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Dong XIN, Spindler BD, Kim M, Stein A, Bühlmann P. Spontaneous Mesoporosity-Driven Sequestration of Ionic Liquids from Silicone-Based Reference Electrode Membranes. ACS Sens 2023; 8:1774-1781. [PMID: 37043696 DOI: 10.1021/acssensors.3c00085] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/14/2023]
Abstract
Nanopore-driven sequestration of ionic liquids from a silicone membrane is presented, a phenomenon that has not been reported previously. Reference electrodes with ionic liquid doped polydimethylsiloxane (PDMS) reference membranes and colloid-imprinted mesoporous carbon (CIM) as solid contact are not functional unless special attention is paid to the porosity of the solid contact. In the fabrication of such reference electrodes, a solution of a hydroxyl-terminated silicone oligomer, ionic liquid, cross-linking reagent, and polymerization catalyst is deposited on top of the carbon layer, rapidly filling the pores of the CIM carbon. The catalyzed polymerization curing of the silicone quickly results in cross-linking of the hydroxyl-terminated polydimethylsiloxane oligomers, forming structures that are too large to penetrate the CIM carbon pores. Therefore, as solvent evaporation from the top of freshly prepared membranes drives the diffusional transport of solvent toward that membrane surface, the solvent molecules that leave the CIM carbon pores can only be replaced by the ionic liquid. This depletes the ionic liquid in the reference membrane that overlies the CIM carbon solid contact and increases the membrane resistance by up to 3 orders of magnitude, rendering the devices dysfunctional. This problem can be avoided by presaturating the CIM carbon with ionic liquid prior to the deposition of the solution that contains the silicone oligomers and ionic liquid. Alternatively, a high amount of ionic liquid can be added into the membrane solution to account for the size-selective sequestration of ionic liquid into the carbon pores. Either way, a wide variety of ionic liquids can be used to prepare PDMS-based reference electrodes with CIM carbon as a solid contact. A similar depletion of the K+ ionophore BME-44 from ion-selective silicone membranes was observed too, highlighting that the depletion of active ingredients from polymeric ion-selective and reference membranes due to interactions with high surface area solid contacts may be a more common phenomenon that so far has been overlooked.
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Affiliation(s)
- Xin I N Dong
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States
| | - Brian D Spindler
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States
| | - Minog Kim
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States
| | - Andreas Stein
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States
| | - Philippe Bühlmann
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States
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Rousseau CR, Honig ML, Bühlmann P. Hydrogels Doped with Redox Buffers as Transducers for Ion-Selective Electrodes. Anal Chem 2021; 94:1143-1150. [PMID: 34932309 DOI: 10.1021/acs.analchem.1c04264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Solid-contact ion-selective electrodes (ISEs) with an unintentional water layer between the sensing membrane and underlying electron conductor are well known to suffer from potential drift caused by the instability of the phase boundary potential between the sensing membrane and the water layer with its uncontrolled ionic composition. The reproducibility and long-term emf stability of ISEs with a miniaturized inner filling solution comprising a hydrogel and a hydrophilic electrolyte have not been studied as thoroughly. Here, such devices are discussed with a view to electrode-to-electrode reproducibility, using both hydrophilic ion-exchange and plasticized PVC membranes, along with a hydrophilic redox buffer composed of ferrocyanide and ferricyanide to control the potential between the hydrogel and the underlying electron conductor. With plasticized PVC sensing membranes, these electrodes showed an E0 reproducibility of ±1.1 mV or better, while with hydrophilic ion-exchange membranes, this variability was slightly larger. Long-term drifts were also assessed with both membranes, and the effect of osmotic pressure on drift was shown to be insignificant for the PVC membranes and very small at most for the hydrophilic membranes.
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Affiliation(s)
- Celeste R Rousseau
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States
| | - Madeline L Honig
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States
| | - Philippe Bühlmann
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States
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Podrażka M, Witkowska Nery E, Henares TG, Jönsson-Niedziółka M, Arrigan DWM. Ion Transfer Voltammetry with an Electrochemical Pen. Anal Chem 2020; 92:15997-16004. [PMID: 33259187 PMCID: PMC7745201 DOI: 10.1021/acs.analchem.0c03530] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We present a new electrochemical system that combines paper-based sensing and ion-transfer voltammetry, bringing the latter a step closer toward point-of-care applications. Studies at the interface between two immiscible electrolyte solutions (ITIES) are often performed to detect redox-inactive species; unfortunately, due to the inherent instability of the interface, it is rather poorly explored outside specialized laboratories. Here, we address this limitation by combining a pen-like device containing the gelled organic phase with a paper-supported aqueous phase. This combination makes the system more user-friendly, potentially low-cost, and easy to assemble. We show the applicability of the new cell to analyze both simple and ionophore-facilitated transfer of ions and proteins, preconcentration of species, and analysis of mixtures through combination with paper chromatography. The native ion content of the paper also enabled measurements without added electrolytes. Those studies could broaden the scope for the application of the label-free electrochemical detection of nonredox-active species at points-of-need.
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Affiliation(s)
- Marta Podrażka
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Emilia Witkowska Nery
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Terence G Henares
- Curtin Institute for Functional Molecules and Interfaces, School of Molecular and Life Sciences, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
| | | | - Damien W M Arrigan
- Curtin Institute for Functional Molecules and Interfaces, School of Molecular and Life Sciences, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
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Chen XV, Stein A, Bühlmann P. Reference Electrodes Based on Ionic Liquid-Doped Reference Membranes with Biocompatible Silicone Matrixes. ACS Sens 2020; 5:1717-1725. [PMID: 32366104 DOI: 10.1021/acssensors.0c00363] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Many reference electrodes with an ionic liquid-doped reference membrane contain a plasticizer that can gradually leach out into the sample. However, because many common plasticizers are known to be endocrine disruptors and may induce inflammatory reactions, they are preferably avoided for wearable or implantable sensors. Therefore, this work tested polymeric reference electrode membranes prepared by solvent casting from seven commercially available biocompatible silicones that are widely used in implantable devices. Only reference electrodes with membranes consisting of poly(3,3,3-trifluoropropylmethylsiloxane) (Fluorosilicone 1) and one of several 1-methyl-3-alkylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids provided a stable and sample-independent potential in electrolyte solutions spanning the range of electrolyte concentrations in human blood, with more hydrophobic ionic liquids performing better. Over 8 days at 37 °C in artificial blood electrolyte solutions, the reference membranes doped with 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide exhibited a potential drift as low as 20 μV/h. In 10% animal serum, a 112 μV/h drift was observed over 5.8 days. The other six silicone materials doped with an ionic liquid either failed to form self-standing membranes or did not provide a sample-independent potential in the ionic concentration range tested. In case of the functional reference electrodes, differential scanning calorimetry confirmed good miscibility between the ionic liquid and the polymer matrix, whereas the poor miscibility of four polymer matrixes and the ionic liquids-as confirmed by differential scanning calorimetry-correlated with an undesirable sample dependence of the reference potential.
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Affiliation(s)
- Xin V. Chen
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States
| | - Andreas Stein
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States
| | - Philippe Bühlmann
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States
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Mazurkiewicz W, Podrażka M, Jarosińska E, Kappalakandy Valapil K, Wiloch M, Jönsson‐Niedziółka M, Witkowska Nery E. Paper‐Based Electrochemical Sensors and How to Make Them (Work). ChemElectroChem 2020. [DOI: 10.1002/celc.202000512] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Wojciech Mazurkiewicz
- Institute of Physical ChemistryPolish Academy of Sciences Kasprzaka 44/52 01-224 Warsaw Poland
| | - Marta Podrażka
- Institute of Physical ChemistryPolish Academy of Sciences Kasprzaka 44/52 01-224 Warsaw Poland
| | - Elżbieta Jarosińska
- Institute of Physical ChemistryPolish Academy of Sciences Kasprzaka 44/52 01-224 Warsaw Poland
| | | | - Magdalena Wiloch
- Institute of Physical ChemistryPolish Academy of Sciences Kasprzaka 44/52 01-224 Warsaw Poland
| | | | - Emilia Witkowska Nery
- Institute of Physical ChemistryPolish Academy of Sciences Kasprzaka 44/52 01-224 Warsaw Poland
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Chen XV, Mousavi MP, Bühlmann P. Fluorous-Phase Ion-Selective pH Electrodes: Electrode Body and Ionophore Optimization for Measurements in the Physiological pH Range. ACS OMEGA 2020; 5:13621-13629. [PMID: 32566827 PMCID: PMC7301372 DOI: 10.1021/acsomega.0c00582] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/09/2020] [Accepted: 05/18/2020] [Indexed: 06/11/2023]
Abstract
Because of their low polarity and polarizability, fluorous sensing membranes are both hydrophobic and lipophobic and exhibit very high ion selectivities. Here, we report on a new fluorous-membrane ion-selective electrode (ISE) with a wide sensing range centered around physiologically relevant pH values. The fluorophilic tris[perfluoro(octyl)butyl]amine (N[(CH2)4Rf8]3) was synthesized and tested as a new H+ ionophore using a redesigned electrode body that provides excellent mechanical sealing and much improved measurement reliability. In a challenging 1 M KCl background, these fluorous-phase ISEs exhibit a sensing range from pH 2.2 to 11.2, which is one of the widest working ranges reported to date for ionophore-based H+ ISEs. High selectivities against common interfering ions such as K+, Na+, and Ca2+ were determined (selectivity coefficients: logK H, K pot = - 11.6; logK H, Na pot = - 12.4; logK H, Ca pot < - 10.2). The use of the N[(CH2)4Rf8]3 ionophore with its -(CH2)4- spacers separating the amino group from the strongly electron-withdrawing perfluorooctyl groups improved the potentiometric selectivity as compared to the less basic tris[perfluoro(octyl)propyl]amine ionophore. The use of N[(CH2)4Rf8]3 also made the ISE less prone to counter anion failure (i.e., Donnan failure) at low pH than the use of tris[perfluoro(octyl)pentyl]amine with its longer -(CH2)5- spacers, which more effectively shield the amino center from the perfluorooctyl groups. In addition, we exposed both conventional plasticized PVC-phase pH ISEs and fluorous-phase pH ISEs to 10% serum for 5 days. Results show that the PVC-phase ISEs lost selectivity while their fluorous-phase counterparts did not.
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Anderson EL, Chopade SA, Spindler B, Stein A, Lodge TP, Hillmyer MA, Bühlmann P. Solid-Contact Ion-Selective and Reference Electrodes Covalently Attached to Functionalized Poly(ethylene terephthalate). Anal Chem 2020; 92:7621-7629. [PMID: 32351106 DOI: 10.1021/acs.analchem.0c00296] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Numerous ion-selective and reference electrodes have been developed over the years. Following the need for point-of-care and wearable sensors, designs have transitioned recently from bulky devices with an aqueous inner filling solution to planarizable solid-contact electrodes. However, unless the polymeric sensing and reference membranes are held in place mechanically, delamination of these membranes from the underlying solid to which they adhere physically limits sensor lifetime. Even minor external mechanical stress or thermal expansion can result in membrane delamination and, thereby, device failure. To address this problem, we designed a sensing platform based on poly(ethylene terephthalate) substrates to which polyacrylate-based sensing and polymethacrylate-based reference membranes are attached covalently. Ion-selective membranes with covalently attached or freely dissolved ionophore- and ionic-liquid-doped reference membranes can be directly photopolymerized onto surface-functionalized poly(ethylene terephthalate), resulting in the formation of covalent bonds between the underlying substrate and the attached membranes. H+- and K+-selective electrodes thus prepared exhibit highly selective responses with the theoretically expected (Nernstian) response slope, and reference electrodes provide sample-independent reference potentials over a wide range of electrolyte concentrations. Even repeated mechanical stress does not result in the delamination of the sensing and reference membranes, leading to electrodes with much improved long-term performance. As demonstrated for poly(ethylene-co-cyclohexane-1,4-dimethanol terephthalate) (PETG), this approach may be expanded to a wide range of other polyester, polyamide, and polyurethane platform materials. Covalent attachment of sensing and reference membranes to an inert plastic platform material is a very promising approach to a problem that has plagued the field of ion-selective electrodes and field effect transistors for over 30 years.
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Berube TR, Buck RP, Lindner E, Tòth K, Pungor E. Response of Liquid-Membrane Calcium-Selective Electrodes to Calcium Ion Activity Steps. ANAL LETT 2006. [DOI: 10.1080/00032719108052921] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Morf WE, Simon W. Berechnung von freien Hydratationsenthalpien und Koordinationszahlen für Kationen aus leicht zugänglichen Parametern. Helv Chim Acta 2004. [DOI: 10.1002/hlca.19710540304] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Wuhrmann HR, Morf WE, Simon W. Modellberechnung der EMK und der Ionenselektivität von Membranelektroden-Messketten. Helv Chim Acta 2004. [DOI: 10.1002/hlca.19730560320] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Bühlmann P, Pretsch E, Bakker E. Carrier-Based Ion-Selective Electrodes and Bulk Optodes. 2. Ionophores for Potentiometric and Optical Sensors. Chem Rev 1998; 98:1593-1688. [PMID: 11848943 DOI: 10.1021/cr970113+] [Citation(s) in RCA: 1272] [Impact Index Per Article: 48.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Philippe Bühlmann
- Department of Chemistry, School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan, Department of Organic Chemistry, Swiss Federal Institute of Technology (ETH), Universitätstrasse 16, CH-8092 Zürich, Switzerland, and Department of Chemistry, Auburn University, Auburn, Alabama 36849
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Cammann K, Lemke U, Rohen A, Sander J, Wilken H, Winter B. Chemo- und Biosensoren - Grundlagen und Anwendungen. Angew Chem Int Ed Engl 1991. [DOI: 10.1002/ange.19911030506] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Jyo A, Torikai M, Ishibashi N. The Selectivity Evaluation of an Ion-selective Electrode with a Liquid Membrane by Electrode Response to a Foreign Ion. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 1974. [DOI: 10.1246/bcsj.47.2862] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Scholer R, Simon W. Membranelektrode zur selektiven, potentiometrischen Erfassung organischer Kationen. Helv Chim Acta 1972. [DOI: 10.1002/hlca.19720550539] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Carr CW. Measurement of protein-small ion interactions with ion-specific electrodes. Methods Enzymol 1972; 26:182-93. [PMID: 4680706 DOI: 10.1016/s0076-6879(72)26011-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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