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Analyst ; 136(16): 3252-8, 2011 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-21735000


Solid-contact (SC) ion-selective electrodes (ISEs) utilizing thin films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and plasticized poly(vinylchloride) (PVC) have been produced using a spin casting procedure. This study was carried out with a view of characterizing this popular and well known SC ISE using a series of complementary surface analysis techniques. This work revealed that PEDOT:PSS prevents the separation of an undesirable water layer at the buried interface of this SC ISE due to the high miscibility of water in the hydrophilic PEDOT:PSS layer. The lack of a clearly defined and molecularly sharp buried interface prohibits the formation of a distinct water layer presumably by eliminating sites that promote the accumulation of water. This outcome is important to the chemical sensor community since it provides further insights into the compatibility of sensor components in SC ISEs.

Anal Chem ; 82(14): 6203-7, 2010 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-20557118


This paper reports on three-dimensional synchrotron radiation/Fourier transform-infrared microspectroscopy (SR/FT-IRM) imaging studies of water inclusions at the buried interface of solid-contact-ion-selective electrodes (SC-ISEs). It is our intention to describe a nondestructive method that may be used in surface studies of the buried interfaces of materials, especially multilayers of polymers. Herein, we demonstrate the power of SR/FT-IRM for studying water inclusions at the buried interfaces of SC-ISEs. A poly(methyl methacrylate)-poly(decyl methacyrlate) [PMMA-PDMA] copolymer revealed the presence of micrometer sized inclusions of water at the gold/membrane interface, while a coupling of a hydrophobic solid contact of poly(3-octylthiophene 2,5-diyl) (POT) prevented the accumulation of water at the buried interface. A similar study with a poly (3,4-ethylenedioxythiophene)/poly (styrenesulfonate) [PEDOT/PSS] solid contact also revealed an absence of distinct micrometer-sized pools of water; however, there were signs of absorption of water accompanied by swelling of the PEDOT/PSS underlayer, and these membrane zones are enriched with respect to water.

Polímeros/química , Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Síncrotrons , Água/química , Ouro/química , Eletrodos Íon-Seletivos , Tiofenos/química
Anal Chem ; 80(17): 6731-40, 2008 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-18671410


This study aimed to develop a novel approach for the production of analytically robust and miniaturized polymeric ion sensors that are vitally important in modern analytical chemistry (e.g., clinical chemistry using single blood droplets, modern 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.

Polímeros/química , Água/química , Impedância Elétrica , Eletroquímica , Eletrodos , Interações Hidrofóbicas e Hidrofílicas , Difração de Nêutrons , Nêutrons , Cloreto de Polivinila/química , Espalhamento a Baixo Ângulo , Sensibilidade e Especificidade , Prata/química , Espectrometria de Massa de Íon Secundário , Análise Espectral , Propriedades de Superfície
Phys Chem Chem Phys ; 10(1): 73-6, 2008 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-18075683


This paper presents the very first direct structural evidence for the formation of a 100 +/- 10 A water layer in coated-wire polymeric-membrane ion-selective electrodes (ISEs).

Eletrodos Íon-Seletivos , Polímeros/química , Água/química , Membranas Artificiais