Search

Direct ammonia-fed fuel cells (DAFCs) are well known for sustainable energy production. However, the issue is a certain amount of unreacted NH 3 fuel is obtained at the outlet. Thus, real-time monitoring and quantification are of utmost importance, nevertheless, this is troublesome due to the harsh thermodynamic conditions. This work aims to develop a mixed-potential sensing electrode for the detection of NH 3 under reducing conditions (H 2 atmosphere) at high temperatures. In this regard, a strontium molybdate (SrMoO 4) sensing electrode (SE) is a potential solution due to its physical and chemical stability, along with its sensitivity to NH 3 under reducing conditions. Therefore, an SrMoO 4 -based mixed-potential sensor is fabricated herein using yttria-stabilized zirconia (YSZ) as the electrolyte and platinum (Pt) as the reference electrode (RE) and is operated at 400–650 ℃. The maximum response exhibits about –21.57 mV toward 80 ppm NH 3 at 500 ℃. Further, the sensitivity is –17.19 mV/decade towards 10–60 ppm and –45.33 mV/decade towards 60–320 ppm NH 3 under 75% H 2 balanced by N 2 at 500 ℃. The as-fabricated sensor also has good selectivity towards NH 3 and good cross-sensitivity towards other interfering gases and is stable in long-term repeated operation. The direct current (DC) polarization curves and electrochemical impedance spectroscopy (EIS) results demonstrate the sensing mechanism in accordance with the mixed-potential theory. [Display omitted] • SrMoO 4 sensing electrode is proposed for NH 3 sensing in reducing conditions. • Novel approach of NH 3 sensing in the low pO 2 conditions at high temperature. • SrMoO4-based sensor's sensitivity was −45.33 mV/decade towards 60–320 ppm at 500 ℃. • Good cross-sensitivity and selectivity towards NH 3 under 75% H 2 balanced by N 2. • Fabricated sensors were operated by following mixed potential sensing mechanisms. [ABSTRACT FROM AUTHOR]

A dual sensitive, simple, and rapid membrane-based potentiometric sensor was developed to determine thorium (Th) ion in nuclear fuel samples which does not require any prior chemical separation of other matrix elements. Sensor was prepared by incorporating N,N,N',N',N",N" -hexa- n -octylnitrilotriacetamide (HONTA) in a polyvinyl chloride (PVC) matrix in presence of 2-nitrophenyl octyl ether (NPOE) and sodium tetraphenyl borate (NaTPB). The optimum membrane composition was found to be 14.1% HONTA, 3.2% NaTPB, 54.9% NPOE, 27.8% PVC, which showed a dual sensitive linear region in the calibration plot with sub-Nernstian and super-Nernstian slopes of 12.1 ± 0.4 mV/decade and 71.7 ± 3.5 mV/decade, respectively, with the corresponding linear dynamic ranges of 2.0 × 10−5 to 5.3 × 10−4 M and 3.8 ×10−3 to 1.4 × 10−2 M, respectively. The super-Nernstian sensitivity exhibited by the sensor increases with Th(IV) as well as HONTA concentrations in the membrane and can be thought to be due to micelle-mediated selective adsorption (MMSA) sensing of the metal ion. Solution speciation of Th(IV) in acetate buffer was determined by laser desorption/ionization mass spectrometry (LDI-MS) and Medusa software. Pristine and used membranes were characterized by Fourier transform infrared (FTIR), scanning electron microscopy–energy dispersive x–rays (SEM-EDS) and small angle neutron scattering (SAXS). Thorium was measured in an actual (Th–U) mixed solution and in a synthetic advance heavy water reactor (AHWR) fuel sample. The present study describes a new approach for the detection of Th(IV) ion through MMSA in an ion selective electrode (ISE). [Display omitted] • A highly sensitive and selective potentiometric sensor for Th estimation was developed. • Sensor exhibited dual sensitivity with sub and super-Nernstian slopes in calibration plot. • Aggregation of the ionophore has been observed from SAXS studies in the membrane. • Micelle mediated selective adsorption (MMSA) mechanism is proposed for sensing. • Sensor can determine thorium in mixed (Th 0.9 –U 0.1)O 2 samples without separation of other elements. [ABSTRACT FROM AUTHOR]

The feasibility of using Zr-porphyrins as ionophores selective towards lactate ions was examined. Zr-tetraphenylporphyrin (Zr-TPP) and Zr-octaethylporphyrin (Zr-OEP) were tested in polyurethane membranes plasticized with dioctyl sebacate or o-nitrophenyl ether and containing cationic or anionic lipophilic sites, respectively. The best lactate response characteristics were registered for membrane plasticized with dioctyl sebacate and doped with Zr-TPP and cationic lipophilic sites. Classical electrodes with this membrane showed high selectivity towards lactate ions with a sensitivity of −76.6 mV dec−1 and linear lactate calibration range from 10−4 M to 10−1 M. Polymeric membranes containing Zr-TPP were then drop-casted on screen-printed transducers with electrodes made of graphene-containing paste. It was found that the potentiometric behavior of these miniature planar sensors is very similar to classical electrodes. In the next step, fully printed sensors, with both graphene electrodes and ion-selective polymeric membranes, were fabricated using aerosol jet printing. The sensitivity of these electrodes towards lactate was −79.01±0.39 mV dec−1 with a linear response range from 10−3.5 M to 10−1 M and a fast response to lactate concentration changes. The proposed electrode demonstrates a rare example of a potentiometric, non-enzymatic sensor for the determination of lactate ions, with the possibility of miniaturization and mass fabrication using printing methods. • Zr-porphyrins show high selectivity towards lactate ion in polyurethane membranes. • Both neutral carrier and charged carrier mechanism are possible for these ionophores. • Fully printed, planar sensors for lactate determination were developed. • A rare example of potentiometric, non-enzymatic lactate sensor was proposed. [ABSTRACT FROM AUTHOR]

The integration of electronic sensors into single-use systems for bioprocessing is challenged by their sensitivity to sterilizing γ-irradiation. This challenge also applies to reference electrodes (REs), whose potentials may be destabilized upon ionization and drift over time. Here we evaluate the performance of thin-film Ag/AgCl REs over a two-month window following γ-ray sterilization using a 60Co source. γ-REs display a characteristic voltage decay during the first few weeks of operation ascribed to dissipation of radiation-induced charge defects, followed by long-term potentiometric stability when stored in phosphate-buffered saline with a 95 % confidence interval of 4 mV over 60 days. γ-REs have a mean insensitivity (inertness) of 0.6 mV/decade in pH buffers (4.5–9.0) and <1 mV/decade in the presence of organic solutes and ions at physiological ionic strength. γ-REs paired with thin-film working electrodes (WE) form sensors with near-Nernstian sensitivity, and irradiation of a thin-film pH sensor (γ-pH/WE plus γ-RE) produces a logarithmic voltage decay that is readily corrected by a single-point calibration function. The γ-irradiated sensor can monitor pH changes in sterile cell culture media over a 3-week period and produces readouts with a mean deviation below 0.04 pH units relative to a commercial meter (ground truth). [Display omitted] • γ-sterilized thin-film pH sensors perform reliably with low materials cost. • γ-irradiated sensors only need single-point calibration after conditioning. • γ-irradiated thin-film sensors can be used for 3 weeks in sterile culture media. • γ-irradiated thin-film sensors produce values within 0.04 units of ground-truth pH. • Irradiated reference electrodes show same inertness as controls over 60 days. [ABSTRACT FROM AUTHOR]

Reference electrodes (REs) based on moderately lipophilic ionic liquids (ILs) are an attractive approach to realize integrated potentiometric sensing systems that do not require a traditional liquid junction. However, it is not sufficiently understood how lipophilic sample ions can result in interference. Less lipophilic ILs should partition more easily into the aqueous phase where they can compete with sample ions and suppress ion-exchange, but since a decreased IL lipophilicity favors ion-exchange interference the overall effect is not immediately clear. We use here the established phase boundary potential model to describe failure of IL-based REs upon exposure to lipophilic solution ions. The traditional definition of the detection limit is employed to find the intersection of the separate Nernstian responses to IL and solution interference, which is mathematically simpler to process. The approach focuses on cation interference and considers ion pairing in the polymeric phase together with appropriate ion-exchange and coextraction equilibria. The range of RE potential stability is shown to depend on 1) the concentration of the IL in the membrane; 2) the lipophilicity of the IL expressed through its partition constant; 3) the relative lipophilicity of the lipophilic interference and the IL ion of the same charge expressed through the corresponding ion-exchange constant; 4) the stability constant of ion pairs between the interfering ion and the counterion from the IL. For the experimental evaluation of the model, two commercially available ionic liquids were selected: [C 8 mim+][C 1 C 1 N-] (IL1) and [TBMOEP+][C 1 C 1 N-] (IL2). Partition constants between water and a polymeric phase based on poly(vinyl chloride) (PVC) and dodecyl 2-nitrophenyl ether (NPDE) were determined for the first time for both IL1 (3.55 ± 0.05) and IL2 (4.68 ± 0.22) using so-called sandwich membrane experiments. Based on these values, the expected reference electrode lifetime is discussed. Tetramethylammonium, tetraethylammonium and tetrabutylammonium cations were selected as model interfering ions and the corresponding exchange constants were obtained experimentally. The model provides excellent RE failure prediction in which calculated critical activities for the tetrabutylammonium cation closely match the experimental values for both ILs. [Display omitted] • The influence of lipophilic ions on the potential of ionic liquid reference electrodes has not been fully understood before. • A model is proposed to describe the failure of reference electrodes based on ionic liquids in presence of lipophilic cations. • Partition constants in a PVC-NPDE/water system are determined for two moderately lipophilic ionic liquids. • The model provides excellent reference electrode failure prediction in terms of critical interfering ion activity. • The expected poor electrode lifetime is addressed and requirements for new ionic liquids are discussed. [ABSTRACT FROM AUTHOR]

Solid-contact polymeric membrane ion-selective electrodes (ISEs) have been an attractive tool for potentiometric sensors. Sufficient transducing performance evaluation and multiple potentiometric analysis are critical to evaluate whether the solid contact transducer material used in ISE is promising. Herein, we describe sandwich-like MXene/MWCNTs-based polymeric membrane ISEs with three-readout strategies of potential response, chronopotentiometric response, and transition time response. The MXene/MWCNTs can be readily prepared by the electrostatic self-assembly strategy, which not only prevented the aggregation of MXene nanosheets and facilitated charge-transfer, but also significantly contributed to the large double-layer capacitance and water-layer free from interference. With Ca2+ as a model, two kinds of Ca2+-ISEs based on thermodynamic response and dynamic response by modulating the polymeric membrane components with three readouts were explored. Moreover, the proposed Ca2+-ISEs under different background electrolytes exhibit the similar Nernstian responses in potentiometry, variable super-Nernstian ranges in chronopotentiometry, and the consistent transition time readout. This study offers a facile MXene/MWCNTs transducer to develop a highly reliable polymeric membrane ISE. [Display omitted] • Sandwich-like MXene/MWCNTs composite is used as a solid contact. • The solid contact contributes to large double-layer capacitance and water-free layer interference. • Three analytical signals of potentiometry, chronopotentiometry and transition time are proposed. • The solid contact is feasible for thermodynamic as well as dynamic potentiometiomeric response. [ABSTRACT FROM AUTHOR]

Developing high-performance sensing electrodes is crucial for solid-electrolyte potentiometric gas sensors. This work reports a surface modification route to tune the H 2 sensing properties of a mixed ionic-electronic conducting Pr 0.1 Ce 0.9 O 2-δ electrode. Loading basic oxides was detrimental, while acidic oxides, particularly SnO 2 , enhanced the sensing performance. SnO 2 modification markedly increased the response and sensitivity and significantly decreased the limit of detection and response time. Electrochemical analyses revealed that SnO 2 modification slightly inhibited the oxygen exchange reaction but considerably accelerated the hydrogen oxidation reaction, primarily due to changes in the gaseous/surface processes. The sensing behavior agreed with the mixed-potential mechanism, and the enhanced sensing properties by SnO 2 were attributed to an increase in the electrochemical activity ratio. These findings offer a facile approach to boost H 2 sensing by tailoring the electrochemical activities. • Mixed-conducting Pr 0.1 Ce 0.9 O 2-δ electrode was surface-modified by simple oxides. • The H 2 sensing performance increased with the acidity of the oxide modifiers. • SnO 2 loading greatly boosted the H 2 response, sensitivity, and response speed. • Electrochemical analyses suggested a mixed-potential sensing mechanism. • Enhanced sensing was ascribed to an increased electrochemical activity ratio. [ABSTRACT FROM AUTHOR]

Reference electrodes are indispensable part of electroanalytical methods; however, their use may often limit the options for miniaturization of the measurement set-up which is an important requirement for handling small sample volumes in biomedical studies. This is also true for potentiometric multisensor systems ("electronic tongues") that are currently being rapidly developed for numerous analytical applications. We describe an approach to potentiometric multisensor measurements allowing the elimination of reference electrode from the measurement scheme. The idea is based on the employment of "cross-voltages" – the potentials of the sensors measured against each particular sensor of multisensor array with subsequent chemometric processing of these data. In this scenario each sensor in turn becomes a pseudo-reference electrode, thus the overall measuring protocol is as simple as direct potentiometry with only difference at the data treatment stage, where chemometric processing is required to extract the analytical information. The feasibility of this scheme is demonstrated for analysis of several model mixtures and for real urine samples. The accuracy attained by this procedure is at least the same as in classical multisensor measurements scheme and in several cases the cross-voltage approach yielded two times better accuracy, thus proving the perspective of the proposed measuring protocol. • Novel approach to potentiometric multisensor measurements without reference electrode. • Cross-voltage scheme with minimal modification in mV-meter. • Comparison with traditional measuring protocol reveals better accuracy of the new scheme. [ABSTRACT FROM AUTHOR]

Minute potential changes at membrane electrodes may be translated to easily detectable current spikes if the cell potential is held constant and the change is imposed onto a capacitive element placed in series. While this results in a very important increase in measurement precision, the current transient passing through the sensing membrane contributes to measurement uncertainty and may not be applicable to all sensing materials. This limitation is overcome by treating the ion-selective electrode as reference electrode, which allows one to avoid current passing through the ion-selective membrane. The potential stability of the Ag/AgCl element upon passage of current was confirmed to be excellent, as expected for an ideally non-polarizable electrode. This greatly increases the reproducibility and precision of the method. The approach also allows one to use the LaF 3 crystal-based fluoride sensitive membrane, for which passage of current transients gives deleterious effects. An electronic circuit was built to automate the control of the capacitive element. An improvement of precision (from 829 to 177 μpH) and a reduction of signal drift (from 1.89% of total charge to 0.38%) was demonstrated with membrane-based pH electrodes while fluoride sensing was achieved for the first time with constant potential coulometry at high reproducibility and precision (RSD of just 0.026% activity change). • Constant potential coulometry at ion-selective membranes greatly increases precision. • A transient current flow is required and may perturb the measurement. • The transient current is here passed through the Ag/AgCl element, overcoming this limitation. • An instrument is developed to automate the measurement, resulting in 10-fold improved precision. • The approach is successfully demonstrated with pH and fluoride-selective membranes. [ABSTRACT FROM AUTHOR]

• The novel functional microgels (PNI-MSPC) were synthesized, which exhibited thermo-sensitivity, redox actuatable size and fluorescence. • The PNI-MSPC microgels can be used as the fluorescent sensor for ultrasensitive and selective detection of MnO 4 − anions in aqueous solution. • The limit of detection for MnO 4 − anions was about 25 nM with a fast response time of 5 min and a linear concentration range of 0–50 μM. The novel functional microgels, namely PNI-MSPC microgels, were fabricated via surfactant free emulsion polymerization (SFEP) by using N -isopropylacrylamide (NIPAm) as the monomer and a home-designed dichlorinated 1,1′-di[4-(vinyl)benzyl]-4,4′-pyridinium salt (MSPC2+.2Cl−) as the cross-linker. The PNI-MSPC microgels exhibited not only thermo-sensitivity but also redox actuatable hydrodynamic diameter and fluorescence properties. The PNI-MSPC microgels were successfully applied as the fluorescent sensor for ultrasensitive and selective detection of trace MnO 4 - anions in aqueous solutions. The presence of MnO 4 - anions led to the significant fluorescence quenching of the PNI-MSPC microgels with a fast response time of 5 min. The limit of detection (D L) for MnO 4 - anions can reach 25 nM with a linear concentration range of 0–50 μM. The co-existence of 16 other species of anions or 17 species of metal ions did not interfere with the detection of trace MnO 4 - anions in aqueous solutions. The potential applications of the PNI-MSPC microgels for sensing trace MnO 4 - anions in real world samples were also validated. [ABSTRACT FROM AUTHOR]

• Hemoglobin-I was covalently grafted to transparent mesoporous GLAD-ITO electrodes. • Covalent attachment leads to stable high surface area bio-functionalized electrodes. • Hb-I/GLAD-ITO allows fast, selective and reversible optical detection of H 2 S. • This versatile strategy paves the way to innovative opto-electrochemical (bio)sensors. Sensitive and selective detection of analytes in complex biological fluids can be an extremely challenging issue. The constructive association of biomolecules and transparent mesoporous electrodes is of interest in this area, as it can lead to innovative biosensors combining optical and electrochemical detection modes. This concept, however, requires the development of appropriate surface functionalization methodologies that are robust enough for long-term operation in physiological environments. In the present work, the high-surface area of 3D transparent mesoporous indium-tin oxide (ITO) electrodes (prepared by glancing angle deposition or GLAD) has been chemically functionalized with recombinant hemoglobin I from Lucina pectinata according to a versatile 2-step process. First, 4-diazoniumbenzoic acid salt is covalently electrografted onto the ITO surface, followed by amide coupling of the protein. The resulting electrodes were quantitatively characterized by cyclic voltammetry and UV–vis absorption spectroscopy, demonstrating high surface coverages (up to 45% of a closed-packed monolayer for Hemoglobin-I) and homogeneous distribution across the entire thickness of the GLAD mesoporous structure. Good stability is also observed when the modified electrodes are immersed for prolonged times in a high ionic strength saline buffer. We also show that the hemoglobin I-modified electrode can be used as an optical biosensor for the selective, reversible, and fast detection of H 2 S in aqueous solutions over a ∼two-decade concentration range (i.e. up to 10 μM) and with a limit of detection of 0.35 μM. Good analytical performance was also achieved in human plasma without significant interference from the biological matrix. [ABSTRACT FROM AUTHOR]

Highlights • pH sensitive electrode developed based on voltammetry of vitamins B 2 and E. • Voltammetric response of vitamin B 2 sensitive to pH. • Voltammetric response of modified vitamin E insensitive to pH. • Voltammetric sensor does not require reference electrode with junction potential. • Sensor can be miniaturized and made disposable. Abstract The determination of pH using the conventional potentiometric glass electrode is widely practised in various fields ranging from academic to industrial environments. Recent research has focused on using various redox active organic and inorganic compounds as a basis of developing novel and miniaturized voltammetric pH sensors. This report describes the electrochemistry of such a sensor that is aimed to be disposable and based on a glassy carbon (GC) electrode drop cast with redox active vitamins. Voltammetric studies in deoxygenated buffered media revealed riboflavin (VB 2) and a vitamin E derivative (VEa) to be suitable as pH-dependent and independent electroactive compounds, respectively. Solid-state square-wave voltammograms of VB 2 and VEa that were concurrently drop cast on a GC electrode in various pH deoxygenated and oxygenated buffered media yielded Nernstian responses of –54.3 and –53.4 mV/ΔpH respectively, with the linear plot of the potential difference of VB 2 against VEa as a function of pH. Poor Nernstian responses were obtained in deoxygenated and oxygenated non-buffered media when the pH was above approximately 4. However, with the addition of a very low concentration of an acidic buffer into the reference solution, Nernstian responses of –50.0 and –50.9 mV/ΔpH were successfully achieved in deoxygenated and oxygenated weakly-buffered media, respectively. Furthermore, a strong correlation of voltammetric versus potentiometric pH highlights the suitability of the redox active vitamin compounds as a basis for a miniaturized voltammetric pH sensor. [ABSTRACT FROM AUTHOR]

Highlights • Single-walled carbon nanohorns is used to prepare solid-state potentiometric sensor. • Single-walled carbon nanohorns could be acted as an ion-to-electron transducer. • The developed sensor exhibits fast response and outstanding potential stability. • This potentiometric sensor holds great promise for routine sensing application. Abstract Single-walled carbon nanohorns (SWCNHs) was utilized as an ion-to-electron transducer to fabricate all-solid-state ion-selective electrodes (ISE) for the first time. To evaluate the performance of developed SWCNHs-based calcium ISE, various electrochemical experiments were carried out. A Nernstian response (29.69 ± 0.24 mV/decade, R 2 = 0.9996) was acquired across a broad linear range between 10−6 and 10−2 M, and the detection limit of 10−6.1 M was achieved in the meantime. Additionally, water layer test and reversed chronopotentiometry were used to estimate the long-term and short-term stability of SWCNHs-based ISE, respectively, indicating SWCNHs is capable of enhancing potential stability on account of its hydrophobicity. Furthermore, a SWCNHs-based reference electrode (RE) was fabricated by directly coating a photo-polymerised reference membrane (RM) onto a SWCNHs modified electrode. Results demonstrated that the SWCNHs-based RE exhibited slight potential fluctuation for common ions with different charges over a wide concentration range of calibration. Based on these superior results, an integrated all-solid-state SWCNHs-based potentiometric sensing device combined SWCNHs-based ISE and SWCNHs-based RE was constructed for detecting calcium, which shows a Nernstian response with a slope of 27.14 mV/decade. This developed electrode in the aid of SWCNHs exhibits fast response as well as outstanding potential stability, making it extreme promising for routine sensing application. [ABSTRACT FROM AUTHOR]

Highlights • Industrial application of potentiometric multisensor system. • Real time monitoring of ammonium and nitrate nitrogen in processed water. • Topological data analysis as a promising tool for multisensor data analysis. Abstract The potential of multisensor array in continuous on-line monitoring of processed water quality at aeration plant is explored. The responses of 23 potentiometric sensors were continuously registered every seven seconds through the 26 days of experiment in a special container having connection with outlet water line of the aeration plant. Using chemometric tools it is shown that potentiometric "electronic tongue" is capable of evaluation of two important parameters of water quality: ammonium nitrogen and nitrate nitrogen. Unlike traditional sampling-based analysis the results of multisensor are available immediately in a real-time mode. Moreover, the achieved precision is sufficient to monitor possible alarm events. The employment of topological data analysis allowed for exploration of the very large dataset (295,828 measurements) accumulated through the long period of continuous measurements with sensors and for judgment on stability of water quality. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Potentiometric microelectrodes are regarded as promising probes for ion sensing when only limited sample volumes are available. In this work, an all-solid-state ion-selective microelectrode (ISμE) has been developed by coating ionophore-based ion-selective membrane on a poly(3,4-ethylenedioxythiophene)-poly(sodium 4-styrenesulfonate) modified gold wire with a diameter of 14 μm for detection of copper. Under the optimized conditions, the proposed all-solid-state Cu2+-ISμE shows a Nernst response toward Cu2+ in 0.5 M NaCl in the range from 2.5 × 10−7 to 2.5 × 10−4 M with a detection limit of 4.0 × 10−8 M. Additionally, the Cu2+-ISμE has been used for monitoring the vertical distribution profile of Cu2+ in coastal sediment pore water with a small volume (e.g., 300 μL). The results agree well with those obtained by anodic stripping voltammetry, which indicates that the proposed potentiometric technique based on the all-solid-state ISμE is promising for detection of Cu2+ in coastal sediment pore water. The method for the preparation of the ISμE can be extended to detect other heavy metal ions in sediments by using different ion-selective membranes. [ABSTRACT FROM AUTHOR]

Highlights • Solid contact ion selective electrodes with two layered PVC membranes. • Characterized by stable standard potential, good slope reproducibility and high readouts stability. • Meet parameters characteristic of the so-called “calibration free” electrodes. Abstract A new type of solid contact ion-selective electrodes (ISEs) with two PVC-based sandwiched membranes are described. The first membrane contains suspension of halogen salts of silver and alkaline metals as well as silver nanoparticles and is placed on Ag substrate or conducting substrate covered with silver. It acts as a solid contact of an ion-selective electrode when covered with the second PVC membrane sensitive to potassium, sodium or chloride ions. In this way, the potassium, sodium and chloride electrodes characterized by very stable and reproducible standard potentials and slope were obtained. For example, all tested potassium electrodes with KBr/AgBr based solid contact exhibited E° values equal to: −191.2 ± 1.7 mV and the slope values equal to: −57.1 ± 0.8 mV/pK. Similarly, good results were also obtained for sodium and chloride ISEs. The solid contact offered allows to fabricate so-called “calibration free” ion-sensors. [ABSTRACT FROM AUTHOR]

A novel potentiometric pH sensor based on polydopamine films coated on a carbon nano-onion conductive surface is introduced. Glassy carbon electrodes containing a carbon nano-onion layer were modified by electropolymerization and self-polymerization of dopamine. The modified surfaces were characterized by ESEM, RAMAN spectroscopy and cyclic voltammetry. The modified electrodes displayed an almost Nernstian potentiometric response over the pH range 2–10. Furthermore, the pH sensors exhibit a fast and reversible behavior toward variations of pH and negligible interference effects from monovalent cations. The sensors showed an excellent correspondence between the pH values obtained using the GCE/CNO/PDA electrodes and those measured with glass electrodes and were applied to the analysis of real samples covering a wide pH range from 2.2 to 8.3. The analytical performance is comparable to other reported devices based on electropolymerized amines over graphite and noble metal electrodes. Their reproducible and stable response and their ease of fabrication is very promising for the miniaturization and integration of pH sensors in (bio)analytical devices. [ABSTRACT FROM AUTHOR]

A new wearable potentiometric tattoo biosensor for real-time on-body monitoring of G-type nerve agents simulant is described. The skin-worn flexible biosensor responds rapidly and selectively to the fluorine-containing organophosphates (OP) nerve agent simulant diisopropyl fluorophosphate (DFP, a model OP analyte) in both liquid and vapor phases. The epidermal potentiometric OP biosensor relies on the pH-sensitive polyaniline (PANi) coating on a flexible printed transducer for monitoring the proton release during the enzymatic hydrolysis of DFP by enzyme organophosphate hydrolase (OPH). The sensing electrodes are screen printed on a temporary tattoo paper and are interfaced to a conformal electronic interface that provides wireless data transmission. The skin-worn OP potentiometric sensor can withstand severe mechanical strains without compromising its analytical performance. The biosensor displays a wide dynamic range, fast response and high selectivity towards DFP (including efficient discrimination against organophosphate pesticides), and good reproducibility. The attractive performance of the new wearable biosensor indicates considerable promise for on-body threat detection towards rapid warning regarding potential exposure to G-series nerve agents. [ABSTRACT FROM AUTHOR]

Electrochemical and optical sensing of polyions were first introduced in the early to mid 1990s via the development and study of the first heparin-sensitive potentiometric and optical polyion sensors. Since then, the number of reports relating to electrochemical and optical polyion sensing technologies have grown substantially. Both biologically and industrially relevant polyions can be detected using these methods. This paper provides an overview of key accomplishments with respect to polyion sensor-based technologies over the past 25+ years. A summary of the basic designs and sensing principles of single-use/fully reversible polymeric membrane-type potentiometric polyion sensors, voltammetric polyion-sensitive electrodes, and single-use polyion-sensitive optodes is provided. The expansion of polyion sensing to more industrial and cosmetic polyions (i.e., polyquaterniums) is also discussed. Lastly, potential new directions/applications are provided for electrochemical and optical polyion sensors based on all-solid-contact designs (for electrochemical) and paper-based sensing devices (both electrochemical and optical). [ABSTRACT FROM AUTHOR]

Polymeric membrane-based electrodes containing a multiple diglycolamide (DGA), such as a N-pivot diglycolamide (diglycolamide-TREN (TREN-DGA) and a C-pivot diglycolamide (tripodal diglycolamide) (T-DGA) as ionophore, and polyvinyl chloride (PVC) as the base polymer were fabricated. These membranes were tested for the potentiometric determination of europium ions in acidic feed solutions. The membrane with a composition of 81.5% PVC and 18.5% TREN-DGA showed a wide dynamic range (3.2 × 10 −7 to 1.0 × 10 −2  M) with a slope of 17.2 ± 0.4 mV per decade for europium ion. The presence of sodium tetraphenyl borate (NaTPB) as ionic additive in the DGA-TREN containing membrane marginally improved the dynamic range in the detection of europium ion. On the other hand, the membrane with a composition of 77.3% PVC and 22.7% T-DGA does not show any systematic potential response against variation of the concentration of europium ions in the external solution containing 1 M HNO 3 . The physical characterization of these membranes was carried out using techniques such as thermogravimetry (TGA), Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) in order to understand the effect of the different constituents of the membrane on the potential response for europium ion. AFM measurements revealed that the morphology of the membrane remained intact even after prolonged use of the membrane. The interference effect of Ca 2+ , Mg 2+ , Cu 2+ , Fe 3+ , Bi 3+ , Zn 2+ , Cd 2+ and UO 2 2+ on the potential response was investigated. The response time of the proposed sensor was found to be less than five seconds. The lifetime of the sensor electrode was found to be three months under proper storing conditions. The membrane sensor was employed in the determination of Eu 3+ in synthetic water samples. [ABSTRACT FROM AUTHOR]

An integrated sensor chip with silicon nanowire ion-sensitive field-effect transistors for simultaneous and selective detection of both molecular and elemental ions in a single sample solution is demonstrated. The sensing selectivity is realized by functionalizing the sensor surface with tailor-made mixed-matrix membranes (MMM) incorporated with specific ionophores for the target ions. A biomimetic container molecule, named metal-organic supercontainer (MOSC), is selected as the ionophore for detection of methylene blue (MB + ), a molecular ion, while a commercially available Na-ionophore is used for Na + , an elemental ion. The sensors show a near-Nernstian response with 56.4 ± 1.8 mV/dec down to a concentration limit of ∼1 μM for MB + and 57.9 ± 0.7 mV/dec down to ∼60 μM for Na + , both with excellent reproducibility. Extensive control experiments on the MB + sensor lead to identification of the critical role of the MOSC molecules in achieving a stable and reproducible potentiometric response. Moreover, the MB + -specific sensor shows remarkable selectivity against common interfering elemental ions in physiological samples, e.g. , H + , Na + , and K + . Although the Na + -specific sensor is currently characterized by insufficient immunity to the interference by MB + , the root cause is identified and remedies generally applicable for hydrophobic molecular ions are discussed. River water experiments are also conducted to prove the efficacy of our sensors. [ABSTRACT FROM AUTHOR]

Gas sensors play an essential bridge in connecting humans and health by helping people monitor the gas quality in their living spaces. In this work, PtNi 3 -WO 3 gas sensors were fabricated and demonstrated superior selectivity, sensitivity, and stability to formic acid, which was sufficient for indoor air gas monitoring. The response to 100 ppm formic acid was as high as 591, with a response time of only 3 s, and detection range down to the ppb level. The bimetal PtNi 3 decorated sensors showed a 30 times improvement in formic acid response compared to pure WO 3 sensors. The cross-sensitivity was investigated, and we observed that the response initially decreased and then increased in a mixed gas with a constant concentration of carboxylic acid and increasing gradually concentration of formaldehyde. The adsorption and desorption mechanisms were studied, which implied that the decomposition and adsorption behavior of the gas could change and produce different intermediate products under different mixing environments. The results of the energy surface testing and density functional theory supported the proposed sensing mechanism. A machine-learning framework was developed for gas identification and concentration prediction, which achieved ultra-high identification accuracy. In addition, Bluetooth-based portable gas sensors were demonstrated, showing promising practical applications. [Display omitted] • The bimetal decorated PtNi x -WO 3 sensors presented superior sensitivity, selectivity, and stability in detecting formic acid. • The mixed gas adsorption was strongly related to the dispersive and polar sites on the sensing material surfaces. • The machine learning model had 100% accuracy in identifying formic acid and 90.8% accuracy in predicting its concentration. • The Bluetooth-based portable gas sensor demonstrated stable performance for 2 months without significant variation. [ABSTRACT FROM AUTHOR]

The detection of the algaecide Irgarol using in-situ and fast potentiometric measurements is reported in this work. For this purpose, three all-solid-state Irgarol-selective microelectrodes based on PVC-type sensitive membrane were prepared using three different plasticizers and the novel ion-pair complex [Irgarol-H] + [Co(C 2 B 9 H 11 ) 2 ] − as the active site for selective irgarol recognition. This strategy enables the sensor’s selectivity to be improved by incorporating the target molecule to the sensitive membrane. The chemical sensors developed have provided excellent and quick response within the range 10 −6  mol/dm 3 to 10 −3  mol/dm 3 of irgarol concentration, a limit of detection between 2 and 4 μmol/dm 3 and a slope between 48 and 57 mV/decade depending on the membrane composition. The potentiometric coefficient of selectivity, K A,Bpot , shown that the Irgarol-selective microsensors were highly selective towards irgarol when compared to some possible interfering phytotoxins. In addition, from the Reilley diagram it can be observed that the sensor signal is stable for a working pH interval between 6.00 and 12.0 making possible its application in sea water monitoring. [ABSTRACT FROM AUTHOR]

In this work, the fluorescent CAU-1-(OH) 2 was successfully exploited as a fluorescent probe for bismuth ion (Bi 3+ ) in aqueous solutions, which is the first MOF-based fluorescent sensor for Bi 3+ up to date. The MOF can exhibit bright green fluorescence in H 2 O for the intramolecular proton transfer process between the ligand and H 2 O molecule. In addition, the carboxylate and hydroxyl groups in the MOF can strongly coordinate with Bi 3+ . Accordingly, CAU-1-(OH) 2 can selectively detect Bi 3+ in water in 24 s. In addition, the limit of detection of this MOF was calculated to be 2.16 μM, superior to those of some traditional methods such as spectrophotometry and flow injection potentiometry. [ABSTRACT FROM AUTHOR]

The light-addressable potentiometric sensor (LAPS) is a spatially resolved biochemical sensor based on a field-effect structure. Over the past three decades, it has gained significant attention for the detection of various ions, biomolecules (e.g. enzymes, antibodies, DNA, and biomarkers), cellular metabolic activities as well as neuronal action potentials. To improve the sensor function and performance, all of these applications rely on the physical or chemical modifications of LAPS with different transducer materials and/or bio(chemical) recognition elements. With the rapid development of biomaterials associated with new sensing and fabrication techniques, remarkable advances in LAPS design, fabrication and applications have been achieved. In this review, the features and fabrication technologies of different gate insulators of LAPS are illustrated. Especially, ultrathin insulators such as organic monolayers are highlighted. The state-of-the-art technologies for LAPS modification and construction as well as their consequent applications in chemical and biological fields are summarized and discussed. Finally, current research challenges and future prospectives, for instance the combination of LAPS with microfluidic chips, will be presented. [ABSTRACT FROM AUTHOR]

Paralytic shellfish toxins (PSTs) are monitored in commercial bivalves in several countries in the world due to their toxicity to human consumers. The present work examines the application of an electronic tongue based on potentiometric chemical sensors to the quantification of PSTs in mussel extracts. The electronic tongue comprised six miniaturized sensors with solid inner contact and plasticized polyvinylchloride membranes. Calibration models were calculated by PLS regression using measurements in sixteen model mixed solutions containing four PSTs commonly found in bivalves from the Portuguese coast. Transfer of the calibration models to sample matrix was done by joint-PLS regression using measurements in five mussel extracts spiked with PST standards. Quantification of PSTs in extracts of naturally contaminated mussels, using the electronic tongue and updated calibration model, was in agreement with values of the chromatographic reference method. Those sensors alone or combined in an electronic tongue are useful tools for rapid screening of PST in bivalves. [ABSTRACT FROM AUTHOR]

Solid-state potentiometric sensors based on surface charge change are well-established tools for measuring ions and biological species. However, their use for detection of small molecules with high sensitivity and good selectivity is still elusive. In this work, a novel potentiometric aptasensing platform for small molecules is presented, using bisphenol A (BPA) as a model. The proposed sensor can be prepared by layer-by-layer assembling of carboxylated multiwall carbon nanotubes, poly(diallyldimethylammonium chloride) (polycation), and aptamer (polyanion) on the electrode surface. The presence of BPA induces the conformational change and detachment of the aptamer at the surface of the modified electrode, which leads to a variation of the surface charge (negative to positive) and therefore a potential change. The introduction of polyions can cause substantial charge change on the electrode surface, thus improving the sensitivity of the sensor. The morphology and electron-transfer properties of the electrode have been characterized. Under optimum conditions, the present sensor shows a stable response to BPA in the concentration range from 3.2 × 10 −8 to 1.0 × 10 −6  M with a detection limit of 1.0 × 10 −8  M. The proposed methodology can be used for sensitive potentiometric sensing of other small molecules involved in aptamer/target binding events. [ABSTRACT FROM AUTHOR]

Inductively coupled plasma reactive-ion etching (ICP-RIE) is first applied to decrease the thickness of a Si substrate for light-addressable potentiometric sensor (LAPS) characterization. A simple and reliable process flow with the self-aligned Al layer as a hard mask layer in ICP-RIE is used to fabricate a thin semiconductor substrate with Al back-side contact. A single-side polished P-type Si wafer with a thickness of 350 μm is decreased to 100 μm by ICP-RIE from the polished side. The thickness of the thin Si substrate and the dimensions of the designed patterns determined by ICP-RIE are verified using scanning electron microscopy (SEM) and an optical microscope (OM). A selective high-dielectric constant insulator, niobium oxide (NbOx), is directly deposited on the unpolished side of the thin Si substrate as the sensing membrane of a LAPS by reactive ratio frequency (rf) sputtering. A high photocurrent was found in the ICP-RIE LAPS sample under back-side illumination, particularly in high-frequency operation. Compared to an Si substrate without ICP-RIE, 3-fold and 6.5-fold higher photocurrents were achieved by the proposed LAPS with ICP-RIE measured at 1 and 50 kHz of light modulated frequency, respectively. The highest modulated frequency of illumination was 50 kHz for an acceptable photocurrent in the LAPS with ICP-RIE, which is sufficient for two-dimensional (2D) images acquired with high-speed scanning. The NbOx layer deposited on the unpolished Si surface could automatically generate higher pH sensitivity than conventional polished Si surfaces because of the higher surface roughness. The calculated pH sensitivity and linearity were 55.8 mV/pH and 99.6%, respectively, in a pH range from 2 to 12. No clear degradation of hysteresis was found for the LAPS with ICP-RIE. For the designed patterns of the Al hard mask layer, the spatial resolution of the 2D image of the LAPS with ICP-RIE could be obtained by the difference between dimensions observed by OM and the dimensions calculated from the photocurrent versus scanning length controlled by the X-Y stage. A pattern with a length of 250 μm generated by ICP-RIE was measured as 255 μm in the LAPS with scanning step of 5 μm. ICP-RIE is demonstrated to achieve a spatial resolution of 5 μm in the Si-based LAPS. Further reduction of the thickness of an Si substrate by ICP-RIE controlling and its ability to create a dynamic 2D image are suggested for future investigation in spatial resolution optimization. [ABSTRACT FROM AUTHOR]

pH measuring and monitoring is fundamental to understand or control many chemical processes in biological, industrial or environmental fields. Potentiometric measurements by a glass electrode is the most common method to measure pH, although single-use paper strips are also widely used. Other methods include the use of hydrogen, quinhydron, and antimony electrodes, the imaging using pH-sensitive indicators such as dyes or proteins, and the use of ion-selective field effect transistor (ISFET). Due to the chemical reactivity of both sides of its 2D structure, nanometer thickness, high electron mobility, high reactivity to oxygen groups such as OH − , and ultrafast optical response, graphene has the potential to be used for the fabrication of nanoscale, wide-range, high-sensitivity and flexible pH sensors. This review describes how graphene, graphene oxide and reduced graphene oxide can be used to fabricate pH-sensitive devices (e.g. solution-gated FETs, solid-gate FETs, electrochemical sensors, and pH-sensitive quantum dots). The various configurations are reported along with the advantages and current limitations. [ABSTRACT FROM AUTHOR]

UV illumination has been confirmed to be essentially increased the response magnitude of potentiometric gas sensors. Nevertheless, the detection limit of the sensor is still inadequate for real application even upon UV light, whilst, how to efficiently enhance the light-regulated mixed-potential signal is still unclear. In this research, the strategy of using the more photoactive ZnO-based composite as the sensing-electrode (SE) for potentially further enhancing the sensing value is proposed and confirmed. Typically, in comparison with ZnO-SE, ZnO-based composite SE is beneficial for further promoting the light-regulation effect. Particularly, when upon illumination, the detection limit of the sensor consisting of the composite electrode (towards benzene) reaches 0.109 ppm, while that of the value for the sensor using ZnO-SE is 0.898 ppm. The promoting mechanism is clarified from the perspective of the electrocatalytic activity & gas-phase reactivity. In summary, forming the ZnO-based composites makes them ideal for generating abundant e − a nd h + when upon illumination, leading to the obvious increase in the catalytic activity of both cathodic & anodic reaction and thereby further raised the mixed-potential signal. Conclusively, this proof-of-concept opens a brighter future for designing future high-performance potentiometric gas sensors. [ABSTRACT FROM AUTHOR]

An all solid-state pH micro-sensor has been developed using anodic electrodeposition of an iridium oxide (IrO x ) film onto a 10 μm platinum ultramicroelectrode. The electrochemical growth of the IrO x film was accomplished by 100 potential sweeps at 50 mV/s, at different potential ranges of electrochemical deposition, followed by heat treatment at 100 °C for 2 h. The pH micro-sensor shows quick response to the pH variation, excellent sensitivity, stability and long lifetime in a wide pH range between 1.0 and 13.0. The slope of potential-pH response curve is found to dependent on the Ir(III)/Ir(IV) ratio of in the film, determined by XPS analysis, which is a consequence of scanning potential range during the anodic electrodeposition. The sensor has been employed to explore the localized pH distribution during the corrosion of 316L stainless steel in NaCl solution at open circuit potential and results show that localized anodic and cathodic sites on the 316L stainless steel can be accurately monitored and the pH difference between the cathodic and anodic zones increases from 0.22 to 1.27 with the prolonging of the immersion time. [ABSTRACT FROM AUTHOR]

The preparation of glassy carbon (GC) ibuprofen (2-(4- isobutylphenyl)propionic acid) membrane sensors was examined in the study described below. The optimal membrane was based on functionalized β -cyclodextrins: heptakis (2,3,6–tri–O–benzoyl)- β- cyclodextrin (GC/MWCNT-HB β CD).The following basic analytical parameters of the drug electrode were determined: sensitivity, measuring range, detection limit, reversibility, and selectivity coefficients for some organic and inorganic anions. The electrode exhibited good Nernstian slope of 59.9 mV/decade, measuring range of 3.2 × 10 −5 –10 −2 , pH range of 5-9, and very good response time of 5 seconds. The advantages of the GC electrode with the use of multi-walled carbon nanotubes, i.e. high conductivity (bulk resistance 5,76 × 10 2 Ω) was confirmed by the impedance spectroscopy method whereas high selectivity and the stable potential are the parameters determined in the potentiometric measurements. [ABSTRACT FROM AUTHOR]

Based on molecular design, with non-porous chloromethylated polysulfone (CMPSF) membrane as basement-membrane, in which lipophilic ion-exchanger was uniformly distributed, graft type atrazine-imprinted membrane was prepared by adopting the novel imprinting method of “pre-graft polymerization and post-imprinting” with methacrylic acid (MAA) as functional monomer. CMPSF membrane was aminated, and a surface-initiating system of –NH 2 /S 2 O 8 2− was constituted at the interfaces between the amination membrane and aqueous solution containing MAA and ammonium persulfate. By the initiating of the free radicals produced on amination membrane, MAA produces graft-polymerization, forming the grafted membrane PSF-g-PMAA. And then the grafted PMAA was crosslinked by ethylene glycol diglycidyl ether (EGDE) in the presence of atrazine molecules, which were beforehand adsorbed by PSF-g-PMAA membrane by right of electrostatic interaction, resulting in atrazine-imprinted membrane with grafting type. A membrane electrode with atrazine-imprinted membrane as sensitive membrane was constituted, and then a galvanic cell was assembled, namely, a potentiometric sensor for atrazine was fabricated. The experimental results show that the atrazine-imprinted membrane has specific recognition ability and excellent binding affinity for atrazine, and the selectivity coefficient of this imprinted membrane for atrazine relative to ametryn is 5.463 and the binding capacity gets up to 243 μg/cm 2 . The potentiometric sensor for atrazine exhibits Nernstian response to atrazine in the pH range of 7.0–8.0 over a wide concentration range of 1.0 × 10 −7 –1.0 × 10 −4 mol/L with a slope of 25.9 mV/decade, and the detection limit is 4.7 × 10 −8 mol/L. This potentiometric sensor has a rapid response time of about 10 s, and it has excellent reversibility. [ABSTRACT FROM AUTHOR]

An indirect way of assessing cadmium concentration in confined volume was attempted. This aim was met by measuring the oxygen concentration before and after reaction with cadmium vapour. The deduced cadmium concentration value corroborated with the data obtained from cadmium vapour pressure at different temperature. [ABSTRACT FROM AUTHOR]

A new selective and highly sensitive potentiometric sensor for cationic surfactants was prepared based on multi-walled carbon nanotubes (MWCNTs) functionalized with a sulfate group and cetylpyridinium ion (CP) as a sensing element. The chemical modification of MWCNTs with CP cations had positive effects on the most important sensor properties, such as greater membrane stability, considerably reduced leaching of the sensing material from the membrane, prolonged life time of the sensor and negligible noise and signal drift. The sensor exhibited a Nernstian response for CP (58.9 and 58.2 mV/decade in water and 0.01 M Na 2 SO 4 , respectively) and sub-Nernstian responses for hexadecyltrimethylammonium ion (CTA) (56.6 and 55.5 mV/decade in water and 0.01 M Na 2 SO 4 , respectively) and Hyamine (52.1 and 49.7 mV/decade in water and 0.01 M Na 2 SO 4 , respectively). The detection limit for CP was 1.2 × 10 −7 M (in water and 0.01 M Na 2 SO 4 ), whereas those for CTA were 2.5 × 10 −7 and 3.2 × 10 −7 M (in water and 0.01 M Na 2 SO 4 , respectively), and that for Hyamine was 1.5 × 10 −6 (in water and in 0.01 M Na 2 SO 4 ). The response time of the sensor was 5 s for cetylpyridinium chloride (CPC) concentration changes greater than 0.005 mM in water and 9 s for CPC concentration changes greater than 0.005 mM in 0.01 M Na 2 SO 4 solution. The signal drift of the sensor was 0.3 mV/h in 4 mM CPC solution and 0.8 mV/h in a hand sanitizer solution. The new sensor exhibited excellent selectivity for CP cations compared to the inorganic and organic cations commonly present in commercial formulations, and it was successfully used as an end-point detector in the potentiometric titration of cationic surfactants in a pH range from 3 to 10. A two-component mixture containing CPC and Hyamine was successfully differentially titrated. [ABSTRACT FROM AUTHOR]

The development of wearable sensors to measure biomarkers in sweat remains a major technological challenge. Here we report on a wearable, potentiometric, thin film sweat chloride sensor. Potentiometric devices provide a relatively simple technology for sweat sensing, however, equilibration between the reference and test solutions is a significant source of error. We have developed a sweat chloride sensor with integrated salt bridge that minimizes equilibration and enables stable measurements over extended periods of time. The sensor shows a very small concentration drift even with small sample volumes. The measurement variation was less than 2 mM at low chloride ion concentration (10 mM) and 5 mM at high concentration (150 mM), spanning the range for healthy individuals and CF patients. Finally, in on-body tests we show that the sweat chloride concentration in healthy individuals is dependent on exercise intensity, indicating that the sensor has a potential for a fitness monitoring applications. [ABSTRACT FROM AUTHOR]

The chemical analysis of spent nuclear fuel (SNF) reprocessing is a very challenging research field due to the high radioactivity of process streams and their complex composition. The process managing requires thorough chemical analysis to ensure safe and efficient performance. Traditional ways of chemical control of SNF reprocessing are based on sampling methods and involve long and tedious procedures, failing to provide immediate information on the process status. Recent literature suggests that potentiometric multisensor systems can be employed for on-line control. However, up to now these systems were only studied in very simple model media. This work reports on the potentiometric multisensor array applied for the first time for the simultaneous quantification of the content of actinides (uranium, plutonium, neptunium) and several other analytes (zirconium, molybdenum and nitric acid) in the complex samples obtained from the pilot extraction unit for SNF reprocessing. The same samples were also analyzed by UV-Vis spectrometry (another prospective method for on-line control) and the analytical performance of these two methods was compared using established analytical figures of merit (sensitivity and analytical sensitivity metrics) for multivariate calibration. In spite of the extremely challenging analytical task, both simple methods provide the characteristics suitable for real industrial applications. • Potentiometric multisensor array for analysis of spent nuclear fuel in at-line mode. • Simultaneous quantification of actinides (U, Np, Pu) and other metals (Zr, Mo). • Analytical figures of merit for multivariate calibrations using PLS and ANN. [ABSTRACT FROM AUTHOR]

A bubble-assisted electroosmotic (EO) micropump is proposed as a miniaturized actuating element to be integrated in a microfluidic chemical sensing system. In this device, a bubble is generated in a narrow channel to form a thin water sheet between the bubble and the wall. Due to the high surface-to-volume ratio of the water sheet, an efficient EO flow is realized at relatively low pumping voltages of 20–60 V without using a porous material. The direction and the flow rate of the EO flow depended on the polarity and the magnitude of the pumping voltage, and the highest flow rate of about ±500 pL/s was obtained at ±60 V. A bubble-assisted EO micropump was combined with a LAPS for measuring the pH value of a droplet with a volume of 1 nL. [ABSTRACT FROM AUTHOR]

The half-cell potential of a Pt/YSZ electrode modified with TiO 2 was strongly dependent on the concentration of VOC in air. The experimentally estimated electron number in the Nernst relation for oxygen increased from 2.0 to 4.0 with increasing temperature from 400 to 600 °C. For the TiO 2 -Pt/YSZ electrode at 400 °C, the following three processes are proposed: [1] O 2(gas) ⇔ O 2(ad) /TiO 2 , [2] O 2(ad) /TiO 2 + 2e − ⇔ 2O − (ad) /TiO 2 , and [3] 2O − (ad) /TiO 2 + 2e − /Pt → 2O 2− (ad) /Pt. The half-cell potential of the TiO 2 -Pt/YSZ electrode is expressed as E = (RT/2F) ln [O 2(ad) /TiO 2 ]. The concentration of the adsorbed oxygen is estimated using a combination of a competitive adsorption model for a mixture of oxygen and VOC and oxidation of the adsorbed VOC with the adsorbed oxygen. Numerically estimated potentials of the TiO 2 -Pt/YSZ electrode are reliable qualitatively for the VOC concentration dependence of the potential. The electrode potential of the sensor with a pristine Pt electrode and the modified electrode with TiO 2 responded to the ppm level of VOCs in air. [ABSTRACT FROM AUTHOR]

Glycopyrronium bromide solid contact ion selective potentiometric sensors using multi-walled carbon nanotubes (MWCNTs), polyaniline nanoparticles (PANI NPs) and microparticles (PANI MPs) as ion-to-electron transducers were fabricated and compared to transducer free blank sensor. Their inclusion in solid contact (SC) sensors offer shorter response time, lower potential drift and longer life time. From a comparative point of view, inclusion of MWCNTs offer longer lifetime (50 days) to the SC sensor compared to PANI based SC sensors. While, the inclusion of PANI showed shorter response times. Hence, PANI-based sensors showed better stability on short term, while MWCNTs offered long term stability. PANI NPs gave faster response than MPs. This may be attributed to the higher surface/volume ratio in NPs which enlarges the contact area with the polymeric membrane, increasing the transduction at the interface. Moreover, PANI NPs showed lower potential drift and relatively longer life time than MPs. Nano-sized particles result in smooth surfaces with a good surface coverage (protection) of the underlying SC. The proposed sensors were successfully applied to content uniformity testing of GLY in a newly approved pharmaceutical dosage form with high accuracy. [ABSTRACT FROM AUTHOR]

A novel and very sensitive potentiometric sensor with excellent electrochemical properties was fabricated for the determination of fluvoxamine. The sensor is based on the use of the PVC-membrane containing ion-association complex of fluvoxamine with reinecke salt coated on the glassy carbon electrode which was modified with polyaniline as a conductive polymeric film. The proposed sensor exhibits a Nernstian slope of 58.9 mV per decade for fluvoxamine over a wide concentration range of 1.8 × 10 −7 –1.3 × 10 −3 M, with a low detection limit of 7.8 × 10 −8 M. The sensor has a fast response time, excellent reproducibility and long life time. It can be used within the pH range of 4.0–7.5 in a long time period. The sensor possesses a high selectivity toward a large variety of inorganic and organic co-existing species. The effect of temperature on the sensor potential response was studied and the isothermal coefficient of the sensor was calculated. The sensor has a good thermal stability within the studied temperature range. The developed sensor was used as an indicator electrode in potentiometric titration of fluvoxamine with sodium tetraphenylborate. The sensor was successfully applied in the determination of fluvoxamine in pharmaceutical solution, blood serum and urine samples. [ABSTRACT FROM AUTHOR]

Sensitive disposable sensors have been introduced for potentiometric determination of gentamicin sulphate (GNS) based on multi-walled carbon nanotubes–polyvinyl chloride (MWNTs–PVC) composite in presence of calixarene as a molecular recognition element. The proposed sensors showed remarkable selectivity and sensitivity in the GNS concentration range from 10 −7 to 10 −2 mol L −1 with Nernstian slope 30.5 ± 0.4 mV decade −1 and detection limit of 7.5 × 10 −8 mol L −1 . Modification with carbon nanotubes improved the sensors performance was through promotion of the electron-transfer processes and enhancing the stability of potential reading, response time, and shelf lifetime of sensors. The proposed method has been applied for the potentiometric assay of GNS in different dosage forms and spiked surface water samples with average recoveries agreeable with the reported official method. [ABSTRACT FROM AUTHOR]

The present review work is devoted to potentiometric sensors based on high-temperature proton-conducting ceramic materials. The technology developments and possible application of such sensors for the determination of concentration of hydrogen-containing components in gases, solids and melts are described and thoroughly discussed. A special attention is devoted to the analysis of experimental data already appeared in international literature and their adequacy to the basic operation principles. On the base of this analysis, the existing problems and future trends are revealed and discussed. [ABSTRACT FROM AUTHOR]

The LAPS (light-addressable potentiometric sensor) platform is one of the most attractive approaches for chemical and biological sensing with many applications ranging from pH and ion/analyte concentration measurements up to cell metabolism detection and chemical imaging. However, although it is generally accepted that LAPS measurements are spatially resolved, the light-addressability feature of LAPS devices has not been discussed in detail so far. In this work, an extended electrical equivalent-circuit model of the LAPS has been presented, which takes into account possible cross-talk effects due to the capacitive coupling of the non-illuminated region. A shunting effect of the non-illuminated area on the measured photocurrent and addressability of LAPS devices has been studied. It has been shown, that the measured photocurrent will be determined not only by the local interfacial potential in the illuminated region but also by possible interfacial potential changes in the non-illuminated region, yielding cross-talk effects. These findings were supported by the experimental investigations of a penicillin-sensitive multi-spot LAPS and a metal-insulator-semiconductor LAPS as model systems. [ABSTRACT FROM AUTHOR]

This paper reports on the capability to detect multiple ions in mixed solutions using the tandem Dynamic Potentiometry-Principal Component Analysis. The treatment of potentiometric transient signals obtained by a single ion-selective electrode based on 18-crown-6 in a flow configuration serves for ion identification as well as quantification in binary mixtures. As a proof-of-concept alkaline, alkaline-earth, proton and ammonium cations are analysed. The developed procedure provides three exploitation points of the raw signals: (i) the complexity grade of the signals is drastically reduced, (ii) the total reconstruction of the experimental signals leads to less noisy ones, and (iii) the relationship found between the principal component scores with both increasing cation concentration (individual and binary mixtures) and type of cation is useful for qualitative and quantitative analysis. Multi-ion detection is currently a valuable characteristic for an analytical technique and the present paper provides a new approach involving the use of only one potentiometric sensor to achieve this purpose. [ABSTRACT FROM AUTHOR]

This work demonstrates a paper-based microfluidic sampling and separation platform that allows potentiometric sensing of chloride ions in presence of strongly interfering salicylate ions using a solid-contact ion-selective electrode as a detector. The device was composed of two pieces of paper with different shapes and pore sizes. A “T” shaped filter paper with a pore size of 12–25 μm was used as the detection zone. A filter paper with a pore size of 2.0 μm was modified with a complexing agent (Fe 3+ ) and served as the separation zone. The two pieces of the paper were joined together just like a jigsaw. A solid-contact Cl − −selective electrode and a reference electrode were gently pressed onto the detection zone to create a direct contact between the electrodes and the solution absorbed in the paper. Utilizing the possibility to form stable complexes between Fe 3+ and salicylate, the proposed platform enables the separation of salicylate and detection of chloride. This system offers a convenient platform for both sampling and separation of ions, in which sample pretreatment procedures can be simplified or avoided. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide in high concentration is a well-known toxic gaseous molecule; nevertheless, H 2 S is synthetized in mammalls’ body in small concentration participating important physiological processes. It also is implicated in inflammation as a mediator molecule. In this work, a potentiometric air gap cell has been developed in order to apply it in the quantitative study of the H 2 S accompanied the inflammatory disease in animal experiments. The cell was tested using aqueous standard sample solutions and super-Nernstian response has been obtained in the concentration range of interest and submicromolar lower detection limit, respectively. Animal experiments have been carried out in healthy and inflamed paws of sacrificed mice. The measurements showed significant difference in the H 2 S level of the control and carrageenan treated tissues of the experimental animals. [ABSTRACT FROM AUTHOR]

The feasibility of using a thin-film RuO 2 (ruthenium oxide) pH sensor for the detection of Helicobacter pylori is investigated. In particular, we demonstrate the ability of the sensor to measure urease activity between 1.0 and 50 U/mL in less than 30 s. The developed sensor exhibited a super-Nernstian response of 77.74 mV/pH and excellent reversibility. The pH sensor⿿s ability to detect H. pylori in real time is demonstrated, and found to be much faster than the rapid urease test. [ABSTRACT FROM AUTHOR]

V 2 O 5 -WO 3 -TiO 2 mixed metal oxide catalyst was synthesized by impregnation method for fabricating sensing electrodes of potentiometric ammonia sensor in this paper. The sensing electrodes were sintered from 650 °C to 900 °C to obtain different electrode microstructures. Crystalline structures of the sensing materials were analyzed by X-ray powder diffraction, and the sensing electrode microstructures were characterized by environmental scanning electron microscopy. Sintering temperature strongly affects the microstructure and the sensitivity of the sensing electrode. With the increment of sintering temperature, the slope of semi-logarithmic characteristic curves increased but began to fall when temperature was more than 750 °C. The effect of sintering temperature on the response and recovery property has similarities, the sensors sintered at 750 °C and 700 °C show the shortest response/recovery times. The increase of the sintering temperature is beneficial for a stronger bond between sensing electrode and YSZ electrolyte, and this could increase the amount of three-phase boundary, and improve the sensor performance. High temperature promotes the V 2 O 5 volatilization, anatase TiO 2 grains growing up and the anatase to rutile phase transition, further cause the reduction of the electrode specific surface area. The volatilization of V 2 O 5 and the destruction of high dispersion V 2 O 5 resulted from the growing up of the carrier TiO 2 , are responsible for the degraded properties of sensing electrode. The suitable operating temperature for this type NH 3 sensor is 550 °C based on the compromise of various factors which could influence the sensor performance. [ABSTRACT FROM AUTHOR]

Fermentation process monitoring is a very important factor for controlled protein biosynthesis in industry. Currently the only method to determine protein concentration in cultivation broth is ELISA (enzyme-linked immunosorbent assay). Having high sensitivity and specificity, ELISA takes several hours to run, which is not suitable for express monitoring. A recent progress in multisensor systems for chemical analysis (electronic tongues) shows a good promise for application of such systems in fermentation-related tasks. The objective of this work was feasibility study of potentiometric multisensor system as an instrument for indirect assessment of protein production through chemical measurements in a cultivation medium. The samples taken from nine fermentation processes intended for production of recombinant protein A of Staphylococcus aureus (SpA) in Escherichia coli were analyzed with the electronic tongue system comprised of 14 potentiometric sensors. The system was able to monitor the global changes in the media composition as the fermentation progressed. By means of PLS regression it was possible to relate the responses of the sensors with the data on protein production from ELISA. The system was able to predict the content of SpA based on potentiometric measurements with accuracy suitable for monitoring purposes. It appears to be attractive alternative for ELISA in fermentation control tasks. [ABSTRACT FROM AUTHOR]