Browsing by Author "Bakker, E"

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    Elimination of undesirable water layers in solid-contact polymeric ion-selective electrodes
    (American Chemical Society, 2008-09-01) Veder, JP; De Marco, R; Clarke, G; Chester, R; Nelson, A; Prince, KE; Pretsch, E; Bakker, E
    This study aimed to develop a novel approach for the production of analytically robust and miniaturized polymeric ion sensors that are vitally important in modem analytical chemistry (e.g., clinical chemistry using single blood droplets, modem biosensors measuring clouds of ions released from nanoparticle-tagged biomolecules, laboratory-on-a-chip applications, etc.). This research has shown that the use of a water-repellent poly(methyl methacrylate)/poly(decyl methacrylate) (PMMA/PDMA) copolymer as the ion-sensing membrane, along with a hydrophobic poly(3-octylthiophene 2,5-diyl) (POT) solid contact as the ion-to-electron transducer, is an excellent strategy for avoiding the detrimental water layer formed at the buried interface of solid-contact ion-selective electrodes (ISEs). Accordingly, it has been necessary to implement a rigorous surface analysis scheme employing electrochemical impedance spectroscopy (EIS), in situ neutron reflectometry/EIS (NR/EIS), secondary ion mass spectrometry (SIMS), and small-angle neutron scattering (SANS) to probe structurally the solid-contact/membrane interface, so as to identify the conditions that eliminate the undesirable water layer in all solid-state polymeric ion sensors. In this work, we provide the first experimental evidence that the PMMA/PDMA copolymer system is susceptible to water "pooling" at the interface in areas surrounding physical imperfections in the solid contact, with the exposure time for such an event in a PMMA/PDMA copolymer ISE taking nearly 20 times longer than that for a plasticized poly(vinyl chloride) (PVC) ISE, and the simultaneous use of a hydrophobic POT solid contact with a PMMA/PDMA membrane can eliminate totally this water layer problem. © 2008, American Chemical Society
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    Evidence for a surface confined ion-to-electron transduction reaction in solid-contact ion-selective electrodes based on poly(3-octylthiophene)
    (American Chemical Society, 2013-11-05) Veder, JP; De Marco, R; Patel, K; Si, P; Grygolowicz-Pawlak, E; James, M; Alam, MT; Sohail, M; Lee, J; Pretsch, E; Bakker, E
    The ion-to-electron transduction reaction mechanism at the buried interface of the electrosynthesized poly(3-octylthiophene) (POT) solid-contact (SC) ion-selective electrode (ISE) polymeric membrane has been studied using synchrotron radiation-X-ray photoelectron spectroscopy (SR-XPS), near edge X-ray absorption fine structure (NEXAFS), and electrochemical impedance spectroscopy (EIS)/neutron reflectometry (NR). The tetrakis[3,5-bis(triflouromethyl)phenyl]borate (TFPB?) membrane dopant in the polymer ISE was transferred from the polymeric membrane to the outer surface layer of the SC on oxidation of POT but did not migrate further into the oxidized POT SC. The TFPB? and oxidized POT species could only be detected at the outer surface layer (≤14 ?) of the SC material, even after oxidation of the electropolymerized POT SC for an hour at high anodic potential demonstrating that the ion-to-electron transduction reaction is a surface confined process. Accordingly, this study provides the first direct structural evidence of ion-to-electron transduction in the electropolymerized POT SC ISE by proving TFPB? transport from the polymeric ISE membrane to the oxidized POT SC at the buried interface of the SC ISE. It is inferred that the performance of the POT SC ISE is independent of the thickness of the POT SC but is instead contingent on the POT SC surface reactivity and/or electrical capacitance of the POT SC. In particular, the results suggest that the electropolymerized POT conducting polymer may spontaneously form a mixed surface/bulk oxidation state, which may explain the unusually high potential stability of the resulting ISE. It is anticipated that this new understanding of ion-to-electron transduction with electropolymerized POT SC ISEs will enable the development of new and improved devices with enhanced analytical performance attributes.© 2013, American Chemical Society.
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    Evidence of a water layer in solid-contact polymeric ion sensors
    (Royal Society of Chemistry, 2008-01-01) De Marco, R; Veder, JP; Clarke, G; Nelson, A; Prince, KE; Pretsch, E; Bakker, E
    This paper presents the very first direct structural evidence for the formation of a 100 +/- 10 angstrom water layer in coated-wire polymeric-membrane ion-selective electrodes (ISEs). © 2008, Royal Society of Chemistry