearing immobilized DNA molecules, which are known to show beneficial properties in stirred samples. Overall, we present new techniques and concerns regarding the development of DNA-containing PPy-based composite electrodes, which may be taken into consideration for increasing genosensor reproducibility, response and performance.

  20. In Situ Identification and Stratification of Monochloramine Inhibition Effects on Nitrifying Biofilms as Determined by the Use of Microelectrodes

    EPA Science Inventory

    The nitrifying biofilm grown in an annular biofilm reactor and the microbial deactivation achieved after monochloramine treatment were investigated using microelectrodes. The nitrifying biofilm ammonium microprofile was measured and the effect of monochloramine on nitrifying bio...

  1. High temperature reactive ion etching of iridium thin films with aluminum mask in CF4/O2/Ar plasma

    NASA Astrophysics Data System (ADS)

    Yeh, Chia-Pin; Lisker, Marco; Kalkofen, Bodo; Burte, Edmund P.

    2016-08-01

    Reactive ion etching (RIE) technology for iridium with CF4/O2/Ar gas mixtures and aluminum mask at high temperatures up to 350 °C was developed. The influence of various process parameters such as gas mixing ratio and substrate temperature on the etch rate was studied in order to find optimal process conditions. The surface of the samples after etching was found to be clean under SEM inspection. It was also shown that the etch rate of iridium could be enhanced at higher process temperature and, at the same time, very high etching selectivity between aluminum etching mask and iridium could be achieved.

  2. Iridium and Spherules in Late Eocene Impact Deposits

    NASA Technical Reports Server (NTRS)

    Kyte, F. T.; Liu, S.

    2002-01-01

    We have been independently examining the Ir (FTK) and spherule (SL) contents of recently discovered late Eocene impact deposits from the south Atlantic and western Indian oceans. These include ODP Sites 1090 [14,15], 709 [lo], and 699 [Liu in prep.]. Iridium abundances at these sites are within the typical range reported for late Eocene deposits, with peak concentrations between 100 and 1000 pg/g. In Table 1 we present estimated net Ir fluences (in ng Ir/cm ) for these and nine other sites. Although there are fewer sites than the K/T boundary, the average of 9 ng Ir/cm2 is probably a good estimate of the late Eocene global flux. This is enough Ir for a 6 km comet (assuming 250 ng/g Ir, p=1.5), is sufficient to produce the Popigai or Chesapeake Bay structures, and is 16% of the flux estimated for the K/T boundary (55 ng/cm2 [ 161). Figure 1 shows the relative abundances of Ir, glassy microtektites and cpx-bearing spherules in sediments from Sites 699 and 1090, which are separated by only 3100 km. Although these two sites have similar Ir anomalies, the abundances of spherules are quite different. Site 1090 has well-defined peaks for both types of spherules, with a peak of 562 cpx spheruledg, while Site 699 contains only a few glassy microtektites and no cpx spherules. While the different abundances of spherules may reflect a heterogeneous distribution of spherules on the Earth s surface, an equally likely cause of this difference may be differential preservation of spherules in the sediment. recovered are only a trace residue of the initial impact deposit. Earlier work found 0.22 ng/g Ir in glassy microtektites from Site 689 [17], an insufficient concentration to support 0.16 ng/g in the bulk sediment at this site. We measured 15 ng/g Ir in a group of 95 cpx spherules from Site 1090 with sizes from 63 to -200 pm, a set typical of the size distribution at this site. Although this is a significant concentration it also cannot support the Ir peak. We presently lack

  3. Production of Oxygen from Lunar Regolith using Molten Oxide Electrolysis

    NASA Technical Reports Server (NTRS)

    Sibille, Laurent; Sadoway, Donald R.; Sirk, Aislinn; Tripathy, Prabhat; Melendez, Orlando; Standish, Evan; Dominquez, Jesus A.; Stefanescu, Doru M.; Curreri, Peter A.; Poizeau, Sophie

    2009-01-01

    This slide presentation reviews the possible use of molten oxide electrolysis to extract oxygen from the Lunar Regolith. The presentation asserts that molten regolith electrolysis has advanced to be a useful method for production of oxygen and metals in situ on the Moon. The work has demonstrated an 8 hour batch of electrolysis at 5 amps using Iridium inert anodes.

  4. The Fabrication of PDMS mould for Microelectrode Array Biochip using NIL

    NASA Astrophysics Data System (ADS)

    Beh, Khi Khim; Samsuri, Fahmi; Lee, Tze Pin; Mohamed, Khairudin

    2016-02-01

    In recent years, low-cost micro and nano fabrication process have gain intention from the manufacturing industry. Biochip is a platform of miniaturized microarrays arranged on a solid substrate that allows various biological tests to achieve immediate results. The development of biochip has established a new platform in biomedical industry. However, to fulfill the demands and availability in the market with affordable cost requires high volume manufacturing techniques for the fabrication of the biochips. In this article we will discuss the fabrication of PDMS mould for replicating microelectrode array of biochip. The fabrication of the microelectrodes utilizes the Nanoimprint lithography (NIL) technique. Finally, the fabrication of PDMS mould has been demonstrated successfully for using Nanoimprint lithography (NIL) technique and achieved 13% of size difference in overall.

  5. Microelectrode mapping of modality-specific somatic sensory cerebral neocortex in slow loris.

    PubMed

    Krishnamurti, A; Sanides, F; Welker, W I

    1976-01-01

    Microelectrode mapping methods and strategies were developed to map fine details of the somatotopic organization of somatic sensory cortex (SI) in slow loris. In-depth, multiple-unit recording, and threshold natural stimulation of skin and hari revealed three modality-specific cortical areas. The centrally located one was activated by extremely light touch and the somatopic organization of peripheral projections to it was mapped in detail. As many as 25 punctures/mm2 were made in delineating these details. The microelectrode mapping method used revealed smaller receptive fields, lesser degrees of overlap, a more differentiated pattern of peripheral projections, and a more precise correlation of electrophysiological results with underlying cytoarchitectonic details than did the usual macroelectrode surface recording method. These results and the correlations found between different physiologically defined areas and cortical sulci are discussed as they pertain to methodological advances in studies of cerebral localization of function.

  6. Carbon-fiber microelectrodes modified with 4-sulfobenzene have increased sensitivity and selectivity for catecholamines

    PubMed Central

    Hermans, Andre; Seipel, Andrew T.; Miller, Charles E.; Wightman, R. Mark

    2008-01-01

    Elliptical and cylindrical geometries of carbon-fiber microelectrodes were modified by covalent attachment of 4-sulfobenzenediazonium tetrafluoroborate following its electroreduction. Elliptical electrodes fabricated from Thornel P-55 carbon fibers show the highest amount of 4-sulfobenzene attached to the electrode. Fast-scan cyclic voltammetry was used to compare the response to dopamine and other neurochemicals at these modified carbon-fiber microelectrodes. The grafted layer causes an increased sensitivity to dopamine and other positively charged analytes that is due to increased adsorption of analyte in the grafted layer. However, this layer remains permeable to negatively charged compounds. Modified electrodes retain the increased sensitivity for dopamine during measurements in mouse brain tissue. PMID:16489775

  7. Rigid spine reinforced polymer microelectrode array probe and method of fabrication

    DOEpatents

    Tabada, Phillipe; Pannu, Satinderpall S

    2014-05-27

    A rigid spine-reinforced microelectrode array probe and fabrication method. The probe includes a flexible elongated probe body with conductive lines enclosed within a polymeric material. The conductive lines connect microelectrodes found near an insertion end of the probe to respective leads at a connector end of the probe. The probe also includes a rigid spine, such as made from titanium, fixedly attached to the probe body to structurally reinforce the probe body and enable the typically flexible probe body to penetrate and be inserted into tissue, such as neural tissue. By attaching or otherwise fabricating the rigid spine to connect to only an insertion section of the probe body, an integrally connected cable section of the probe body may remain flexible.

  8. Diamond microelectrodes for in vitro electroanalytical measurements: current status and remaining challenges.

    PubMed

    Park, Jinwoo; Quaiserová-Mocko, Veronika; Patel, Bhavik Anil; Novotný, Martin; Liu, Aihua; Bian, Xiaochun; Galligan, James J; Swain, Greg M

    2008-01-01

    An emerging research field in electrochemistry today is the preparation, characterization and application of diamond microelectrodes for electroanalytical measurements in biological media. Interest in this new electrode material stems from its outstanding properties: (i) hardness, (ii) low, stable and pH-independent background current, (iii) morphological and microstructural stability over a wide range of potentials, (iv) good electrochemical responsiveness for multiple redox analytes without any conventional pre-treatment and (v) weak molecular adsorption of polar molecules that leads to a high level of resistance to response deactivation and electrode fouling. Diamond electrodes have advanced in recent years from being simply a scientific curiosity into a viable material for electroanalysis. In this article, we highlight the current state of progress by our laboratory and others on the preparation, study of the basic electrochemical properties, and application of this new type of microelectrode for in vitro electroanalytical measurements, and discuss some of the remaining challenges.

  9. The effect of site placement within silicon microelectrodes on the long-term electrophysiological recordings.

    PubMed

    Lee, Heui Chang; Gaire, Janak; McDowell, Sean P; Otto, Kevin J

    2014-01-01

    Intracortical microelectrodes can be used to treat various neurological disorders given their capabilities to interface with single or multiple populations of neurons. However, most of these penetrating devices have been reported to fail over time, within weeks to months, putatively due to the foreign body response (FBR) which persistently aggravates the surrounding brain tissues. A number of studies have confirmed that various electrode properties, such as size, shape, and surface area, may play a role in the biological responses to the microelectrode. Further experimental data is needed to determine the effect of these properties on the FBR and the recording performance. In this paper, we evaluate the effect of site placement using Michigan arrays with sites on the center, edge, and tip of the shank. The results show that there is significant performance variance between the center, edge, and tip sites.

  10. Enhanced electroanalysis in lithium potassium eutectic (LKE) using microfabricated square microelectrodes.

    PubMed

    Corrigan, Damion K; Blair, Ewen O; Terry, Jonathan G; Walton, Anthony J; Mount, Andrew R

    2014-11-18

    Molten salts (MSs) are an attractive medium for chemical and electrochemical processing and as a result there is demand for MS-compatible analysis technologies. However, MSs containing redox species present a challenging environment in which to perform analytical measurements because of their corrosive nature, significant thermal convection and the high temperatures involved. This paper outlines the fabrication and characterization of microfabricated square microelectrodes (MSMs) designed for electrochemical analysis in MS systems. Their design enables precise control over electrode dimension, the minimization of stress because of differential thermal expansion through design for high temperature operation, and the minimization of corrosive attack through effective insulation. The exemplar MS system used for characterization was lithium chloride/potassium chloride eutectic (LKE), which has potential applications in pyrochemical nuclear fuel reprocessing, metal refining, molten salt batteries and electric power cells. The observed responses for a range of redox ions between 400 and 500 °C (673 and 773 K) were quantitative and typical of microelectrodes. MSMs also showed the reduced iR drop, steady-state diffusion-limited response, and reduced sensitivity to convection seen for microelectrodes under ambient conditions and expected for these electrodes in comparison to macroelectrodes. Diffusion coefficients were obtained in close agreement with literature values, more readily and at greater precision and accuracy than both macroelectrode and previous microelectrode measurements. The feasibility of extracting individual physical parameters from mixtures of redox species (as required in reprocessing) and of the prolonged measurement required for online monitoring was also demonstrated. Together, this demonstrates that MSMs provide enhanced electrode devices widely applicable to the characterization of redox species in a range of MS systems.

  11. Enhanced electroanalysis in lithium potassium eutectic (LKE) using microfabricated square microelectrodes.

    PubMed

    Corrigan, Damion K; Blair, Ewen O; Terry, Jonathan G; Walton, Anthony J; Mount, Andrew R

    2014-11-18

    Molten salts (MSs) are an attractive medium for chemical and electrochemical processing and as a result there is demand for MS-compatible analysis technologies. However, MSs containing redox species present a challenging environment in which to perform analytical measurements because of their corrosive nature, significant thermal convection and the high temperatures involved. This paper outlines the fabrication and characterization of microfabricated square microelectrodes (MSMs) designed for electrochemical analysis in MS systems. Their design enables precise control over electrode dimension, the minimization of stress because of differential thermal expansion through design for high temperature operation, and the minimization of corrosive attack through effective insulation. The exemplar MS system used for characterization was lithium chloride/potassium chloride eutectic (LKE), which has potential applications in pyrochemical nuclear fuel reprocessing, metal refining, molten salt batteries and electric power cells. The observed responses for a range of redox ions between 400 and 500 °C (673 and 773 K) were quantitative and typical of microelectrodes. MSMs also showed the reduced iR drop, steady-state diffusion-limited response, and reduced sensitivity to convection seen for microelectrodes under ambient conditions and expected for these electrodes in comparison to macroelectrodes. Diffusion coefficients were obtained in close agreement with literature values, more readily and at greater precision and accuracy than both macroelectrode and previous microelectrode measurements. The feasibility of extracting individual physical parameters from mixtures of redox species (as required in reprocessing) and of the prolonged measurement required for online monitoring was also demonstrated. Together, this demonstrates that MSMs provide enhanced electrode devices widely applicable to the characterization of redox species in a range of MS systems. PMID:25284431

  12. Neural stimulation and recording with bidirectional, soft carbon nanotube fiber microelectrodes.

    PubMed

    Vitale, Flavia; Summerson, Samantha R; Aazhang, Behnaam; Kemere, Caleb; Pasquali, Matteo

    2015-01-01

    The development of microelectrodes capable of safely stimulating and recording neural activity is a critical step in the design of many prosthetic devices, brain-machine interfaces, and therapies for neurologic or nervous-system-mediated disorders. Metal electrodes are inadequate prospects for the miniaturization needed to attain neuronal-scale stimulation and recording because of their poor electrochemical properties, high stiffness, and propensity to fail due to bending fatigue. Here we demonstrate neural recording and stimulation using carbon nanotube (CNT) fiber electrodes. In vitro characterization shows that the tissue contact impedance of CNT fibers is remarkably lower than that of state-of-the-art metal electrodes, making them suitable for recording single-neuron activity without additional surface treatments. In vivo chronic studies in parkinsonian rodents show that CNT fiber microelectrodes stimulate neurons as effectively as metal electrodes with 10 times larger surface area, while eliciting a significantly reduced inflammatory response. The same CNT fiber microelectrodes can record neural activity for weeks, paving the way for the development of novel multifunctional and dynamic neural interfaces with long-term stability. PMID:25803728

  13. Neural stimulation and recording with bidirectional, soft carbon nanotube fiber microelectrodes.

    PubMed

    Vitale, Flavia; Summerson, Samantha R; Aazhang, Behnaam; Kemere, Caleb; Pasquali, Matteo

    2015-01-01

    The development of microelectrodes capable of safely stimulating and recording neural activity is a critical step in the design of many prosthetic devices, brain-machine interfaces, and therapies for neurologic or nervous-system-mediated disorders. Metal electrodes are inadequate prospects for the miniaturization needed to attain neuronal-scale stimulation and recording because of their poor electrochemical properties, high stiffness, and propensity to fail due to bending fatigue. Here we demonstrate neural recording and stimulation using carbon nanotube (CNT) fiber electrodes. In vitro characterization shows that the tissue contact impedance of CNT fibers is remarkably lower than that of state-of-the-art metal electrodes, making them suitable for recording single-neuron activity without additional surface treatments. In vivo chronic studies in parkinsonian rodents show that CNT fiber microelectrodes stimulate neurons as effectively as metal electrodes with 10 times larger surface area, while eliciting a significantly reduced inflammatory response. The same CNT fiber microelectrodes can record neural activity for weeks, paving the way for the development of novel multifunctional and dynamic neural interfaces with long-term stability.

  14. How far can we go? Quantum-chemical investigations of oxidation state +IX.

    PubMed

    Himmel, Daniel; Knapp, Carsten; Patzschke, Michael; Riedel, Sebastian

    2010-03-15

    The highest known oxidation state of any element is +VIII. After the recent discovery of Ir(VIII)O(4) under cryogenic conditions, we have investigated the stability of cationic species [MO(4)](+) (M=Rh,Ir,Mt). Such compounds would formally represent the new oxidation state +IX, which is experimentally unknown so far for the whole periodic table. [IrO(4)](+) is predicted to be the most promising candidate. The calculated spin-orbit (SO) coupling shows only minor effects on the stability of the iridium species, whereas SO-coupling increases enormously for the corresponding Eka-Iridium (Meitnerium) complexes and destabilizes these.

  15. How far can we go? Quantum-chemical investigations of oxidation state +IX.

    PubMed

    Himmel, Daniel; Knapp, Carsten; Patzschke, Michael; Riedel, Sebastian

    2010-03-15

    The highest known oxidation state of any element is +VIII. After the recent discovery of Ir(VIII)O(4) under cryogenic conditions, we have investigated the stability of cationic species [MO(4)](+) (M=Rh,Ir,Mt). Such compounds would formally represent the new oxidation state +IX, which is experimentally unknown so far for the whole periodic table. [IrO(4)](+) is predicted to be the most promising candidate. The calculated spin-orbit (SO) coupling shows only minor effects on the stability of the iridium species, whereas SO-coupling increases enormously for the corresponding Eka-Iridium (Meitnerium) complexes and destabilizes these. PMID:20127784

  16. Contrasting Anticancer Activity of Half-Sandwich Iridium(III) Complexes Bearing Functionally Diverse 2-Phenylpyridine Ligands

    PubMed Central

    2015-01-01

    We report the synthesis, characterization, and antiproliferative activity of 15 iridium(III) half-sandwich complexes of the type [(η5-Cp*)Ir(2-(R′-phenyl)-R-pyridine)Cl] bearing either an electron-donating (−OH, −CH2OH, −CH3) or electron-withdrawing (−F, −CHO, −NO2) group at various positions on the 2-phenylpyridine (2-PhPy) chelating ligand giving rise to six sets of structural isomers. The X-ray crystal structures of [(η5-Cp*)Ir(2-(2′-fluorophenyl)pyridine)Cl] (1) and [(η5-Cp*)Ir(2-(4′-fluorophenyl)pyridine)Cl] (2) exhibit the expected “piano-stool” configuration. DFT calculations showed that substituents caused only localized effects on the electrostatic potential surface of the chelating 2-PhPy ligand of the complexes. Hydrolysis of all complexes is rapid, but readily reversed by addition of NaCl. The complexes show preferential binding to 9-ethylguanine over 9-methyladenine and are active catalysts for the oxidation of NADH to NAD+. Antiproliferative activity experiments in A2780 ovarian, MCF-7 breast, A549 lung, and HCT116 colon cancer cell lines showed IC50 values ranging from 1 to 89 μM, with the most potent complex, [(η5-Cp*)Ir(2-(2′-methylphenyl)pyridine)Cl] (13) (A2780 IC50 = 1.18 μM), being 10× more active than the parent, [(η5-Cp*)Ir(2-phenylpyridine)Cl], and 2× more active than [(η5-CpxPh)Ir(2-phenylpyridine)Cl]. Intriguingly, contrasting biological activities are observed between structural isomers despite exhibiting similar chemical reactivity. For pairs of structural isomers both the nature and position of the functional group can affect the hydrophobicity of the complex. An increase in hydrophobicity resulted in enhanced cellular-iridium accumulation in A2780 ovarian cells, which generally gave rise to an increase in potency. The structural isomers [(η5-Cp*)Ir(2-(4′-fluorophenyl)pyridine)Cl] (2) and [(η5-Cp*)Ir(2-phenyl-5-fluoropyridine)Cl] (4) preferentially localized in the cytosol > membrane and particulate

  17. Manipulating the Excited States of Cyclometalated Iridium Complexes with β-Ketoiminate and β-Diketiminate Ligands.

    PubMed

    Radwan, Yousf K; Maity, Ayan; Teets, Thomas S

    2015-07-20

    A series of cyclometalated iridium complexes with β-ketoiminate and β-diketiminate ligands are described. Two different cyclometalating (C^N) ligands-2-phenylpridine (ppy) and 2-phenylbenzothiazole (bt)-are used in concert with three different ancillary (LX) ligands-a phenyl-substituted β-ketoiminate (acNac(Me)), a phenyl-substituted β-diketiminate (NacNac(Me)), and a fluorinated version of the β-diketiminate (NacNac(CF3))-to furnish a suite of six complexes. The complexes are prepared by metathesis reactions of chloro-bridged dimers [Ir(C^N)2(μ-Cl)]2 with potassium or lithium salts of the ancillary LX ligand. Four of the complexes are characterized by X-ray crystallography, and all six were subjected to in-depth optical and electrochemical interrogation. Cyclic voltammetry shows both reduction and oxidation waves, with the latter strongly dependent on the identity of the LX ligand. The complexes are all luminescent, with the nature of the emissive excited state and the quantum yield (Φ) dependent on the identity of both the C^N and LX ligands. Whereas the complexes Ir(ppy)2(NacNac(Me)) and Ir(ppy)2(acNac(Me)) are weakly luminescent (Φ ≈ 0.01), the complexes Ir(bt)2(NacNac(Me)) and Ir(bt)2(acNac(Me)) are strongly luminescent, with the latter's quantum efficiency (Φ = 0.82) among the highest ever observed for cyclometalated iridium complexes. Fluorination of the NacNac ligand gives rise to completely disparate emission behavior suggestive of a NacNac-centered emissive state. The results described here, in comparison with previous groups' studies on acetylacetonate (acac) analogues, suggest that the weaker-field NacNac and acNac ligands raise the energy of the metal-centered HOMO, with energy of the HOMO increasing in the order NacNac(CF3) < acNac(Me) < NacNac(Me). PMID:26158354

  18. Synthesis, characterization and chemistry of platinum and iridium nanoparticles in solution and nanoporous silicas

    NASA Astrophysics Data System (ADS)

    Jagassar, Parbatee Samaroo

    This project focuses on the synthesis of catalytically-active, transition-metal nanoparticles, their adsorption into porous Vycor glass (PVG), the removal of the poly(vinylpyrrolidone) (PVP) surfactant employed in their synthesis and their chemistry with Ru(II) diimine complexes. Platinum and iridium nanoparticles with a narrow size distribution were prepared by the alcohol reduction method with poly(vinylpyrrolidone) (PVP) as the size limiting surfactant. PVP/Pt nanoparticles adsorb into PVG and as much as 46 ± 4% of the PVP can be removed without further nanoparticle aggregation. XANES spectra show that removal of the PVP surfactant occurs without oxidation of the Pt nanoparticle. EXAFS of the adsorbed Pt nanoparticles after removal of the PVP yield a Pt-Pt bond length of 2.74 ± 0.01 Å which is slightly shorter than the Pt-Pt bond length measured in Pt foil, 2.78 Å. We have shown that the Pt nanoparticles, both the stripped and the unstripped of PVP in porous Vycor glass, does not influence their reactivity with either the [Ru(bpy)2 dpp]2+ or the [Ru(bpy)2ppz]2+ complexes. The addition of PVP/Pt or PVP/Ir nanoparticles to aqueous-ethanol solutions of [Ru(bpy)2ppz]2+ (ppz denotes 4,7-phenanthro-lino-5:6,5'6'pyrazine) leads to the spontaneous aggregation of the nanoparticles about the complex. A comparison of the aggregation about different Ru(II) diimines indicates aggregation initiates at the heteroleptic ligand. Although initiating at the ppz ligand, continued aggregation of the nanoparticles about the complex dilutes the specificity of the initial interaction leading to larger aggregates of differing shape. TEM analyses of the aggregates indicate the volume occupied by the individual nanoparticles is a small fraction of the total volume of the aggregate suggesting a somewhat open structure interlaced with the solvent. Correlating TEM analyses of the aggregation with the electronic spectra of the solutions reveals a new absorption assigned to the formation

  19. The treatment of malignant diseases in Romania using stainless steel encapsulated iridium-192 sources

    NASA Astrophysics Data System (ADS)

    Stanef, I.; Matache, G.; Ciocǎltei, V.; Gheorghiev, G.

    1994-01-01

    Iridium-192 sources supplied by the Institute for Nuclear Physics and Engineering have been used in Romanian radiotherapy clinics since 1980. The source assembly is sealed in a protective stainless steel sheath which satisfies the requirements of international standards. Since this sheath acts as a filter to change the characteristic spectrum it has been necessary to determine experimentally an accurate value of the specific gamma-ray constant. Some clinical aspects of the complex treatment of carcinomas with iridium-192 are reviewed. Results of the calculation of the dose distribution around single and multiple sources are given for different applications in the treatment of carcinomas of the vaginal and uterine cervix, oral cavity, rectum and vagina.

  20. Iridium-bearing sublimates at a hot-spot volcano (Piton de la Fournaise, Indian Ocean)

    SciTech Connect

    Toutain, J.P. ); Meyer, G.

    1989-12-01

    Sublimates and incrustations derived upon the cooling of volcanic gases have been collected on various sites (Piton de la Fournaise, Poas, Momotombo, Etna, Ardoukoba and Erta-Ale). They have been analyzed for Ir and other volatile elements (Se, As, Cu, Au, Ag, Pb, Tl) by means of instrumental neutron activation analysis (INAA) and proton induced X-Ray emission (PIXE). Among the investigated volcanoes, only Piton de la Fournaise is found to release detectable amounts of iridium. Ir in Piton de la Fournaise sublimates is associated with F-minerals. This confirms its gaseous transport as a volatile fluoride compound. Iridium seems to be preferentialy released by hot-spot type volcanoes, and its detection in Piton de la Fournaise sublimates provides a positive argument in favor of a volcanic hypothesis to explain the KTB events.

  1. First Applications of DoD Iridium RUDICS in the NSF Polar Programs

    NASA Astrophysics Data System (ADS)

    Valentic, T.; Stehle, R.

    2008-12-01

    We will present the first deployment and application of the new Iridium RUDICS service to remote instrumentation projects within the National Science Foundation's polar programs. The rise of automated observing networks has increased the demand for real-time connectivity to remote instruments, not only for immediate access to data, but to also interrogate health and status. Communicating with field sites in the polar regions is complicated by the remoteness from existing infrastructure, low temperatures and limited connection options. Sites located above 78° latitude are not able to see geostationary satellites, leaving the Iridium constellation as the only one that provide a direct connection. Some others, such as Orbcomm, only provide a store-and-forward service. Iridium is often used as a dial up modem to establish a PPP connection to the Internet with data files transferred via FTP. On low-bandwidth, high-latency networks like Iridium (2400bps with ping times of seconds), this approach is time consuming and inefficient. The dial up time alone takes upwards of a minute, and standard TCP/IP and FTP protocols are hampered by the long latencies. Minimizing transmission time is important for reducing battery usage and connection costs. The new Iridium RUDICS service can be used for more efficient transfers. RUDICS is an acronym for "Router-based Unstructured Digital Inter-working Connectivity Solution" and provides a direct connection between an instrument in the field and a server on the Internet. After dialing into the Iridium gateway, a socket connection is opened to a registered port on a user's server. Bytes sent to or from the modem appear at the server's socket. The connection time is reduced to about 10 seconds because the modem training and PPP negotiation stages are eliminated. The remote device does not need to have a full TCP/IP stack, allowing smaller instruments such as data loggers to directly handle the data transmission. Alternative protocols can

  2. An inconvenient influence of iridium(III) isomer on OLED efficiency.

    PubMed

    Baranoff, Etienne; Bolink, Henk J; De Angelis, Filippo; Fantacci, Simona; Di Censo, Davide; Djellab, Karim; Grätzel, Michael; Nazeeruddin, Md Khaja

    2010-10-14

    The recently reported heteroleptic cyclometallated iridium(III) complex [Ir(2-phenylpyridine)(2)(2-carboxy-4-dimethylaminopyridine)] N984 and its isomer N984b have been studied more in detail. While photo- and electrochemical properties are very similar, DFT/TDDFT calculations show that the two isomers have different HOMO orbital characteristics. As a consequence, solution processed OLEDs made using a mixture of N984 and isomer N984b similar to vacuum processed devices show that the isomer has a dramatic detrimental effect on the performances of the device. In addition, commonly used thermogravimetric analysis is not suitable for showing the isomerization process. The isomer could impact performances of vacuum processed OLEDs using heteroleptic cyclometallated iridium(III) complexes as dopant.

  3. Research of remote control for Chinese Antarctica Telescope based on iridium satellite communication

    NASA Astrophysics Data System (ADS)

    Xu, Lingzhe; Yang, Shihai

    2010-07-01

    Astronomers are ever dreaming of sites with best seeing on the Earth surface for celestial observation, and the Antarctica is one of a few such sites only left owing to the global air pollution. However, Antarctica region is largely unaccessible for human being due to lacking of fundamental living conditions, travel facilities and effective ways of communication. Worst of all, the popular internet source as a general way of communication scarcely exists there. Facing such a dilemma and as a solution remote control and data transmission for telescopes through iridium satellite communication has been put forward for the Chinese network Antarctic Schmidt Telescopes 3 (AST3), which is currently under all round research and development. This paper presents iridium satellite-based remote control application adapted to telescope control. The pioneer work in China involves hardware and software configuration utilizing techniques for reliable and secure communication, which is outlined in the paper too.

  4. The activity of platinum, iridium and rhodium drug complexes against Leishmania donovani.

    PubMed

    Croft, S L; Neal, R A; Craciunescu, D G; Certad-Fombona, G

    1992-03-01

    The activities of twenty seven Platinum, Rhodium and Iridium drug complexes were determined against Leishmania donovani amastigotes in mouse peritoneal macrophages in vitro. Eight compounds showed antileishmanial activity of which only three, Rh(III)-mepacrine, Ir(III) pyrrolidine dithiocarbamate and Ir(III) diethyl dithiocarbamate had ED50 values of less than 1 microM. The two Iridium complexes produced, respectively, a 50% and 39% suppression of L. donovani amastigotes in the liver of BALB/c mice following the subcutaneous administration of 200 mg/kg for 5 consecutive days. Ultrastructural studies suggest that the amastigote kinetoplast-mitochondrion complex is the primary site of action of the Ir and Rh complexes. PMID:1598504

  5. Rhodium(i), rhodium(iii) and iridium(iii) carbaporphyrins.

    PubMed

    Adiraju, Venkata A K; Ferrence, Gregory M; Lash, Timothy D

    2016-09-21

    Treatment of a benzocarbaporphyrin with [Rh(CO)2Cl]2 in refluxing dichloromethane gave a rhodium(i) dicarbonyl complex, and further reaction in refluxing pyridine afforded an organometallic rhodium(iii) derivative. The carbaporphyrin also reacted with [Ir(COD)Cl]2 and pyridine in refluxing p-xylene to generate a related iridium(iii) compound. These novel metalated porphyrinoids retained strongly diatropic characteristics and were fully characterized by XRD. PMID:27529466

  6. Iridium complexes of new NCP pincer ligands: catalytic alkane dehydrogenation and alkene isomerization.

    PubMed

    Jia, Xiangqing; Zhang, Lei; Qin, Chuan; Leng, Xuebing; Huang, Zheng

    2014-09-28

    Iridium complexes of novel NCP pincer ligands containing pyridine and phosphinite arms have been synthesized. One Ir complex shows good catalytic activity for alkane dehydrogenation, and all complexes are highly active for olefin isomerization. A combination of the Ir complex and a (PNN)Fe pincer complex catalyzes the formation of linear alkylboronates selectively from internal olefins via sequential olefin isomerization-hydroboration. PMID:25101950

  7. Solvent free selective dehydrogenation of indolic and carbazolic molecules with an iridium pincer catalyst.

    PubMed

    Brayton, Daniel F; Jensen, Craig M

    2014-06-01

    A previously known iridium POCOP pincer catalyst was found to selectively dehydrogenate the heterocyclic portion of several indolic and carbazolic molecules. These molecules were found to have an "activity window" (172-178 °C) upon which only the heterocyclic ring underwent dehydrogenation. All reactions were run solvent free, yields for selected substrates were excellent, and the products were isolated by either distillation or alumina plug filtration. PMID:24763968

  8. Selective Aromatic C–H Hydroxylation Enabled by η6-Coordination to Iridium(III)

    PubMed Central

    D'Amato, Erica M.; Neumann, Constanze N.; Ritter, Tobias

    2016-01-01

    We report an aromatic C–H hydroxylation protocol in which the arene is activated through η6-coordination to an iridium(III) complex. η6-Coordination of the arene increases its electrophilicity and allows for high positional selectivity of hydroxylation at the site of least electron density. Through investigation of intermediate η5-cyclohexadienyl adducts and arene exchange reactions, we evaluate incorporation of arene π-activation into a catalytic cycle for C–H functionalization. PMID:26877574

  9. Branch-Selective Alkene Hydroarylation by Cooperative Destabilization: Iridium-Catalyzed ortho-Alkylation of Acetanilides.

    PubMed

    Crisenza, Giacomo E M; Sokolova, Olga O; Bower, John F

    2015-12-01

    An iridium(I) catalyst system, modified with the wide-bite-angle and electron-deficient bisphosphine d(F) ppb (1,4-bis(di(pentafluorophenyl)phosphino)butane) promotes highly branch-selective hydroarylation reactions between diverse acetanilides and aryl- or alkyl-substituted alkenes. This provides direct and ortho-selective access to synthetically challenging anilines, and addresses long-standing issues associated with related Friedel-Crafts alkylations. PMID:26490739

  10. An iridium abundance anomaly at the palynological cretaceous-tertiary boundary in northern new Mexico.

    PubMed

    Orth, C J; Gilmore, J S; Knight, J D; Pillmore, C L; Tschudy, R H; Fassett, J E

    1981-12-18

    An iridium abundance anomaly, with concentrations up to 5000 parts per trillion over a background level of 4 to 20 parts per trillion, has been located in sedimentary rocks laid down under freshwater swamp conditions in the Raton Basin of northeastern New Mexico. The anomaly occurs at the base of a coal bed, at the same stratigraphic position at which several well-known species of Cretaceous-age pollen became extinct.

  11. Branch-Selective Alkene Hydroarylation by Cooperative Destabilization: Iridium-Catalyzed ortho-Alkylation of Acetanilides

    PubMed Central

    Crisenza, Giacomo E M; Sokolova, Olga O; Bower, John F

    2015-01-01

    An iridium(I) catalyst system, modified with the wide-bite-angle and electron-deficient bisphosphine dFppb (1,4-bis(di(pentafluorophenyl)phosphino)butane) promotes highly branch-selective hydroarylation reactions between diverse acetanilides and aryl- or alkyl-substituted alkenes. This provides direct and ortho-selective access to synthetically challenging anilines, and addresses long-standing issues associated with related Friedel–Crafts alkylations. PMID:26490739

  12. An improved method for constructing and selectively silanizing double-barreled, neutral liquid-carrier, ion-selective microelectrodes

    PubMed Central

    Deveau, Jason S.T.; Grodzinski, Bernard

    2005-01-01

    We describe an improved, efficient and reliable method for the vapour-phase silanization of multi-barreled, ion-selective microelectrodes of which the silanized barrel(s) are to be filled with neutral liquid ion-exchanger (LIX). The technique employs a metal manifold to exclusively and simultaneously deliver dimethyldichlorosilane to only the ion-selective barrels of several multi-barreled microelectrodes. Compared to previously published methods the technique requires fewer procedural steps, less handling of individual microelectrodes, improved reproducibility of silanization of the selected microelectrode barrels and employs standard borosilicate tubing rather than the less-conventional theta-type glass. The electrodes remain stable for up to 3 weeks after the silanization procedure. The efficacy of a double-barreled electrode containing a proton ionophore in the ion-selective barrel is demonstrated in situ in the leaf apoplasm of pea (Pisum) and sunflower (Helianthus). Individual leaves were penetrated to depth of ~150 μm through the abaxial surface. Microelectrode readings remained stable after multiple impalements without the need for a stabilizing PVC matrix. PMID:16136222

  13. Determination of Sediment Oxygen Demand in the Ziya River Watershed, China: Based on Laboratory Core Incubation and Microelectrode Measurements

    PubMed Central

    Rong, Nan; Shan, Baoqing; Wang, Chao

    2016-01-01

    A study coupling sedimentcore incubation and microelectrode measurementwas performed to explore the sediment oxygen demand (SOD) at 16 stations in the Ziya River Watershed, a severely polluted and anoxic river system in the north of China. Total oxygen flux values in the range 0.19–1.41 g/(m2·d) with an average of 0.62 g/(m2·d) were obtained by core incubations, and diffusive oxygen flux values in the range 0.15–1.38 g/(m2·d) with an average of 0.51 g/(m2·d) were determined by microelectrodes. Total oxygen flux obviously correlated with diffusive oxygen flux (R2 = 0.842). The microelectrode method produced smaller results than the incubation method in 15 of 16 sites, and the diffusive oxygen flux was smaller than the total oxygen flux. Although the two sets of SOD values had significant difference accepted by the two methods via the Wilcoxon signed-rank test (p < 0.05), the microelectrode method was shown to produce results that were similar to those from the core incubation method. The microelectrode method, therefore, could be used as an alternative method for traditional core incubation method, or as a method to verify SOD rates measured by other methods. We consider that high potential sediment oxygen demand would occur in the Ziya River Watershed when the dissolved oxygen (DO) recovered in the overlying water. PMID:26907307

  14. Determination of Sediment Oxygen Demand in the Ziya River Watershed, China: Based on Laboratory Core Incubation and Microelectrode Measurements.

    PubMed

    Rong, Nan; Shan, Baoqing; Wang, Chao

    2016-02-19

    A study coupling sedimentcore incubation and microelectrode measurement was performed to explore the sediment oxygen demand (SOD) at 16 stations in the Ziya River Watershed, a severely polluted and anoxic river system in the north of China. Total oxygen flux values in the range 0.19-1.41 g/(m²·d) with an average of 0.62 g/(m²·d) were obtained by core incubations, and diffusive oxygen flux values in the range 0.15-1.38 g/(m²·d) with an average of 0.51 g/(m²·d) were determined by microelectrodes. Total oxygen flux obviously correlated with diffusive oxygen flux (R² = 0.842). The microelectrode method produced smaller results than the incubation method in 15 of 16 sites, and the diffusive oxygen flux was smaller than the total oxygen flux. Although the two sets of SOD values had significant difference accepted by the two methods via the Wilcoxon signed-rank test (p < 0.05), the microelectrode method was shown to produce results that were similar to those from the core incubation method. The microelectrode method, therefore, could be used as an alternative method for traditional core incubation method, or as a method to verify SOD rates measured by other methods. We consider that high potential sediment oxygen demand would occur in the Ziya River Watershed when the dissolved oxygen (DO) recovered in the overlying water.

  15. Single cell and neural process experimentation using laterally applied electrical fields between pairs of closely apposed microelectrodes with vertical sidewalls.

    PubMed

    Chang, Wesley C; Sretavan, David W

    2009-08-15

    As biomedical research has moved increasingly towards experimentation on single cells and subcellular structures, there has been a need for microscale devices that can perform manipulation and stimulation at a correspondingly small scale. We propose a microelectrode array (MEA) featuring thickened microelectrodes with vertical sidewalls (VSW) to focus electrical fields horizontally on targets positioned in between paired electrodes. These microelectrodes were fabricated using gold electroplating that was molded by photolithographically patterned SU-8 photoresist. Finite element modeling showed that paired VSW electrodes produce more uniform electrical fields compared to conventional planar microelectrodes. Using paired microelectrodes, 3 microm thick and spaced 10 microm apart, we were able to perform local electroporation of individual axonal processes, as demonstrated by entry of EGTA to locally chelate intra-axonal calcium, quenching the fluorescence of a pre-loaded calcium indicator dye. The same electrode configuration was used to electroporate individual cells, resulting in the targeted transfection of a transgene expressing a cytoplasmically soluble green fluorescent protein (GFP). In addition to electroporation, our electrode configuration was also capable of precisely targeted field stimulation on individual neurons, resulting in action potentials that could be tracked by optical means. With its ability to deliver well-characterized electrical fields and its versatility, our configuration of paired VSW electrodes may provide the basis for a new tool for high-throughput and high-content experimentation in broad areas of neuroscience and biomedical research.

  16. Neutron activation determination of iridium, gold, platinum, and silver in geologic samples

    USGS Publications Warehouse

    Millard, H.T.

    1987-01-01

    Low-level methods for the determination of iridium and other noble metals have become increasingly important in recent years due to interest in locating abundance anomalies associated with the Cretaceous and Tertiary (K-T) boundary. Typical iridium anomalies are in the range of 1 to 100 ??g/kg (ppb). Thus methods with detection limits near 0.1 ??g/kg should be adequate to detect K-T boundary anomalies. Radiochemical neutron activation analysis methods continue to be required although instrumental neutron activation analysis techniques employing elaborate gamma-counters are under development. In the procedure developed in this study samples irradiated in the epithermal neutron facility of the U. S. Geological Survey TRIGA Reactor (Denver, Colorado) are treated with a mini-fire assay technique. The iridium, gold, and silver are collected in a 1-gram metallic lead button. Primary contaminants at this stage are arsenic and antimony. These can be removed by heating the button with a mixture of sodium perioxide and sodium hydroxide. The resulting 0.2-gram lead bead is counted in a Compton suppression spectrometer. Carrier yields are determined by reirradiation of the lead beads. This procedure has been applied to the U.S.G.S. Standard Rock PCC-1 and samples from K-T boundary sites in the Western Interior of North America. ?? 1987 Akade??miai Kiado??.

  17. The kinetics and mechanism of the organo-iridium catalysed racemisation of amines.

    PubMed

    Stirling, Matthew J; Mwansa, Joseph M; Sweeney, Gemma; Blacker, A John; Page, Michael I

    2016-08-01

    The dimeric iodo-iridium complex [IrCp*I2]2 (Cp* = pentamethylcyclopentadiene) is an efficient catalyst for the racemisation of secondary and tertiary amines at ambient and higher temperatures with a low catalyst loading. The racemisation occurs with pseudo-first-order kinetics and the corresponding four rate constants were obtained by monitoring the time dependence of the concentrations of the (R) and (S) enantiomers starting with either pure (R) or (S) and show a first-order dependence on catalyst concentration. Low temperature (1)H NMR data is consistent with the formation of a 1 : 1 complex with the amine coordinated to the iridium and with both iodide anions still bound to the metal-ion, but at the higher temperatures used for kinetic studies binding is weak and so no saturation zero-order kinetics are observed. A cross-over experiment with isotopically labelled amines demonstrates the intermediate formation of an imine which can dissociate from the iridium complex. Replacing the iodides in the catalyst by other ligands or having an amide substituent in Cp* results in a much less effective catalysts for the racemisation of amines. The rate constants for a deuterated amine yield a significant primary kinetic isotope effect kH/kD = 3.24 indicating that hydride transfer is involved in the rate-limiting step.

  18. Formic acid dehydrogenation with bioinspired iridium complexes: a kinetic isotope effect study and mechanistic insight.

    PubMed

    Wang, Wan-Hui; Xu, Shaoan; Manaka, Yuichi; Suna, Yuki; Kambayashi, Hide; Muckerman, James T; Fujita, Etsuko; Himeda, Yuichiro

    2014-07-01

    Highly efficient hydrogen generation from dehydrogenation of formic acid is achieved by using bioinspired iridium complexes that have hydroxyl groups at the ortho positions of the bipyridine or bipyrimidine ligand (i.e., OH in the second coordination sphere of the metal center). In particular, [Ir(Cp*)(TH4BPM)(H2 O)]SO4 (TH4BPM: 2,2',6,6'-tetrahydroxyl-4,4'-bipyrimidine; Cp*: pentamethylcyclopentadienyl) has a high turnover frequency of 39 500 h(-1) at 80 °C in a 1 M aqueous solution of HCO2 H/HCO2 Na and produces hydrogen and carbon dioxide without carbon monoxide contamination. The deuterium kinetic isotope effect study clearly indicates a different rate-determining step for complexes with hydroxyl groups at different positions of the ligands. The rate-limiting step is β-hydrogen elimination from the iridium-formate intermediate for complexes with hydroxyl groups at ortho positions, owing to a proton relay (i.e., pendent-base effect), which lowers the energy barrier of hydrogen generation. In contrast, the reaction of iridium hydride with a proton to liberate hydrogen is demonstrated to be the rate-determining step for complexes that do not have hydroxyl groups at the ortho positions.

  19. Consumable arc-melting, extruding, and rolling process for iridium sheet

    SciTech Connect

    Heestand, R.L.; Copeland, G.L.; Martin, M.M.

    1986-06-01

    An iridium alloy has been used as cladding for the /sup 238/PuO/sub 2/ fuel in radioisotope thermoelectric generators (RTGs) for recent interplanetary spacecraft such as Voyagers 1 and 2 and will be used for the Galileo and Ulysses spacecraft. The iridium alloy sheet for the fuel cladding used on these missions was fabricated by hot and cold rolling of arc-melted and drop-cast 0.5-kg ingots. Upon completion of production for these spacecraft, an opportunity was taken to conduct process improvement studies that would increase processing batch sizes, develop a more uniform product, decrease rejections due to internal delaminations and surface defects, and reduce costs. The studies to scale up and improve the fabrication process are described. In the new process, iridium is electron beam melted, alloyed by arc melting, and then consumable arc melted to form a cylindrical ingot of approximately 7 kg for extrusion. The ingot is extruded to sheet bar and hot and cold rooled into sheet. Sheet evaluated from the first two ingots showed 100% acceptance with no defects on inspection. An improved uniformity of microstructure was obtained, and chemistry was controlled within specification limits.

  20. Ultrasonic detection of laminar-type defects in iridium alloy blanks

    SciTech Connect

    Cook, K.V.; Cunningham, R.A. Jr.; Simpson, W.A. Jr.; McClung, R.W.

    1986-07-01

    Encapsulated isotopic heat sources for use in generating electrical power for space applications require flight-quality hardware material. Iridium is the chosen material for such applications, and Oak Ridge National Laboratory has been the prime supplier of iridium alloy forming blanks 52 mm in diameter by 0.66 mm thick (1.0 by 0.026 in.). Prior to the work reported here, these blanks were ultrasonically examined by using 0.9-mm-diam (0.035-in.) simulated flaw standards. However, as a result of this effort, the sensitivity of our ultrasonic pulse-echo test system has been increased. The improved ultrasonic test system permits blank inspection at the 0.5-mm-diam (0.020-in.) simulated flaw detection level. This test system was successfully demonstrated on the initial blanks provided via an improved processing route (consumable arc-melting, extruding, and rolling). The equipment modification and/or selection and the specific focused search unit immersion technique developed to provide this capability are described. The improved flaw detection capability also provides data maps of a common type of defect in iridium (delaminations).

  1. Electrocatalytic Microelectrode Detectors for Choline and Acetylcholine following Separation by Capillary Electrophoresis

    PubMed Central

    Mukherjee, Jhindan; Kirchhoff, Jon R.

    2009-01-01

    Two electrocatalytic enzyme modified microelectrode systems were employed as end-column amperometric detectors of choline (Ch) and acetylcholine (ACh) following separation by capillary electrophoresis (CE). Horseradish peroxidase crosslinked in an Os based redox polymer hydrogel (HRP-Os) was physically adsorbed on Au microelectrodes followed by chemical crosslinking of the enzymes acetylcholinesterase (AChE) and choline oxidase (ChO). An alternative approach utilized the deposition of the transition metal catalyst, Prussian Blue (PB), on Pt microelectrodes as the electrocatalyst. Utilizing butyrylcholine (BuCh) as an internal standard, the HRP-Os/AChE-ChO and PB/AChE-ChO electrodes exhibited excellent linear responses from 2–2000 μM and 10–2000 μM, respectively, for both Ch and ACh. Detection limits of 0.1 μM or 38 amol were determined for the HRP-Os/AChE-ChO electrode. The limit of detection for ACh and Ch at the PB/AChE-ChO electrode was 5 μM or 9.5 fmol. The electrodes were operated at potentials of +0.10 and −0.10 V vs. Ag/AgCl (3M NaCl), respectively, and thus minimized the potential response from oxidizable interferences. In addition, both electrocatalytic electrodes showed good operational stability for more than 70 hours. The enhanced detection capability of the HRP-Os/AChE-ChO and PB/AChE-ChO electrodes in combination with efficient CE separation of Ch and ACh provides a new sensitive and selective strategy for monitoring and quantifying these cholinergic biomarkers in biological fluids. PMID:20337384

  2. BioMEA: a versatile high-density 3D microelectrode array system using integrated electronics.

    PubMed

    Charvet, Guillaume; Rousseau, Lionel; Billoint, Olivier; Gharbi, Sadok; Rostaing, Jean-Pierre; Joucla, Sébastien; Trevisiol, Michel; Bourgerette, Alain; Chauvet, Philippe; Moulin, Céline; Goy, François; Mercier, Bruno; Colin, Mikael; Spirkovitch, Serge; Fanet, Hervé; Meyrand, Pierre; Guillemaud, Régis; Yvert, Blaise

    2010-04-15

    Microelectrode arrays (MEAs) offer a powerful tool to both record activity and deliver electrical microstimulations to neural networks either in vitro or in vivo. Microelectronics microfabrication technologies now allow building high-density MEAs containing several hundreds of microelectrodes. However, dense arrays of 3D micro-needle electrodes, providing closer contact with the neural tissue than planar electrodes, are not achievable using conventional isotropic etching processes. Moreover, increasing the number of electrodes using conventional electronics is difficult to achieve into compact devices addressing all channels independently for simultaneous recording and stimulation. Here, we present a full modular and versatile 256-channel MEA system based on integrated electronics. First, transparent high-density arrays of 3D-shaped microelectrodes were realized by deep reactive ion etching techniques of a silicon substrate reported on glass. This approach allowed achieving high electrode aspect ratios, and different shapes of tip electrodes. Next, we developed a dedicated analog 64-channel Application Specific Integrated Circuit (ASIC) including one amplification stage and one current generator per channel, and analog output multiplexing. A full modular system, called BIOMEA, has been designed, allowing connecting different types of MEAs (64, 128, or 256 electrodes) to different numbers of ASICs for simultaneous recording and/or stimulation on all channels. Finally, this system has been validated experimentally by recording and electrically eliciting low-amplitude spontaneous rhythmic activity (both LFPs and spikes) in the developing mouse CNS. The availability of high-density MEA systems with integrated electronics will offer new possibilities for both in vitro and in vivo studies of large neural networks.

  3. Massively-parallel neuromonitoring and neurostimulation rodent headset with nanotextured flexible microelectrodes.

    PubMed

    Bagheri, Arezu; Gabran, S R I; Salam, Muhammad Tariqus; Perez Velazquez, Jose Luis; Mansour, Raafat R; Salama, M M A; Genov, Roman

    2013-10-01

    We present a compact wireless headset for simultaneous multi-site neuromonitoring and neurostimulation in the rodent brain. The system comprises flexible-shaft microelectrodes, neural amplifiers, neurostimulators, a digital time-division multiplexer (TDM), a micro-controller and a ZigBee wireless transceiver. The system is built by parallelizing up to four 0.35 μm CMOS integrated circuits (each having 256 neural amplifiers and 64 neurostimulators) to provide a total maximum of 1024 neural amplifiers and 256 neurostimulators. Each bipolar neural amplifier features 54 dB-72 dB adjustable gain, 1 Hz-5 kHz adjustable bandwidth with an input-referred noise of 7.99 μVrms and dissipates 12.9 μW. Each current-mode bipolar neurostimulator generates programmable arbitrary-waveform biphasic current in the range of 20-250 μA and dissipates 2.6 μW in the stand-by mode. Reconfigurability is provided by stacking a set of dedicated mini-PCBs that share a common signaling bus within as small as 22 × 30 × 15 mm³ volume. The system features flexible polyimide-based microelectrode array design that is not brittle and increases pad packing density. Pad nanotexturing by electrodeposition reduces the electrode-tissue interface impedance from an average of 2 MΩ to 30 kΩ at 100 Hz. The rodent headset and the microelectrode array have been experimentally validated in vivo in freely moving rats for two months. We demonstrate 92.8 percent seizure rate reduction by responsive neurostimulation in an acute epilepsy rat model.

  4. Chronic Tissue Response to Untethered Microelectrode Implants in the Rat Brain and Spinal Cord

    PubMed Central

    ERSEN, Ali; ELKABES, Stella; FREEDMAN, David S.; SAHIN, Mesut

    2015-01-01

    Objective Microelectrodes implanted in the central nervous system (CNS) often fail in long term implants due to the immunological tissue response caused by tethering forces of the connecting wires. In addition to the tethering effect, there is a mechanical stress that occurs at the device-tissue interface simply because the microelectrode is a rigid body floating in soft tissue and it cannot reshape itself to comply with changes in the surrounding tissue. In the current study we evaluated the scar tissue formation to tetherless devices with two significantly different geometries in the rat brain and spinal cord in order to investigate the effects of device geometry. Approach One of the implant geometries resembled the wireless, floating microstimulators that we are currently developing in our laboratory and the other was a (shank only) Michigan probe for comparison. Both electrodes were implanted into either the cervical spinal cord or the motor cortices, one on each side. Main Results The most pronounced astroglial and microglial reactions occurred within 20 μm from the device and decreased sharply at larger distances. Both cell types displayed the morphology of non-activated cells past the 100 μm perimeter. Even though the aspect ratios of the implants were different, the astroglial and microglial responses to both microelectrode types were very mild in the brain, stronger and yet limited in the spinal cord. Significance These observations confirm previous reports and further suggest that tethering may be responsible for most of the tissue response in chronic implants and that the electrode size has a smaller contribution with floating electrodes. The electrode size may be playing primarily an amplifying role to the tethering forces in the brain whereas the size itself may induce chronic response in the spinal cord where the movement of surrounding tissues is more significant. PMID:25605679

  5. Massively-parallel neuromonitoring and neurostimulation rodent headset with nanotextured flexible microelectrodes.

    PubMed

    Bagheri, Arezu; Gabran, S R I; Salam, Muhammad Tariqus; Perez Velazquez, Jose Luis; Mansour, Raafat R; Salama, M M A; Genov, Roman

    2013-10-01

    We present a compact wireless headset for simultaneous multi-site neuromonitoring and neurostimulation in the rodent brain. The system comprises flexible-shaft microelectrodes, neural amplifiers, neurostimulators, a digital time-division multiplexer (TDM), a micro-controller and a ZigBee wireless transceiver. The system is built by parallelizing up to four 0.35 μm CMOS integrated circuits (each having 256 neural amplifiers and 64 neurostimulators) to provide a total maximum of 1024 neural amplifiers and 256 neurostimulators. Each bipolar neural amplifier features 54 dB-72 dB adjustable gain, 1 Hz-5 kHz adjustable bandwidth with an input-referred noise of 7.99 μVrms and dissipates 12.9 μW. Each current-mode bipolar neurostimulator generates programmable arbitrary-waveform biphasic current in the range of 20-250 μA and dissipates 2.6 μW in the stand-by mode. Reconfigurability is provided by stacking a set of dedicated mini-PCBs that share a common signaling bus within as small as 22 × 30 × 15 mm³ volume. The system features flexible polyimide-based microelectrode array design that is not brittle and increases pad packing density. Pad nanotexturing by electrodeposition reduces the electrode-tissue interface impedance from an average of 2 MΩ to 30 kΩ at 100 Hz. The rodent headset and the microelectrode array have been experimentally validated in vivo in freely moving rats for two months. We demonstrate 92.8 percent seizure rate reduction by responsive neurostimulation in an acute epilepsy rat model. PMID:24144667

  6. Chronic tissue response to untethered microelectrode implants in the rat brain and spinal cord

    NASA Astrophysics Data System (ADS)

    Ersen, Ali; Elkabes, Stella; Freedman, David S.; Sahin, Mesut

    2015-02-01

    Objective. Microelectrodes implanted in the central nervous system (CNS) often fail in long term implants due to the immunological tissue response caused by tethering forces of the connecting wires. In addition to the tethering effect, there is a mechanical stress that occurs at the device-tissue interface simply because the microelectrode is a rigid body floating in soft tissue and it cannot reshape itself to comply with changes in the surrounding tissue. In the current study we evaluated the scar tissue formation to tetherless devices with two significantly different geometries in the rat brain and spinal cord in order to investigate the effects of device geometry. Approach. One of the implant geometries resembled the wireless, floating microstimulators that we are currently developing in our laboratory and the other was a (shank only) Michigan probe for comparison. Both electrodes were implanted into either the cervical spinal cord or the motor cortices, one on each side. Main results. The most pronounced astroglial and microglial reactions occurred within 20 μm from the device and decreased sharply at larger distances. Both cell types displayed the morphology of non-activated cells past the 100 μm perimeter. Even though the aspect ratios of the implants were different, the astroglial and microglial responses to both microelectrode types were very mild in the brain, stronger and yet limited in the spinal cord. Significance. These observations confirm previous reports and further suggest that tethering may be responsible for most of the tissue response in chronic implants and that the electrode size has a smaller contribution with floating electrodes. The electrode size may be playing primarily an amplifying role to the tethering forces in the brain whereas the size itself may induce chronic response in the spinal cord where the movement of surrounding tissues is more significant.

  7. A method for electrophysiological characterization of hamster retinal ganglion cells using a high-density CMOS microelectrode array

    PubMed Central

    Jones, Ian L.; Russell, Thomas L.; Farrow, Karl; Fiscella, Michele; Franke, Felix; Müller, Jan; Jäckel, David; Hierlemann, Andreas

    2015-01-01

    Knowledge of neuronal cell types in the mammalian retina is important for the understanding of human retinal disease and the advancement of sight-restoring technology, such as retinal prosthetic devices. A somewhat less utilized animal model for retinal research is the hamster, which has a visual system that is characterized by an area centralis and a wide visual field with a broad binocular component. The hamster retina is optimally suited for recording on the microelectrode array (MEA), because it intrinsically lies flat on the MEA surface and yields robust, large-amplitude signals. However, information in the literature about hamster retinal ganglion cell functional types is scarce. The goal of our work is to develop a method featuring a high-density (HD) complementary metal-oxide-semiconductor (CMOS) MEA technology along with a sequence of standardized visual stimuli in order to categorize ganglion cells in isolated Syrian Hamster (Mesocricetus auratus) retina. Since the HD-MEA is capable of recording at a higher spatial resolution than most MEA systems (17.5 μm electrode pitch), we were able to record from a large proportion of RGCs within a selected region. Secondly, we chose our stimuli so that they could be run during the experiment without intervention or computation steps. The visual stimulus set was designed to activate the receptive fields of most ganglion cells in parallel and to incorporate various visual features to which different cell types respond uniquely. Based on the ganglion cell responses, basic cell properties were determined: direction selectivity, speed tuning, width tuning, transience, and latency. These properties were clustered to identify ganglion cell types in the hamster retina. Ultimately, we recorded up to a cell density of 2780 cells/mm2 at 2 mm (42°) from the optic nerve head. Using five parameters extracted from the responses to visual stimuli, we obtained seven ganglion cell types. PMID:26528115

  8. Grain Growth Behavior, Tensile Impact Ductility, and Weldability of Cerium-Doped Iridium Alloys

    SciTech Connect

    McKamey, C.G.

    2002-05-28

    An iridium alloy doped with small amounts of cerium and thorium is being developed as a potential replacement for the iridium-based DOP-26 alloy (doped with thorium only) that is currently used by the National Aeronautics and Space Administration (NASA) for cladding and post-impact containment of the radioactive fuel in radioisotope thermoelectric generator (RTG) heat sources which provide electric power for interplanetary spacecraft. This report summarizes results of studies conducted to date under the Iridium Alloy Characterization and Development subtask of the Radioisotope Power System Materials Production and Technology Program to characterize the properties of the iridium-based alloy (designated as DOP-40) containing both cerium and thorium. Included within this report are data on grain growth of sheet material in vacuum and low-pressure oxygen environments, grain growth in vacuum of the clad vent set cup material, weldability, and the effect of grain size and test temperature on tensile properties. Where applicable, data for the DOP-26 alloy are included for comparison. Both grain size and grain-boundary cohesion affect the ductility of iridium alloys. In this study it was found that cerium and thorium, when added together, refine grain size more effectively than when thorium is added by itself (especially at high temperatures). In addition, the effect of cerium additions on grain-boundary cohesion is similar to that of thorium. Mechanical testing at both low ({approx} 10{sup -3}s{sup -1}) and high ({approx} 10{sup -3}s{sup -1}) strain rates showed that the Ce/Th-doped alloys have tensile ductilities that are as good or better than the DOP-26 alloy. The general conclusion from these studies is that cerium can be used to replace some of the radioactive thorium currently used in DOP-26 while maintaining or improving its metallurgical properties. The current DOP-26 alloy meets all requirements for cladding the radioactive fuel in the RTG heat source, but the

  9. Materials approaches for modulating neural tissue responses to implanted microelectrodes through mechanical and biochemical means

    PubMed Central

    Sommakia, Salah; Lee, Heui C.; Gaire, Janak; Otto, Kevin J.

    2014-01-01

    Implantable intracortical microelectrodes face an uphill struggle for widespread clinical use. Their potential for treating a wide range of traumatic and degenerative neural disease is hampered by their unreliability in chronic settings. A major factor in this decline in chronic performance is a reactive response of brain tissue, which aims to isolate the implanted device from the rest of the healthy tissue. In this review we present a discussion of materials approaches aimed at modulating the reactive tissue response through mechanical and biochemical means. Benefits and challenges associated with these approaches are analyzed, and the importance of multimodal solutions tested in emerging animal models are presented. PMID:25530703

  10. Fabrication and testing of microelectrodes for small-field cortical surface recordings.

    PubMed

    Kitzmiller, Joseph; Beversdorf, David; Hansford, Derek

    2006-03-01

    A microfabrication approach to produce a microelectrode array that is suitable for use with human patients has been developed. The device is comprised of materials that are consistent with those of clinically used macroelectrodes (platinum electrode contacts suspended within a biomedical grade polydimethylsiloxane, PDMS). Photolithography, metal deposition, wire bonding, and PDMS encapsulation were used to fabricate the device. Cytotoxicity testing with both mammalian and human cortical cells suggests that the device is suitable for use with human patients and implementation of the device in animal studies revealed that reliable evoked potentials could be acquired with the designed spatial resolution. PMID:16491335

  11. Estimation of the membrane potential of cultured macrophages from the fast potential transient upon microelectrode entry.

    PubMed

    Ince, C; Ypey, D L; Van Furth, R; Verveen, A A

    1983-03-01

    Analysis of membrane potential recordings upon microelectrode impalement of four types of macrophages (cell lines P388D1 and PU5-1.8, cultured mouse peritoneal macrophages, and cultured human monocytes) reveals that these cells have membrane potentials at least two times more negative than sustained potential values (E(s)) frequently reported. Upon microelectrode entry into the cell (P388D1), the recorded potential drops to a peak value (E(p)) (mean -37 mV for 50 cells, range -15 to -70 mV) within 2 ms, after which it decays to a depolarized potential (E(n)) (mean -12 mV) in about 20 ms. Thereafter, the membrane develops one or a series of slow hyperpolarizations before a final sustained membrane potential (E(s)) (mean -14 mV, range -5 to -40) is established. The mean value of the peak of the first hyperpolarization (E(h)) is -30 mV (range -10 to -55 mV). The initial fast peak transient, measured upon microelectrode entry, was first described and analyzed by Lassen et al. (Lassen, U.V., A.M. T. Nielson, L. Pape, and L. O. Simonsen, 1971, J. Membr. Biol. 6:269-288 for other change in the membrane potential from its real value before impalement to a sustained depolarized value. This was shown to be true for macrophages by two-electrode impalements of single cells. Values of E(p), E(n), E(h), E(s), and membrane resistance (R(m)) measured for the other macrophages were similar to those of P388D1. From these results we conclude that E(p) is a better estimate of the true membrane potential of macrophages than E(s), and that the slow hyperpolarizations upon impalement should be regarded as transient repolarizations back to the original membrane potentials. Thus, analysis of the initial fast impalement transient can be a valuable aid in the estimation of the membrane potential of various sorts of small isolated cells by microelectrodes.

  12. Structure-property relationships based on Hammett constants in cyclometalated iridium(III) complexes: their application to the design of a fluorine-free FIrPic-like emitter.

    PubMed

    Frey, Julien; Curchod, Basile F E; Scopelliti, Rosario; Tavernelli, Ivano; Rothlisberger, Ursula; Nazeeruddin, Mohammad K; Baranoff, Etienne

    2014-04-21

    While phosphorescent cyclometalated iridium(iii) complexes have been widely studied, only correlations between oxidation potential EOX and Hammett constant σ, and between the redox gap (ΔEREDOX = EOX-ERED) and emission or absorption wavelength (λabs, λem) have been reported. We present now a quantitative model based on Hammett parameters that rationalizes the effect of the substituents on the properties of cyclometalated iridium(iii) complexes. This simple model allows predicting the apparent redox potentials as well as the electrochemical gap of homoleptic complexes based on phenylpyridine ligands with good accuracy. In particular, the model accounts for the unequal effect of the substituents on both the HOMO and the LUMO energy levels. Consequently, the model is used to anticipate the emission maxima of the corresponding complexes with improved reliability. We demonstrate in a series of phenylpyridine emitters that electron-donating groups can effectively replace electron-withdrawing substituents on the orthometallated phenyl to induce a blue shift of the emission. This result is in contrast with the common approach that uses fluorine to blue shift the emission maximum. Finally, as a proof of concept, we used electron-donating substituents to design a new fluorine-free complex, referred to as EB343, matching the various properties, namely oxidation and reduction potentials, electrochemical gap and emission profile, of the standard sky-blue emitter FIrPic. PMID:24345847

  13. Negative thermal ion mass spectrometry of osmium, rhenium, and iridium

    NASA Technical Reports Server (NTRS)

    Creaser, R. A.; Papanastassiou, D. A.; Wasserburg, G. J.

    1991-01-01

    This paper describes a technique for obtaining, in a conventional surface ionization mass spectrometer, intense ion beams of negatively charged oxides of Os, Re, and Ir by thermal ionization. It is shown that the principal ion species of these ions are OsO3(-), ReO4(-), and IrO2(-), respectively. For Re-187/Os-187 studies, this technique offers the advantage of isotopic analyses without prior chemical separation of Re from Os.

  14. Visualization of Zn²⁺ ions in live zebrafish using a luminescent iridium(III) chemosensor.

    PubMed

    Ma, Dik-Lung; He, Hong-Zhang; Zhong, Hai-Jing; Lin, Sheng; Chan, Daniel Shiu-Hin; Wang, Liang; Lee, Simon Ming-Yuen; Leung, Chung-Hang; Wong, Chun-Yuen

    2014-08-27

    A novel luminescent cyclometalated iridium(III) complex-based chemosensor (1) bearing a zinc-specific receptor, tris(2-pyridylmethyl)amine, and the 3-phenyl-1H-pyrazole ligand has been designed and synthesized. Upon the addition of Zn(2+) ions to a solution of iridium(III) complex 1, a pronounced luminescence color change from blue to green can be observed, which may be attributed to the suppression of photoinduced electron transfer upon complexation of complex 1 with Zn(2+) ions. The interaction of iridium(III) complex 1 with Zn(2+) ions was investigated by UV-vis absorption titration, emission titration, and (1)H NMR titration. Furthermore, the iridium(III) complex 1 exhibited good selectivity for Zn(2+) over 13 other common metal ions, including K(+), Ag(+), Na(+), Ni(2+), Fe(3+), Hg(2+), Cd(2+), Mg(2+), Ca(2+), Cu(2+), Mn(2+), Co(2+), and Pb(2+) ions. The practical application of the iridium(III) complex 1 in visualizing intracellular Zn(2+) distribution in live zebrafish was also demonstrated.

  15. Iridium contents in the Late Cretaceous-Early Tertiary clays in relation to the K/T boundary, North Jordan

    NASA Astrophysics Data System (ADS)

    Abboud, Iyad Ahmed

    2016-06-01

    The mineralogy, lithology, and geochemistry of five discrete laminations across the K/T boundary of clayey shale at the Yarmouk River area, Jordan, were examined. There were no marked changes in the mineralogy of the clayey shale within the K/T boundary. This outcrop consists of more than 100 m of Maastrichtian oil shale overlying about 20 m limestone. Marly limestone included many clay laminations from organic and volcanic origins, which are considered an evidence of the K/T boundary through detected iridium anomalies. Any of these particular lamellae range from 2 mm to 5 mm in thickness. Smectite was the predominant clay mineral in smectitic shale laminations. It was located at eight meters above the K/T boundary and includes some anomalous concentrations of iridium and traces of other elements. The analysis of geochemical platinum group at the K/T boundary clays showed anomalous enrichments of iridium, compared with other carbonate rocks as a result of weathering processes of oil shale, or through concentration from weathering of basalt flows, but not pointing to an impact process. The clays in late Maastrichtian have Ir-Sc prevailed anomalies and synchronize with increasing of terrigenous and volcanogenic traced elements. Kaolin, smectite, and volkonskoite were the dominant clay minerals at the K/T boundary with high concentrations of iridium. The concentration levels of iridium in some laminations of the Yarmouk sediments ranged between 1.6 and 7.8 ppb.

  16. Formation and reactivity of a porphyrin iridium hydride in water: acid dissociation constants and equilibrium thermodynamics relevant to Ir-H, Ir-OH, and Ir-CH2- bond dissociation energetics.

    PubMed

    Bhagan, Salome; Wayland, Bradford B

    2011-11-01

    Aqueous solutions of group nine metal(III) (M = Co, Rh, Ir) complexes of tetra(3,5-disulfonatomesityl)porphyrin [(TMPS)M(III)] form an equilibrium distribution of aquo and hydroxo complexes ([(TMPS)M(III)(D(2)O)(2-n)(OD)(n)]((7+n)-)). Evaluation of acid dissociation constants for coordinated water show that the extent of proton dissociation from water increases regularly on moving down the group from cobalt to iridium, which is consistent with the expected order of increasing metal-ligand bond strengths. Aqueous (D(2)O) solutions of [(TMPS)Ir(III)(D(2)O)(2)](7-) react with dihydrogen to form an iridium hydride complex ([(TMPS)Ir-D(D(2)O)](8-)) with an acid dissociation constant of 1.8(0.5) × 10(-12) (298 K), which is much smaller than the Rh-D derivative (4.3 (0.4) × 10(-8)), reflecting a stronger Ir-D bond. The iridium hydride complex adds with ethene and acetaldehyde to form organometallic derivatives [(TMPS)Ir-CH(2)CH(2)D(D(2)O)](8-) and [(TMPS)Ir-CH(OD)CH(3)(D(2)O)](8-). Only a six-coordinate carbonyl complex [(TMPS)Ir-D(CO)](8-) is observed for reaction of the Ir-D with CO (P(CO) = 0.2-2.0 atm), which contrasts with the (TMPS)Rh-D analog which reacts with CO to produce an equilibrium with a rhodium formyl complex ([(TMPS)Rh-CDO(D(2)O)](8-)). Reactivity studies and equilibrium thermodynamic measurements were used to discuss the relative M-X bond energetics (M = Rh, Ir; X = H, OH, and CH(2)-) and the thermodynamically favorable oxidative addition of water with the (TMPS)Ir(II) derivatives.

  17. A Multi-Channel, Flex-Rigid ECoG Microelectrode Array for Visual Cortical Interfacing

    PubMed Central

    Tolstosheeva, Elena; Gordillo-González, Víctor; Biefeld, Volker; Kempen, Ludger; Mandon, Sunita; Kreiter, Andreas K.; Lang, Walter

    2015-01-01

    High-density electrocortical (ECoG) microelectrode arrays are promising signal-acquisition platforms for brain-computer interfaces envisioned, e.g., as high-performance communication solutions for paralyzed persons. We propose a multi-channel microelectrode array capable of recording ECoG field potentials with high spatial resolution. The proposed array is of a 150 mm2 total recording area; it has 124 circular electrodes (100, 300 and 500 μm in diameter) situated on the edges of concentric hexagons (min. 0.8 mm interdistance) and a skull-facing reference electrode (2.5 mm2 surface area). The array is processed as a free-standing device to enable monolithic integration of a rigid interposer, designed for soldering of fine-pitch SMD-connectors on a minimal assembly area. Electrochemical characterization revealed distinct impedance spectral bands for the 100, 300 and 500 μm-type electrodes, and for the array's own reference. Epidural recordings from the primary visual cortex (V1) of an awake Rhesus macaque showed natural electrophysiological signals and clear responses to standard visual stimulation. The ECoG electrodes of larger surface area recorded signals with greater spectral power in the gamma band, while the skull-facing reference electrode provided higher average gamma power spectral density (γPSD) than the common average referencing technique. PMID:25569757

  18. Stretchable Silver Nanowire-Elastomer Composite Microelectrodes with Tailored Electrical Properties.

    PubMed

    Martinez, Vincent; Stauffer, Flurin; Adagunodo, Mohammed O; Forro, Csaba; Vörös, Janos; Larmagnac, Alexandre

    2015-06-24

    We introduce a photolithography process compatible with soft and rigid substrates, enabling the fabrication of complex 3D interconnected patterns of silver nanowire (AgNW) networks embedded in polydimethylsiloxane (PDMS). Dimensions of the AgNW micropatterns are controlled within the film plane by photolithography, whereas thickness is controlled via a novel and uniform deposition technique using centrifugation. We report the first systematic characterization of the electromechanical properties of such microelectrodes with finest stretchable feature of 15 μm. We observe a geometry-dependent behavior of the gauge factor not only by changing the thickness of the microelectrodes, as it has been commonly reported so far, but also by varying their lateral dimensions. The presented nanocomposites exhibited sheet resistances down to 0.6 Ω/sq, gauge factors ranging from 0.01 to 100, and stretchability above 50% uniaxial strain. This versatile process allows for the production of highly sensitive strain sensors and robust high-density stretchable conductors on a wafer scale with direct implications in mass production of stretchable electronic devices.

  19. Real time measurement of cytoplasmic ions with ion-selective microelectrodes.

    PubMed

    Miller, Anthony J

    2013-01-01

    Ion-selective microelectrodes can be used to report intracellular ion concentrations. The ion-selective barrels of microelectrodes are filled with a sensor cocktail containing several different components including an ion-selective molecule, sensor or exchanger, a solvent or plasticizer, lipophilic cation/anion additives, and a matrix to solidify the membrane. For many ions, the readymade membrane cocktail can be purchased, but the individual chemical components can be bought from suppliers and mixing the cocktail saves money. For commercially available liquid membrane cocktails the membrane matrix is often not included. For plants a matrix is essential for intracellular impalements because without it cell turgor will displace the liquid membrane from the electrode tip, giving decreased or even lost sensitivity. The matrix frequently used is a high molecular weight poly(vinyl chloride). This addition increases the electrical resistance of the electrode, slowing the response time of the electrode. The use of multi-barreled electrodes enables the identification of the cellular compartment. For example, the inclusion of a pH-selective electrode enables the cytoplasm and vacuole to be distinguished.

  20. 3D-nanostructured boron-doped diamond for microelectrode array neural interfacing.

    PubMed

    Piret, Gaëlle; Hébert, Clément; Mazellier, Jean-Paul; Rousseau, Lionel; Scorsone, Emmanuel; Cottance, Myline; Lissorgues, Gaelle; Heuschkel, Marc O; Picaud, Serge; Bergonzo, Philippe; Yvert, Blaise

    2015-06-01

    The electrode material is a key element in the design of long-term neural implants and neuroprostheses. To date, the ideal electrode material offering high longevity, biocompatibility, low-noise recording and high stimulation capabilities remains to be found. We show that 3D-nanostructured boron doped diamond (BDD), an innovative material consisting in a chemically stable material with a high aspect ratio structure obtained by encapsulation of a carbon nanotube template within two BDD nanolayers, allows neural cell attachment, survival and neurite extension. Further, we developed arrays of 20-μm-diameter 3D-nanostructured BDD microelectrodes for neural interfacing. These microelectrodes exhibited low impedances and low intrinsic recording noise levels. In particular, they allowed the detection of low amplitude (10-20 μV) local-field potentials, single units and multiunit bursts neural activity in both acute whole embryonic hindbrain-spinal cord preparations and long-term hippocampal cell cultures. Also, cyclic voltammetry measurements showed a wide potential window of about 3 V and a charge storage capacity of 10 mC.cm(-2), showing high potentiality of this material for neural stimulation. These results demonstrate the attractiveness of 3D-nanostructured BDD as a novel material for neural interfacing, with potential applications for the design of biocompatible neural implants for the exploration and rehabilitation of the nervous system.

  1. Electrochemical Activation of Diamond Microelectrodes: Implications for the In Vitro Measurement of Serotonin in the Bowel

    PubMed Central

    Duran, Boris; Brocenschi, Ricardo F.; France, Marion; Galligan, James J.; Swain, Greg M.

    2014-01-01

    The electrochemical pretreatment of diamond microelectrodes was investigated for the purpose of learning how an anodic, cathodic or a combined anodic + cathodic polarization affects the charge-transfer kinetics for two surface-sensitive redox systems: ferri/ferrocyanide and serotonin (5-hydroxytryptamine, 5-HT). The pretreatments were performed in 0.5 mol L−1 H2SO4. The anodic pretreatment was performed galvanically for 30 s at 250 mA cm−2. The 10 cathodic pretreatment was performed for 180 s at −250 mA cm−2. The combined pretreatment involved application of the anodic step first followed by the cathodic step. The results clearly demonstrate that the best performance for both redox systems is obtained after the cathodic polarization, which presumably activates the electrode by cleaning the surface and removing site-blocking surface carbon-oxygen functionalities. The cathodic pretreatment was found to be effective at activating a fouled microelectrode in situ. This observation has important implication for the measurement of 5-HT in the bowel. PMID:24802953

  2. Hydrophilic modification of neural microelectrode arrays based on multi-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Chen, Chang-Hsiao; Su, Huan-Chieh; Chuang, Shih-Chang; Yen, Shiang-Jie; Chen, Yung-Chan; Lee, Yu-Tao; Chen, Hsin; Yew, Tri-Rung; Chang, Yen-Chung; Yeh, Shih-Rung; Yao, Da-Jeng

    2010-12-01

    To decrease the impedance of microelectrode arrays, for neuroscience applications we have fabricated and tested MEA based on multi-walled carbon nanotubes. With decreasing physical size of a microelectrode, its impedance increases and charge-transfer capability decreases. To decrease the impedance, the effective surface area of the electrode must generally be increased. We explored the effect of plasma treatment on the surface wettability of MWCNT. With a steam-plasma treatment the surface of MWCNT becomes converted from superhydrophobic to superhydrophilic; this hydrophilic property is attributed to -OH bonding on the surface of MWCNT. We reported the synthesis at 400 °C of MWCNT on nickel-titanium multilayered metal catalysts by thermal chemical vapor deposition. Applying plasma with a power less than 25 W for 10 s improved the electrochemical and biological properties, and circumvented the limitation of the surface reverting to a hydrophobic condition; a hydrophilic state is maintained for at least one month. The MEA was used to record neural signals of a lateral giant cell from an American crayfish. The response amplitude of the action potential was about 275 µV with 1 ms period; the recorded data had a ratio of signal to noise up to 40.12 dB. The improved performance of the electrode makes feasible the separation of neural signals and the recognition of their distinct shapes. With further development the rapid treatment will be useful for long-term recording applications.

  3. All-Diamond Microelectrodes as Solid State Probes for Localized Electrochemical Sensing.

    PubMed

    Silva, Eduardo L; Gouvêa, Cristol P; Quevedo, Marcela C; Neto, Miguel A; Archanjo, Braulio S; Fernandes, António J S; Achete, Carlos A; Silva, Rui F; Zheludkevich, Mikhail L; Oliveira, Filipe J

    2015-07-01

    The fabrication of an all-diamond microprobe is demonstrated for the first time. This ME (microelectrode) assembly consists of an inner boron doped diamond (BDD) layer and an outer undoped diamond layer. Both layers were grown on a sharp tungsten tip by chemical vapor deposition (CVD) in a stepwise manner within a single deposition run. BDD is a material with proven potential as an electrochemical sensor. Undoped CVD diamond is an insulating material with superior chemical stability in comparison to conventional insulators. Focused ion beam (FIB) cutting of the apex of the ME was used to expose an electroactive BDD disk. By cyclic voltammetry, the redox reaction of ferrocenemethanol was shown to take place at the BDD microdisk surface. In order to ensure that the outer layer was nonelectrically conductive, a diffusion barrier for boron atoms was established seeking the formation of boron-hydrogen complexes at the interface between the doped and the undoped diamond layers. The applicability of the microelectrodes in localized corrosion was demonstrated by scanning amperometric measurements of oxygen distribution above an Al-Cu-CFRP (Carbon Fiber Reinforced Polymer) galvanic corrosion cell.

  4. Microfabrication, characterization and in vivo MRI compatibility of diamond microelectrodes array for neural interfacing.

    PubMed

    Hébert, Clément; Warnking, Jan; Depaulis, Antoine; Garçon, Laurie Amandine; Mermoux, Michel; Eon, David; Mailley, Pascal; Omnès, Franck

    2015-01-01

    Neural interfacing still requires highly stable and biocompatible materials, in particular for in vivo applications. Indeed, most of the currently used materials are degraded and/or encapsulated by the proximal tissue leading to a loss of efficiency. Here, we considered boron doped diamond microelectrodes to address this issue and we evaluated the performances of a diamond microelectrode array. We described the microfabrication process of the device and discuss its functionalities. We characterized its electrochemical performances by cyclic voltammetry and impedance spectroscopy in saline buffer and observed the typical diamond electrode electrochemical properties, wide potential window and low background current, allowing efficient electrochemical detection. The charge storage capacitance and the modulus of the electrochemical impedance were found to remain in the same range as platinum electrodes used for standard commercial devices. Finally we observed a reduced Magnetic Resonance Imaging artifact when the device was implanted on a rat cortex, suggesting that boron doped-diamond is a very promising electrode material allowing functional imaging.

  5. A novel electroporation system for efficient molecular delivery into Chlamydomonas reinhardtii with a 3-dimensional microelectrode.

    PubMed

    Kang, Seongsu; Kim, Kwon-Ho; Kim, Yeu-Chun

    2015-01-01

    Electroporation is one of the most widely used transfection methods because of its high efficiency and convenience among the various transfection methods. Previous micro-electroporation systems have some drawbacks such as limitations in height and design, time-consuming and an expensive fabrication process due to technical constraints. This study fabricates a three dimensional microelectrode using the 3D printing technique. The interdigitated microstructure consisting of poly lactic acid was injected by a 3D printer and coated with silver and aluminum with a series of dip-coatings. With the same strength of electric field (V cm(-1)), a higher efficiency for molecular delivery and a higher cellular viability are achieved with the microelectrode than with a standard cuvette. In addition, this study investigates chemicophysical changes such as Joule heating and dissolved metal during electroporation and showed the micro-electroporation system had less chemicophysical changes. It was concluded that the proposed micro-electroporation system will contribute to genetic engineering as a promising delivery tool, and this combination of 3D printing and electroporation has many potential applications for diverse designs or systems. PMID:26522846

  6. Ultrasmall implantable composite microelectrodes with bioactive surfaces for chronic neural interfaces

    NASA Astrophysics Data System (ADS)

    Yoshida Kozai, Takashi D.; Langhals, Nicholas B.; Patel, Paras R.; Deng, Xiaopei; Zhang, Huanan; Smith, Karen L.; Lahann, Joerg; Kotov, Nicholas A.; Kipke, Daryl R.

    2012-12-01

    Implantable neural microelectrodes that can record extracellular biopotentials from small, targeted groups of neurons are critical for neuroscience research and emerging clinical applications including brain-controlled prosthetic devices. The crucial material-dependent problem is developing microelectrodes that record neural activity from the same neurons for years with high fidelity and reliability. Here, we report the development of an integrated composite electrode consisting of a carbon-fibre core, a poly(p-xylylene)-based thin-film coating that acts as a dielectric barrier and that is functionalized to control intrinsic biological processes, and a poly(thiophene)-based recording pad. The resulting implants are an order of magnitude smaller than traditional recording electrodes, and more mechanically compliant with brain tissue. They were found to elicit much reduced chronic reactive tissue responses and enabled single-neuron recording in acute and early chronic experiments in rats. This technology, taking advantage of new composites, makes possible highly selective and stealthy neural interface devices towards realizing long-lasting implants.

  7. A novel electroporation system for efficient molecular delivery into Chlamydomonas reinhardtii with a 3-dimensional microelectrode

    NASA Astrophysics Data System (ADS)

    Kang, Seongsu; Kim, Kwon-Ho; Kim, Yeu-Chun

    2015-11-01

    Electroporation is one of the most widely used transfection methods because of its high efficiency and convenience among the various transfection methods. Previous micro-electroporation systems have some drawbacks such as limitations in height and design, time-consuming and an expensive fabrication process due to technical constraints. This study fabricates a three dimensional microelectrode using the 3D printing technique. The interdigitated microstructure consisting of poly lactic acid was injected by a 3D printer and coated with silver and aluminum with a series of dip-coatings. With the same strength of electric field (V cm-1), a higher efficiency for molecular delivery and a higher cellular viability are achieved with the microelectrode than with a standard cuvette. In addition, this study investigates chemicophysical changes such as Joule heating and dissolved metal during electroporation and showed the micro-electroporation system had less chemicophysical changes. It was concluded that the proposed micro-electroporation system will contribute to genetic engineering as a promising delivery tool, and this combination of 3D printing and electroporation has many potential applications for diverse designs or systems.

  8. A novel electroporation system for efficient molecular delivery into Chlamydomonas reinhardtii with a 3-dimensional microelectrode.

    PubMed

    Kang, Seongsu; Kim, Kwon-Ho; Kim, Yeu-Chun

    2015-11-02

    Electroporation is one of the most widely used transfection methods because of its high efficiency and convenience among the various transfection methods. Previous micro-electroporation systems have some drawbacks such as limitations in height and design, time-consuming and an expensive fabrication process due to technical constraints. This study fabricates a three dimensional microelectrode using the 3D printing technique. The interdigitated microstructure consisting of poly lactic acid was injected by a 3D printer and coated with silver and aluminum with a series of dip-coatings. With the same strength of electric field (V cm(-1)), a higher efficiency for molecular delivery and a higher cellular viability are achieved with the microelectrode than with a standard cuvette. In addition, this study investigates chemicophysical changes such as Joule heating and dissolved metal during electroporation and showed the micro-electroporation system had less chemicophysical changes. It was concluded that the proposed micro-electroporation system will contribute to genetic engineering as a promising delivery tool, and this combination of 3D printing and electroporation has many potential applications for diverse designs or systems.

  9. 3D-nanostructured boron-doped diamond for microelectrode array neural interfacing.

    PubMed

    Piret, Gaëlle; Hébert, Clément; Mazellier, Jean-Paul; Rousseau, Lionel; Scorsone, Emmanuel; Cottance, Myline; Lissorgues, Gaelle; Heuschkel, Marc O; Picaud, Serge; Bergonzo, Philippe; Yvert, Blaise

    2015-06-01

    The electrode material is a key element in the design of long-term neural implants and neuroprostheses. To date, the ideal electrode material offering high longevity, biocompatibility, low-noise recording and high stimulation capabilities remains to be found. We show that 3D-nanostructured boron doped diamond (BDD), an innovative material consisting in a chemically stable material with a high aspect ratio structure obtained by encapsulation of a carbon nanotube template within two BDD nanolayers, allows neural cell attachment, survival and neurite extension. Further, we developed arrays of 20-μm-diameter 3D-nanostructured BDD microelectrodes for neural interfacing. These microelectrodes exhibited low impedances and low intrinsic recording noise levels. In particular, they allowed the detection of low amplitude (10-20 μV) local-field potentials, single units and multiunit bursts neural activity in both acute whole embryonic hindbrain-spinal cord preparations and long-term hippocampal cell cultures. Also, cyclic voltammetry measurements showed a wide potential window of about 3 V and a charge storage capacity of 10 mC.cm(-2), showing high potentiality of this material for neural stimulation. These results demonstrate the attractiveness of 3D-nanostructured BDD as a novel material for neural interfacing, with potential applications for the design of biocompatible neural implants for the exploration and rehabilitation of the nervous system. PMID:25890717

  10. Ultrasmall implantable composite microelectrodes with bioactive surfaces for chronic neural interfaces

    PubMed Central

    Kozai, Takashi D. Yoshida; Langhals, Nicholas B.; Patel, Paras R.; Deng, Xiaopei; Zhang, Huanan; Smith, Karen L.; Lahann, Joerg; Kotov, Nicholas A.; Kipke, Daryl R.

    2012-01-01

    Implantable neural microelectrodes that can record extracellular biopotentials from small, targeted groups of neurons are critical for neuroscience research and emerging clinical applications including brain-controlled prosthetic devices. The crucial material-dependent problem is developing microelectrodes that record neural activity from the same neurons for years with high fidelity and reliability. Here, we report the development of an integrated composite electrode consisting of a carbon-fibre core, a poly(p-xylylene)-based thin-film coating that acts as a dielectric barrier and that is functionalized to control intrinsic biological processes, and a poly(thiophene)-based recording pad. The resulting implants are an order of magnitude smaller than traditional recording electrodes, and more mechanically compliant with brain tissue. They were found to elicit much reduced chronic reactive tissue responses and enabled single-neuron recording in acute and early chronic experiments in rats. This technology, taking advantage of new composites, makes possible highly selective and stealthy neural interface devices towards realizing long-lasting implants. PMID:23142839

  11. A novel electroporation system for efficient molecular delivery into Chlamydomonas reinhardtii with a 3-dimensional microelectrode

    PubMed Central

    Kang, Seongsu; Kim, Kwon-Ho; Kim, Yeu-Chun

    2015-01-01

    Electroporation is one of the most widely used transfection methods because of its high efficiency and convenience among the various transfection methods. Previous micro-electroporation systems have some drawbacks such as limitations in height and design, time-consuming and an expensive fabrication process due to technical constraints. This study fabricates a three dimensional microelectrode using the 3D printing technique. The interdigitated microstructure consisting of poly lactic acid was injected by a 3D printer and coated with silver and aluminum with a series of dip-coatings. With the same strength of electric field (V cm−1), a higher efficiency for molecular delivery and a higher cellular viability are achieved with the microelectrode than with a standard cuvette. In addition, this study investigates chemicophysical changes such as Joule heating and dissolved metal during electroporation and showed the micro-electroporation system had less chemicophysical changes. It was concluded that the proposed micro-electroporation system will contribute to genetic engineering as a promising delivery tool, and this combination of 3D printing and electroporation has many potential applications for diverse designs or systems. PMID:26522846

  12. Ultrasmall implantable composite microelectrodes with bioactive surfaces for chronic neural interfaces.

    PubMed

    Kozai, Takashi D Yoshida; Langhals, Nicholas B; Patel, Paras R; Deng, Xiaopei; Zhang, Huanan; Smith, Karen L; Lahann, Joerg; Kotov, Nicholas A; Kipke, Daryl R

    2012-12-01

    Implantable neural microelectrodes that can record extracellular biopotentials from small, targeted groups of neurons are critical for neuroscience research and emerging clinical applications including brain-controlled prosthetic devices. The crucial material-dependent problem is developing microelectrodes that record neural activity from the same neurons for years with high fidelity and reliability. Here, we report the development of an integrated composite electrode consisting of a carbon-fibre core, a poly(p-xylylene)-based thin-film coating that acts as a dielectric barrier and that is functionalized to control intrinsic biological processes, and a poly(thiophene)-based recording pad. The resulting implants are an order of magnitude smaller than traditional recording electrodes, and more mechanically compliant with brain tissue. They were found to elicit much reduced chronic reactive tissue responses and enabled single-neuron recording in acute and early chronic experiments in rats. This technology, taking advantage of new composites, makes possible highly selective and stealthy neural interface devices towards realizing long-lasting implants. PMID:23142839

  13. Dual-side and three-dimensional microelectrode arrays fabricated from ultra-thin silicon substrates

    NASA Astrophysics Data System (ADS)

    Du, Jiangang; Roukes, Michael L.; Masmanidis, Sotiris C.

    2009-07-01

    A method for fabricating planar implantable microelectrode arrays was demonstrated using a process that relied on ultra-thin silicon substrates, which ranged in thickness from 25 to 50 µm. The challenge of handling these fragile materials was met via a temporary substrate support mechanism. In order to compensate for putative electrical shielding of extracellular neuronal fields, separately addressable electrode arrays were defined on each side of the silicon device. Deep reactive ion etching was employed to create sharp implantable shafts with lengths of up to 5 mm. The devices were flip-chip bonded onto printed circuit boards (PCBs) by means of an anisotropic conductive adhesive film. This scalable assembly technique enabled three-dimensional (3D) integration through formation of stacks of multiple silicon and PCB layers. Simulations and measurements of microelectrode noise appear to suggest that low impedance surfaces, which could be formed by electrodeposition of gold or other materials, are required to ensure an optimal signal-to-noise ratio as well a low level of interchannel crosstalk.

  14. Ultrasmall implantable composite microelectrodes with bioactive surfaces for chronic neural interfaces.

    PubMed

    Kozai, Takashi D Yoshida; Langhals, Nicholas B; Patel, Paras R; Deng, Xiaopei; Zhang, Huanan; Smith, Karen L; Lahann, Joerg; Kotov, Nicholas A; Kipke, Daryl R

    2012-12-01

    Implantable neural microelectrodes that can record extracellular biopotentials from small, targeted groups of neurons are critical for neuroscience research and emerging clinical applications including brain-controlled prosthetic devices. The crucial material-dependent problem is developing microelectrodes that record neural activity from the same neurons for years with high fidelity and reliability. Here, we report the development of an integrated composite electrode consisting of a carbon-fibre core, a poly(p-xylylene)-based thin-film coating that acts as a dielectric barrier and that is functionalized to control intrinsic biological processes, and a poly(thiophene)-based recording pad. The resulting implants are an order of magnitude smaller than traditional recording electrodes, and more mechanically compliant with brain tissue. They were found to elicit much reduced chronic reactive tissue responses and enabled single-neuron recording in acute and early chronic experiments in rats. This technology, taking advantage of new composites, makes possible highly selective and stealthy neural interface devices towards realizing long-lasting implants.

  15. Synthesis And Characterization of Dendrimer-Derived Supported Iridium Catalysts

    SciTech Connect

    Jesus, Y.Lopez-De; Vicente, A.; Lafaye, G.; Marecot, P.; Williams, C.T.

    2009-05-19

    The synthesis of Ir/{gamma}-Al{sub 2}O{sub 3} using the dendrimer metal nanocomposites (DMN) approach is reported. Fourth generation hydroxyl-terminated polyamidoamine dendrimer was complexed with Ir{sup 3+} in aqueous solution and the process monitored using ultraviolet-visible and X-ray absorption spectroscopy. No discernible reduction of Ir{sup 3+} to form zerovalent nanoparticles was observed after bubbling hydrogen or adding NaBH{sub 4} into the complex solution. Standard wet impregnation of the DMN precursors were used to prepare Ir/{gamma}-Al{sub 2}O{sub 3}, which were compared with conventionally prepared samples. In situ transmission Fourier transform infrared spectroscopy during dendrimer thermal decomposition in different atmospheres and CO adsorption allowed for identification of catalyst activation treatments that expose the maximum metal surface area. The particle size distributions of these catalysts were investigated using high resolution transmission electron microscopy, revealing that all of the catalysts have small particle sizes (0.4-3 nm) with narrow distributions. An optimized oxidation/reduction treatment produced a DMN-derived supported catalyst with higher metallic dispersion. DMN-derived catalysts were tested for liquid-phase hydrogenation of benzonitrile, and show an increase in TOF with increasing dispersion. The selectivity toward dibenzylamine is affected by the catalyst preparation method, with the oxidation/reduction treatment resulting in lower selectivity.

  16. Iridium nanoparticles supported on hierarchical porous N-doped carbon: an efficient water-tolerant catalyst for bio-alcohol condensation in water

    NASA Astrophysics Data System (ADS)

    Liu, Di; Chen, Xiufang; Xu, Guoqiang; Guan, Jing; Cao, Quan; Dong, Bo; Qi, Yunfei; Li, Chunhu; Mu, Xindong

    2016-02-01

    Nitrogen-doped hierarchical porous carbons were synthesized successfully by a controllable one-pot method using glucose and dicyandiamide as carbon source and nitrogen source via hydrothermal carbonization process. The nitrogen-doped materials, possessing high nitrogen content (up to 7 wt%), large surface area (>320 m2 g-1) and excellent hierarchical nanostructure, were employed as catalyst supports for immobilization of iridium nanoparticles for bio-alcohol condensation in water. The introduction of nitrogen atoms into the carbon framework significantly improved iridium nanoparticles dispersion and stabilization. The novel iridium catalysts exhibited superior catalytic activity in the aqueous phase condensation of butanol, offering high butanol conversion of 45% with impressive 2-ethylhexanol selectivity of 97%. The heterogeneous catalysts had great advantages of easy recovery and high catalytic stability. The outstanding catalytic performance could be attributed to excellent dispersion of iridium nanoparticles, stronger iridium-support interactions and interaction of nitrogen species with alcohol substrates.

  17. Iridium nanoparticles supported on hierarchical porous N-doped carbon: an efficient water-tolerant catalyst for bio-alcohol condensation in water

    PubMed Central

    Liu, Di; Chen, Xiufang; Xu, Guoqiang; Guan, Jing; Cao, Quan; Dong, Bo; Qi, Yunfei; Li, Chunhu; Mu, Xindong

    2016-01-01

    Nitrogen-doped hierarchical porous carbons were synthesized successfully by a controllable one-pot method using glucose and dicyandiamide as carbon source and nitrogen source via hydrothermal carbonization process. The nitrogen-doped materials, possessing high nitrogen content (up to 7 wt%), large surface area (>320 m2 g−1) and excellent hierarchical nanostructure, were employed as catalyst supports for immobilization of iridium nanoparticles for bio-alcohol condensation in water. The introduction of nitrogen atoms into the carbon framework significantly improved iridium nanoparticles dispersion and stabilization. The novel iridium catalysts exhibited superior catalytic activity in the aqueous phase condensation of butanol, offering high butanol conversion of 45% with impressive 2-ethylhexanol selectivity of 97%. The heterogeneous catalysts had great advantages of easy recovery and high catalytic stability. The outstanding catalytic performance could be attributed to excellent dispersion of iridium nanoparticles, stronger iridium-support interactions and interaction of nitrogen species with alcohol substrates. PMID:26912370

  18. Electrochemical and photophysical properties of new triazole-bridged heterobimetallic ruthenium-rhodium and ruthenium-iridium complexes

    SciTech Connect

    Diemen, J.H. van; Hage, R.; Haasnoot, J.G.; Lempers, H.E.B.; Reedijk, J. ); Vos, J.G. ); Cola, L. de; Barigelletti, F.; Balzani, V. )

    1992-08-19

    The synthesis, characterization, and the electrochemical and photophysical properties of ((bpy){sub 2}Ru{sup II}(bpt)Rh{sup III}(ppy){sub 2}){sup 2+}, ((bpy){sub 2}Ru{sup II}(bpt)Ir{sup III}(ppy){sub 2}){sup 2+}, ((Rh{sup III}(ppy){sub 2}){sub 2}(bpt)){sup +}, and ((Ir{sup III}(ppy){sub 2}){sub 2}(bpt)){sup +} are reported (Hppy = 2-phenylpyridine; bpy = 2,2{prime}-bipyridine, Hbpt = 3,5-bis(pyridin-2-yl)-1,2,4-triazole). The Ru(bpy){sub 2} moiety is bound via N1 of the triazole ring, while the M(ppy){sub 2} center (M = Rh or Ir) is coordinated via the N4 of the triazole ring. The electrochemical measurements show that in the mixed-metal complexes the first oxidized metal is Ru and the first reduced ligand is bpy. The homobimetallic Ir and Rh complexes exhibit a bpt{sup {minus}}-based reduction. The absorption spectra of the mixed-metal complexes exhibit both Ru {yields} bpy and M {yields} ppy{sup {minus}} transitions. The energies of these transitions are different from those of their homobimetallic analogs. The emission observed for ((Rh(ppy){sub 2}){sub 2}-(bpt)){sup +} at 77 K corresponds to a ligand-centered excited state, while for the analogous iridium complex a charge-transfer emission, which involves the bpt{sup {minus}} ligand, is observed. In the mixed-metal complexes efficient energy transfer occurs from higher energy excited states centered on the M(ppy){sub 2} component to the lowest energy excited state, which is a metal-to-ligand charge transfer level localized on the Ru(bpy){sub 2} component.

  19. Development of U.S. Government General Technical Requirements for UAS Flight Safety Systems Utilizing the Iridium Satellite Constellation

    NASA Technical Reports Server (NTRS)

    Murray, Jennifer; Birr, Richard

    2010-01-01

    This slide presentation reviews the development of technical requirements for Unmanned Aircraft Systems (UAS) utilization of the Iridium Satellite Constellation to provide flight safety. The Federal Aviation Authority (FAA) required an over-the-horizon communication standard to guarantee flight safety before permitting widespread UAS flights in the National Air Space (NAS). This is important to ensure reliable control of UASs during loss-link and over-the-horizon scenarios. The core requirement was to utilize a satellite system to send GPS tracking data and other telemetry from a flight vehicle down to the ground. Iridium was chosen as the system because it is one of the only true satellite systems that has world wide coverage, and the service has a highly reliable link margin. The Iridium system, the flight modems, and the test flight are described.

  20. Techniques for Achieving Zero Stress in Thin Films of Iridium, Chromium, and Nickel

    NASA Technical Reports Server (NTRS)

    Broadway, David M.; O'Dell, Stephen L.; Ramsey, Brian D.; Weimer, Jeffrey

    2015-01-01

    We examine techniques for achieving zero intrinsic stress in thin films of iridium, chromium, and nickel deposited by magnetron sputter deposition. The intrinsic stress is further correlated to the microstructural features and physical properties such as surface roughness and optical density at a scale appropriate to soft X-ray wavelengths. The examination of the stress in these materials is motivated by efforts to advance the optical performance of light-weight X-ray space telescopes into the regime of sub-arcsecond resolution through various deposition techniques that rely on control of the film stress to values within 10-100 MPa. A characteristic feature of the intrinsic stress behavior in chromium and nickel is their sensitivity to the magnitude and sign of the intrinsic stress with argon gas pressure and deposition rate, including the existence of a critical argon process pressure that results in zero film stress which scales linearly with the atomic mass of the sputtered species. While the effect of stress reversal with argon pressure has been previously reported by Hoffman and others for nickel and chromium, we report this effect for iridium. In addition to stress reversal, we identify zero stress in the optical functioning iridium layer shortly after island coalescence for low process pressures at a film thickness of approximately 35nm. The measurement of the low values of stress during deposition was achieved with the aid of a sensitive in-situ instrument capable of a minimum detectable level of stress, assuming a 35nm thick film, in the range of 0.40-6.0 MPa for <111> oriented crystalline silicon substrate thicknesses of 70-280 microns, respectively.

  1. Efficient light harvesting and energy transfer in a red phosphorescent iridium dendrimer.

    PubMed

    Cho, Yang-Jin; Hong, Seong Ahn; Son, Ho-Jin; Han, Won-Sik; Cho, Dae Won; Kang, Sang Ook

    2014-12-15

    A series of red phosphorescent iridium dendrimers of the type [Ir(btp)2(pic-PCn)] (Ir-Gn; n = 0, 1, 2, and 3) with two 2-(benzo[b]thiophen-2-yl)pyridines (btp) and 3-hydroxypicolinate (pic) as the cyclometalating and ancillary ligands were prepared in good yields. Dendritic generation was grown at the 3 position of the pic ligand with 4-(9H-carbazolyl)phenyl dendrons connected to 3,5-bis(methyleneoxy)benzyloxy branches (PCn; n = 0, 2, 4, and 8). The harvesting photons on the PCn dendrons followed by efficient energy transfer to the iridium center resulted in high red emissions at ∼600 nm by metal-to-ligand charge transfer. The intensity of the phosphorescence gradually increased with increasing dendrimer generation. Steady-state and time-resolved spectroscopy were used to investigate the energy-transfer mechanism. On the basis of the fluorescence quenching rate constants of the PCn dendrons, the energy-transfer efficiencies for Ir-G1, Ir-G2, and Ir-G3 were 99, 98, and 96%, respectively. The energy-transfer efficiency for higher-generation dendrimers decreased slightly because of the longer distance between the PC dendrons and the core iridium(III) complex, indicating that energy transfer in Ir-Gn is a Förster-type energy transfer. Finally, the light-harvesting efficiencies for Ir-G1, Ir-G2, and Ir-G3 were determined to be 162, 223, and 334%, respectively.

  2. Cyclometalated iridium(III) complexes for phosphorescence sensing of biological metal ions.

    PubMed

    You, Youngmin; Cho, Somin; Nam, Wonwoo

    2014-02-17

    Phosphorescence signaling provides a valuable alternative to conventional bioimaging based on fluorescence. The benefits of using phosphorescent molecules include improved sensitivity and capabilities for effective elimination of background signals by time-gated acquisition. Cyclometalated Ir(III) complexes are promising candidates for facilitating phosphorescent bioimaging because they provide synthetic versatility and excellent phosphorescence properties. In this Forum Article, we present our recent studies on the development of phosphorescence sensors for the detection of metal ions based on cyclometalated iridium(III) complexes. The constructs contained cyclometalating (C^N) ligands with the electron densities and band-gap energies of the C^N ligand structures systematically varied. Receptors that chelated zinc, cupric, and chromium ions were tethered to the ligands to create phosphorescence sensors. The alterations in the C^N ligand structures had a profound influence on the phosphorescence responses to metal ions. Mechanistic studies suggested that the phosphorescence responses could be explained on the basis of the modulation of photoinduced electron transfer (PeT) from the receptor to the photoexcited iridium species. The PeT behaviors strictly adhered to the Rehm-Weller principle, and the occurrence of PeT was located in the Marcus-normal region. It is thus anticipated that improved responses will be obtainable by increasing the excited-state reduction potential of the iridium(III) complexes. Femtosecond transient absorption experiments provided evidence for the presence of an additional photophysical mechanism that involved metal-ion-induced alteration of the intraligand charge-transfer (ILCT) transition state. Utility of the mechanism by PeT and ILCT has been demonstrated for the phosphorescence sensing of biologically important transition-metal ions. In particular, the phosphorescence zinc sensor could report the presence of intracellular zinc pools by

  3. Evaluation of the Neuroactivity of ToxCast Compounds Using Multi-well Microelectrode Array Recordings in Primary Cortical Neurons

    EPA Science Inventory

    Evaluation of the Neuroactivity of ToxCast Compounds Using Multi-well Microelectrode Array Recordings in Primary Cortical Neurons P Valdivia1, M Martin2, WR LeFew3, D Hall3, J Ross1, K Houck2 and TJ Shafer3 1Axion Biosystems, Atlanta GA and 2NCCT, 3ISTD, NHEERL, ORD, US EPA, RT...

  4. Further Evaluation of DNT Hazard Screening using Neural Networks from Rat Cortical Neurons on Multi-well Microelectrode Arrays

    EPA Science Inventory

    Thousands of chemicals have not been characterized for their DNT potential. Due to the need for DNT hazard identification, efforts to develop screening assays for DNT potential is a high priority. Multi-well microelectrode arrays (MEA) measure the spontaneous activity of electr...

  5. Multiwalled carbon-nanotube-functionalized microelectrode arrays fabricated by microcontact printing: platform for studying chemical and electrical neuronal signaling.

    PubMed

    Fuchsberger, Kai; Le Goff, Alan; Gambazzi, Luca; Toma, Francesca Maria; Goldoni, Andrea; Giugliano, Michele; Stelzle, Martin; Prato, Maurizio

    2011-02-18

    A facile method is proposed for the deposition of multiwalled carbon nanotube (MWCNT) layers onto microelectrode arrays by means of a microcontact printing technique, leading to the fabrication of MEAs characterized by well defined electrical and morphological properties. Using polydimethyl siloxane stamps, produced from different mold designs, a flexibility of printing is achieved that provides access to microscale, nanostructured electrodes. The thickness of MWCNT layers can be exactly predetermined by evaluating the concentration of the MWCNT solution employed in the process. The electrode morphology is further characterized using laser scanning and scanning electron microscopy. Next, by means of impedance spectroscopy analysis, the MWCNT-electrode contact resistance and MWCNT film resistance is measured, while electrochemical impedance spectroscopy is used to estimate the obtained electrode-electrolyte interface. Structural and electrochemical properties make these electrodes suitable for electrical stimulation and recording of neurons and electrochemical detection of dopamine. MWCNT-functionalized electrodes show the ability to detect micromolar amounts of dopamine with a sensitivity of 19 nA μm(-1) . In combination with their biosensing properties, preliminary electrophysiological measurements show that MWCNT microelectrodes have recording properties superior to those of commercial TiN microelectrodes when detecting neuronal electrical activity under long-term cell-culture conditions. MWCNT-functionalized microelectrode arrays fabricated by microcontact printing represent a versatile and multipurpose platform for cell-culture monitoring.

  6. In–situ Spatiotemporal Chemical Reactions at Water-Solid Interfacial Processes using Microelectrode Techniques: from Biofilm to Metal Corrosion

    EPA Science Inventory

    Recent developments in microscale sensors allows the non-destructive and in–situ measurement of both the absolute and changes in chemical concentrations in engineered and natural aquatic systems. Microelectrodes represent a unique tool for studying in–situ chemical reactions in b...

  7. Intercalated samarium as an agent enabling the intercalation of oxygen under a monolayer graphene film on iridium

    NASA Astrophysics Data System (ADS)

    Afanas'eva, E. Yu.; Rut'kov, E. V.; Gall', N. R.

    2016-06-01

    Using thermal desorption time-of-flight mass spectrometry and thermionic methods, it is shown that oxygen does not intercalate under a graphene monolayer grown correctly on iridium, at least at temperatures of T = 300-400 K and exposures below 12000 L. However, if the graphene film on iridium is preliminary intercalated with samarium atoms (up to coverage of θSm = 0.2-0.45), the penetration of oxygen atoms under the graphene film is observed. The oxygen atoms in the intercalated state are chemically bonded to samarium atoms and remain under graphene up to high temperatures (~2150 K).

  8. Stereodivergent α-allylation of linear aldehydes with dual iridium and amine catalysis.

    PubMed

    Krautwald, Simon; Schafroth, Michael A; Sarlah, David; Carreira, Erick M

    2014-02-26

    We describe the fully stereodivergent, dual catalytic α-allylation of linear aldehydes. The reaction proceeds via direct iridium-catalyzed substitution of racemic allylic alcohols with enamines generated in situ. The use of an Ir(P,olefin) complex and a diarylsilyl prolinol ether as catalysts in the presence of dimethylhydrogen phosphate as the promoter proved to be crucial for achieving high enantio- and diastereoselectivity (>99% ee, up to >20:1 dr). The utility of the method is demonstrated in a concise enantioselective synthesis of the antidepressant (-)-paroxetine. PMID:24506196

  9. Palynological and iridium anomalies at Cretaceous-Tertiary boundary, south-central Saskatchewan

    USGS Publications Warehouse

    Nichols, D.J.; Jarzen, D.M.; Orth, C.J.; Oliver, P.Q.

    1986-01-01

    The Cretaceous-Tertiary boundary in south-central Saskatchewan is marked by coincident anomalies in abundance of iridium and fern spores at the extinction level of a suite of Cretaceous pollen taxa. Evidence of disruption of the terrestrial flora includes the fern-spore abundance anomaly and local extinction of as much as 30 percent of angiosperm species. The reorganized earliest Tertiary flora is made up largely of surviving species that assumed new roles of dominance. Persistence of climatically sensitive taxa across the boundary indicates that if paleoclimate was altered by the terminal Cretaceous event, it returned quickly to the pre-event condition.

  10. Catalytic dehydrogenation of cycloalkanes to arenes by a dihydrido iridium P-C-P pincer complex

    SciTech Connect

    Gupta, M.; Hagen, C.; Cramer, R.E.; Jensen, C.M.; Kaska, W.C.

    1997-01-29

    We recently found that the iridium P-C-P pincer complex IrH{sub 2}[C{sub 6}H{sub 3}-2,6-(CH{sub 2}-PBu{sup T}{sub 2}){sub 2}] (1) is a highly active, homogeneous catalyst for the transfer dehydrogenation of cyclooctane with unusual long-term stability at temperatures as high as 200 {degree}C. This reactivity has now been extended to the catalytic transfer dehydrogenation of cycloalkanes to arenes. We report this novel catalytic activity as well as the results of an X-ray structure determination of 1. 15 refs., 1 fig., 1 tab.

  11. Salvage irradiation of oropharynx and mobile tongue about /sup 192/iridium brachytherapy in Centre Alexis Vautrin

    SciTech Connect

    Langlois, D.; Hoffstetter, S.; Malissard, L.; Pernot, M.; Taghian, A.

    1988-05-01

    Between 1972 and 1984, 123 patients were treated using /sup 192/Iridium afterloading techniques for recurrence or new cancer of the tongue or oropharynx arising in previously irradiated tissues. The actuarial local control was 67% at 2 years and 59% at 5 years. Local control of the tumor was achieved in the majority of these patients, the actuarial survival was only 48% at 2 years and 24% at 5 years. Twenty-eight patients developed mucosal necrosis. We analyzed prognostic factors for survival, local control, and complication. We proposed a selection for this salvage therapy.

  12. Iridium/Copper Co-catalyzed Anti-Stereoselective Ring Opening of Oxabenzonorbornadienes with Grignard Reagents.

    PubMed

    Cheng, Guo; Yang, Wen; Li, Yue; Yang, Dingqiao

    2016-09-01

    Cooperative catalysis has been widely considered as one of the most powerful strategies to improve synthetic efficiency. A new iridium/copper cocatalyst was developed for the ring-opening reaction of oxabenzonorbornadienes with a wide variety of Grignard reagents, which afforded the corresponding anti-2-substituted 1,2-dihydronaphthalen-1-ols in high yields (up to 99% yield) under mild conditions. The effects of catalyst loading, Lewis acid, Grignard reagent loading, and reaction temperature on the yield were investigated. To the best of our knowledge, it represents the first example of ring-opening reactions of oxabicyclic alkenes with Grignard reagent nucleophiles in a trans-stereoselective manner. PMID:27455165

  13. Theoretical studies on the photophysical properties of some Iridium (III) complexes used for OLED

    NASA Astrophysics Data System (ADS)

    Urinda, Sharmistha; Das, Goutam; Pramanik, Anup; Sarkar, Pranab

    2016-09-01

    The structural and photophysical properties of four heteroleptic Iridium (III) complexes, based on 1-phenylpyrazole ligand, have been investigated theoretically. The effect of chemical substitution on the absorption and the emission spectra of the complexes has been studied and compared with the experimental data. We observe a significant structural change in the lowest triplet excited state as compared to the ground singlet state. We compute the emission wavelength of the complexes by considering the spin-orbit coupling. Using these understandings, we predict two new complexes having deeper blue emission which are supposed to be better efficient OLED materials.

  14. Iridium Complexes and Clusters in Dealuminated Zeolite HY: Distribution between Crystalline and Impurity Amorphous Regions

    SciTech Connect

    Martinez-Macias, Claudia; Xu, Pinghong; Hwang, Son-Jong; Lu, Jing; Chen, Cong-Yan; Browning, Nigel D.; Gates, Bruce C.

    2014-07-08

    Dealuminated zeolite HY was used to support Ir(CO)2 complexes formed from Ir(CO)2(C5H7O2). Infrared and X-ray absorption spectra and atomic-resolution electron microscopy images identify these complexes, and the images and 27Al NMR spectra identify impurity amorphous regions in the zeolite where the iridium is more susceptible to aggregation than in the crystalline regions. The results indicate a significant stability limitation of metal in amorphous impurity regions of zeolites.

  15. Iridium-Catalyzed Asymmetric Ring-Opening of Oxabenzonorbornadienes with N-Substituted Piperazine Nucleophiles.

    PubMed

    Yang, Wen; Luo, Renshi; Yang, Dingqiao

    2015-01-01

    Iridium-catalyzed asymmetric ring-opening of oxabenzonorbornadienes with N-substituted piperazines was described. The reaction afforded the corresponding ring-opening products in high yields and moderate enantioselectivities in the presence of 2.5 mol % [Ir(COD)Cl]₂ and 5.0 mol % (S)-p-Tol-BINAP. The effects of various chiral bidentate ligands, catalyst loading, solvent, and temperature on the yield and enantioselectivity were also investigated. A plausible mechanism was proposed to account for the formation of the corresponding trans-ring opened products based on the X-ray structure of product 2i. PMID:26633315

  16. Relationship between mass extinction and iridium across the Cretaceous-Paleogene boundary in New Jersey

    USGS Publications Warehouse

    Miller, K.G.; Sherrell, Robert M.; Browning, J.V.; Field, M.P.; Gallagher, W.; Olsson, R.K.; Sugarman, P.J.; Tuorto, S.; Wahyudi, H.

    2010-01-01

    We directly link iridium (Ir) anomalies in New Jersey to the mass extinction of marine plankton marking the Cretaceous-Paleogene (K-Pg) boundary. We confirm previous reports of an Ir anomaly 20 cm below the extinction of Cretaceous macrofauna (the "Pinna" bed) with new results from a muddy sand section from Tighe Park, Freehold, New Jersey (United States), but we also show that Ir anomalies correlate with marine mass extinctions at three other clay-rich New Jersey sections. Thus, we attribute the anomaly at Freehold to the downward movement of Ir and reaffirm the link between impact and mass extinction. ?? 2010 Geological Society of America.

  17. Iridium/N-heterocyclic carbene-catalyzed C–H borylation of arenes by diisopropylaminoborane

    PubMed Central

    Igarashi, Takuya

    2016-01-01

    Summary Catalytic C–H borylation of arenes has been widely used in organic synthesis because it allows the introduction of a versatile boron functionality directly onto simple, unfunctionalized arenes. We report herein the use of diisopropylaminoborane as a boron source in C–H borylation of arenes. An iridium(I) complex with 1,3-dicyclohexylimidazol-2-ylidene is found to efficiently catalyze the borylation of arenes and heteroarenes. The resulting aminoborylated products can be converted to the corresponding boronic acid derivatives simply by treatment with suitable diols or diamines. PMID:27340457

  18. Stereodivergent α-allylation of linear aldehydes with dual iridium and amine catalysis.

    PubMed

    Krautwald, Simon; Schafroth, Michael A; Sarlah, David; Carreira, Erick M

    2014-02-26

    We describe the fully stereodivergent, dual catalytic α-allylation of linear aldehydes. The reaction proceeds via direct iridium-catalyzed substitution of racemic allylic alcohols with enamines generated in situ. The use of an Ir(P,olefin) complex and a diarylsilyl prolinol ether as catalysts in the presence of dimethylhydrogen phosphate as the promoter proved to be crucial for achieving high enantio- and diastereoselectivity (>99% ee, up to >20:1 dr). The utility of the method is demonstrated in a concise enantioselective synthesis of the antidepressant (-)-paroxetine.

  19. Iridium-catalyzed intermolecular dehydrogenative silylation of polycyclic aromatic compounds without directing groups.

    PubMed

    Murai, Masahito; Takami, Keishi; Takai, Kazuhiko

    2015-03-16

    This study describes the iridium-catalyzed intermolecular dehydrogenative silylation of C(sp(2))-H bonds of polycyclic aromatic compounds without directing groups. The reaction produced various arylsilanes through both Si-H and C-H bond activation, with hydrogen as the sole byproduct. Reactivity was affected by the electronic nature of the aromatic compounds, and silylation of electron-deficient and polycyclic aromatic compounds proceeded efficiently. Site-selectivity was controlled predominantly by steric factors. Therefore, the current functionalization proceeded with opposite chemo- and site-selectivity compared to that observed for general electrophilic functionalization of aromatic compounds.

  20. Iridium(III)-Catalyzed Regioselective Intermolecular Unactivated Secondary Csp(3) -H Bond Amidation.

    PubMed

    Xiao, Xinsheng; Hou, Cheng; Zhang, Zhenhui; Ke, Zhuofeng; Lan, Jianyong; Jiang, Huanfeng; Zeng, Wei

    2016-09-19

    For the first time, a highly regioselective intermolecular sulfonylamidation unactivated secondary Csp(3) -H bond has been achieved using Ir(III) catalysts. The introduced N,N'-bichelating ligand plays a crucial role in enabling iridium-nitrene insertion into a secondary Csp(3) -H bond via an outer-sphere pathway. Mechanistic studies and density functional theory (DFT) calculations demonstrated that a two-electron concerted nitrene insertion was involved in this Csp(3) -H amidation process. This method tolerates a broad range of linear and branched-chain N-alkylamides, and provides efficient access to diverse γ-sulfonamido-substituted aliphatic amines. PMID:27561950

  1. Sizeable Kane-Mele-like spin orbit coupling in graphene decorated with iridium clusters

    NASA Astrophysics Data System (ADS)

    Qin, Yuyuan; Wang, Siqi; Wang, Rui; Bu, Haijun; Wang, Xuefeng; Wang, Xinran; Song, Fengqi; Wang, Baigeng; Wang, Guanghou

    2016-05-01

    The spin-orbit coupling strength of graphene can be enhanced by depositing iridium nanoclusters. Weak localization is intensely suppressed near zero fields after the cluster deposition, rather than changing to weak anti-localization. Fitting the magnetoresistance gives the spin relaxation time, which increases by two orders with the application of a back gate. The spin relaxation time is found to be proportional to the electronic elastic scattering time, demonstrating the Elliot-Yafet spin relaxation mechanism. A sizeable Kane-Mele-like coupling strength of over 5.5 meV is determined by extrapolating the temperature dependence to zero.

  2. Quantitative Analysis of Rat Dorsal Root Ganglion Neurons Cultured on Microelectrode Arrays Based on Fluorescence Microscopy Image Processing.

    PubMed

    Mari, João Fernando; Saito, José Hiroki; Neves, Amanda Ferreira; Lotufo, Celina Monteiro da Cruz; Destro-Filho, João-Batista; Nicoletti, Maria do Carmo

    2015-12-01

    Microelectrode Arrays (MEA) are devices for long term electrophysiological recording of extracellular spontaneous or evocated activities on in vitro neuron culture. This work proposes and develops a framework for quantitative and morphological analysis of neuron cultures on MEAs, by processing their corresponding images, acquired by fluorescence microscopy. The neurons are segmented from the fluorescence channel images using a combination of segmentation by thresholding, watershed transform, and object classification. The positioning of microelectrodes is obtained from the transmitted light channel images using the circular Hough transform. The proposed method was applied to images of dissociated culture of rat dorsal root ganglion (DRG) neuronal cells. The morphological and topological quantitative analysis carried out produced information regarding the state of culture, such as population count, neuron-to-neuron and neuron-to-microelectrode distances, soma morphologies, neuron sizes, neuron and microelectrode spatial distributions. Most of the analysis of microscopy images taken from neuronal cultures on MEA only consider simple qualitative analysis. Also, the proposed framework aims to standardize the image processing and to compute quantitative useful measures for integrated image-signal studies and further computational simulations. As results show, the implemented microelectrode identification method is robust and so are the implemented neuron segmentation and classification one (with a correct segmentation rate up to 84%). The quantitative information retrieved by the method is highly relevant to assist the integrated signal-image study of recorded electrophysiological signals as well as the physical aspects of the neuron culture on MEA. Although the experiments deal with DRG cell images, cortical and hippocampal cell images could also be processed with small adjustments in the image processing parameter estimation.

  3. μ-Oxido-bis­[hydridotris(tri­methyl­phosphane-κP)iridium(III)](Ir—Ir) bis­(tetra­fluorido­borate) dihydrate

    PubMed Central

    Merola, Joseph; Husebo, Trang Le

    2014-01-01

    The title compound, [Ir2H2O(C3H9P)6](BF4)2·2H2O, was isolated from the reaction between [Ir(COD)(PMe3)3]BF4 and H2 in water (COD is cyclo­octa-1,5-diene). The asymmetric unit consists of one IrIII atom bonded to three PMe3 groups, one hydride ligand and half an oxide ligand, in addition to a BF4 − counter-ion and one water molecule of hydration. The single oxide ligand bridging two IrIII atoms is disordered across an inversion center with each O atom having a 50% site occupancy. Each IrIII atom has three PMe3 groups occupying facial positions, with the half-occupancy O atoms, a hydride ligand and an Ir—Ir bond completing the coordination sphere. The Ir—Ir distance is 2.8614 (12) Å, comparable to other iridium(III) metal–metal bonds. Two water mol­ecules hydrogen bond to two BF4 − anions in the unit cell. PMID:24826089

  4. Communication—Microelectrode Detection of Cholesterol Efflux from the Human Buccel Mucosa

    PubMed Central

    Yu, Xiaochun; Kelley, Thomas J.; Chiel, Hillel J.; Burgess, James D.

    2016-01-01

    It has previously demonstrated that cholesterol efflux from the cell plasma membrane is increased in a mouse model of cystic fibrosis (CF) compared to a wild-type control. A noninvasive means of characterizing plasma membrane cholesterol efflux at the surface of airway tissue of CF patients is needed to extend the trends found in animal models of CF to the human disease state. Microelectrode-induced cholesterol efflux from the plasma membrane of cells at the surface of tissue is proposed as a strategy to demonstrate increased cholesterol efflux for CF in human subjects. Data demonstrating detection of cholesterol efflux from the human buccal mucosa is reported as proof-of-concept for an in vivo diagnostic assay. PMID:27546897

  5. Zinc Nanoparticles-equipped Bioelectronic Nose Using a Microelectrode Array for Odorant Detection.

    PubMed

    Zhang, Qian; Zhang, Diming; Li, Nantao; Lu, Yanli; Yao, Yao; Li, Shuang; Liu, Qingjun

    2016-01-01

    Bioelectronic noses, such as olfactory cell- and receptor-based biosensors, have important applications for biomimetic odorant detection in various fields. Here, a nanoparticle-equipped biosensor was designed to record extracellular potentials from olfactory receptor cells effectively. In this research, a microelectrode array (MEA) was combined with olfactory epitheliums as the olfactory biosensor to record electrophysiological signals of receptor cells in the epitheliums. Zinc nanoparticles (NanoZn) were employed along with the biosensor for different kinds of odorant measurements, which improved the electrophysiological responses to odor molecules. The NanoZn-equipped biosensor showed greater performance, such as a higher sensitivity and a larger signal-to-noise ratio, than that without the nanoparticles. Thus, this approach provided a promising method to improve the detecting performance of biosensors based on olfactory cells and receptors, which would bring broad application prospects for bioelectronic noses in environmental monitoring, food analysis, and healthcare diagnosis.

  6. Identification and quantification of electrical leakage pathways in floating microelectrode arrays.

    PubMed

    Bredeson, Samuel D; Troyk, Philip R; Suh, Sungjae; Bak, M

    2013-01-01

    The long-term reliability of neural recording and stimulation electrode arrays is becoming the limiting factor for neural interfaces. For effective electrode design, electrical connection to the surrounding neural tissue and fluid should be limited to the electrode tips, with all other leakage currents minimized. It is the goal of this study to identify and quantify electrical leakage within commercially available floating microelectrode arrays (FMAs). Both short term and accelerated stress tests were performed on entire FMAs, as well as on individual electrodes typical of such arrays. Preliminary results of these tests indicate that leakage currents are present due to water penetration of their insulation layer initially, but that prolonged water exposure at high temperature may seal the defects that cause these currents. SEM photos taken of the electrode shafts show extensive defect regions that may correlate with the test data.

  7. Construction of an integrated biomodule composed of microfluidics and digitally controlled microelectrodes for processing biomolecules.

    NASA Astrophysics Data System (ADS)

    Wagler, Patrick F.; Tangen, Uwe; Maeke, Thomas; Mathis, Harald P.; McCaskill, John S.

    2003-01-01

    This work focuses on the development of an online programmable microfluidic bioprocessing unit (BioModule) using digital logic microelectrodes for rapid pipelined selection and transfer of DNA molecules and other charged biopolymers. The design and construction technique for this hybrid programmable biopolymer processing device is presented along with the first proof of principle functionality. The electronically controlled collection, separation and channel transfer of the biomolecules is monitored by a sensitive fluorescence setup. This hybrid reconfigurable architecture couples electronic and biomolecular information processing via a single module combination of fluidics and electronics and opens new fields of applications not only in DNA computing and molecular diagnostics but also in applications of combinatorial chemistry and lab-on-a-chip biotechnology to the drug discovery process. Fundamentals of the design and silicon-PDMS-based construction of these electronic microfluidic devices and their functions are described as well as the experimental results.

  8. Microfabrication of a BioModule composed of microfluidics and digitally controlled microelectrodes for processing biomolecules

    NASA Astrophysics Data System (ADS)

    Wagler, Patrick F.; Tangen, Uwe; Maeke, Thomas; Mathis, Harald P.; McCaskill, John S.

    2003-10-01

    This work focuses on the development of an online programmable microfluidic bioprocessing unit (BioModule) using digital logic microelectrodes for rapid pipelined selection and transfer of deoxyribonucleic acid (DNA) molecules and other charged biopolymers. The design and construction technique for this hybrid programmable biopolymer processing device is presented along with the first proof of principle functionality. The electronically controlled collection, separation and channel transfer of the biomolecules is monitored by a sensitive fluorescence set-up. This hybrid reconfigurable architecture couples electronic and biomolecular information processing via a single module combination of fluidics and electronics and opens new fields of applications not only in DNA computing and molecular diagnostics but also in applications of combinatorial chemistry and lab-on-a-chip biotechnology to the drug discovery process. Fundamentals of the design and silicon-polydimethylsiloxane (PDMS)-based construction of these electronic microfluidic devices and their functions are described as well as the experimental results.

  9. Addressing of LnCaP Cell Using Magnetic Particles Assisted Impedimetric Microelectrode.

    PubMed

    Nguyen, Dung Thi Xuan; Tran, Trong Binh; Nguyen, Phuong-Diem; Min, Junhong

    2016-03-01

    In this study, we provide a facile, effective technique for a simple isolation and enrichment of low metastatic prostate tumor cell LNCaP using biocompatible, magnetic particles asissted impedimetric sensing system. Hydrophobic cell membrane anchors (BAM) were generated onto magnetic particles which diameters vary from 50 nm to 5 μm and were used to capture LNCaP cells from the suspension. Finally, magnetic particle-LNCaP complex were addressed onto the surface of the interdigitated microelectrode (IDM). Cell viability was monitored by our laboratory developed-technique Electrical Cell Substrate Impedance Sensing (ECIS). The results reavealed that 50 nm-magnetic particles showed best performance in terms of cell separation and cell viability. This technique provides a simple and efficient method for the direct addressing of LNCaP cell on the surface and enhances better understanding of cell behavior for cancer management in the near future. PMID:27455737

  10. Automated navigation of a glass micropipette on a high-density microelectrode array.

    PubMed

    Jing Lin; Obien, Marie Engelene J; Hierlemann, Andreas; Frey, Urs

    2015-08-01

    High-density microelectrode arrays (HDMEAs) provide the capability to monitor the extracellular electric potential of multiple neurons at subcellular resolution over extended periods of time. In contrast, patch clamp allows for intracellular, sub-threshold recordings from a single patched neuron for very limited time on the order of an hour. Therefore, it will be beneficial to combine HDMEA and patch clamp for simultaneous intra- and extracellular recording of neuronal activity. Previously, it has been shown that the HDMEA can be used to localize and steer a glass micropipette towards a target location without using an optical microscope [1]. Here, we present an automated system, implemented in LabVIEW, which automatically locates and moves the glass micropipette towards a user-defined target. The presented system constitutes a first step towards developing an automated system to navigate a pipette to patch a neuron in vitro. PMID:26736403

  11. A Multimodal, SU-8 - Platinum - Polyimide Microelectrode Array for Chronic In Vivo Neurophysiology.

    PubMed

    Márton, Gergely; Orbán, Gábor; Kiss, Marcell; Fiáth, Richárd; Pongrácz, Anita; Ulbert, István

    2015-01-01

    Utilization of polymers as insulator and bulk materials of microelectrode arrays (MEAs) makes the realization of flexible, biocompatible sensors possible, which are suitable for various neurophysiological experiments such as in vivo detection of local field potential changes on the surface of the neocortex or unit activities within the brain tissue. In this paper the microfabrication of a novel, all-flexible, polymer-based MEA is presented. The device consists of a three dimensional sensor configuration with an implantable depth electrode array and brain surface electrodes, allowing the recording of electrocorticographic (ECoG) signals with laminar ones, simultaneously. In vivo recordings were performed in anesthetized rat brain to test the functionality of the device under both acute and chronic conditions. The ECoG electrodes recorded slow-wave thalamocortical oscillations, while the implanted component provided high quality depth recordings. The implants remained viable for detecting action potentials of individual neurons for at least 15 weeks. PMID:26683306

  12. Simultaneous recording of rat auditory cortex and thalamus via a titanium-based, microfabricated, microelectrode device

    PubMed Central

    McCarthy, PT; Rao, MP; Otto, KJ

    2011-01-01

    Direct recording from sequential processing stations within the brain has provided opportunity for enhancing understanding of important neural circuits, such as the corticothalamic loops underlying auditory, visual, and somatosensory processing. However, the common reliance upon microwire-based electrodes to perform such recordings often necessitates complex surgeries and increases trauma to neural tissues. This paper reports the development of titanium-based, microfabricated, microelectrode devices designed to address these limitations by allowing acute recording from the thalamic nuclei and associated cortical sites simultaneously in a minimally-invasive manner. In particular, devices were designed to simultaneously probe rat auditory cortex and auditory thalamus, with the intent of recording auditory response latencies and isolated action potentials within the separate anatomical sites. Details regarding the design, fabrication, and characterization of these devices are presented, as are preliminary results from acute in vivo recording. PMID:21628772

  13. Surface modified microelectrodes for selective electroanalysis of metal ions in environmental components.

    PubMed

    Barancok, D; Cirák, J; Tomcík, P; Gmucová, K

    2002-01-01

    The surface modification of electrodes was achieved by the Langmuir-Blodgett technique. The monolayers of laponite clay and polythiophene were formed at the air-water interface and these films were then transferred onto carbon microelectrodes. The behaviour of both untreated and coated electrodes was tested by originally developed double-step voltcoulometry (DSVCM). The dependence of charge response on the concentration of Cu(2+) species was investigated. Straight calibration curves were obtained and enhanced sensitivity of coated electrodes was documented. It is shown that the accumulation of Cu ions into laponite clay was maintained even after transferring the electrode into a pure water. The characteristic features of the "memory effect" are discussed.

  14. Boron-doped nanocrystalline diamond microelectrode arrays monitor cardiac action potentials.

    PubMed

    Maybeck, Vanessa; Edgington, Robert; Bongrain, Alexandre; Welch, Joseph O; Scorsone, Emanuel; Bergonzo, Philippe; Jackman, Richard B; Offenhäusser, Andreas

    2014-02-01

    The expansion of diamond-based electronics in the area of biological interfacing has not been as thoroughly explored as applications in electrochemical sensing. However, the biocompatibility of diamond, large safe electrochemical window, stability, and tunable electronic properties provide opportunities to develop new devices for interfacing with electrogenic cells. Here, the fabrication of microelectrode arrays (MEAs) with boron-doped nanocrystalline diamond (BNCD) electrodes and their interfacing with cardiomyocyte-like HL-1 cells to detect cardiac action potentials are presented. A nonreductive means of structuring doped and undoped diamond on the same substrate is shown. The resulting BNCD electrodes show high stability under mechanical stress generated by the cells. It is shown that by fabricating the entire surface of the MEA with NCD, in patterns of conductive doped, and isolating undoped regions, signal detection may be improved up to four-fold over BNCD electrodes passivated with traditional isolators.

  15. Close-Packed Silicon Microelectrodes for Scalable Spatially Oversampled Neural Recording

    PubMed Central

    Scholvin, Jörg; Kinney, Justin P.; Bernstein, Jacob G.; Moore-Kochlacs, Caroline; Kopell, Nancy; Fonstad, Clifton G.; Boyden, Edward S.

    2015-01-01

    Objective Neural recording electrodes are important tools for understanding neural codes and brain dynamics. Neural electrodes that are close-packed, such as in tetrodes, enable spatial oversampling of neural activity, which facilitates data analysis. Here we present the design and implementation of close-packed silicon microelectrodes, to enable spatially oversampled recording of neural activity in a scalable fashion. Methods Our probes are fabricated in a hybrid lithography process, resulting in a dense array of recording sites connected to submicron dimension wiring. Results We demonstrate an implementation of a probe comprising 1000 electrode pads, each 9 × 9 μm, at a pitch of 11 μm. We introduce design automation and packaging methods that allow us to readily create a large variety of different designs. Significance Finally, we perform neural recordings with such probes in the live mammalian brain that illustrate the spatial oversampling potential of closely packed electrode sites. PMID:26699649

  16. K+-selective microelectrode study of internally dialyzed squid giant axons.

    PubMed Central

    Fong, C N; Chang, D C

    1988-01-01

    Intracellular potassium activity, (aK)i, and axoplasmic K+ concentration, [K+]i, were measured by means of K+-selective microelectrodes and atomic absorption spectroscopy, respectively, in squid giant axons dialyzed with K+-free dialysis solution and bathed in K+-free artificial sea water. (aK)i measurements indicated that axoplasmic free K+ could be depleted by dialysis, whereas [K+]i measurements on axoplasm extruded from these axons suggest substantial retention of K+ (15.5 +/- 1.7 mmol/kg axoplasm K+; n = 9). In comparison, [K+]i in axoplasm extruded from freshly dissected axons was 330 +/- 16 mmol/kg axoplasm (n = 6). These data suggest that approximately 5% of the axoplasmic K+ ions are not easily removed by dialysis and that these ions are either bound to macromolecular sites or sequestered into membrane-enclosed organelles. PMID:3395659

  17. Flexible and biocompatible microelectrode arrays fabricated by supersonic cluster beam deposition on SU-8

    NASA Astrophysics Data System (ADS)

    Marelli, Mattia; Divitini, Giorgio; Collini, Cristian; Ravagnan, Luca; Corbelli, Gabriele; Ghisleri, Cristian; Gianfelice, Antonella; Lenardi, Cristina; Milani, Paolo; Lorenzelli, Leandro

    2011-04-01

    We fabricated highly adherent and electrically conductive micropatterns on SU-8 by supersonic cluster beam deposition (SCBD). This technique is based on the aerodynamical acceleration of neutral metallic nanoparticles produced in the gas phase. The kinetic energy acquired by the nanoparticles allows implantation in an SU-8 layer, thus producing a metal-polymer nanocomposite thin layer. The nanocomposite shows ohmic electrical conduction and it can also be used as an adhesion layer for further metallization with a metallic overlayer. We characterized the electrical conduction, adhesion and biocompatibility of microdevices obtained by SCBD on SU-8 demonstrating the compatibility of our approach with standard lift-off technology on 4'' wafer. A self-standing and flexible microelectrode array has been produced. Cytological tests with neuronal cell lines demonstrated improved cell growth on the nanocomposite layer.

  18. A Multimodal, SU-8 - Platinum - Polyimide Microelectrode Array for Chronic In Vivo Neurophysiology.

    PubMed

    Márton, Gergely; Orbán, Gábor; Kiss, Marcell; Fiáth, Richárd; Pongrácz, Anita; Ulbert, István

    2015-01-01

    Utilization of polymers as insulator and bulk materials of microelectrode arrays (MEAs) makes the realization of flexible, biocompatible sensors possible, which are suitable for various neurophysiological experiments such as in vivo detection of local field potential changes on the surface of the neocortex or unit activities within the brain tissue. In this paper the microfabrication of a novel, all-flexible, polymer-based MEA is presented. The device consists of a three dimensional sensor configuration with an implantable depth electrode array and brain surface electrodes, allowing the recording of electrocorticographic (ECoG) signals with laminar ones, simultaneously. In vivo recordings were performed in anesthetized rat brain to test the functionality of the device under both acute and chronic conditions. The ECoG electrodes recorded slow-wave thalamocortical oscillations, while the implanted component provided high quality depth recordings. The implants remained viable for detecting action potentials of individual neurons for at least 15 weeks.

  19. Purification of carbon nanotubes through an electric field near the arranged microelectrodes

    NASA Astrophysics Data System (ADS)

    Shim, Hyung Cheoul; Lee, Hyung Woo; Yeom, Sujin; Kwak, Yoon Keun; Lee, Seung S.; Kim, Soo Hyun

    2007-03-01

    In this work, we attempt to purify multi-walled carbon nanotubes (MWNTs) using electrophoresis induced by the application of an AC electric field to a set of microelectrodes in a microliquid channel. This purifying method is different from conventional methods based on chemical processes. It was observed that most of the MWNTs could pass along the microliquid channel without attaching to the electrode under specific conditions of 1 kHz, at 0.2 Vrms μm-1. On the other hand, the majority of the carbon impurities attached to the electrodes under identical conditions. Field emission scanning electron microscopy (FESEM) images and Raman spectra confirm that this condition is beneficial for removing carbon impurities. The proposed approach has potential applicability in the development of microdevices that can simultaneously perform the purification and fabrication of MWNTs.

  20. Mechanical Flexibility Reduces the Foreign Body Response to Long-Term Implanted Microelectrodes in Rabbit Cortex

    PubMed Central

    Sohal, Harbaljit S.; Clowry, Gavin J.

    2016-01-01

    Micromotion between the brain and implanted electrodes is a major contributor to the failure of invasive microelectrodes. Movements of the electrode tip cause recording instabilities while spike amplitudes decline over the weeks/months post-implantation due to glial cell activation caused by sustained mechanical trauma. We compared the glial response over a 26–96 week period following implantation in the rabbit cortex of microwires and a novel flexible electrode. Horizontal sections were used to obtain a depth profile of the radial distribution of microglia, astrocytes and neurofilament. We found that the flexible electrode was associated with decreased gliosis compared to the microwires over these long indwelling periods. This was in part due to a decrease in overall microgliosis and enhanced neuronal density around the flexible probe, especially at longer periods of implantation. PMID:27788240