Ion-selective Membrane Electrodes Research Articles

Potentiometric/time resolved chronopotentiometric sensing for an all-solid-state ion-selective electrode based on MXene/MWCNTs as solid contact

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.

Maintenance-free antifouling polymeric membrane potentiometric sensors based on self-polishing coatings.

Polymeric membrane ion-selective electrodes (ISEs) have been widely used in environmental monitoring. However, in complicated marine environments, marine biofouling usually becomes a sticky problem for these electrodes. Herein, for the first time, a novel maintenance-free antifouling potentiometric marine sensor based on a self-polishing coating (SPC) is proposed. The SPC is synthesized by using the seeded emulsion polymerization method based on the triisopropylsilyl methacrylate monomer as the regulator of the self-renewal rate. This coating can be simply modified onto the electrode surface by drop-casting. The silyl acrylate side groups of the obtained SPC on the sensor surface can be hydrolyzed in the marine alkaline medium. The shear movement of seawater driven by sea waves, wind, gravity, or vibration removes the leftover (fouled) brittle polymer backbone and thus the fouling marine microorganisms. As a proof-of-concept experiment, a polymeric membrane Ca2+-ISE is chosen as a model. Compared to the unmodified electrode, the SPC-coated Ca2+-ISE exhibits remarkable improved antifouling properties in terms of superior anti-adhesive abilities towards marine microorganisms, such as bacterial cells and algae and excellent long-term stability even in the presence of high levels of marine microorganisms. Since no additional manual maintenance is required for maintaining the antifouling abilities of the sensor, the proposed self-polishing sensor may lay an important foundation for construction of unattended long-term potentiometric monitoring systems in real marine environments.

The Influence of the Nature of the Polymer Incorporating the Same A3B Multifunctional Porphyrin on the Optical or Electrical Capacity to Recognize Procaine.

The multifunctionality of an A3B mixed-substituted porphyrin, namely 5-(4-carboxyphenyl)-10,15,20-tris(4-methylphenyl)porphyrin (5-COOH-3MPP), was proven due to its capacity to detect procaine by different methods, depending on the polymer matrix in which it is incorporated. The hybrid nanomaterial containing k-carrageenan and AuNPs (5-COOH-3MPP-k-carrageenan-AuNPs) was able to optically detect procaine in the concentration range from 5.76 × 10-6 M to 2.75 × 10-7 M, with a limit of detection (LOD) of 1.33 × 10-7 M. This method for the detection of procaine gave complementary results to the potentiometric one, which uses 5-COOH-3MPP as an electroactive material incorporated in a polyvinylchloride (PVC) membrane plasticized with o-NPOE. The detected concentration range by this ion-selective membrane electrode is wider (enlarged in the field of higher concentrations from 10-2 to 10-6 M), linearly dependent with a 53.88 mV/decade slope, possesses a detection limit of 7 × 10-7 M, a response time of 60 s, and has a certified stability for a working period of six weeks.

Modern Potentiometric Biosensing Based on Non-Equilibrium Measurement Techniques.

Modern potentiometric sensors based on polymeric membrane ion-selective electrodes (ISEs) have achieved new breakthroughs in sensitivity, selectivity, and stability and have extended applications in environmental surveillance, medical diagnostics, and industrial analysis. Moreover, nonclassical potentiometry shows promise for many applications and opens up new opportunities for potentiometric biosensing. Here, we aim to provide a concept to summarize advances over the past decade in the development of potentiometric biosensors with polymeric membrane ISEs. This Concept article articulates sensing mechanisms based on non-equilibrium measurement techniques. In particular, we emphasize new trends in potentiometric biosensing based on attractive dynamic approaches. Representative examples are selected to illustrate key applications under zero-current conditions and stimulus-controlled modes. More importantly, fruitful information obtained from non-equilibrium measurements with dynamic responses can be useful for artificial intelligence (AI). The combination of ISEs with advanced AI techniques for effective data processing is also discussed. We hope that this Concept will illustrate the great possibilities offered by non-equilibrium measurement techniques and AI in potentiometric biosensing and encourage further innovations in this exciting field.

Determination of forced convection effects on the response of membrane-based ion-selective electrodes via numerical solution to the Navier-Stokes-Nernst-Plank-Poisson equations

Ion selective electrodes (ISEs) enable measurements via the build-up of a phase boundary potential at the surface of a sensing membrane. While a framework exists to understand the performance of ISEs in stagnant samples, the influences of fluid flow on ISEs are less studied. We model the transport of ions in solution occurring near interfaces between ISE membranes and aqueous samples when subject to an external flow. We developed a numerical model extending the Pressure-Implicit with Splitting of Operators (PISO) algorithm to incorporate the Navier-Stokes-Nernst-Plank-Poisson system of equations. We find that external flow distorts the aqueous side of the formed double layer at the ISE membrane and aqueous sample interface, leading to an increase in the phase boundary potential. The change in potential is shown to be a function of a novel set of dimensionless numbers, most notably the Debye Length Reynolds number, i.e., the Reynolds number with the Debye Length as the system dimension.

Electrochemical Visualization of an Ion-Selective Membrane Using a Carbon Nanoelectrode.

Molecular and physical probes have been widely employed to investigate physicochemical properties and mechanisms of interfaces due to their ability to provide accurate measurements with temporal and spatial resolution. However, the direct measurement of electroactive species diffusion in ion-selective electrode (ISE) membranes and quantification of the water layer have been challenging due to the high impedance and optical opacity of polymer membranes. In the present work, carbon nanoelectrodes with ultrathin insulating encapsulation and good geometrical structure are reported as physical probes for direct electrochemical measurement of the water layer. The scanning electrochemical microscopy experiment exhibits positive feedback at the interface of the fresh ISE, and negative feedback after conditioning for 3 h. The thickness of the water layer was estimated to be ca. 13 nm. For the first time, we provide direct evidence that, during conditioning, the water molecules diffuse through the chloride ion selective membrane (Cl-ISM) until a water layer establishes at almost 3 h. Furthermore, the diffusion coefficient and concentration of oxygen molecules in the Cl-ISM are also directly electrochemical measured by introducing ferrocene (Fc) as a redox molecule probe. The oxygen concentration in the Cl-ISM decreases during conditioning, suggesting the diffusion of oxygen from ISM to the water layer. The proposed method can be used for the electrochemical measurement of solid contact, providing theoretical guidance and advice for the performance optimization of ISEs.

Solid-contact polymeric membrane ion-selective electrodes using a covalent organic framework@reduced graphene oxide composite as ion-to-electron transducer.

A solid-contact ion-selective electrode (SC-ISE) based on a covalent organic framework@reduced graphene oxide (rGO) composite is proposed. The composite can be synthesized through the polycondensation of 1,3,5-triformylphloroglucinol (TFP) and 2,6-diaminoanthraquinone (DAAQ) on the rGO nanosheets, which shows high capacitance and good redox-active properties. By applying Cd2+-ISE as a model, the electrode exhibits a Nernstian slope of 29.7±0.4 mV/decade in the activity range of 1.0×10-7 - 7.9×10-4M and the limit of detection is 6.8×10-8M. Particularly, the electrode based on DAAQ-TFP@rGO exhibits a low potential drift of 1.2±0.2μV/h over 70h due to the large capacitance of 2.0mF. Moreover, the DAAQ-TFP@rGO-based Cd2+-ISE shows good reproducibility and the standard deviations of the standard potentials for single batch and batch-to-batch are 0.28 (n=4) and 0.30mV (n=4), respectively. The developed SC-Cd2+-ISE is not disturbed by light or gas and no aqueous layer occurs between the sensing membrane and DAAQ-TFP@rGO layer. The DAAQ-TFP@rGO composite is highly promising for construction of calibration-free SC-ISEs.

Anti-fouling TiO2-Coated Polymeric Membrane Ion-Selective Electrodes with Photocatalytic Self-Cleaning Properties

Nowadays, using a polymeric membrane ion-selective electrode (ISE) to achieve reliable ion sensing in complex samples remains challenging because of electrode fouling. To address this challenge, we describe a polymeric membrane ISE with excellent anti-fouling and self-cleaning properties based on surface covalent modification of an anatase TiO2 coating. Under ultraviolet illumination, the reactive oxygen species produced by photocatalytic TiO2 can not only kill microorganisms but also degrade organic foulants into carbon dioxide and water, and a formed superhydrophilic film can effectively prevent the adsorption of foulants, thus inhibiting the occurrence of biofouling and organic fouling of the sensors. More importantly, residual foulants could be fully self-cleaned through the flow of water droplets. By using Ca2+-ISE as a model, an anti-fouling polymeric membrane potentiometric sensor has been developed. Compared to the unmodified electrode, the TiO2-coated Ca2+-ISE exhibits remarkably improved anti-biofouling properties with a low bacterial adhesion rate of 4.74% and a high inhibition rate of 96.62%. In addition, the proposed electrode displays unique properties of anti-organic dye fouling and a superior self-cleaning ability even after soaking in a concentrated bacterial suspension of 109 CFU mL-1 for 60 days. The present approach can be extended to improve the fouling resistance of other electrochemical or optical membrane sensors and is promising for the construction of contamination-free sensors.

Study on fabrication ion-selective membrane electrodes to improve electrochemical characteristics of electrodes for applied in water analysis

In this paper, we report the photolithography manufacturing of solid- ion selective membrane electrodes ammonium and nitrate in a cleanroom, using ammonium ionophore I (nonactin) and nitrate ionophore VI as starting materials. The developed probes are utilized with multipurpose electrochemical devices to potentiometrically monitor the concentration of ammonium and nitrate ions. 
 The research results showed that, S-ISM ammonium and nitrate can be used to measure ammonium and nitrate ions with high selectivity; it is also stable under research circumstances, with hardly any change in the OCP signals over time and a low limit of detection (LOD) of 2.0 ppm for NH4+ and 2.5 ppm for NO3-.

Preparation of Nitrate Bilayer Membrane Ion-Selective Electrode Modified by Pericarpium Granati-Derived Biochar and Its Application in Practical Samples

Preparation of Nitrate Bilayer Membrane Ion-Selective Electrode Modified by Pericarpium Granati-Derived Biochar and Its Application in Practical Samples

Ion-Selective Membrane Electrode for Determination of the Octahydrotriborate Anion

Ion-Selective Membrane Electrode for Determination of the Octahydrotriborate Anion

Design and Synthesis of the Poly Vinyl Chloride (PVC) Membrane for Fe(III) Ion Selective Electrode (ISE) Based on Ester Modified Humic Acid (EHA) as an Ionophore

Design and synthesis of the poly vinyl chloride (PVC) membrane as Fe(III) ion selective electrode (ISE) sensor based on EHA ionophore as an excellent sensory molecule for monitoring Fe(III) in the sample solution had been done. Simple and efficient EHA was made by condensation of carboxylic acid HA with ethanol and sulfuric acid as catalist. PVC membrane was prepared by mixed all component such as PVC powder, EHA, plasticizer (o-NPOE and DOP) and anion lipophilic (Sodium-TPB and oleic acid) with a total weight of 100 mg and dissolved in 1 mL of dry THF. The electrode membrane responses showed that the electrodes were highly selective to ion Fe3+ at pH 3 with response time of ±50 seconds. The dynamic range of the membrane ISE sensor was 10-1–10-7 M with the value of Nernst factor was ±19 mV per decade. The membrane electrode can be used for at least 5 weeks. The analytical results of Fe(III) measurement showed good confirmity with reference method (AAS), suggesting that the developed analytical tool could be used to measure and monitor Fe(III) in the real water samples.

Potentiometric MIP-Modified Screen-Printed Cell for Phenoxy Herbicides Detection

In this study, a molecularly imprinted polymer (MIP)-based screen-printed cell is developed for detecting phenoxy herbicides using 2-methyl-4-chlorophenoxyacetic acid (MCPA) as the template. MCPA is a phenoxy herbicide widely used since 1945 to control broadleaf weeds via growth regulation, primarily in pasture and cereal crops. The potentiometric cell consists of a silver/silver chloride pseudo-reference electrode and a graphite working electrode coated with a MIP film. The polymeric layer is thermally formed after drop-coating of a pre-polymeric mixture composed of the reagents at the following molar ratio: 1 MCPA: 15 MAA (methacrylic acid): 7 EGDMA (ethylene glycol dimethacrylate). After template removal, the recognition cavities function as the ionophore of a classical ion selective electrode (ISE) membrane. The detected ion is the deprotonated MCPA specie, negatively charged, so the measurements were performed in phosphate buffer at pH 5.5. A linear decrease of the potential with MCPA concentration, ranging from 4 × 10-8 to 1 × 10-6 mol L-1, was obtained. The detection limit and the limit of quantification were, respectively, 10 nmol L-1 and 40 nmol L-1. A Nernstian slope of about -59 mV/dec was achieved. The method has precision and LOD required for MCPA determination in contaminated environmental samples.

A feasible, fast and reliable method for estimating ion-site association constants in plasticized PVC ion-selective electrode membranes

A feasible, fast and reliable method for estimating ion association constants in PVC plasticized membranes of ion-selective electrodes from potentiometric data has been theoretically and experimentally substantiated. The method is based on the established fact of complete dissociation of salts of quaternary ammonium cations R4N + An‒ (except for those containing methyl substituents at the nitrogen atom) in a membrane plasticized with o-nitrophenyl octyl ether (o-NPOE). Therefore, the boundary potential at the interface of the membrane with an aqueous solution of R4N+ depends only upon the concentrations of the corresponding solution and the ion exchanger in the membrane and is independent of the presence of a lipophilic ionic additive (LIA), which makes it possible to use such ions as reference ones in the internal filling solution. If the ions studied (i+) are capable of forming ion associates with the ion exchanger, then the introduction of LIA into the membrane will lead to a decrease in the concentration of free i+ ions and to a corresponding increase in the boundary potential, from which the ion association constant can be directly calculated. The results obtained agree with the known literature data and the results of quantum chemical calculations. The prospective of applying the proposed method to the study of other membrane compositions is discussed.

Multiplexed Electrochemical Device for the Detection of Biomarkers of Parkinson’s Disease Using 3D Printing

Acetylcholine and dopamine are two important neurotransmitters when diagnosing Parkinson’s disease, as the imbalance in acetylcholine and dopamine levels can lead to progressive neurological disorders. Currently, there are many detection methods for the individual neurotransmitters with their own advantages and disadvantages. Previously, dopamine has been highlighted as the most relevant biomarker for diagnosis, but interest in combined detection of acetylcholine and dopamine has increased. Since it has been discovered that both motor function and learning difficulties in Parkinsonism is dependent on dopamine and acetylcholine levels, determination of both biomarkers simultaneously has increased therapeutic relevance. This work reports the detection of acetylcholine and dopamine using 3D printed potentiometric and 3D printed voltammetric sensors, respectively. Linear responses were obtained over broad concentration ranges for both biomarkers with a fully 3D printed ion-selective membrane (acetylcholine) and conductive carbon electrodes (dopamine). This work describes a novel fabrication protocol for sensors that have the capability to detect both biomarkers simultaneously when integrated into a low-cost, reliable, and user-friendly multiplexed device, also fabricated with 3D printing technologies.

Ion-Selective Electrode Based on a Novel Biomimetic Nicotinamide Compound for Phosphate Ion Sensor.

Phosphorus is not only an import nutrient to aquatic habitats, but it also acts as a growth inhibitor in aquatic ecosystems; however, it also aggravates environmental issues, such as eutrophication. There is a growing interest in rapid phosphorus detection to manage and protect water resources. Due to the large molecular structure and high hydration energy of phosphate ions, ion-selective electrodes (ISEs) remain in their infancy for real-time measurements in terms of practical application. In this study, a newly developed ionophore based on a biomimetic nicotinamide functional group was used to detect phosphate selectively, displaying efficient binding through charge interactions and hydrogen bonds. The ISE membrane containing silicone rubber demonstrated an effective detection performance over a long period of time. With a dynamic range between 10−6 and 10−2 M and a limit of detection of 0.85 × 10−6 M (26 μg/L), the newly synthesized ISE membranes demonstrated selectivity for phosphate ions over other ions, including acetate, sulfate, and chloride.

Electrically Enhanced Sensitivity (EES) of Ion-Selective Membrane Electrodes and Membrane-Based Ion Sensors.

The use of external electronic enforcement in ion-sensor measurements is described. The objective is to improve the open-circuit (potentiometric) sensitivity of ion sensors. The sensitivity determines the precision of analyte determination and has been of interest since the beginning of ion-sensor technology. Owing to the theoretical interpretation founded by W.E. Nernst, the sensitivity is characterized by the slope and numerically predicted. It is empirically determined and validated during calibration by measuring an electromotive force between the ion sensor and the reference electrode. In practice, this measurement is made with commercial potentiometers that function as unaltered “black boxes”. This report demonstrates that by gaining access to a meter’s electrical systems and allowing for versatile signal summations, the empirical slope can be increased favorably. To prove the validity of the approach presented, flow-through ion-sensor blocks used in routine measurements of blood electrolytes (Na+, K+, Li+, Cl−) and multielectrode probes with flat surfaces, similar to those applied previously for monitoring transmembrane fluxes of Na+, K+, Cl− through living biological cells, are used. Several options to serve real-life electroanalytical challenges, including linear calibration for sensors with high-resistance membranes, responses with non-Nernstian slopes, non-linear calibration, and discrimination of nonfunctional sensors, are shown.

A new sensor for direct potentiometric determination of thiabendazole in fruit peels using the Gran method

A new sensor for direct potentiometric determination of thiabendazole (TBZ) was prepared. The ionic pair of TBZ cation and the 5-sulfosalicylate anion was used as the new sensor material incorporated in liquid type of ion-selective electrode membrane for TBZ determination. For optimization of the membrane of the sensor for TBZ determination, six different plasticizers and the content of the sensor material in the membrane were varied. The chosen sensor with dibutyl sebacate (DS) as plasticizer and 1% of sensor material in the membrane was characterized with Nernstian response towards TBZ (62.2 mV/decade of activity), a wide working range (8.6∙10−7–1.0∙10−3 M), and a low limit of detection (3.2·10−7 M). Also, it proved to be an accurate and reliable sensor for TBZ determination in pure and real samples (peel of oranges, lemons and bananas) where it was determined using direct potentiometry and Gran method.

Innovation in potentiometry: 3D-printed polylactic acid-based ion-selective bulk electrode membranes

Although ion-selective membrane-based potentiometric sensors have already proved their analytical performance in several fields of life, their applicability is still limited in practice. Biodegradable, ionic additive-free, polylactic acid-based bulk electrode membrane matrix containing various environmentally friendly polyethylene glycol derivatives as plasticizer was developed for the first time to replace the conventional PVC-based ones. Moreover, the first introduction of 3D printing in potentiometric chemosensing was also reported. It was demonstrated that a thoroughly optimized and generalizable procedure for filament extrusion combined with 3D printing technology provides a unique tool for series production of the redesigned ion-selective bulk electrochemical membranes. Finally, the potentiometric detection of Hg2+ in water was carried out as a proof-of-concept study on sensing. Results showed an unexpected improvement in electrochemical characteristics of the novel membranes compared to their conventional analogues. The present work expanded the practical applicability of conventional potentiometric cation-selective electrode membranes enabling their green, decentralized, and automated state-of-the-art manufacturing using a novel matrix composition.Graphical abstract

Potentiometric Determination of Mercury Ions by Sol-gel Synthesized Multi-walled Carbon Nanotubes Zr (IV) Phosphate Composite Fabricated Membrane Electrode

Background: The nanocomposites are formed by introducing inorganic nano-clusters, fullerenes, clays, metals, oxides with numerous organic polymers. The assembly of these materials exhibits better properties such as catalytic, thermal stability and adsorption properties, etc. than the individual materials. Objective: The nanocomposite synthesized here by sol-gel method was primarily evaluated for cation exchange properties viz, elution concentration, elution behavior, effect of temperature on ion-exchange capacity. The synthesized composite was used as an electro-active component for fabrication of Hg2+ ion selective membrane electrode. Method : The sol-gel technique was used to synthesize multi-walled carbon nanotubes Zr(IV) phosphate composite cation exchanger. By the technique of solution casting the material as an electroactive part was used for the fabrication of mercury ion-selective membrane electrode. The potential response of the electrode was also investigated as a function of membrane composition and plasticizer. Results: The composite cation exchanger exhibited 1.8 meq g-1 ion-exchange capacity (IEC). It retained almost 65 % of its initial IEC upto a temperature of 400 °C. Distribution studies showed the selective nature of the composite for Hg(II) ions. The ion-selective membrane electrode exhibited typical Nernstian response towards Hg2+ ions in the concentration range 1×10-1 -1×10-7 M. Conclusion: The results discussed reveal that a new cation composite exchanger-multi-walled carbon nanotubes Zr (IV) phosphate exhibited excellent cation exchange properties and was found to be preferentially selective towards the Hg2+ ions. It was also used as an indicator electrode in the titration of Hg2+ using ethylenediaminetetraacetic acid as a titrant.