ORCID Profile
0000-0001-8970-4343
Current Organisation
Université de Genève
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Publisher: Wiley
Date: 07-01-2015
Publisher: American Chemical Society (ACS)
Date: 27-10-2017
Publisher: Elsevier BV
Date: 05-1997
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B907893B
Abstract: We report here on the selective voltammetric cation transfer into a polymeric thin layer film that is back side contacted with an anion-exchanging conducting polymer, poly(3-octylthiophene).
Publisher: Elsevier
Date: 2008
Publisher: American Chemical Society (ACS)
Date: 10-02-2000
DOI: 10.1021/AC991146N
Abstract: Selectivities of solvent polymeric membrane ion-selective electrodes (ISEs) are quantitatively related to equilibria at the interface between the s le and the electrode membrane. However, only correctly determined selectivity coefficients allow accurate predictions of ISE responses to real-world s les. Moreover, they are also required for the optimization of ionophore structures and membrane compositions. Best suited for such purposes are potentiometric selectivity coefficients as defined already in the 1960s. This paper briefly reviews the basic relationships and focuses on possible biases in the determination of selectivity coefficients. The traditional methods to determine selectivity coefficients (separate solution method, fixed interference method) are still the same as those originally proposed by IUPAC in 1976. However, several precautions are needed to obtain meaningful data. For ex le, errors arise when the response to a weakly interfering ion is also influenced by the primary ion leaching from the membrane. Wrong selectivity coefficients may be also obtained when the interfering agent is highly preferred and the electrode shows counterion interference. Recent advances show how such pitfalls can be avoided. A detailed recipe to determine correct potentiometric selectivity coefficients unaffected by such biases is presented.
Publisher: American Chemical Society (ACS)
Date: 24-01-2020
Publisher: American Chemical Society (ACS)
Date: 22-01-2013
DOI: 10.1021/AC303534V
Abstract: A new type of carbon dioxide sensor comprising a pH glass electrode measured against a carbonate-selective membrane electrode based on a tweezer type carbonate ionophore is presented here for the first time. No cumbersome liquid junction based reference element is utilized in this measurement. The sensor shows an expected nernstian alent response slope to dissolved CO(2) over a wide range covering the routine environmental and physiological PCO(2) levels. Unlike the conventional Severinghaus CO(2) probe for which the response is substantially delayed to up to 10 min due to diffusion of carbon dioxide into the internal compartment, the ion-selective CO(2) sensor proposed here shows a response time (t(95%)) of 5 s. When used together with a traditional reference electrode, the sensor system is confirmed to also monitor s le pH and carbonate along with carbon dioxide. A selectivity analysis suggests that Cl(-) does not interfere even at high concentrations, allowing one to explore this type of sensor probe for use in seawater or undiluted blood s les. The CO(2) probe has been used in an aquarium to monitor the CO(2) levels caused by the diurnal cycles caused by the metabolism of the aquatic plants and shows stable and reproducible results.
Publisher: The Electrochemical Society
Date: 05-1997
DOI: 10.1149/1.1837633
Publisher: American Chemical Society (ACS)
Date: 15-09-1995
DOI: 10.1021/AC00114A005
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7CC05908F
Abstract: A new lipophilic dinonyl bipyridyl Os( ii )/Os( iii ) complex successfully mediates ion transfer processes across voltammetric thin membranes.
Publisher: Elsevier BV
Date: 10-2009
Publisher: American Chemical Society (ACS)
Date: 15-02-1994
DOI: 10.1021/AC00076A016
Publisher: American Chemical Society (ACS)
Date: 28-02-2020
Publisher: Swiss Chemical Society
Date: 26-11-2014
Abstract: Aquatic environments are complex living systems where biological and chemical constituents change rapidly with time and space and may exhibit synergistic interactions. To understand these processes, the traditional approach based on a typically monthly collection of s les followed by laboratory analysis is not adequate. It must be replaced by high-resolution autonomous in situ detection approaches. In our group at the University of Geneva, we aim to develop and deploy chemical sensor probes to understand complex aquatic systems. Most research centers around electrochemical sensing approaches, which involves: stripping voltammetry at gel-coated microelectrode arrays for direct measurements of bioavailable essential or toxic trace metals direct potentiometry for the measurement of nutrients and other species involved in the nitrogen and carbon cycles online desalination for oceanic measurements the development of robust measurement principles such as thin layer coulometry, and speciation analysis by tandem electrochemical detection with potentiometry and dynamic electrochemistry. These fundamental developments are combined with instrument design, both in-house and with external partners, and result in field deployments in partnership with environmental researchers in Switzerland and the European Union.
Publisher: Elsevier BV
Date: 05-2004
Publisher: American Chemical Society (ACS)
Date: 09-1992
DOI: 10.1021/AC00041A012
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D1CC06636F
Abstract: Selectivity remains a constant challenge in the development of optical extraction-based sensors. Fortunately, there are several mechanistic and compositional changes with the potential to improve selectivity without developing new ionophores.
Publisher: Elsevier BV
Date: 07-2008
Publisher: American Chemical Society (ACS)
Date: 03-09-2018
Abstract: We present a new potentiometric sensor principle and a calibration protocol for in situ profiling of dissolved CO
Publisher: American Chemical Society (ACS)
Date: 12-04-2017
DOI: 10.1021/ACSSENSORS.7B00165
Abstract: While the titrimetric assay is one of the most precise analytical techniques available, only a limited list of complexometric chelators is available, as many otherwise promising reagents are not water-soluble. Recent work demonstrated successful titrimetry with ion-exchanging polymeric nanospheres containing hydrophobic complexing agents, so-called ionophores, opening an exciting avenue in this field. However, this method was limited to ionophores of very high affinity to the analyte and exhibited a relatively limited titration capacity. To overcome these two limitations, we report here on solvent based titration reagents. This heterogeneous titration principle is based on the dissolution of all hydrophobic recognition components in a solvent such as dichloromethane (CH
Publisher: Swiss Chemical Society
Date: 17-12-2014
Publisher: American Chemical Society (ACS)
Date: 31-03-2000
DOI: 10.1021/AC991092H
Abstract: Polymeric membrane ion-selective electrodes exhibit an apparently super-Nernstian response at low s le activities if inner solutions are used that induce strong zero-current fluxes of primary ions toward the inner compartment. This is due to the limited ion fluxes in the aqueous boundary layer near the membrane. In the presence of labile complexes, the effective flux rate is increased and the emf depends on the total concentration of the ions. The concept is illustrated experimentally with calcium-selective electrodes based on the ionophore N,N-dicyclohexyl-N',N'-dioctadecyl-3-oxapentanediamide (ETH 5234) that either respond to total or free ion concentrations. S les can be distinguished that contain varying levels of total calcium but are all buffered with EDTA to the same free calcium concentration of 5 x 10(-8) M.
Publisher: Elsevier BV
Date: 04-2008
DOI: 10.1016/J.ACA.2008.02.069
Abstract: Optical dihydrogen phosphate-selective sensors that function on the basis of bulk optode principles and are based on two different uranyl salophene ionophores are reported here for the first time. The influence of the optode composition and measuring conditions such as s le pH on the optode response are characterized, along with sensor selectivity and long-term stability. Three plasticizers of different polarity are considered for optode fabrication: bis(2-ethylhexyl)sebacate (DOS), dodecyl 2-nitrophenyl ether (o-NPDDE), o-nitrophenyloctylether (o-NPOE). The compounds 9-(diethylamino)-5-(octadecanoylimino)-5H-benzo[a]phenoxazine (ETH 5294, chromoionophore I) and 9-(diethylamino)-5-[(2-octyldecyl)imino]benzo[a]phenoxazine (ETH 5350, chromoionophore III) are used as H(+)-selective fluoroionophores that also act as reference ionophores. The resulting optode-based sensors are compared with their ion-selective electrode (ISE) counterparts, and it is revealed that optodes are better suited for operation at physiological pH. The best optode performance was found for the two component optode sensors doped with ETH 5350 and phosphate ionophore(I). The linear range of these sensor was loga=-6.0 to -2.6. Dihydrogen phosphate-selective optode sensors of optimized composition are fabricated in microsphere format and preliminary measurements in diluted sheep blood s les are presented.
Publisher: American Chemical Society (ACS)
Date: 09-12-2008
DOI: 10.1021/LA802728P
Publisher: Elsevier BV
Date: 10-2021
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6CC07841A
Abstract: A reversible and pH-independent fluorescent ion optode is introduced with an ionophore and surface confined solvatochromic dye transducer doped onto microporous nylon membranes.
Publisher: Swiss Chemical Society
Date: 29-04-2015
Abstract: We summarize here recent advancements on thin layer s les controlled by dynamic electrochemistry techniques for determining different ions that include potassium, calcium, protamine, nitrate, nitrite and halides in erse environmental and clinical s les. Generally, a thin layer liquid (less than 100 μm in thickness) is confined between a working electrode and an ion-selective membrane. Once an external electrical perturbation (i.e. constant potential) is applied to the system, an exhaustive ion transfer process is imposed in the entire thin layer solution. As a result, the observed charge (integration of the current decay) is proportional to the depleted ion concentration. Other electrochemical protocols such as linear sweep voltammetry were also explored aiming at the discrimination of several ions presented in the thin layer. One of the most attractive ex les involves the detection of a mixture of three halides (iodide, bromide and chloride), which can be well resolved at moderated scan rates (10 mV.s–1). Paper-based coulometric sensing on thin layers defined by cellulose papers are being developed in view of translating these new concepts into a reliable and low cost sensing platform.
Publisher: American Chemical Society (ACS)
Date: 13-02-2020
Publisher: American Chemical Society (ACS)
Date: 19-03-2018
DOI: 10.1021/ACS.ANALCHEM.8B00559
Abstract: In this study, paper-based microfluidic devices (μPADs) capable of K
Publisher: Elsevier BV
Date: 08-1993
Publisher: American Chemical Society (ACS)
Date: 22-07-2016
Publisher: Springer Science and Business Media LLC
Date: 27-03-2017
DOI: 10.1038/NG.3826
Publisher: American Chemical Society (ACS)
Date: 29-09-2006
DOI: 10.1021/JA065899K
Publisher: American Chemical Society (ACS)
Date: 20-12-2007
DOI: 10.1021/JA0775467
Publisher: Elsevier BV
Date: 07-2007
DOI: 10.1016/J.ACA.2007.06.015
Abstract: Ionophore-based microsphere sensors are characterized here in transmission mode. These sensors contain a lipophilic ionophore for the analyte cation, a chromoionophore for recognizing H+, and a lipophilic cation-exchanger. They function on the basis of an ion-exchange equilibration step where an increased concentration of analyte ion leads to increased level of extraction into the bulk of the microsphere, expelling protons in return and deprotonating the chromoionophore. Since the path length is variable across the microsphere, such bead-based sensors are normally characterized in fluorescence mode. In this paper, the response of the sensing microspheres is calculated from the ratio of transmitted light intensities at the absorbance peak maxima of the protonated and unprotonated forms of the chromoionophore. At a fixed position of the particle, the resulting responses are found to be independent of light scattering, incident light intensity and the shape or size of the microsphere. The responses of potassium-selective microspheres obtained by this method agree quantitatively with corresponding fluorescence-based data.
Publisher: Society for Industrial & Applied Mathematics (SIAM)
Date: 2003
Publisher: American Chemical Society (ACS)
Date: 23-09-2013
DOI: 10.1021/AC402564M
Abstract: We present a convenient precipitation procedure to fabricate ultrasmall fluorescent ion-selective nanosensors that operate on the basis of bulk ion-exchange sensing principles. The nanosphere matrix is composed of bis(2-ethylhexyl) sebacate (DOS) and a triblock copolymer Pluronic(®) F-127, which also functions as a surfactant to stabilize the nanoparticle. The particles can be prepared easily in large quantity without resorting to further complicated purification. Dynamic light scattering shows that these particles have a monodisperse size distribution with an average diameter of ∼40 nm, suggesting that the nanoparticles are among the smallest ionophore-based ion-selective nanosensors reported to date. A newly reported oxazinoindoline (Ox) as well as a Nile blue derivative (chromoionophore I) was used as a chromoionophore. Na(+)- and H(+)-selective nanospheres were characterized by absorbance and fluorescence spectroscopy. Owing to the very small size of the nanospheres, the suspension containing the particles is transparent. In the additional presence of the pH indicator HPTS, spectroscopic interrogation of pH and Na(+) in the same s le was demonstrated. As an ex le, the nanospheres were used to measure the Na(+) level in commercial mineral waters, and the results showed good agreement with atomic absorption spectroscopy (AAS).
Publisher: American Chemical Society (ACS)
Date: 22-05-2017
Publisher: American Chemical Society (ACS)
Date: 10-07-2013
DOI: 10.1021/AC401367B
Abstract: We propose here a new class of fluorescent H(+) turn-on oxazinoindoline (Ox) dyes as chromoionophores suitable for the development of polymeric ion-selective membranes. Through rational design, oxazinoindolines with varying basicities and tunable absorption bands that extend to the near-infrared region were prepared. The basicities of the compounds were evaluated by potentiometry and fluorescence spectroscopy. By comparing the potentiometric lower detection limit with chromoionophore I (pKa = 14.80 ± 0.03 in PVC-NPOE), pKa values were determined for Ox Y, Ox R, and Ox B to be 9.80 ± 0.03, 12.85 ± 0.03, and 12.95 ± 0.03, respectively. Unlike conventional pH indicators that involve only a protonated and deprotonated form, a third species, arising from the thermal isomerization of the Ox compounds in polar solvents, may influence the overall protonation equilibrium. Interestingly, this results in an apparent pKa increase in the fluorescence mode when more polar PVC-NPOE membranes were utilized. The isomerization is suppressed in nonpolar PVC-DOS membranes. Na(+)-selective optical sensors were successfully prepared using the Ox dyes as an early application of the compounds in ion-selective optical sensors. The compounds were also successfully evaluated in a dynamic electrochemistry (chronopotentiometry) sensing mode for the detection of total alkalinity.
Publisher: Elsevier BV
Date: 12-11-2002
DOI: 10.1016/S0039-9140(02)00405-8
Abstract: The binding properties of neutral or charged chromoionophores and anion ionophores in solvent polymeric membranes were characterized in situ by the so-called sandwich membrane method. Acidity constants (pK(a)) of eight chromoionophores (ETH 5294, ETH 2439, ETH 5350, ETH 5418, ETH 5315, ETH 7061, ETH 7075, ETH 2412) were measured in bis(2-ethylhexyl)sebacate (DOS) and o-nitrophenyloctylether (NPOE) plasticized poly(vinyl chloride) (PVC) membranes commonly used in optical and potentiometric ion sensors. The pK(a) values of all chromoionophores in DOS membranes are by 2-3 orders of magnitude smaller than in NPOE membranes. The weak alkali metal ion binding properties with neutral H(+)-chromoionophore and anion binding with electrically charged chromoionophores were also studied quantitatively. The complex formation constants of the commercially available Co(III)cobyrinate nitrite ionophore and the organomercury chloride ionophore, ETH 9009, were also measured. The very low stability constant observed for ETH 9009 (logbeta(2)=3.60+/-0.03 in PVC-DOS and 3.61+/-0.01 in PVC-NPOE) was explained by the decomposition of the ionophore in contact with chloride s les. On the other hand, the electrically charged nitrite ionophore showed strong complexation with nitrite ions, with logbeta=10.58 and 10.59 in DOS and NPOE membranes, respectively. In contrast to cation ionophores, the stability constant of the NO(2)(-) ionophore does not change with different plasticizers.
Publisher: American Chemical Society (ACS)
Date: 22-11-2021
DOI: 10.1021/ACS.ANALCHEM.1C03232
Abstract: We compare here the effect of surfactants on ion-selective membranes measured via voltammetry and optode emulsions measured optically. Cyclic voltammetry on a thin-film ion-selective membrane is shown to be a useful screening technique for the estimation of effective complex formation constants and selectivity coefficients for different surfactants with various cations. This technique is particularly useful for its ability to identify separate ion-transfer events (free, surfactant complexed, ionophore complexed) for a specific membrane. However, we also caution against the over-reliance on this technique as changes in membrane characteristics are observed following surfactant partitioning. Of the surfactants explored here, a zwitterionic sulfobetaine-based surfactant was found to stabilize sensors without reducing effective binding constants and selectivity, with greatly superior characteristics to other commonly utilized surfactants. Those include Brij-35, F-127, and Triton X-100, all of which showed significant binding to so-called free ions in the membrane, resulting in peak potential shifts of 199 ± 10, 180 ± 24, 278 ± 11 mV, respectively, for potassium following the subtraction of transducing layer effects. This peak shift translated to a much larger undesired free ion response in optode emulsions. The selectivity in emulsion-based systems was also shown to decrease in the presence of nonionic surfactants compared to that containing the zwitterion.
Publisher: American Chemical Society (ACS)
Date: 14-11-2017
DOI: 10.1021/ACS.ANALCHEM.7B03726
Abstract: A new method for the determination of unbiased low selectivity coefficients for two of the most prevalent cases of multivalent ions (z
Publisher: American Chemical Society (ACS)
Date: 16-07-2003
DOI: 10.1021/AC034409T
Abstract: This paper describes a pulsed galvanostatic technique to interrogate ion-selective electrodes (ISEs) with no intrinsic ion-exchange properties. Each applied current pulse is followed by a longer baseline potential pulse to regenerate the phase boundary region of the ion-selective membrane. The applied current fully controls the magnitude and sign of the ion flux into the membrane, thus offering instrumental control over an effect that has become very important in ion-selective electrode research in recent years. The resulting chronopotentiometric response curves essentially mimic traditional ISE behavior, with apparently Nernstian response slopes and selectivities that can be described with the Nicolsky equation. Additionally, the magnitude and sign of the current pulse may be used to tune sensor selectivity. Perhaps most important, however, appears to be the finding that the extent of concentration polarization near the membrane surface can be accurately controlled by this technique. A growing number of potentiometric techniques are starting to make use of nonequilibrium principles, and the method introduced here may prove to be very useful to advance these areas of research. The basic characteristics of this pulsed galvanostatic technique are here evaluated with plasticized poly(vinyl chloride) membranes containing the sodium-selective ionophore tert-butyl calix[4]arene tetramethyl ester and a lipophilic inert salt.
Publisher: Elsevier BV
Date: 09-2007
DOI: 10.1016/J.ACA.2007.07.058
Abstract: Lipophilic H+-selective fluorophores such as Nile Blue derivatives are widely used in ISE-based pH sensors and bulk optodes, and are commonly dissolved in a plasticized matrix such as PVC. Unfortunately, leaching of the active sensing ingredients and plasticizer from the matrix dictates the lifetime of the sensors and h ers their applications in vivo, especially with miniaturized particle based sensors. We find that classical copolymerization of Nile Blue derivatives containing an acrylic side group gives rise to multiple reaction products with different spectral and H+-binding properties, making this approach unsuitable for the development of reliable sensor materials. This limitation was overcome by grafting Nile Blue to a self-plasticized poly(n-butyl acrylate) matrix via an urea or amide linkage between the Nile Blue base structure and the polymer. Optode leaching experiments into methanol confirmed the successful covalent attachment of the two chromoionophores to the polymer matrix. Both polymerized Nile Blue derivatives have satisfactory pH response and appropriate optical properties that are suitable for use in ion-selective electrodes and optodes. Plasticizer-free Na+-selective microsphere sensors using the polymerized chromoionophores were fabricated under mild conditions with an in-house sonic microparticle generator for the measurement of sodium activities at physiological pH. The measuring range for sodium was found as 10(-1)-10(-4) M and 1-10(-3) M, for Nile Blue derivatives linked via urea and amide functionalities, respectively, at physiological pH. The observed ion-exchange constants of the plasticizer-free microsphere were log K(exch) = -5.6 and log K(exch) = -6.5 for the same two systems, respectively. Compared with earlier Na+-selective bulk optodes, the fabricated optical sensing microbeads reported here have agreeable selectivity patterns, reasonably fast response times, and more appropriate measuring ranges for determination of Na+ activity at physiological pH in undiluted blood s les.
Publisher: American Chemical Society (ACS)
Date: 19-08-2003
DOI: 10.1021/JA037167N
Abstract: Selective extraction principles for the recognition of nonelectroactive polyions such as heparin and protamine exist, but the high ionic valency renders the extraction process irreversible. A response principle for the reversible detection of such polyions is proposed here. The extraction of the polyionic analyte to the membrane and its subsequent back-extraction is now controlled electrochemically. The principle is established with a protamine electrode, and excellent stability and reproducibility are demonstrated. This method has important implications for the design of chemical recognition principles for polyionic analytes.
Publisher: FapUNIFESP (SciELO)
Date: 2008
Publisher: American Chemical Society (ACS)
Date: 07-05-2002
DOI: 10.1021/AC0202278
Publisher: American Chemical Society (ACS)
Date: 13-11-2015
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9CC06729A
Abstract: A range of ionic solvatochromic dye (SD) transducers for use in ion-selective emulsified optical sensors are introduced and characterized.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6CC04876E
Abstract: We report on the first direct spectroscopic evidence of the capacitive ion-to-electron transducing mechanism of carbon nanomaterials in solid contact polymeric ion-selective electrodes (SC-ISEs).
Publisher: Springer New York
Date: 2014
Publisher: Springer Science and Business Media LLC
Date: 09-02-2016
Publisher: Elsevier BV
Date: 15-05-2008
Publisher: American Chemical Society (ACS)
Date: 26-01-2018
Publisher: American Chemical Society (ACS)
Date: 17-09-2020
Publisher: Elsevier BV
Date: 12-2011
Publisher: American Chemical Society (ACS)
Date: 26-08-2022
Publisher: Elsevier BV
Date: 08-2009
DOI: 10.1016/J.ACA.2009.07.004
Abstract: Ionophore-based ion-selective electrodes are widely used for potentiometric electrolyte measurements, in which case they are known to detect the free ion activity. Total ion concentrations cannot be directly assessed by this methodology if the ion is predominantly present in a complexed form. We present here the direct measurement of total calcium using a calcium ion-selective electrode interrogated in a flash chronopotentiometric transduction mode. A high magnitude of cathodic current pulse is applied across a calcium ion-selective membrane containing the ionophore ETH 5234 but void of ion-exchanger to prevent spontaneous extraction. This induces a defined flux of calcium ions from the s le side to the membrane and results in the release of labile bound calcium and a concomitant depletion at the membrane surface at a critical current or time. This is observed as an inflection point on the potential-time curve and the square root of the transition time is linearly related to the total concentration in the s le. It is shown that the responses to solutions of labile calcium complexes of nitrilotriacetic acid (NTA) are in a good agreement with that of the same concentration of calcium chloride in saline solution with this protocol. Initial applications are aimed towards assaying extracellular calcium. Calcium binding to albumin is shown to be inconsequential with s le dilutions typical for clinical assays. Calcium calibration curves in real and artificial dilute serum are finally shown to correspond to that of calcium chloride, suggesting that the methodology is indeed capable of detecting total calcium under these conditions. The present membrane materials allow detection of up to over 0.5mM total calcium in serum, currently requiring such s les to be diluted about 5-fold. The slopes of the square root of time-concentration dependence for the calibrations of free calcium in a background of NaCl and total serum calcium were found to be 3.857 and 3.717 s(1/2)mM(-1), respectively, deviating by just 3.6%. The lower detection limit (3x SD) was calculated as 12 microM.
Publisher: American Chemical Society (ACS)
Date: 12-07-2017
DOI: 10.1021/ACS.ANALCHEM.7B01777
Abstract: Finite difference analysis of ion-selective membranes is a valuable tool for understanding a range of time dependent phenomena such as response times, long and medium term potential drifts, determination of selectivity, and (re)conditioning kinetics. It is here shown that an established approach based on the diffusion layer model applied to an ion-exchange membrane fails to use mass transport to account for concentration changes at the membrane side of the phase boundary. Instead, such concentrations are imposed by the ion-exchange equilibrium condition, without taking into account the source of these ions. The limitation is illustrated with a super-Nernstian potential jump, where a membrane initially void of analyte ion is exposed to incremental concentrations of analyte in the s le. To overcome this limitation, the two boundary elements, one at either side of the s le-membrane interface, are treated here as a combined entity and its total concentration change is dictated by diffusional fluxes into and out of the interface. For each time step, the concentration distribution between the two boundary elements is then computed by ion-exchange theory. The resulting finite difference simulation is much more robust than the earlier model and gives a good correlation to experiments.
Publisher: American Chemical Society (ACS)
Date: 13-07-2011
DOI: 10.1021/CG101636R
Publisher: Swiss Chemical Society
Date: 27-04-2022
Abstract: Heparin quantification at the point of care has been of medical interest for years but a suitable point of care measurement method for whole blood is still elusive. Our group has recently developed a nanoparticle-based optical sensor for protamine that allows for heparin quantification in plasma. This work discusses the effect of the transducing-dye structure and the promise of embedding the sensors in an agarose gel for avoiding red blood cell interference.
Publisher: American Chemical Society (ACS)
Date: 07-08-2014
DOI: 10.1021/ED4008149
Publisher: American Chemical Society (ACS)
Date: 25-08-2017
Publisher: American Chemical Society (ACS)
Date: 21-12-2011
DOI: 10.1021/JA210600K
Abstract: We report here on a generic approach to read out potentiometric sensors with electrogenerated chemiluminescence (ECL). In a first ex le, a potassium ion-selective electrode acts as the reference electrode and is placed in contact with the s le solution. The working electrode of the three-electrode cell is responsible for ECL generation and placed in a detection solution containing tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3)(2+)] and the coreactant 2-(dibutylamino)ethanol (DBAE), physically separated from the s le by a bridge. Changes in the s le potassium concentration directly modulate the potential at the working electrode, and hence the ECL output, when a constant-potential pulse is applied between the two electrodes. A linear response of the ECL intensity to the logarithmic potassium concentration between 10 μm and 10 mM was found.
Publisher: American Chemical Society (ACS)
Date: 14-11-2014
DOI: 10.1021/JA5107578
Abstract: Potentiometric sensors require the implementation of conducting wires for signal transduction, but this is impractical for the readout of in idual nanoparticles. It is here demonstrated for the first time that the potentiometric response of ion-selective nanospheres can be observed with voltage-sensitive dyes, thereby converting nanoscale electrochemical signals into an optical readout. No reference electrode is needed since the readout is by fluorescence. The results strongly support the potentiometric origin for the fluorescence response. The ion-selective nanospheres exhibit excellent selectivity and respond to ion concentration changes independent of s le pH, providing a new platform of potentiometric nanosensors with optical readout compatible with optical imaging equipment.
Publisher: Wiley
Date: 19-12-2019
Abstract: The design of solid-state reference electrodes without a liquid junction is important to allow miniature and cost-effective electrochemical sensors. To address this, a pulse control is proposed using an Ag/AgI element as reliable solid-state reference electrode. It involves the local release of iodide by a cathodic current that is immediately followed by an electromotive force (EMF) measurement that serves as the reference potential. The recapture of iodide ions is achieved by potentiostatic control. This results in intermittent potential values that are reproducible to less than one millivolt (SD=0.27 mV, n=50). The ionic strength is shown to influence the activity coefficient of released iodide in accordance with the extended Debye-Hückel equation, resulting in a predictable change of the potential reading. The principle is applied to potentiometric potassium detection with a valinomycin-based ion-selective electrode (ISE), demonstrating a completely solid-state sensor configuration.
Publisher: American Chemical Society (ACS)
Date: 08-1996
DOI: 10.1021/AC960035A
Abstract: An extension into the fluorescence mode of ion-exchange optodes is described, allowing miniaturization and its concomitant benefits. A micrometer-size, fluorescent fiber-optic sodium sensor is described, based on a highly sodium-selective, crown ether-capped calix[4]arene ionophore, capable of ratiometric operation. Three sensor configurations are given, employing different lipophilic, fluorescent pH chromoionophores (Nile Blue derivatives), demonstrating the ability to improve the detection limit and tune the dynamic range to the desired region of interest. Two of the sensors are of special interest in that their working ranges lie within those desired for measuring intracellular cytosolic or blood levels of sodium at the respective physiological pH. These optodes have excellent sodium selectivity, with other physiologically relevant cations (e.g., potassium, calcium, and magnesium) being highly discriminated. Three simple mathematical relationships are given for the three experimentally used fluorescent signal mechanisms (intensity, intensity ratios, and inner-filter or energy transfer effects), permitting visualization on a single graph and enabling direct comparison of the different sensors' optical responses on a common platform. Finally, these optodes measure the s le's sodium activity, rather than the concentration, provided that the s le's pH is measured simultaneously by another sensor, such as a glass electrode.
Publisher: American Chemical Society (ACS)
Date: 05-03-2019
DOI: 10.1021/ACS.ANALCHEM.9B00787
Abstract: We introduce here a general strategy to read out chronopotentiometric sensors by electrogenerated chemiluminescence (ECL). The potentials generated in chronopotentiometry in a s le compartment are used to control the ECL in a separate detection compartment. A three-electrode cell is used to monitor the concentration changes of the analyte, while the luminol-H
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D2EM00341D
Abstract: A new autonomous, pre-programmable nitrate ion-selective submersible probe with a drift correction protocol, in-line calibration and a new reference system gives direct access to concentration and not activity.
Publisher: American Chemical Society (ACS)
Date: 12-09-2002
DOI: 10.1021/AC025596I
Abstract: The development and characterization of small, uniform, and mass-produced plasticized PVC-based sensing microspheres in view of rapid trace level analysis of lead ions is reported. Micrometer-sized particles obtained via an automated casting process were rendered selective for lead ions by doping them with highly selective components in a manner analogous to traditional optode sensing films. Single particles that contained the lipophilic ionophore N,N,N',N'-tetradodecyl-3-6-dioxaoctane-1-thio-8-oxodiamide (ETH 5493), the chromoionophore ETH 5418 together with a lipophilized indocarbocyanine derivative as internal reference dye (DiIC18), and lipophilic ion-exchanger sites sodium tetrakis[3,5-bistrifluoromethylphenyl]borate, yielded measurable lead responses at the low nanomolar level in pH buffered solutions. The detection limit for single particles was 3 x 10(-9) M at pH 5.7. The microspheres were fabricated via a reproducible formation of polymer droplets within a flowing aqueous phase followed by collection of spherical particles of approximately 13 microm in size. The particles were immobilized and assayed in idually in a microflow cell via fluorescence microscopy. Selectivity patterns found were in agreement with those reported earlier for the lead-selective ligand ETH 5493, and all response functions were fully described by theory. In contrast to optode films that necessitated very long equilibration times and large s le volumes in diluted s les of analyte, particles exhibited extremely enhanced equilibrium response times. Thus, for lead s le concentrations at and above 5 x 10(-8) M, response times were approximately 3 min, whereas at the detection limit, complete equilibrium was recorded after just 15 min, with required s le volumes on the order of 1 mL This new class of microspheres appears to be suitable for rapid and sensitive ion detection at trace levels in environmental and biological applications.
Publisher: American Chemical Society (ACS)
Date: 20-11-2019
DOI: 10.1021/ACSSENSORS.9B01802
Abstract: Colorimetric measurements by image analysis, giving RGB or HSV data, have become commonplace with optical indicator-based assays and as a readout for paper-based analytical devices (PADs). Yet, most works on PADs tend to ignore the quantitative relationship between color data and concentration, which may h er their establishment as analytical devices and make it difficult to properly understand chemical or biological reactions on the paper substrate. This Perspective Article discusses how image color data are computed into colorimetric absorbance values that correlate linearly to dye concentration and compare well to traditional spectrophotometry. Thioflavin T (ThT), Neutral Red (NR), and Orange IV are used here as model systems. Absorbance measurements in solution correlate well to image data (and Beer's law) from the color channel of relevance if the gamma correction normally used to render the picture more natural to the human eye is removed. This approach also allows one to correct for color cast and variable background color, which may otherwise limit quantitation in field measurements. Reflectance measurements on paper color spots are equally found to correlate quantitatively between spectroscopy and imaging devices. In this way, deviations from Beer's law are identified that are explained with dye interactions on the paper substrate.
Publisher: American Chemical Society (ACS)
Date: 02-12-2022
DOI: 10.1021/ACSSENSORS.2C02154
Abstract: Point-of-care quantification of the anticoagulant heparin still remains a significant clinical challenge as the reference method (colorimetric anti-factor Xa assay) cannot be performed in whole blood. Our group recently put forth the novel optical nanosensing principle using an ionic solvatochromic dye as a signal transducer. These nanosensors demonstrated significantly improved selectivity and sensitivity compared to ion-exchange-type polyion nanosensors and enabled protamine/heparin quantification in blood plasma s les. However, because the readout is absorbance-based, they are still not suitable for whole blood measurements. To overcome the background absorbance of blood, the nanosensors were here embedded in an agarose hydrogel capable of filtering out red blood cells while allowing plasma components to diffuse into the gel. Calibration curves for both protamine and heparin were successfully obtained in buffer, undiluted plasma, and undiluted whole blood using different colorimetric image analysis methods and a simple experimental setup.
Publisher: Wiley
Date: 08-03-2018
Publisher: American Chemical Society (ACS)
Date: 23-08-2019
Publisher: Wiley
Date: 18-10-2011
Publisher: Wiley
Date: 20-02-2014
Publisher: American Chemical Society (ACS)
Date: 12-02-1999
DOI: 10.1021/AC980944V
Publisher: Wiley
Date: 09-1999
DOI: 10.1002/(SICI)1521-4109(199909)11:13<915::AID-ELAN915>3.0.CO;2-J
Publisher: Wiley
Date: 07-02-2023
Abstract: Ionophore‐based carbonate‐selective sensors have become reliable analytical tools due to their high selectivity and versatility of applications. Nonetheless, successful ex les of their implementation in nanoscale devices are yet to be found in the literature. Herein we describe the first attempt to develop carbonate sensors with ionophores using ion‐selective nanoemulsions. Classical chromoionophore‐based sensors were shown to perform poorly upon transfer to the nanoscale. We hypothesize that this is caused by the heightened surface activity of the ion‐ionophore complex. This challenge is overcome by the addition of a positively charged solvatochromic dye X3 + to the aqueous phase instead of the sensing particles. The presence of this dye facilitates transfer of carbonate from the particle surface into the sensor bulk, which is followed by an unexpected change of fluorescence with the emergence of a new peak at longer wavelengths, allowing for a ratiometric signal transduction. We have found that this spectral change originates from dye hyper‐polarization by the charged moiety of carbonate complex with the ionophore, in analogy to earlier work with protamine nanosensors. The dye‐coextraction‐based sensing protocol is shown to be reversible and selective with regard to both anionic and cationic interferences present in the s le and forms the foundation for further mechanistic advances for anion sensing with ionophores.
Publisher: Elsevier BV
Date: 09-2012
DOI: 10.1016/J.ACA.2012.07.026
Abstract: A nitrate ion-selective electrode (ISE) employing a permeable tubular membrane impregnated with a conventional ISE cocktail has been used successfully in the coulometric analysis of nitrate in fresh waters. The liquid ISE membrane comprising a nitrate ionophore [tridodecylmethylammonium nitrate (TDMAN)], lipophilic electrolyte [tetradodecyl-ammoniumtetrakis(4-chlorophenyl)borate (ETH 500)] and plasticizer [bis(3-ethyl-hexyl)sebacate (DOS)] was supported on a porous polypropylene tube. Coulometric analysis with the tubular membrane ISE showed that nitrate could be detected in the range 10-100 μM with a precision of 2.3% relative standard deviation (RSD), limit of detection of 1.1 μM and relative accuracy of 4.4% compared to a certified reference material (CRM) Lake s le.
Publisher: American Chemical Society (ACS)
Date: 16-07-1999
DOI: 10.1021/AC990195X
Abstract: This paper describes basic response features of solvent polymeric membrane ion sensors with voltammetric and erometric transduction. The model systems used here contain no ionophore for simplicity reasons. Reasonable simplifications of the theory are introduced that allow one to understand the response mechanism in view of a practical application of these sensors. It is shown that ion-sensing membranes preferentially contain no ion-exchanger properties in order to function optimally in a voltammetric mode. As with the systems studied by Kihara, both liquid-polymer interfaces of the membrane are preferably polarizable. Specifically, they contain the highly lipophilic electrolyte tetradodecylammonium tetrakis(4-chlorophenyl)borate (ETH 500) in the membrane to improve lifetime, increase the magnitude of the potential window, and prohibit exchange reactions with s le ions. An ohmic behavior that is associated with an assisted electrolyte-transfer process is observed only above a threshold potential which can be quantitatively predicted by theory. The threshold potential depends on the nature and activity of s le anions and cations in the s le and inner filling solution of the membrane electrode. Within the experimental conditions discussed in this paper, these sensors seem to measure s le ion activities, not concentrations, since the rate-limiting step is the diffusion of extracted ions away from the interface into the membrane bulk. Similarly, no effect of s le stirring on the measured current is observed. This contrasts to work done on liquid-liquid electrolyte-transfer reactions, where large diffusion coefficients in the organic phase often lead to substantial s le depletion effects. The detection of anions and cations with the same membrane is demonstrated in a cyclic voltammetric mode. Direct continuous detection of one type of anion is accomplished by pulsed erometry to ensure a rapid, repetitive renewal of the membrane composition between measurements.
Publisher: Elsevier BV
Date: 02-2021
Publisher: Springer Science and Business Media LLC
Date: 27-04-2016
DOI: 10.1038/NCOMMS11375
Abstract: Common variants in 94 loci have been associated with breast cancer including 15 loci with genome-wide significant associations ( P × 10 −8 ) with oestrogen receptor (ER)-negative breast cancer and BRCA1 -associated breast cancer risk. In this study, to identify new ER-negative susceptibility loci, we performed a meta-analysis of 11 genome-wide association studies (GWAS) consisting of 4,939 ER-negative cases and 14,352 controls, combined with 7,333 ER-negative cases and 42,468 controls and 15,252 BRCA1 mutation carriers genotyped on the iCOGS array. We identify four previously unidentified loci including two loci at 13q22 near KLF5 , a 2p23.2 locus near WDR43 and a 2q33 locus near PPIL3 that display genome-wide significant associations with ER-negative breast cancer. In addition, 19 known breast cancer risk loci have genome-wide significant associations and 40 had moderate associations ( P .05) with ER-negative disease. Using functional and eQTL studies we implicate TRMT61B and WDR43 at 2p23.2 and PPIL3 at 2q33 in ER-negative breast cancer aetiology. All ER-negative loci combined account for ∼11% of familial relative risk for ER-negative disease and may contribute to improved ER-negative and BRCA1 breast cancer risk prediction.
Publisher: American Chemical Society (ACS)
Date: 24-03-1998
DOI: 10.1021/AC970903J
Abstract: Lipophilic inert electrolytes, i.e., salts without ion-exchange properties, may influence the selectivity of ionophore-based liquid membrane electrodes by affecting the activity coefficients in the organic phase. It is expected by a theoretical model that the addition of a lipophilic salt renders the ion-selective electrode more selective for alent over monovalent ions. These predictions are confirmed with Ca(2+)-responsive membranes containing the ionophores ETH 2120, ETH 1001, and ETH 129. The effect is especially pronounced with nonpolar membrane phases containing a low concentration of charged species, where up to 2 orders of magnitude selectivity improvement is observed.
Publisher: Public Library of Science (PLoS)
Date: 04-2015
Publisher: Springer Science and Business Media LLC
Date: 02-04-2021
DOI: 10.1007/S00604-021-04805-1
Abstract: The capacitance of the ion-to-electron transducer layer helps to maintain a high potential stability of solid-contact ion-selective electrodes (SC-ISEs), and its estimation is therefore an essential step of SC-ISE characterization. The established chronopotentiometric protocol used to evaluate the capacitance of the single-walled carbon nanotube transducer layer was revised in order to obtain more reliable and better reproducible values and also to allow capacitance to be measured before membrane deposition for electrode manufacturing quality control purposes. The capacitance values measured with the revised method increased linearly with the number of deposited carbon nanotube–based transducer layers and were also found to correlate linearly before and after ion-selective membrane deposition, with correlation slopes close to 1 for nitrate-selective electrodes, to 0.7 and to 0.5 for potassium- and calcium-selective electrodes. Graphical abstract
Publisher: Wiley
Date: 19-12-2019
Publisher: FapUNIFESP (SciELO)
Date: 10-2006
Publisher: Elsevier BV
Date: 05-2005
Publisher: Elsevier BV
Date: 10-2004
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1SC04930E
Abstract: Novel optical nanosensors for the selective detection of the polycationic protamine based on solvatochromic signal change allow one to detect heparin in plasma.
Publisher: American Chemical Society (ACS)
Date: 12-03-2019
DOI: 10.1021/ACSSENSORS.9B00179
Abstract: We show here that the response of ion-selective membrane electrodes (ISEs) based on traditional PVC membranes can be directly translated to a colorimetric readout by a closed bipolar electrode (BPE) arrangement. Because the resulting optical response is based on the turnover of the redox probe, ferroin, dissolved in a thin layer compartment, it directly indicates the potential change at the ISE in combination with a reference electrode. This class of probes measures ion activity, analogous to their ISE counterparts. Unlike other ion optodes, the response is also fully tunable over a wide concentration range by the application of an external potential and occurs in a compartment that is physically separate from the s le. To allow for the electrical charge to pass across the ion-selective electrodes, the membranes are doped with inert lipophilic electrolyte, ETH 500, but otherwise have an established composition. The observed response behavior correlates well with theory. A wide range of ion-selective membranes are confirmed to work with this readout principle, demonstrating the detection of potassium, sodium, calcium, and carbonate ions. The corresponding sigmodal calibration curve is used for quantitative analysis in a range of s les including commercial beverages and river and lake s les. The data are successfully correlated with atomic emission spectroscopy and direct potentiometry.
Publisher: Springer Science and Business Media LLC
Date: 22-01-2015
DOI: 10.1007/S00216-014-8413-4
Abstract: This review describes recent advances in the miniaturization of ion selective optodes into microscale and nanoscale sensors. The topics include a comparison between film-based and miniaturized ion optodes, equilibrium and exhaustive detection modes, recent preparation methodologies and applications of microscale and nanoscale ion optodes, criteria for the design of optode sensors, and other future perspectives.
Publisher: Wiley
Date: 29-01-2008
Publisher: American Chemical Society (ACS)
Date: 05-2004
DOI: 10.1021/AC049580Z
Publisher: American Chemical Society (ACS)
Date: 05-1996
DOI: 10.1021/AC951017G
Abstract: The influence of poly(ethylene oxide)-based nonionic surfactants (i.e., Triton X-100 and Brij 35) in the s le phase on the response properties of hydrogen ion-selective polymeric membrane electrodes containing mobile (lipophilic amines) or covalently bound (aminated-poly-(vinyl chloride)) hydrogen ion carriers is reported. In the presence of these nonionic surfactants, membrane electrode response toward interfering cation activity (e.g., Na+) in the s le phase is increased substantially and the pH measuring range shortened. The degree of cation interference for pH measurements is shown to correlate with the basicity of the hydrogen ion carrier doped within the membrane phase. The observed deterioration in selectivity arises from the partitioning of the surfactant into the membrane and concomitant extraction of metal cations by the surfactants in the organic phase. The effect of nonionic surfactants on pH electrodes prepared with aminated-PVC membranes is shown to be more complex, with additional large shifts in EMF values apparently arising from multidentate interactions between the surfactant molecules and the polymeric amine in the membrane, leading to a change in the apparent pKa values for the amine sites. The effects induced by nonionic surfactants on the EMF response function of hydrogen ion-selective polymeric membrane electrodes are modeled, and experimental results are shown to correlate well with theoretical predictions.
Publisher: American Chemical Society (ACS)
Date: 28-08-2018
Publisher: American Chemical Society (ACS)
Date: 05-08-2004
DOI: 10.1021/JA047728Q
Abstract: Ion-selective electrode membranes based on hydrophobic materials doped with chemically selective host molecules are an attractive sensing technology but normally suffer from a limited sensitivity, given by the Nernst equation, and a direct reliance on the reference electrode potential, which makes miniaturization difficult. These fundamental problems are addressed here by imposing a multipulse electrochemical excitation signal onto ion-selective membranes that lack ion-exchange properties. Current pulses are responsible for the generation of ion fluxes in the direction of the membrane, which give reproducible super-Nernstian response slopes that originate from depletion processes at the membrane surface. Membranes may also be measured at zero current after this pulse, giving super-Nernstian response regions at lower concentrations. Difference potentials obtained from subsequent pulses give about 10-fold higher sensitivities than predicted on the basis of the Nernst equation.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2CC30657C
Abstract: We aim to introduce photoactivated optical ion sensors based on a triggered ion exchange process as novel dynamic tools. The quantification of the acidity change upon photoactivation of spiropyran within an organic membrane phase during photoexcitation is described here for the first time, suggesting a large pK(a) change of more than 6 orders of magnitude.
Publisher: Royal Society of Chemistry (RSC)
Date: 2007
DOI: 10.1039/B614562K
Abstract: Fluorescent optode microspheres doped with the halide-selective receptor [9]mercuracarborand-3 and a lipophilic pH fluoroionophore were found to exhibit picomolar limits of detection to iodide at pH 3.5, and were used to monitor the precipitation of iodide by silver ions at subnanomolar concentrations, just above their calculated solubility.
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/B602906J
Abstract: Coulometry belongs to one of the few known calibration-free techniques and is therefore highly attractive for chemical analysis. Titrations performed by the coulometric generation of reactants is a well-known approach in electrochemistry, but suffers from limited selectivity and is therefore not generally suited for s les of varying or unknown composition. Here, the selective coulometric release of ionic reagents from ion-selective polymeric membrane materials ordinarily used for the fabrication of ion-selective electrodes is described. The selectivity of such membranes can be tuned to a significant extent by the type and concentration of ionophore and lipophilic ion-exchanger and is today well understood. An anodic current of fixed magnitude and duration may be imposed across such a membrane to release a defined quantity of ions with high selectivity and precision. Since the applied current relates to a defined ion flux, a variety of non-redox active ions may be accurately released with this technique. In this work, the released titrant's activity was measured with a second ionophore-based ion-selective electrode and corresponded well with expected dosage levels on the basis of Faraday's law of electrolysis. Initial ex les of coulometric titrations explored here include the release of calcium ions for complexometric titrations, including back titrations, and the release of barium ions to determine sulfate.
Publisher: American Chemical Society (ACS)
Date: 05-02-2016
DOI: 10.1021/JACS.5B09972
Abstract: Late endosomes are a major trafficking hub in the cell at the crossroads between endocytosis, autophagy, and degradation in lysosomes. Herein is disclosed the first small molecule allowing their selective imaging and monitoring in the form of a diazaoxatriangulene fluorophore, 1a (hexadecyl side chain). The compound is prepared in three steps from a simple carbenium precursor. In nanospheres, this pH-sensitive (pKa = 7.3), photochemically stable dye fluoresces in the red part of visible light (601 and 578 nm, acid and basic forms, respectively) with a quantum yield between 14 and 16% and an excited-state lifetime of 7.7-7.8 ns. Importantly, the protonated form 1a·H(+) provokes a specific staining of late endosome compartments (pH 5.0-5.5) after 5 h of incubation with HeLa cells. Not surprisingly, this late endosome marking depends on the intra-organelle pH, and changing the nature of the lipophilic chain provokes a loss of selectivity. Interestingly, fixation of the fluorophore is readily achieved with paraformaldehyde, giving the possibility to image both live and fixed cells.
Publisher: Wiley
Date: 06-2023
Publisher: Elsevier BV
Date: 03-2005
Publisher: American Chemical Society (ACS)
Date: 11-11-1998
DOI: 10.1021/AC980678L
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4CC01313A
Abstract: Ion-selective microspheres based on surface modification of polystyrene particles (0.8 and 2.4 μm, diameter) are presented here for the first time.
Publisher: American Chemical Society (ACS)
Date: 25-10-2005
DOI: 10.1021/AC051362Y
Abstract: Supported liquid membranes are used here to establish steady-state concentration profiles across ion-selective membranes rapidly and reproducibly. This opens up new avenues in the area of nonequilibrium potentiometry, where reproducible accumulation and depletion processes at ion-selective membranes may be used to gain valuable analytical information about the s le. Until today, drifting signals originating from a slowly developing concentration profile across the ion-selective membrane made such approaches impractical in zero current potentiometry. Here, calcium- and silver-selective membranes were placed between two identical aqueous electrolyte solutions, and the open circuit potential was monitored upon changing the composition of one solution. Steady state was reached in approximately 1 min with 25-microm porous polypropylene membranes filled with bis(2-ethylhexyl) sebacate doped with ionophore and lipophilic ion exchanger. Ion transport across the membrane resulted on the basis of nonsymmetric ion-exchange processes at both membrane sides. The steady-state potential was calculated as the sum of the two membrane phase boundary potentials, and good correspondence to experiment was observed. Concentration polarizations in the contacting aqueous phases were confirmed with stirring experiments. It was found that interferences (barium in the case of calcium electrodes and potassium with silver electrodes) induce a larger potential change than expected with the Nicolsky equation because they influence the level of polarization of the primary ion (calcium or silver) that remains potential determining.
Publisher: Wiley
Date: 05-12-2017
Publisher: Elsevier BV
Date: 02-2019
Publisher: Springer Science and Business Media LLC
Date: 27-06-2008
Publisher: American Chemical Society (ACS)
Date: 06-2006
DOI: 10.1021/JA0625780
Publisher: American Chemical Society (ACS)
Date: 28-07-2017
Publisher: American Chemical Society (ACS)
Date: 24-04-2020
Publisher: American Chemical Society (ACS)
Date: 21-08-2015
Publisher: American Chemical Society (ACS)
Date: 07-1994
DOI: 10.1021/AC00086A009
Abstract: The potentiometric response mechanism of a previously reported polymer membrane-based electrode sensitive to the polyanion heparin is established. Based on transport and extraction studies, the heparin response is attributed to a nonequilibrium change in the phase boundary potential at the s le/membrane interface. While true equilibrium polyion response, obtained for low heparin concentrations only after very long equilibration times (> 20 h), yields the expected Nernstian response slope of < 1 mV/decade, the observed large and reproducible EMF response to clinically relevant heparin concentrations (approximately 10(-7) M) during typical measurement periods (2-5 min) is ascribed to a steady-state kinetic process defined by the flux of the polyion both to the surface and into the bulk of the polymer membrane. A model describing this nonequilibrium response is presented. With this model, the uniqueness of the polymer membrane composition (e.g., very low plasticizer content, strictly controlled cationic site concentration, etc.) required to achieve analytically useful heparin response becomes clear. Practical working conditions and limitations of the sensor are discussed. To support the generality of the steady-state model proposed, corresponding EMF response data for a newly developed membrane electrode sensitive to a polycationic protein (protamine) are also presented. It is shown that the protamine-responsive membrane electrode appears to operate via the exact same kinetic mechanism as the heparin sensing system.
Publisher: Elsevier BV
Date: 10-2014
Publisher: American Chemical Society (ACS)
Date: 15-12-2016
DOI: 10.1021/ACS.ANALCHEM.6B03354
Abstract: Voltammetric thin layer (∼200 nm) ionophore-based polymeric films of defined ion-exchange capacity have recently emerged as a promising approach to acquire multi-ion information about the s le, in analogy to performing multiple potentiometric measurements with in idual membranes. They behave under two different regimes that are dependent on the ion concentration. A thin layer control (no mass transport limitation of the polymer film or solution) is identified for ion concentrations of >10 μM, in which case the peak potential serves as the readout signal, in analogy to a potentiometric sensor. On the other hand, ion transfer at lower concentrations is chiefly controlled by diffusional mass transport from the solution to the sensing film, resulting in an increase of peak current with ion concentration. This concentration range is suitable for electrochemical ion transfer stripping analysis. Here, the transition between the two mentioned scenarios is explored experimentally, using a highly silver-selective membrane as a proof-of-concept under different conditions (variation of ion concentration in the s le from 0.1 μM to 1 mM, scan rate from 25 mV s
Publisher: American Chemical Society (ACS)
Date: 15-12-2016
DOI: 10.1021/ACS.ANALCHEM.6B03355
Abstract: This work reports on a semiempirical treatment that allows one to rationalize and predict experimental conditions for thin-layer ionophore-based films with cation-exchange capacity read out with cyclic voltammetry. The transition between diffusional mass transport and thin-layer regime is described with a parameter (α), which depends on membrane composition, diffusion coefficient, scan rate, and electrode rotating speed. Once the thin-layer regime is fulfilled (α = 1), the membrane behaves in some analogy to a potentiometric sensor with a second discrimination variable (the applied potential) that allows one to operate such electrodes in a multianalyte detection mode owing to the variable applied ion-transfer potentials. The limit of detection of this regime is defined with a second parameter (β = 2) and is chosen in analogy to the definition of the detection limit for potentiometric sensors provided by the IUPAC. The analytical equations were validated through the simulation of the respective cyclic voltammograms under the same experimental conditions. While simulations of high complexity and better accuracy satisfactorily reproduced the experimental voltammograms during the forward and backward potential sweeps (companion paper 1), the semiempirical treatment here, while less accurate, is of low complexity and allows one to quite easily predict relevant experimental conditions for this emergent methodology.
Publisher: Elsevier BV
Date: 02-2010
Publisher: Swiss Chemical Society
Date: 30-03-2011
Abstract: While potentiometric sensors experienced a golden age in the 1970s that drove innovation and implementation in the clinical laboratory as sensors of choice, it has been only fairly recently that a theoretical understanding coupled with modern materials approaches transformed the area of membrane electrodes from a playful, yet empirical field to one firmly rooted in scientific understanding. This paper summarizes key progress in the field during the past two decades, emphasizing that the key impulses at the time originated from the emerging field of optical ion sensors. This simplified and transformed the underlying theory of their potentiometric membrane electrode counterparts, where subsequently substantial progress was made, including the realization of ultra-trace detection limits. The better understanding of zero-current ion fluxes and transport processes in turn allowed the development of approaches utilizing dynamic electrochemistry principles, thereby drastically expanding the field of membrane electrodes and making available a range of new methodologies that would have been difficult to predict only a few years ago. These significant developments are now starting to come back and influence the field of optical sensors, where the control and triggering of dynamic processes, away from simpler equilibrium principles, are becoming a highly promising field of research.
Publisher: Elsevier BV
Date: 04-2005
Publisher: American Chemical Society (ACS)
Date: 28-09-2021
Publisher: Elsevier BV
Date: 2020
DOI: 10.1016/J.ACA.2019.10.011
Abstract: Magnetic ion-selective colorimetric microspheres based on surface modification of polystyrene beads (0.8 μm diameter) are reported for the first time. The common components of ion-selective optode sensing (chromoionophore, ion-exchanger and ionophore) and magnetic nanoparticles are adsorbed onto the surface of the polystyrene particles using a simple mixed solvent method. The average diameter of the magnetic microspheres is evaluated by dynamic light scattering as 0.79 ± 0.06 μm. The reversible microsensors are circulated by flow and accumulated at a single spot by an applied magnet to become observable by digital camera. Hue signals are extracted from the recorded images to quantify the ratio of protonated and deprotonated form of the chromoionophore, which is the basis for optode response. The resulting magnetic microsensors respond to K
Publisher: Wiley
Date: 04-11-2012
Abstract: A permselective membrane electrode allows the rapid and operationally reversible detection of the polycationic polypeptide protamine in physiological s les. Anticoagulant levels of heparin can be measured in undiluted whole blood by adding a known excess of its antidote protamine to discrete blood s les.
Publisher: American Chemical Society (ACS)
Date: 30-10-2018
DOI: 10.1021/ACSSENSORS.8B01096
Abstract: There is an urgent need for reliable seawater phosphate measuring tools to better assess eutrophication. Today, most accepted sensing approaches are based on the established colorimetric molybdenum blue assay. It requires one to modify the s le to strongly acidic conditions and to add various reagents, principally molybdate and reducing agent (e.g., ascorbic acid), to form a blue colored phosphate complex that is subsequently detected spectrophotometrically. The associated need for large s le and mobile phase reservoirs and mixing coils are, unfortunately, not ideally adapted for the development of operationally simple in situ sensing instruments. It is here demonstrated for the first time that the key reagents needed to achieve phosphate detection by the molybdate method may be delivered by passive counter transport across ion-exchange membranes. A cation-exchange Donnan exclusion membrane placed in contact with a s le flow (450 μm thick) is shown to provide the strongly acidic conditions (pH ∼ 1) necessary for phosphate determination. Proton transport is driven, via cation-exchange, by the high sodium content of the seawater s le. Molybdate was similarly released through an anion-exchange membrane by chloride counter transport. Consequently, an in-line flow system containing the two membrane modules in series was used for delivering both hydrogen and molybdate ions into the s le to form the desired phosphomolybdate complex for subsequent spectrophotometric detection. A linear calibration in the range of 0.1-10 μM phosphate (3-300 ppb inorganic P) was achieved, which is sufficiently attractive for environmental work. A range of seawater s les was tested and the results from this membrane delivery device showed no significant differences compared to the classical molybdate assay chosen as the reference method.
Publisher: Wiley
Date: 08-05-2018
Abstract: Ion-selective optical microsensors based on surface-modified polystyrene (PS) beads with positively charged lipophilic solvatochromic dye (SD) on the surface were studied with K
Publisher: Wiley
Date: 1997
Publisher: Elsevier BV
Date: 08-2001
Publisher: American Chemical Society (ACS)
Date: 22-02-2013
DOI: 10.1021/AC4000283
Publisher: American Chemical Society (ACS)
Date: 22-01-2021
Publisher: American Chemical Society (ACS)
Date: 10-03-2006
DOI: 10.1021/AC052211Y
Abstract: Ion-selective electrodes ideally operate on the basis of the Nernst equation, which predicts less than 60- and 30-mV potential change for a 10-fold activity change of monovalent and alent ions measured at room temperature, respectively. Typical concentration ranges in extracellular fluids are quite narrow for the electrolytes of key importance. A range of 2.2-2.6 mM for calcium ions, for instance, translates into just a 2.2-mV potential change. The direct potentiometric measurement of physiological electrolytes is certainly possible with direct potentiometry and is done routinely in clinical analyzers and handheld measuring devices. It places, however, strong demands on the precision of the reference electrode and requires careful temperature control and frequent calibration runs. In this paper, a robust 10-20-fold sensitivity enhancement for calcium measurements is attained by departing from the classical response mechanism and operating in a non-Nernstian response mode. Stable and reproducible super-Nernstian responses of these so-called pulstrodes in a narrow calcium activity range can be controlled by instrumental means in good agreement with theory. The potentials may be measured during a galvanostatic excitation pulse (mode I) or immediately after it (mode II), under open-circuit conditions. Subtraction of the potentials, s led at different times during a single pulse, allows one to obtain a sensitive differential peak-shaped signal at a critical and fully adjustable analyte activity range. Calcium pulstrodes based on the diamide ionophore AU-1 were characterized and applied to the measurement in model physiological liquids. Super-Nernstian responses exceeding 700 mV/decade were observed in a physiological range of calcium concentration. Such remarkable sensitivity of the pulstrodes, complemented with the well-documented high selectivity of these potentiometric sensors, may provide a significant increase in the accuracy and precision of electrolyte measurements in clinical analysis.
Publisher: American Chemical Society (ACS)
Date: 31-01-2019
DOI: 10.1021/ACSSENSORS.8B01521
Abstract: A distance-based analysis of potassium ion (K
Publisher: American Chemical Society (ACS)
Date: 03-1996
DOI: 10.1021/AC9618536
Abstract: This work aims to determine the orthotropic linear elastic constitutive parameters of
Publisher: American Chemical Society (ACS)
Date: 21-05-2018
DOI: 10.1021/ACS.ANALCHEM.8B01585
Abstract: We present here a general strategy to translate potential change at a potentiometric probe into a tunable color readout. It is achieved with a closed bipolar electrode where the ion-selective component is confined to one end of the electrode while color is generated at the opposite pole, allowing one to physically separate the detection compartment from the s le. An electrical potential is imposed across the bipolar electrode by solution contact such that the potentiometric signal change at the s le side modulates the potential at the detection side. This triggers the turnover of a redox indicator in the thin detection layer until a new equilibrium state is established. The approach is demonstrated in separate experiments with a chloride responsive Ag/AgCl element and a liquid membrane based calcium-selective membrane electrode, using the redox indicator ferroin in the detection compartment. The principle can be readily extended to other ion detection materials and optical readout principles.
Publisher: American Chemical Society (ACS)
Date: 08-10-2012
DOI: 10.1021/JA307037Z
Publisher: American Chemical Society (ACS)
Date: 24-05-2022
Publisher: Elsevier BV
Date: 09-2010
Publisher: Wiley
Date: 17-09-2003
Publisher: American Chemical Society (ACS)
Date: 04-08-2015
DOI: 10.1021/ACS.ANALCHEM.5B01973
Abstract: We report on a methodology for the direct potentiometric determination of nitrate in seawater by in-line coupling to an electrochemical desalination module. A microfluidic custom-fabricated thin layer flat cell allows one to electrochemically reduce the chloride concentration of seawater more than 100-fold, from 600 mM down to ∼2.8 mM. The desalinator operates by the exhaustive electrochemical plating of the halides from the thin layer s le onto a silver element as silver chloride, which is coupled to the transfer of the counter cations across a permselective ion-exchange membrane to an outer solution. As a consequence of suppressing the major interference of an ion-exchanger based membrane, the 80 μL desalinated s le plug is passed to a potentiometric flow cell of 13 μL volume. The potentiometric sensor is composed of an all-solid-state nitrate selective electrode based on lipophilic carbon nanotubes (f-MWCNTs) as an ion-to-electron transducer (slope of -58.9 mV dec(-1), limit of detection of 5 × 10(-7) M, and response time of 5 s in batch mode) and a miniaturized reference electrode. Nitrate is successfully determined in desalinated seawater using ion chromatography as the reference method. It is anticipated that this concept may form an attractive platform for in situ environmental analysis of a variety of ions that normally suffer from interference by the high saline level of seawater.
Publisher: American Chemical Society (ACS)
Date: 26-06-2001
DOI: 10.1021/AC001475B
Abstract: Zero-current ion fluxes through polymer membranes of ion-selective electrodes (ISEs) may lead to biased endpoints of potentiometric titrations. The bias is eliminated, and the sensitivity of the end-point detection is improved through reducing transmembrane ion fluxes by an appropriate choice of the inner solution. Surprisingly, ISE membranes that have a significant primary ion flux toward the inner solution show much larger sensitivities than expected by titration theory however, depending on the experimental conditions, their application may bias the endpoint. With the optimal systems, endpoint detection is now possible with total s le concentrations below 10(-6) M, as demonstrated by the titration of EDTA with a Pb2+ solution.
Publisher: American Chemical Society (ACS)
Date: 23-12-2010
DOI: 10.1021/AC102016Y
Abstract: The electrochemical response behavior of controlled-potential thin-layer coulometric sensors based on solvent polymeric membranes doped with ionophores is elucidated by numerical simulation. This treatment forms the theoretical basis for the design of potentially recalibration-free ion-selective chemical sensors that operate by exhaustive coulometry. Mass transport is assumed to occur primarily by diffusion in each bulk phase, and interfacial ion exchange with interfering ions is described with modern ion-selective electrode theory. The ion-selective membrane is assumed to contain an ion exchanger that can form concentration gradients as a result of transmembrane ion fluxes. It is shown that the diffusion of ions in the membrane phase will become rate limiting for membrane components with diffusion coefficients of 10(-8) cm(2) s(-1) that are typical for traditional ion-selective electrode formulations. This characteristic may be advantageous for s le thicknesses of 20 μm or less, where otherwise exhaustive depletion occurs too quickly to be distinguishable from nonfaradic processes. In most other cases, however, it will be necessary to formulate membrane materials that permit much faster diffusion characteristics. Indeed, the simulations give guidance on sensor design for s le concentrations that approach millimolar levels. The treatment also considers interferences from ions of the same charge sign as the analyte ion, and it is shown that the required selectivity for a given analysis must be about 1 order of magnitude higher than in direct potentiometry. This is because the coulometric exhaustive depletion process occurs only for the analyte ion, not for the interfering one, and to avoid interference, the required selectivity must be maintained even if the s le contains a fraction of the original analyte levels.
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3EM90017G
Abstract: Correction for ‘A submersible probe with in-line calibration and a symmetrical reference element for continuous direct nitrate concentration measurements' by Tara Forrest et al. , Environ. Sci.: Processes Impacts , 2023, 25 , 519–530, 0.1039/D2EM00341D.
Publisher: American Chemical Society (ACS)
Date: 1998
DOI: 10.1021/AC970878H
Publisher: Walter de Gruyter GmbH
Date: 08-04-2012
Abstract: Ion-selective membrane materials based on poly(vinyl chloride) (PVC)-containing covalently attached redox-active ferrocene (Fc) groups are characterized here as all-solid-state pulsed voltammetric ion sensors. The redox capacity of the membrane increases 7-fold with a doubling of the Fc content and 3-fold with the addition of 10 wt % of the lipophilic electrolyte ETH 500, tetradodecylammonium tetrakis(4-chlorophenyl)borate. This salt improves the ionic conductivity of the membrane and appears to make the Fc groups electrochemically more accessible. A too high content of the two, on the other hand, was found to cause undesired sensitivity to redox-active species present in the s le solution. Dilution of the membrane with a plasticizer eliminated this redox sensitivity while preserving its high redox capacity. A practical application of the designed electrodes in electrochemical analysis was demonstrated with a multi-pulse protocol that includes a current-controlled ion uptake pulse, followed by an open-circuit potential (OCP) measurement and a regeneration pulse. Potentiometric calibration curves obtained with this protocol exhibited a linear response with near-Nernstian slopes for acetate, nitrate, chloride, and perchlorate ions with the selectivity expected for an ion-exchanging membrane.
Publisher: Elsevier BV
Date: 2001
Publisher: Elsevier BV
Date: 09-1996
Publisher: Swiss Chemical Society
Date: 29-04-2015
Abstract: Ionophore-based ion-selective optical nanosensors have been explored for a number of years. Voltage sensitive dyes (VSDs) have been introduced into this type of sensors only very recently, forming a new class of analytical tools. Here, K+-sensitive nanospheres incorporating a lipophilic VSD were successfully fabricated and characterized. The nanosensors were readily delivered into the social amoeba Dictyostelium discoideum in a non-invasive manner, forming a promising new platform for intracellular ion quantification and imaging.
Publisher: American Chemical Society (ACS)
Date: 27-12-2021
DOI: 10.1021/ACS.ANALCHEM.1C04722
Abstract: By its nature, a traditional potentiometric cell composed of an Ag/AgCl-based reference electrode and a solid-contact indicating electrode is not symmetric. This results in undesirable potential drifts in response to a common perturbation such as a temperature change of the s le. We propose here an approach to restore symmetry by constructing a cell with two identical solid-contact ISEs used as reference and indicating electrodes. In this arrangement, the reference electrode is immersed in a compartment containing a constant background of an ion of interest, while the indicating electrode is directly immersed in the s le solution. This approach was successfully demonstrated for a cell composed of nitrate-selective electrodes with the hydrophobic derivative of poly(3,4-ethylenedioxythiophene) as a transducer layer. In particular, the symmetric setup is shown to lower by 4-5 times the observed potential drift resulting from temperature changes between +25 and +5 °C.
Publisher: American Chemical Society (ACS)
Date: 06-1998
DOI: 10.1021/CR970113+
Publisher: Wiley
Date: 07-1999
DOI: 10.1002/(SICI)1521-4109(199907)11:10/11<788::AID-ELAN788>3.0.CO;2-4
Publisher: American Chemical Society (ACS)
Date: 17-10-2022
DOI: 10.1021/ACSSENSORS.2C01826
Abstract: Mobile integrated electrochemical sensors normally require a power supply for operation. Unfortunately, the practice of discarding batteries associated with these devices runs counter to our desire for a sustainable world. Self-powered sensing concepts that draw the energy directly from the measurement itself would overcome this limitation. Potentiometric sensors for the measurement of pH, many electrolytes, and gases are ubiquitous in analytical practice. However, in potentiometry, the voltage is acquired in the absence of current flow, making it seemingly impossible to draw power. Fortunately, it has been recently established that transient currents may be tolerated across potentiometric measurement cells to charge a capacitive or electrochromic element such as Prussian blue integrated in the measurement cell and whose absorbance then directly follows the potential changes in a reversible manner. We have shown here that commercial electronic paper (e-paper), widely used to make electronic ink and ebook readers, can directly be driven by a potentiometric measurement cell in a reversible manner at mild potentials of >100 mV typical for such sensors. The capacitance of the e-paper pixel studied here was found to be 0.53 μF mm
Publisher: American Chemical Society (ACS)
Date: 20-08-2013
DOI: 10.1021/AM401958E
Publisher: American Chemical Society (ACS)
Date: 04-10-2022
Publisher: American Association for Cancer Research (AACR)
Date: 14-09-2018
DOI: 10.1158/0008-5472.CAN-18-0951
Abstract: Large-scale genome-wide association studies (GWAS) have identified approximately 35 loci associated with epithelial ovarian cancer (EOC) risk. The majority of GWAS-identified disease susceptibility variants are located in noncoding regions, and causal genes underlying these associations remain largely unknown. Here, we performed a transcriptome-wide association study to search for novel genetic loci and plausible causal genes at known GWAS loci. We used RNA sequencing data (68 normal ovarian tissue s les from 68 in iduals and 6,124 cross-tissue s les from 369 in iduals) and high-density genotyping data from European descendants of the Genotype-Tissue Expression (GTEx V6) project to build ovarian and cross-tissue models of genetically regulated expression using elastic net methods. We evaluated 17,121 genes for their cis-predicted gene expression in relation to EOC risk using summary statistics data from GWAS of 97,898 women, including 29,396 EOC cases. With a Bonferroni-corrected significance level of P & 2.2 × 10−6, we identified 35 genes, including FZD4 at 11q14.2 (Z = 5.08, P = 3.83 × 10−7, the cross-tissue model 1 Mb away from any GWAS-identified EOC risk variant), a potential novel locus for EOC risk. All other 34 significantly associated genes were located within 1 Mb of known GWAS-identified loci, including 23 genes at 6 loci not previously linked to EOC risk. Upon conditioning on nearby known EOC GWAS-identified variants, the associations for 31 genes disappeared and three genes remained (P & 1.47 × 10−3). These data identify one novel locus (FZD4) and 34 genes at 13 known EOC risk loci associated with EOC risk, providing new insights into EOC carcinogenesis. Significance: Transcriptomic analysis of a large cohort confirms earlier GWAS loci and reveals FZD4 as a novel locus associated with EOC risk. Cancer Res 78(18) 5419–30. ©2018 AACR.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2JM31118F
Publisher: Wiley
Date: 26-02-2004
Publisher: Springer Science and Business Media LLC
Date: 02-02-2014
DOI: 10.1038/NCHEM.1858
Abstract: Biological light-driven proton pumps use light to move protons across a cell membrane, creating a proton gradient. Although photochromic compounds such as spiropyrans can reversibly convert between two structures with differing pKa values, spiropyrans have not been used to generate either a light-driven proton pump or an electrical current. Here, we report an artificial light-harvesting system based on a supported liquid membrane doped with a spiropyran. Irradiating the membrane with ultraviolet light induces a ring-opening reaction, converting spiropyran to merocyanine, whereas irradiation with visible light induces the reverse reaction. When the membrane is irradiated with ultraviolet and visible light on opposite sides, H(+) is taken up by merocyanine, carried through the polymeric membrane and released on the other side. We show that this system produces a light-induced proton flux, an electrical current with an efficiency of ∼0.12%, an open-circuit voltage of ∼210 mV and a membrane gradient of ∼3.6 ΔpH units. Alternating the sides illuminated with ultraviolet and visible light generates an alternating current.
Publisher: Elsevier BV
Date: 10-1993
Publisher: American Chemical Society (ACS)
Date: 02-1994
DOI: 10.1021/AC00075A013
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2AN35516G
Abstract: We report here on an electrogenerated chemiluminescence (ECL) readout for potentiometric ion-sensors, thereby offering an optical sensor output without the need for a reference ion (typically the hydrogen ion) that inconveniences ionophore based optical sensor principles. The compartment for ECL generation is physically separated from the s le by a bridge, and no current flows through the s le compartment. Here, three different types of ion selective membranes (Ca(2+), Na(+) and K(+)) are read-out in idually and sequentially with this methodology. The repeatabilities are found as 0.5 to 1% of integrated light output, which translates into a relative uncertainty in the activity measurement of about 10%. This uncertainty appears to originate primarily at the ECL generating gold electrode, not at the potentiometric sensor. Other analytical figures of merit such as measuring range, sensitivity, optimal applied potential for ECL generation, and ion selectivity are also described.
Publisher: American Chemical Society (ACS)
Date: 20-05-2014
DOI: 10.1021/JA503491K
Abstract: Making efficient use of solar energy is one of the biggest challenges of our time. In nature, solar energy can be harvested by photosynthesis where proton-coupled electron transfer (PCET) plays a critical role. Here, PCET is utilized for the first time to directly convert light energy to electrical energy. Quinone/hydroquinone PCET redox couples were used to produce a photovoltage along with spiropyrans, photoswitchable compounds that undergo reversible transformation between a ring-closed (Sp) and ring-opened form (Mc). The Mc form is more basic than the Sp form, and the open-circuit voltage (V(oc)) is related to the proton concentration and that of the Sp/Mc ratio controlled by light. V(oc) values from 100 to 140 mV were produced. In addition to direct current (J(sc) ca. 9 μA cm(-2)), alternating current in the range of 0.1 to 200 Hz was also produced by manipulating the input light.
Publisher: Elsevier BV
Date: 09-1994
Publisher: Elsevier BV
Date: 11-2013
Publisher: Wiley
Date: 08-01-2020
Publisher: American Chemical Society (ACS)
Date: 13-08-2022
DOI: 10.1021/ACS.ANALCHEM.2C01728
Abstract: In potentiometric sensing, the preparation of the electrodes preceding a measurement is often the most time-consuming step. Eliminating the conditioning process can significantly speed up the preparation procedure, but it can also compromise the need for proper pre-equilibration of the membrane. We propose here a symmetric setup to address this challenge with an identical indicator and reference elements measured against each other, thereby compensating for potential drift. This strategy allows one to achieve potentiometric measurements using non-conditioned all-solid-state ion-selective electrodes for the detection of nitrate and potassium ions with Nernstian response slopes and detection ranges identical to those of conventional systems. To establish symmetry, a set of solid-contact ion-selective electrodes placed in a reference cell is measured against a set of identical electrodes in a s le cell. By subtracting the potentials between the two cells, potential instabilities not directly relevant to the measuring s le are eliminated, giving minimal potential drifts and stable 5-day potential responses. The
Publisher: Elsevier BV
Date: 09-1997
Publisher: American Chemical Society (ACS)
Date: 1998
DOI: 10.1021/AC970690Y
Publisher: Swiss Chemical Society
Date: 29-05-2013
Publisher: American Chemical Society (ACS)
Date: 08-03-2018
DOI: 10.1021/ACS.ANALCHEM.7B05299
Abstract: A new submersible probe for the in situ detection of nitrate, nitrite, and chloride in seawater is presented. Inline coupling of a desalination unit, an acidification unit, and a sensing flow cell containing all-solid-state membrane electrodes allows for the potentiometric detection of nitrate and nitrite after removal of the key interfering ions in seawater, chloride and hydroxide. Thus, the electrodes exhibited attractive analytical performances for the potentiometric detection of nitrate and nitrite in desalinated and acidified seawater: fast response time ( t
Publisher: Elsevier BV
Date: 03-2009
Abstract: We report here on a highly sensitive and rapid detection technique, multipulse flash chronopotentiometry, for the anticoagulant polyion heparin and its antidote protamine. The technique is based on a localized titration of the polyions at the surface of an appropriately formulated polymeric ion-selective membrane devoid of ion exchange properties to prohibit spontaneous extraction processes. A defined ion flux from the s le side to the membrane is induced electrochemically by applying a current pulse of appropriate litude and sign. The resulting depletion of the measured ions at the membrane surface gives rise to a characteristic limiting current or transition time and is observed as an inflection point in the resulting chronopotentiogram. The limiting current and the square root of the transition time are linear functions of the concentration of the polyion and yield sensitive and rapid analytical information attractive for clinical diagnostics applications. The polyion protamine is detected in 10-fold diluted blood s les in a matter of seconds via a cathodic current pulse. The utility of the technique for monitoring heparin rotamine titrations in physiological saline solutions is demonstrated.
Publisher: Springer Science and Business Media LLC
Date: 23-10-2017
DOI: 10.1038/NG.3785
Publisher: American Chemical Society (ACS)
Date: 24-04-2019
DOI: 10.1021/ACS.ACCOUNTS.9B00056
Abstract: Selective molecular ion probes are often insoluble in water and require a hydrophobic solvent environment for strong and selective binding, which runs counter to the desire of utilizing them in a homogeneous solution. This Account aims to guide the reader on how such molecules, often coined ionophores, can be harnessed to design exceptionally useful optical and electrochemical sensors. We start here with some historical context on the design of such ionophores and continue with the explanation of the response mechanism of optical and potentiometric sensors and the role of combined components to build a robust ion sensor. This Account is addressed to nonspecialist readers and for this reason avoids extensive use of equations or theoretical considerations. The interested reader should turn to the original literature for further reading. Emulsified optical sensors are introduced as an initial ex le. Here, multiple reagents are confined in an attoliter sensing nanodroplet of the organic phase, immiscible with the aqueous s le phase. In this case, the ionophore molecules may retain their high affinity and selectivity to the target ion and the aqueous s le phase does not have to be modified. Emulsified optical sensors allow one to achieve the selective chemical sensing of ions, even with optically silent ionophores. Such ionophore-based nanodroplets are also discussed as a useful novel class of complexometric titration reagents and optical end point indicators with unique selectivities. We then turn our attention to potentiometric sensing probes and briefly discuss the unique opportunity of a direct characterization of ion-ionophore complexation properties offered by membrane electrodes. A carbonate-selective membrane electrode containing a highly selective tweezer-type ionophore with trifluoroacetophenone functional groups is then used as an ex le for the construction of a robust all-solid-state sensor. This potentiometric probe, in combination with a pH electrode, can directly measure PCO
Publisher: Elsevier BV
Date: 02-1999
DOI: 10.1016/S0731-7085(98)00185-X
Abstract: The growing importance of polymer membrane-based potentiometric polyion sensors in biomedical research and clinical measurements has brought up the question of how accurate and reproducible these sensors are. Indeed, recent research has revealed that these sensors behave quite differently than classical ion-selective electrodes. This paper explores ways to improve measurement reproducibility and long term potential stability by considering the unique pseudo steady-state response mechanism of the polyion sensors developed so far. Heparin may be stripped out of the phase boundary membrane surface with a high s le NaCl concentration and this characteristic is used to modify the calibration procedure in order to avoid memory effects. It is also attempted to reduce long term potential drifts by continuously stripping heparin out of the membrane at the membrane-inner filling solution side.
Publisher: Elsevier BV
Date: 10-2018
DOI: 10.1016/J.ACA.2018.05.012
Abstract: Potassium ion concentration can be successfully determined volumetrically by moving the titration from a homogeneous phase to a two phase solvent system. This is because potassium can be readily complexed in a selective and thermodynamically stable manner by ionophores such as valinomycin. Previous work demonstrated the successful titration of potassium by ion-exchange into an organic phase containing valinomycin, but the s le itself served as titrant, which is not sufficiently practical for routine applications. This problem is overcome here by a co-extraction based approach, with the sodium salt of the water soluble lipophilic anion tetraphenylborate as titrant. The extraction of potassium tetraphenylborate must be preferred over that of the hydrogen ion-tetraphenylborate pair, which is used to indicate the endpoint by the presence of a lipophilic indicator in the organic phase. This is controlled by the s le pH, which for the conditions chosen here is around 7 for optimal sharpness and accuracy of the endpoint. The approach is demonstrated in a colorimetric detection approach, by use of a tethered digital camera and subsequent automated analysis of the resulting image files. The potassium analysis in a variety of s les is successfully demonstrated, including blood serum.
Publisher: American Chemical Society (ACS)
Date: 08-2002
DOI: 10.1021/AC022086F
Publisher: Wiley
Date: 03-08-2022
Abstract: Nitrate sensing is an important application for potentiometry in environmental applications. Its recognition is by ion‐exchangers whose selectivity is governed by the lipophilicity of the ions in solution. Yet, considerable research efforts have been dedicated to the development of such ionophores and some have already been commercialized. This work examines two commercially available nitrate ionophores, nitrate ionophores V and VI, and compares their performance with widely used ion‐exchangers by determining the resulting membrane selectivity and complexation to nitrate. Unfortunately, adding a nitrate ionophore to the membrane did not result in improved selectivity. Sandwich membrane experiments indicated that binding interaction is too weak to be measurable, with a logarithmic formation constant of just 1.36±0.14 for ionophore V with nitrate. Ways to improve the reporting of relevant data are suggested.
Publisher: Hindawi Limited
Date: 12-03-2018
DOI: 10.1002/HUMU.23406
Publisher: Wiley
Date: 04-11-2012
Publisher: American Chemical Society (ACS)
Date: 09-02-2015
DOI: 10.1021/AC504213Q
Abstract: Traditionally, optical titrations of inorganic ions are based on a rapid and visible color change at the end point with water-soluble organic dyes as indicators. Adequate selectivity is required for both the indicator and the complexing agent, which is often limited. We present here alternative, heterogeneous ionophore-based ion-selective nanospheres as indicators and chelators for optical titrations. The indicating nanospheres rely on a weaker extraction of the analyte of interest by ion-exchange, owing to the additional incorporation of a lipophilic pH indicator in the nanosphere core. Ca(2+) titration was demonstrated as a proof-of-concept. Both the chelating and the indicating nanospheres showed good selectivity and a wide working pH range.
Publisher: Elsevier BV
Date: 06-1994
DOI: 10.1016/0039-9140(94)E0048-V
Abstract: The development of nitrite-selective liquid membrane microelectrodes based on a synthetic charged ionophore is described. The addition of potassium tetrakis(4-chlorophenyl)borate and poly(vinyl chloride) to the membrane phase is essential to lower the ohmic resistance and to prolong the lifetime of the microelectrodes. The detection limits for sodium nitrite solutions without and with an ion background of 0.1M chloride are 10(-5.1) and 10(-4.2)M, respectively. The comparison with macroelectrodes shows that the miniaturization reduces, to some extent, the selectivity and the slopes of the EMF response functions.
Publisher: Springer Science and Business Media LLC
Date: 11-2019
DOI: 10.1038/S41523-019-0127-5
Abstract: Breast cancer is a common disease partially caused by genetic risk factors. Germline pathogenic variants in DNA repair genes BRCA1 , BRCA2 , PALB2 , ATM , and CHEK2 are associated with breast cancer risk. FANCM , which encodes for a DNA translocase, has been proposed as a breast cancer predisposition gene, with greater effects for the ER-negative and triple-negative breast cancer (TNBC) subtypes. We tested the three recurrent protein-truncating variants FANCM :p.Arg658*, p.Gln1701*, and p.Arg1931* for association with breast cancer risk in 67,112 cases, 53,766 controls, and 26,662 carriers of pathogenic variants of BRCA1 or BRCA2 . These three variants were also studied functionally by measuring survival and chromosome fragility in FANCM −/− patient-derived immortalized fibroblasts treated with diepoxybutane or olaparib. We observed that FANCM :p.Arg658* was associated with increased risk of ER-negative disease and TNBC (OR = 2.44, P = 0.034 and OR = 3.79 P = 0.009, respectively). In a country-restricted analysis, we confirmed the associations detected for FANCM :p.Arg658* and found that also FANCM :p.Arg1931* was associated with ER-negative breast cancer risk (OR = 1.96 P = 0.006). The functional results indicated that all three variants were deleterious affecting cell survival and chromosome stability with FANCM :p.Arg658* causing more severe phenotypes. In conclusion, we confirmed that the two rare FANCM deleterious variants p.Arg658* and p.Arg1931* are risk factors for ER-negative and TNBC subtypes. Overall our data suggest that the effect of truncating variants on breast cancer risk may depend on their position in the gene. Cell sensitivity to olaparib exposure, identifies a possible therapeutic option to treat FANCM -associated tumors.
Publisher: American Chemical Society (ACS)
Date: 02-06-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4CC05754F
Abstract: Complexometric titrations rely on a drastic change of the pM value at the equivalence point with a water soluble chelator forming typically 1 : 1 complexes of high stability.
Publisher: Royal Society of Chemistry (RSC)
Date: 2005
DOI: 10.1039/B503548A
Abstract: The adsorption of the neutral surfactant Brij35 at a liquid-liquid interface is reversibly monitored via its disturbance of an electrochemically imposed ion flux across the interface, forming a promising experimental tool for the detection of surface confined reactions at such liquids and polymers.
Publisher: American Chemical Society (ACS)
Date: 21-01-1999
DOI: 10.1021/AC980962C
Abstract: The response of ion-selective membrane electrodes is usually still described with the semiempirical Nicolskii-Eisenman equation although it cannot correctly reproduce experimental data if ions of different charges are involved. The recently published self-consistent model that was derived for two ions of any charges is now extended to any number of ions of any charge. One single explicit equation is here given for the first time for any number of monovalent, alent, and trivalent ions. Deviations relative to the Nicolskii-Eisenman equation are shown to be especially high at low interferences and bias calibrations if done in a mixed solution of a target s le as well as multivariate calibrations with sensor arrays.
Publisher: Wiley
Date: 23-01-2014
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1CC14822B
Abstract: We demonstrate here for the first time the detection of electrogenerated chemiluminescence (ECL) upon selective, electrochemically triggered tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)) transport across a supported liquid membrane doped with a lipophilic cation-exchanger. This approach allows one to separate the location of ECL generation from the s le compartment, thereby avoiding the contamination of the s le with compounds necessary for ECL.
Publisher: American Chemical Society (ACS)
Date: 11-09-1999
DOI: 10.1021/AC990387S
Abstract: Polymer membrane-based potentiometric sensors have been developed earlier to provide a rapid and direct method of analysis for polyions such as heparin, a natural anticoagulant administered to prevent thrombus formation during cardiovascular surgery. These heparin sensors are irreversible, requiring a membrane renewal procedure between measurements which currently prevents the sensors from being used for continuous monitoring of blood heparin. A newly developed heparin sensor is shown here to allow an alternate and more practical method of membrane renewal. The electrically charged H+ ionophore 5-(octadecanoyloxy)-2-(4-nitrophenylazo)-phenol (ETH 2412) is incorporated as an additional ionophore into a heparin-sensing membrane. This membrane will respond to pH only at low H+ concentrations, while s le anions are coextracted with H+ ions into the membrane at physiological pH. In buffered s les at physiological pH, the sensors will therefore respond to heparin via an ion-exchange mechanism with chloride anions. The pH cross-sensitive heparin-sensing membranes are shown to give an excellent potentiometric response toward heparin in aqueous s les at physiological pH and Cl-levels as well as in undiluted whole blood with no loss of heparin response. The membrane renewal is accomplished by moderately increasing the pH of the s le, causing heparin to diffuse out of the membrane with H+ ions. Reproducibilities are, with less than 1 mV standard deviation, improved over the classical system. Unlike the high NaCl concentration used to strip heparin from the previously established heparin sensor, the pH change used here could ultimately be performed locally at the s le-membrane interface, allowing the sensor to be used for automated long-term monitoring of heparin in blood. A theoretical model is presented to explain the experimental results.
Publisher: American Chemical Society (ACS)
Date: 12-1997
DOI: 10.1021/CR940394A
Publisher: American Chemical Society (ACS)
Date: 03-09-2020
Publisher: Wiley
Date: 11-2002
DOI: 10.1002/1521-4109(200211)14:19/20<1375::AID-ELAN1375>3.0.CO;2-8
Publisher: American Chemical Society (ACS)
Date: 27-01-2017
Publisher: American Chemical Society (ACS)
Date: 10-01-2006
DOI: 10.1021/AC050749Y
Publisher: American Chemical Society (ACS)
Date: 12-05-2020
Publisher: American Chemical Society (ACS)
Date: 12-07-2022
Publisher: Wiley
Date: 26-05-0011
Publisher: American Chemical Society (ACS)
Date: 11-2003
DOI: 10.1021/ED080P1303
Publisher: American Chemical Society (ACS)
Date: 17-04-2007
DOI: 10.1021/AC0701233
Abstract: Multicolor quantum dot-encoded polymeric microspheres are prepared with controllable and uniform doping levels that function as chemical sensors on the basis of bulk optode theory. TOP/TOPO-capped CdSe quantum dots and CdTe quantum dots capped with CdS (lambdaem = 610 and 700 nm, lambdaex = 510 nm) are blended with a THF solution of poly(methyl methacrylate-co-decyl methacrylate), poly(n-butylacrylate), or poly(vinyl chloride) plasticized with bis(2-ethylhexyl) sebacate without a need for ligand exchange. Polymeric microspheres are generated under mild, nonreactive conditions with a particle caster that breaks down a polymer stream containing the quantum dots into fine droplets by the vibration of a piezocrystal. The resulting microspheres exhibit uniform size and fluorescence emission intensities. Fluorescent bar codes are obtained by subsequent doping of two quantum dots with different colors and mass ratios into the microspheres. A linear relationship is found between the readout fluorescence ratio of the two types of nanocrystals and the mixing ratio. Quantum dot-encoded ion sensing optode microspheres are prepared by simultaneous doping of sodium ionophore X, chromoionophore II, a lipophilic tetraphenylborate cation exchanger, and TOPO-capped CdSe/CdS quantum dot as the fluorescent label. A net positive charge of the quantum dots is found to induce an anion-exchange effect on the sensor function, and therefore, an increased concentration of the lipophilic cation exchanger is required to achieve proper ion sensing properties. The modified quantum dot-labeled sodium sensing microspheres show satisfactory sodium response between 10(-4) and 0.1 M at pH 4.8, with excellent selectivity toward common interferences. The amount of the carried positive charges of the CdSe quantum dots is estimated as 2.8 mumol/g of quantum dots used in this study.
Publisher: Elsevier BV
Date: 10-05-2004
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0LC00028K
Abstract: A pixel-level colorimetric absorbance analysis can measure the total quantity of dye on paper, irrespective of shape and size.
Publisher: Elsevier BV
Date: 2010
Publisher: American Chemical Society (ACS)
Date: 28-09-2017
Publisher: American Chemical Society (ACS)
Date: 21-12-2016
DOI: 10.1021/ACS.ANALCHEM.6B03946
Abstract: We report on a novel approach for in-line s le acidification that results in a significant improvement in the limit of detection of potentiometric anion-selective electrodes aiming at determining nutrients in natural waters. The working principle of the developed acidification module relies on the cation-exchange process between the s le and an ion-exchange Donnan exclusion membrane in its protonated form. The resulting in-line acidification of natural waters with millimolar sodium chloride level (freshwater, drinking water, and aquarium water, as well as dechloridized seawater) decreases the pH down to ∼5. By using the acidification module, the limit of detection of nitrite-selective electrodes significantly improves by more than 2 orders of magnitude with respect to that observed at environmental pH. The originality of the proposed flow cell lies in the possibility to adjust the pH of the s le by modifying its exposure time with the membrane by varying the volumetric flow rate. Facile coupling with a detection technique of choice, miniaturized configuration and simple implementation for long-term monitoring with submersible probes for environmental analysis are possible analytical configurations. This approach was here successfully applied for the potentiometric detection of nitrite in aquarium and dechloridized seawater s les.
Publisher: Springer Science and Business Media LLC
Date: 25-01-2019
DOI: 10.1038/S41467-018-08054-4
Abstract: Quantifying the genetic correlation between cancers can provide important insights into the mechanisms driving cancer etiology. Using genome-wide association study summary statistics across six cancer types based on a total of 296,215 cases and 301,319 controls of European ancestry, here we estimate the pair-wise genetic correlations between breast, colorectal, head/neck, lung, ovary and prostate cancer, and between cancers and 38 other diseases. We observed statistically significant genetic correlations between lung and head/neck cancer ( r g = 0.57, p = 4.6 × 10 −8 ), breast and ovarian cancer ( r g = 0.24, p = 7 × 10 −5 ), breast and lung cancer ( r g = 0.18, p =1.5 × 10 −6 ) and breast and colorectal cancer ( r g = 0.15, p = 1.1 × 10 −4 ). We also found that multiple cancers are genetically correlated with non-cancer traits including smoking, psychiatric diseases and metabolic characteristics. Functional enrichment analysis revealed a significant excess contribution of conserved and regulatory regions to cancer heritability. Our comprehensive analysis of cross-cancer heritability suggests that solid tumors arising across tissues share in part a common germline genetic basis.
Publisher: Elsevier BV
Date: 05-2004
DOI: 10.1016/J.TALANTA.2003.10.006
Abstract: The response of ion-selective electrodes (ISEs) can be described on the basis of two different theoretical approaches. On one hand, the phase-boundary model is based on the assumption of local equilibria at the aqueous/organic interface. The phase-boundary model allows the description of all practically relevant cases of steady state and even transient responses with sufficient accuracy. Moreover, it has the advantage of relating simple thermodynamic parameters to the response function of the electrodes and hence allowing an intuitive interpretation of many observed facts. On the other hand, the comprehensive but quite involved dynamic model requires knowledge of mobilities and ion transfer rate constants. It has never been applied to ionophore-based electrodes in its full complexity. Both models were first suggested decades ago but have been recently extended to explain so far poorly understood aspects of ionophore-based ISEs. Due to space restrictions, only the most important original references are given in this paper, which summarizes the major assumptions of the phase-boundary potential model and discusses the usefulness and limits of this approach. Recent applications are discussed towards understanding sensor selectivity, upper and lower detection limits (even when concentration polarizations are relevant), the so-called sandwich membrane method to determine thermodynamic parameters, apparently non-Nernstian responses, potential drifts with solid contact electrodes, polyion sensors, and galvanostatically controlled ion sensors.
Publisher: American Chemical Society (ACS)
Date: 27-10-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3RA43751E
Publisher: Elsevier BV
Date: 03-2005
Publisher: American Chemical Society (ACS)
Date: 13-06-2013
DOI: 10.1021/AC400470N
Abstract: Potentiometric sensors that exhibit a non-Hofmeister selectivity sequence are normally designed by selective chemical recognition elements in the membrane. In other situations, when used as detectors in separation science, for ex le, membranes that respond equally to most ions are preferred. With so-called liquid membranes, a low selectivity is difficult to accomplish since these membranes are intrinsically responsive to lipophilic species. Instead, the high solubility of s le lipids in an ionophore-free sensing matrix results in a deterioration of the response. We explore here potentiometric sensors on the basis of ion-exchange membranes commonly used in fuel cell applications and electrodialysis, which have so far not found their way into the field of ion-selective electrodes. These membranes act as Donnan exclusion membranes as the ions are not stripped of their hydration shell as they interact with the membrane. Because of this, lipophilic ions are no longer preferred over hydrophilic ones, making them promising candidates for the detection of abundant ions in the presence of lipophilic ones or as detectors in separation science. Two types of cation-exchanger membranes and one anion-exchange membrane were characterized, and potentiometric measuring ranges were found to be Nernstian over a wide range down to about 10 μM concentrations. Depending on the specific membrane, lipophilic ions gave equal response to hydrophilic ones or were even somewhat discriminated. The medium and long-term stability and reproducibility of the electrode signals were found to be promising when evaluated in synthetic and whole blood s les.
Publisher: American Chemical Society (ACS)
Date: 15-07-1992
DOI: 10.1021/AC00038A007
Publisher: Cold Spring Harbor Laboratory
Date: 25-10-2018
DOI: 10.1101/453480
Abstract: Quantifying the genetic correlation between cancers can provide important insights into the mechanisms driving cancer etiology. Using genome-wide association study summary statistics across six cancer types based on a total of 296,215 cases and 301,319 controls of European ancestry, we estimate the pair-wise genetic correlations between breast, colorectal, head/neck, lung, ovary and prostate cancer, and between cancers and 38 other diseases. We observed statistically significant genetic correlations between lung and head/neck cancer ( r g =0.57, p=4.6×10 −8 ), breast and ovarian cancer ( r g =0.24, p=7×10 −5 ), breast and lung cancer ( r g =0.18, p=1.5×10 −6 ) and breast and colorectal cancer ( r g =0.15, p=1.1×10 −4 ). We also found that multiple cancers are genetically correlated with non-cancer traits including smoking, psychiatric diseases and metabolic characteristics. Functional enrichment analysis revealed a significant excess contribution of conserved and regulatory regions to cancer heritability. Our comprehensive analysis of cross-cancer heritability suggests that solid tumors arising across tissues share in part a common germline genetic basis.
Publisher: American Chemical Society (ACS)
Date: 16-09-2015
DOI: 10.1021/ACS.ANALCHEM.5B02856
Abstract: A selective electrochemical calcium pump based on a fast diffusive calcium ionophore-based membrane is reported. An initially nonpolarized ionophore-based membrane allows one to establish a net calcium flux by applying a potential step function (i.e., 250 mV for 30 s). The resulting calcium flux is released into a microliter scale thin layer reservoir, and the resulting ion perturbation is monitored by either a potentiometric or a coulometric readout. This chemical perturbation in the thin layer thus acts as a titration agent that is precisely controlled by coulometry. A linear correlation between released and detected calcium is confirmed by the two different readout modes. Having demonstrated the efficiency of the calcium pump in background electrolyte solutions, a complexometric titration with known concentrations of EDTA in the thin layer s le was performed. With the potentiometric readout, titrations in the range of 0.25-0.75 mM gave a precision of 3%, whereas the coulometric readout gave a range of 0.02-0.12 mM and a precision of 2%. Improved precision is expected by better control of the thin layer geometry by microfabrication. The significance of this work is that the coupling of a selective calcium pump with a thin layer element can give rise to rapid and complete s le concentration changes and result in a promising platform for titrations either on the laboratory bench or for in situ measurements in environmental or diagnostic settings.
Publisher: American Chemical Society (ACS)
Date: 17-10-2018
Publisher: American Chemical Society (ACS)
Date: 28-04-2017
Publisher: American Chemical Society (ACS)
Date: 09-12-2006
DOI: 10.1021/AC061467G
Publisher: American Chemical Society (ACS)
Date: 29-01-2020
DOI: 10.1021/ACS.ANALCHEM.9B05187
Abstract: The sensitivity of potentiometric sensors functioning in equilibrium mode is limited by the value predicted according to the Nernst equation and inversely proportional to the charge in the analyte ion. Therefore, an increased ion charge results in a dramatic decrease in the sensor sensitivity. We propose an approach to allow one to increase the sensitivity of the potentiometric measurements by using a combined electrochemical cell composed of several identical ion-selective electrodes immersed into separate s le solutions of equal composition. The combination of
Publisher: American Chemical Society (ACS)
Date: 13-06-2019
DOI: 10.1021/ACS.ANALCHEM.9B01145
Abstract: It has recently been reported that polystyrene microbeads may be modified to realize plasticizer-free ion-selective optical sensors (optodes) on the basis of solvatochromic dye transducers. We show here that the functionalized microbeads, in idually isolated by flow cytometry, exhibit unexpectedly poor fluorescent properties and that the sensor response is instead attributed to the supernatant. A more thorough study reveals that such optical microemulsion sensors can be made operationally functional and chemically selective, seemingly in the absence of any solvent matrix or added surfactant. Instead, it is shown that residual THF used in the fabrication of the emulsified sensors may solubilize the sensing components and give a functional optode response. To evaluate this further, the number of sensing components was stepwise simplified to assess their need. Variation of residual THF levels has no effect on the ion optode response when plasticizer is present, in support of established results. Lipophilic solvatochromic dye transducers are also shown not to require an added surfactant as their nature already endows the emulsified sensors with a stabilizing ionic surface charge. The ionophores are shown to exhibit much larger stability constants in the surfactant-free formulations than surfactant-based ones (valionomycin, log β > 9.2 compared to 6.1 Na
Publisher: American Chemical Society (ACS)
Date: 15-06-2004
DOI: 10.1021/AC049577F
Abstract: The spontaneous hydroxy-bridged dimer formation of metalloporphyrins in ion-selective membranes gives rise to a short sensor lifetime (typically days), triggered by solubility problems, the occurrence of a super-Nernstian response slope, and a pH cross response. This dimer formation is eliminated here by covalent attachment of the ionophore to the polymer matrix. Specifically, two different indium(III)porphyrins containing polymerizable groups, the chloride-selective chloro(3-[18-(3-acryloyloxypropyl)-7,12-bis(1-methoxyethyl)-3,8,13,17-tetramethylporphyrin-2-yl]propyl ester)indium(III) and the nitrite-selective Chloro(5-(4-acryloyloxyphenyl)-10,15,20-triphenylporphyrinato)indium(III), were synthesized and copolymerized with methyl methacrylate and decyl methacrylate. The covalent attachment of the ionophore to the polymer matrix indeed prevents the metalloporphyrin from forming dimeric species, as confirmed by UV/visible spectroscopy. The ion-selective membranes with grafted indium porphyrin showed Nernstian response slopes to chloride, nitrite, perchlorate, and thiocyanate anions, with a selectivity comparable to membranes with freely dissolved or underivatized metalloporphyrin. The membranes containing grafted ionophores showed a lifetime of at least two months, apparently since crystallization of the poorly soluble dimeric species may no longer occur. This is one of the first ex les where the covalent attachment of an ionophore drastically improves on a number of important sensor characteristics.
Publisher: American Chemical Society (ACS)
Date: 15-06-2018
DOI: 10.1021/ACS.ANALCHEM.8B02145
Abstract: We present here a capacitive model for the coulometric signal transduction readout of solid-contact ion-selective membrane electrodes (SC-ISE) with a conducting polymer (CP) as an intermediate layer for the detection of anions. The capacitive model correlates well with experimental data obtained for chloride-selective SC-ISEs utilizing poly(3,4-ethylenedioxythiophene) (PEDOT) doped with chloride as the ion-to-electron transducer. Additionally, Prussian blue is used as a simple sodium capacitor to further demonstrate the role of the transduction layer. The influence of different thicknesses of PEDOT as a conducting polymer transducer, different thicknesses of the overlaying ion-selective membranes deposited by drop casting and spin coating, and different compositions of the chloride-selective membrane are explored. The responses are evaluated in terms of current-time, charge-time, and charge-chloride activity relationships. The utility of the sensor with coulometric readout is illustrated by the monitoring of very small concentration changes in solution.
Publisher: American Chemical Society (ACS)
Date: 29-04-2010
DOI: 10.1021/AC100524Z
Abstract: We are demonstrating here for the first time a thin layer coulometric detection mode for ionophore based liquid ion-selective membranes. Coulometry promises to achieve the design of robust, calibration free sensors that are especially attractive for applications where recalibration in situ is difficult or undesirable. This readout principle is here achieved with porous polypropylene tubing doped with the membrane material and which contains a chlorinated silver wire in the inner compartment, together with the fluidically delivered s le solution. The membrane material consists of the lipophilic plasticizer dodecyl 2-nitrophenyl ether, the lipophilic electrolyte ETH 500, and the calcium ionophore ETH 5234. Importantly and in contrast to earlier work on voltammetric liquid membrane electrodes, the membrane also contains a cation-exchanger salt, KTFPB. This renders the membrane permselective and allows one to observe open circuit potentiometric responses for the device, which is confirmed to follow the expected Nernstian equation. Moreover, as the same cationic species is now potential determining at both interfaces of the membrane, it is possible to use rapidly diffusing and/or thin membrane systems where transport processes at the inner and outer interface of the membrane do not perturb each other or the overall composition of the membrane. The tubing is immersed in an electrolyte solution where the counter and working electrode are placed, and the potentials are applied relative to the measured open circuit potentials. Exhaustive current decays are observed in the range of 10 to 100 muM calcium chloride. The observed charge, calculated as integrated currents, is linearly dependent on concentration and forms the basis for the coulometric readout of ion-selective membrane electrodes.
Publisher: American Chemical Society (ACS)
Date: 28-04-2006
DOI: 10.1021/AC060637M
Publisher: Wiley
Date: 27-08-2002
DOI: 10.1002/9783527610426.BARD090009
Abstract: The sections in this article are
Publisher: Elsevier BV
Date: 2014
Publisher: The Electrochemical Society
Date: 04-1996
DOI: 10.1149/1.1836608
Publisher: Elsevier BV
Date: 10-1999
Publisher: Springer Science and Business Media LLC
Date: 24-06-2014
Publisher: American Chemical Society (ACS)
Date: 08-1995
DOI: 10.1021/MA00121A021
Publisher: American Chemical Society (ACS)
Date: 12-07-2005
DOI: 10.1021/AC050101L
Abstract: We describe here in detail the first reversible electrochemical sensors for the polyion protamine. Potentiometric sensors were proposed in recent years, mainly for the determination of the polyions heparin and protamine. Such potentiometric polyion sensors functioned on the nonequilibrium extraction of polyions into a hydrophobic membrane phase via ion pairing with lipophilic ion exchangers. This made it difficult to design sensors that operate in a truly reversible fashion. The reversible sensors described here utilize the same basic response mechanism as their potentiometric counterparts, but the processes of extraction and ion stripping are now fully controlled electrochemically. Spontaneous polyion extraction is avoided by using membranes containing highly lipophilic electrolytes that possess no ion-exchange properties. Reversible extraction of polyions is induced if a constant current pulse of fixed duration is applied across the membrane, followed by a baseline potential pulse. The key theoretical response principles of this new class of polyion sensors are discussed here and compared to those of its classical potentiometric counterpart. The electrochemical sensing system is characterized in terms of optimal working conditions, membrane composition, selectivity, and influence of s le stirring and organic-phase diffusion coefficient on the response characteristics. Excellent potential stability and reversibility of the sensors are observed, and measurements of heparin concentration in whole blood s les via protamine titration are demonstrated.
Publisher: Elsevier BV
Date: 08-2014
DOI: 10.1038/GIM.2014.5
Publisher: Wiley
Date: 26-05-2015
Abstract: We report a general concept based on a selective electrochemical ion pump used for creating concentration perturbations in thin layer s les (∼40 μL). As a first ex le, hydrogen ions are released from a selective polymeric membrane (proton pump) and the resulting pH is assessed potentiometrically with a second membrane placed directly opposite. By applying a constant potential modulation for 30 s, an induced proton concentration of up to 350 mM may be realized. This concept may become an attractive tool for in situ titrations without the need for s ling, because the thin layer eventually re-equilibrates with the contacting bulk s le. Acid-base titrations of NaOH and Na2 CO3 are demonstrated. The determination of total alkalinity in a river water s le is carried out, giving levels (23.1 mM) comparable to that obtained by standard methods (23.6 mM). The concept may be easily extended to other ions (cations, anions, polyions) and may become attractive for environmental and clinical applications.
Publisher: Elsevier BV
Date: 06-1999
Publisher: American Chemical Society (ACS)
Date: 07-07-2005
DOI: 10.1021/AC050856S
Abstract: An optical microsensor array is described for the rapid analysis of silver ions at low parts per trillion levels. Because the ionophore o-xylylenebis(N,N-diisobutyldithiocarbamate) (Cu-I) was reevaluated and shown to exhibit excellent selectivity for silver ions, ion-selective electrode (ISE) membranes were optimized and found to exhibit the lowest reported detection limit so far (3 x 10(-10) M). A corresponding Ag+-selective fluorescent optical microsensor array for the rapid sensing of trace level Ag+ was then developed. It was fabricated using plasticized PVC-based micrometer-scale fluorescent microspheres that were produced via a sonic particle casting device. They contained 156 mmol/kg Cu-I, 10 mmol/kg 9-(diethylamino)-5-[4-(15-butyl-1,13-dioxo-2,14-dioxanodecyl) phenylimino]benzo[a]phenoxazine (chromoionophore VII, ETH 5418), 2.3 mmol/kg 1,1' '-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (internal reference dye), and 14 mmol/kg sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate and were deposited onto the etched distal end of a 3200-microm-diameter optical fiber bundle. The microarray was characterized by fluorescence spectroscopy in s les containing 10(-12)-10(-8) M AgNO3 at pH 7.4, with selectivity characteristics comparable to the corresponding ISEs. The response time of the microsensor array was found to be less than 15 min for 10(-9) M AgNO3, which is drastically shorter than earlier data on optode films (8 h) and corresponding ISEs (30 min). A detection limit of 4 x 10(-11) M for Ag+ was observed, lower than any previously reported optode or silver-selective ISE. The microsensor array was applied for measurement of free silver levels in buffered pond water s les.
Publisher: American Chemical Society (ACS)
Date: 18-02-2021
Publisher: American Chemical Society (ACS)
Date: 28-05-2018
DOI: 10.1021/ACS.ANALCHEM.8B01282
Abstract: We present here for the first time a solid contact ion-selective electrode suitable for the simultaneous sensing of cations (tetrabutylammonium) and anions (hexafluorophosphate), achieved by electrochemical switching. The membrane is based on a thin plasticized polyurethane membrane deposited on poly(3-octylthiophene) (POT) and contains a cation exchanger and lipophilic electrolyte (ETH 500). The cation exchanger is initially in excess the ion-selective electrode exhibits an initial potentiometric response to cations. During an oxidative current pulse, POT is converted into POT
Publisher: American Chemical Society (ACS)
Date: 03-1997
DOI: 10.1021/AC960891M
Publisher: American Chemical Society (ACS)
Date: 15-10-1999
DOI: 10.1021/AC9905930
Abstract: A potentiometric method to determine ionophore complex formation constants in solvent polymeric membrane phases, proposed originally by Russian researchers, is critically evaluated and compared to other established methods. It requires membrane potential measurements on two-layer sandwich membranes, where only one side contains the ionophore. The resulting initial membrane potential reflects the ion activity ratio at both aqueous phase--membrane interfaces and can be conveniently used to calculate complex formation constants in situ. This method is potentially useful, since it does not require the use of a reference ion or second ionophore in the measurement. In this paper, the five ionophores valinomycin, BME-44, ETH 2120, tert-butylcalix[4]arene tetraethyl ester, and S,S'-methylenebis(diisobutyldithiocarbamate) are characterized in poly(vinyl chloride) (PVC) plasticized with dioctyl sebacate (DOS) and compared with other established methods. The resulting formation constants correspond well to literature values. The influence of varying membrane concentrations and different anionic site additives is studied and found to be relatively small. Experiments are also performed with and without lipophilic inert electrolytes and with ionophore-free sandwich membranes to illustrate the effect of ion pairing and the membrane internal diffusion potential on the response of such sandwich membranes. These experiments suggest that ions are completely associated in PVC-DOS membranes, but that such ion pairs are rather nonspecific. Diffusion potentials seem to play a minor role with these systems. The results are explained with theory. This work indicates that the characterization of electrically charged ionophores, anion-selective ionophores, and ionophores in membrane matrixes other than PVC plasticized with DOS may now be experimentally accessible.
Publisher: American Chemical Society (ACS)
Date: 27-07-2018
Publisher: American Chemical Society (ACS)
Date: 23-02-2021
Publisher: American Chemical Society (ACS)
Date: 19-09-2022
DOI: 10.1021/ACSSENSORS.2C01599
Abstract: The last decade has witnessed a rapid development of nano- and microparticle-based optical ion sensors, including ion-selective optodes (ISOs). While the application of nano-ISOs has shown promising performance for sensing inorganic ions, polyion sensing using nanoscale ISOs has encountered significant interference in complex s les such as blood plasma. Recently, we have reported on a new polyion sensing principle that operates through a novel mechanism to overcome this challenge. The new sensing mechanism showed improved characteristics not observed with conventional ion-exchange type sensors, but the precise mechanism of operation remained thus far unclear. This paper aims to clarify how protamine, the arginine-rich target polycation, behaves during optical signal transduction to give dramatically improved selectivity. Based on thermodynamic data, sensor performance and ζ-potential analysis, two discrete phases of protamine extraction are identified. Initially, protamine extracts into the bulk nanosensor phase, a process that is concurrent with the optical signal change. This is then followed by protamine accumulation onto the nanosensor surface, which starts only upon saturation of the optical signal change. The data indicate that the improved selectivity is due to the inability of small ions to form a sufficiently strong interaction with an active sensing ingredient, DNNS
Publisher: Elsevier BV
Date: 06-1994
DOI: 10.1016/0039-9140(94)E0041-O
Abstract: The role of lipophilic anionic and cationic additives on the potentiometric anion selectivities of polymer membrane electrodes prepared with various metalloporphyrins as anion selective ionophores is examined. The presence of lipophilic anionic sites (e.g. tetraphenylborate derivatives) is shown to enhance the non-Hofmeister anion selectivities of membranes doped with In(III) and Sn(IV) porphyrins. In contrast, membranes containing Co(III) porphyrins require the addition of lipophilic cationic sites (e.g. tridodecylmethylammonium ions) in order to achieve optimal anion selectivity (for nitrite and thiocyanate) as well as rapid and reversible Nernstian response toward these anionic species. These experimental results coupled with appropriate theoretical models that predict the effect of lipophilic anion and cation sites on the selectivities of membranes doped with either neutral or charged carrier type ionophores may be used to determine the operative ionophore mechanism of each metalloporphyrin complex within the organic membrane phase.
No related grants have been discovered for Eric Bakker.