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N,O-hybrid donor ligands are promising compounds for the isolation and separation of actinides and lanthanides from process solutions of spent nuclear fuel reprocessing. Newly synthesized N,O-hybrid donor ligands – derivatives of 2,6-pyridinedicarboxylic acid were studied as extractants and membrane components for potentiometric sensors. The extraction ability of solutions of these compounds in meta-nitrobenzotrifluoride towards d- and f-elements from nitric and perchloric acid solutions was investigated. It was shown that the replacement of amide groups with ester groups reduces the extraction ability of the ligands. Switching from nitric acid to perchloric acid gives a dramatic increase in extraction capacity due to the perchlorate effect. Also, a significant increase in extraction capacity is observed when chlorinated cobalt dicarbolide is added to the organic phase: the highest distribution coefficient is observed at a 1 : 1 ratio of extractant and additive concentrations. Potentiometric membrane sensors based on the new ligands showed significant sensitivity to Cd2+. Correlations between extraction and sensing behavior of new ligands were studied. [ABSTRACT FROM AUTHOR]

Antibiotic resistance is a crisis that is escalating nowadays. Thus, therapeutic drug monitoring (TDM) is crucial to personalize the dose. Point‐of‐care (POC) devices are very effective in TDM where drug concentration can be easily and continuously monitored. This work describes for the first time the use of inexpensive, transportable, efficacious, and eco‐friendly POC solid‐state potentiometric sensor for the TDM of Flucloxacillin (FLU) in spiked plasma samples. This was achieved by using an innovative glassy carbon electrode modified with ion sensing membrane doped with carbon nanotubes. Optimization of the sensing membrane composition was performed using different plasticizers and by adding an ionophore. This was followed by doping the ion sensing membrane with carbon nanotubes which resulted in enhancing the sensor's sensitivity towards FLU. Over a concentration range from 1.0×10−5–1.0×10−2 M FLU, a linear response was obtained with a slope of 56.6 mV/decade. Our proposed sensor has been validated according to IUPAC recommendations with acceptable results. It was effectively employed for a selective determination of FLU in the presence of a co‐formulated antibiotic (Amoxicillin), along with other excipients in the dosage form, and in spiked plasma samples, without any interference. The whiteness of the method was assessed, which proves the high greenness and superb functionality of our proposed method. [ABSTRACT FROM AUTHOR]

A simple and reliable methodology for the detection of paralytic shellfish toxins (PSTs) in bivalve tissues using potentiometric chemical sensors was developed. Five methods of PST extraction from mussel and oyster tissues were evaluated, including the AOAC-recommended method, which served as the reference. The main objective was to minimize the matrix effect of the extracts on the sensors' responses and ensure efficient toxin recovery. Extraction procedures using acetic acid with heating and water yielded the highest responses from the potentiometric chemical sensors to PSTs. The highest recovery of PSTs from bivalve tissues was achieved with extraction using acetic acid and heating. Further extract purification, which is indispensable for liquid chromatography with fluorometric detection (LC-FLD) analysis, was found to be unnecessary for analysis with chemical sensors. While water extraction can also be used as a rapid and simple PST extraction method, the lower recoveries should be considered when interpreting the results. Further research is needed to identify the compounds remaining in the extracts that cause a decrease in sensor responses and to develop procedures for their elimination. [ABSTRACT FROM AUTHOR]

The performance of an electronic tongue can be optimized by varying the number and types of sensors in the array and by employing data-processing methods. Sensor selection is typically performed empirically, with sensors picked up either by analyzing their characteristics or through trial and error, which does not guarantee an optimized sensor array composition. This study focuses on developing a method for sensor selection for an electronic tongue using simulated sensor data and Lasso regularization. Simulated sensor responses were calculated using sensor parameters such as sensitivity and selectivity, which were determined in the individual analyte solutions. Sensor selection was carried out using Lasso regularization, which removes redundant or highly correlated variables without much loss of information. The objective of the optimization of the sensor array was twofold, aiming to minimize both quantification errors and the number of sensors in the array. The quantification of toxins belonging to one of the groups of marine toxins—paralytic shellfish toxins (PSTs)—using arrays of potentiometric chemical sensors was used as a case study. Eight PSTs corresponding to the toxin profiles in bivalves due to the two common toxin-producing phytoplankton species, G. catenatum (dcSTX, GTX5, GTX6, and C1+2) and A. minitum (STX, GTX2+3), as well as total sample toxicity, were included in the study. Experimental validation with mixed solutions of two groups of toxins confirmed the suitability of the proposed method of sensor array optimization with better performance obtained for the a priori optimized sensor arrays. The results indicate that the use of simulated sensor responses and Lasso regularization is a rapid and efficient method for the selection of an optimized sensor array. [ABSTRACT FROM AUTHOR]

AbstractElectrochemical sensors have been the subject of much research and development as of late, with several publications detailing new designs boasting enhanced performance metrics. That is, without a doubt, because such sensors stand out from other analytical tools thanks to their excellent analytical characteristics, low cost, and ease of use. Their progress has shown a trend toward seeking out novel useful nano structure materials. A variety of nanostructure metal oxides have been utilized in the creation of potentiometric sensors, which are the subject of this article. For screen-printed pH sensors, metal oxides have been utilized as sensing layers due to their mixed ion-electron conductivity and as paste-ion-selective electrode components and in solid-contact electrodes. Further significant uses include solid-contact layers. All the metal oxide uses mentioned are within the purview of this article. Nanoscale metal oxides have several potential uses in the potentiometry method, and this paper summarizes such uses, including hybrid materials and single-component layers. Potentiometric sensors with outstanding analytical properties can be manufactured entirely from metal oxides. These novel sensors outperform the more traditional, conventional electrodes in terms of useful characteristics. In this review, we looked at the potentiometric analytical properties of different building solutions with various nanoscale metal oxides. [ABSTRACT FROM AUTHOR]

Wearable potentiometric ion sensors (WPISs) have emerged as exciting analytical platforms that combine chemical, material, and electronic advancements to provide physiological information during various human activities. The real possibility of wearing an analytical device with diverse configurations, such as sweatbands, patches, or garments, without disturbing the wearer's comfort has enabled potentiometric ion sensors to serve as both healthcare monitoring and improve the performance of athletes. [ABSTRACT FROM AUTHOR]

A paper-based analytical device (PAD) with an integrated composite electrode has been designed and fabricated for non-enzymatic creatinine sensing. Reduced graphene oxide (rGO) was employed to modify the PAD so that it could function as a solid-contact transducer. A new macrocyclic pyrido-hexapeptide derivative was made and used as a special ionophore in the creatinine membrane sensor. The synthesized PAD showed a detection limit of 1.0 µM (S/N = 3) and a potentiometric response towards creatinine throughout a log-linear range of 2.0 µM–10 mM (R2 = 0.9998). The sensor shows significant selectivity for a few related substances, including ephedrine, codeine, ketamine, caffeine, urea, urate, carbinoxamine, and dextromethorphan. It has been established that the testing method is appropriate for the direct potentiometric detection of creatinine in a variety of human urine sample types. When an indicating electrode and a reference electrode are put on the same flexible disposable, this lets applications with a small sample volume be done. For point-of-care creatinine measurement, the developed paper-based analytical equipment is a good choice because it is affordable, easily accessible, and self-pumping (especially when combined with potentiometric detection). [ABSTRACT FROM AUTHOR]

A simple and reliable methodology for the detection of paralytic shellfish toxins (PSTs) in bivalve tissues using potentiometric chemical sensors was developed. Five methods of PST extraction from mussel and oyster tissues were evaluated, including the AOAC-recommended method, which served as the reference. The main objective was to minimize the matrix effect of the extracts on the sensors’ responses and ensure efficient toxin recovery. Extraction procedures using acetic acid with heating and water yielded the highest responses from the potentiometric chemical sensors to PSTs. The highest recovery of PSTs from bivalve tissues was achieved with extraction using acetic acid and heating. Further extract purification, which is indispensable for liquid chromatography with fluorometric detection (LC-FLD) analysis, was found to be unnecessary for analysis with chemical sensors. While water extraction can also be used as a rapid and simple PST extraction method, the lower recoveries should be considered when interpreting the results. Further research is needed to identify the compounds remaining in the extracts that cause a decrease in sensor responses and to develop procedures for their elimination.

Plant-available nitrogen, often in the form of nitrate, is an essential nutrient for plant growth. However, excessive nitrate in the environment and watershed has harmful impacts on natural ecosystems and consequently human health. A distributed network of nitrate sensors could help to quantify and monitor nitrogen in agriculture and the environment. Here, we have developed fully printed potentiometric nitrate sensors and characterized their sensitivity and selectivity to nitrate. Each sensor comprises an ion-selective electrode and a reference electrode that are functionalized with polymeric membranes. The sensitivity of the printed ion-selective electrodes was characterized by measuring their potential with respect to a commercial silver/silver chloride reference electrode in varying concentrations of nitrate solutions. The sensitivity of the printed reference electrodes to nitrate was minimized with a membrane containing polyvinyl butyral (PVB), sodium chloride, and sodium nitrate. Selectivity studies with sulphate, chloride, phosphate, nitrite, ammonium, calcium, potassium, and magnesium showed that high concentrations of calcium can influence sensor behavior. The printed ion-selective and reference electrodes were combined to form a fully printed sensor with sensitivity of -48.0 ± 3.3 mV/dec between 0.62 and 6200 ppm nitrate in solution and -47 ± 4.1 mV/dec in peat soil.

The performance of an electronic tongue can be optimized by varying the number and types of sensors in the array and by employing data-processing methods. Sensor selection is typically performed empirically, with sensors picked up either by analyzing their characteristics or through trial and error, which does not guarantee an optimized sensor array composition. This study focuses on developing a method for sensor selection for an electronic tongue using simulated sensor data and Lasso regularization. Simulated sensor responses were calculated using sensor parameters such as sensitivity and selectivity, which were determined in the individual analyte solutions. Sensor selection was carried out using Lasso regularization, which removes redundant or highly correlated variables without much loss of information. The objective of the optimization of the sensor array was twofold, aiming to minimize both quantification errors and the number of sensors in the array. The quantification of toxins belonging to one of the groups of marine toxins—paralytic shellfish toxins (PSTs)—using arrays of potentiometric chemical sensors was used as a case study. Eight PSTs corresponding to the toxin profiles in bivalves due to the two common toxin-producing phytoplankton species, G. catenatum (dcSTX, GTX5, GTX6, and C1+2) and A. minitum (STX, GTX2+3), as well as total sample toxicity, were included in the study. Experimental validation with mixed solutions of two groups of toxins confirmed the suitability of the proposed method of sensor array optimization with better performance obtained for the a priori optimized sensor arrays. The results indicate that the use of simulated sensor responses and Lasso regularization is a rapid and efficient method for the selection of an optimized sensor array.

Potentiometric ion-selective electrode (ISE) sensors are powerful electrochemical tools used in various applications in different fields, including the biological, clinical, and environmental fields, owing to their high selectivity, sensitivity, simplicity, and versatility. This review highlights recent advancements in ionophore-based polymeric ISE sensors over the past five years, with a particular focus on progress at the micro- and nanoscales. After discussing the conventional ISE configuration and its general operational principles, we explore the notable advancements in terms of the key ion-selective membrane components, such as ionophores, and other techniques combined with ISEs. These advancements have significantly improved the sensing performances and expanded the practical applications. We also examine the progress in the field of miniaturized solid-contact microelectrodes and the incorporation of novel functional materials for efficient ion-to-electron transduction. Miniaturized solid-state ISEs provide low limits of detection with reduced sample volume requirements, extended stability, and rapid response times. When combined with scanning electrochemical microscopy, ion-selective microelectrodes enable highly spatially resolved ion analyses. The integration of solid-contact ISEs into compact, portable, wearable devices has advanced the field of wearable on-body ISE sensors. Finally, we briefly introduce the development of ion-selective optode sensors as promising optical sensors based on ionophores that are particularly advantageous for cellular imaging.

Wearable Potentiometric Ion Sensors (WPISs) have emerged as a highly promising analytical tool that amalgamates advancements in chemistry, materials science, and electronics to provide essential physiological insights during various human activities. The remarkable capability of seamlessly integrating these analytical devices into everyday wearables, such as sweatbands, patches, and garments, without causing any discomfort to the wearer, has transformed WPISs into indispensable tools for both monitoring health parameters and enhancing athletic performance. Recent research has demonstrated a significant role for WPISs in tracking critical biomarkers, including sodium, potassium, calcium, magnesium, ammonium, and chloride, which are present in relatively high concentrations in sweat. The utilization of these innovative devices empowers us to continuously monitor patients' wellbeing and optimize athletes' performance. In this comprehensive review, we delve into a plethora of studies concerning wearable sensors designed for sodium detection and explore the latest materials utilized in the development of sodium-sensing wearables. [ABSTRACT FROM AUTHOR]

2,4,6‐trichlorophenol (TCP) is regarded as a very harmful persistent organic pollutant. It is prohibited by the US EPA due to its stability, possible toxicity, and substantial carcinogenicity, which could result in long‐term harm to both the environment and living things. A novel solid‐contact electrode (SCE) is fabricated and characterized for potentiometric determination of 2,4,6‐trichlorophenol (2,4,6‐TCP). Molecularly imprinted trichlorophenol polymer (MIP) beads are used as a recognition receptor for potentiometric determination of this persistent organic pollutant. The MIPs are synthesized using 4‐vinyl pyridine (4‐VP) and N,N′‐Methylene bis(acrylamide) (N,N‐MBAA) as functional monomer and cross‐linking agent, respectively. They are embedded in a selective polyvinyl chloride (PVC) membrane on the top of multi‐walled carbon nanotubes (MWCNTs), which is used as an ion to electron transducer. The SCE exhibits a Nernstian response with a slope of −55.4±2.1 mV/decade (R2=0.999) over the concentration range of 8.0×10−6 to 1.0×10−4 M, a detection limit of 5.0×10−7 M (0.98 μg/mL), and a response time of <10 s. Using electrochemical impedance spectroscopy (EIS) and chronopotentiometry (CP), the suggested SCE′s interfacial capacitance is measured. The interfacial capacitance was increased using MWCNTs and reached 39.7 μF. Also, it prevented the undesirable thin water layer from forming between the conducting glassy carbon (GC) substrate and the sensing membrane. As a result, potential stability is improved, and membrane delamination is avoided. The suggested SCE had a wide range of applications for monitoring TCP in various environmental samples because of the high selectivity, sensitivity, and possible stability that were attained. [ABSTRACT FROM AUTHOR]

Monitoring the content of dissolved ozone in purified water is often mandatory to ensure the appropriate levels of disinfection and sanitization. However, quantification bears challenges as colorimetric assays require laborious off‐line analysis, while commercially available instruments for electrochemical process analysis are expensive and often lack the possibility for miniaturization and discretionary installation. In this study, potentiometric ionic polymer metal composite (IPMC) sensors for the determination of dissolved ozone in ultrapure water (UPW) systems are presented. Commercially available polymer electrolyte membranes are treated via an impregnation‐reduction method to obtain nanostructured platinum layers. By applying 25 different synthesis conditions, layer thicknesses of 2.2 to 12.6 µm are obtained. Supporting radiographic analyses indicate that the platinum concentration of the impregnation solution has the highest influence on the obtained metal loading. The sensor response behavior is explained by a Langmuir pseudo‐isotherm model and allows the quantification of dissolved ozone to trace levels of less than 10 µg L−1. Additional statistical evaluations show that the expected Pt loading and radiographic blackening levels can be predicted with high accuracy and significance (R2adj. > 0.90, p < 10−10) solely from given synthesis conditions. [ABSTRACT FROM AUTHOR]

This paper presents new paste ion-selective electrodes for the determination of nitrate ions in soil. The pastes used in the construction of the electrodes are based on carbon black doped with transition metal oxides: ruthenium, iridium, and polymer-poly(3-octylthiophene-2,5-diyl). The proposed pastes were electrically characterized by chronopotentiometry and broadly characterized potentiometrically. The tests showed that the metal admixtures used increased the electric capacitance of the pastes to 470 μF for the ruthenium-doped paste. The polymer additive used positively affects the stability of the electrode response. All tested electrodes were characterized by a sensitivity close to that of the Nernst equation. In addition, the proposed electrodes have a measurement range of 10−5 to 10−1 M NO3− ions. They are impervious to light conditions and pH changes in the range of 2–10. The utility of the electrodes presented in this work was demonstrated during measurements directly in soil samples. The electrodes presented in this paper show satisfactory metrological parameters and can be successfully used for determinations in real samples. [ABSTRACT FROM AUTHOR]

The review discloses the historical and technological evolution of enzyme‐based field‐effect transistors (EnFETs) underlying the importance of gate electrode modification toward the implementation of novel FETs configurations such as extended‐gate FET (EG‐FETs) or EG organic FETs (EG‐OFETs). The working principle of the EnFETs as postulated by Bergveld in 1970, who defined the EnFET as an ion‐selective FET (ISFET) modified with enzyme‐membrane, is also discussed considering the analytical equations related to the EnFET output response. For each category, namely EnFETs, EG‐FETs, and EG‐OFETs, we reviewed the key devices' configurations that addressed the research in this field in the last 40 years with particular attention to the analytical figures of merit. [ABSTRACT FROM AUTHOR]

A new potentiometric method based on the screen-printed ion-selective electrode (SPISE) was described for the determination of Bi(III) ion in different authentic samples. The novelty is based on, for the first time, the utilization of the cerium zirconium phosphotungstate (CZPT) in a screen-printed electrode (SPE) as a sensing material. In the literature, there is no screen-printed ion-selective electrode for the determination of Bi(III) ion. The influences of the paste composition, different conditioning parameters and foreign ions on the electrode performance were investigated. The reversibility and also response time of the electrode have been studied. The electrode showed a Nernstian response of 18.2 mV decade−1 in the concentration range of 3.3 × 10−7–1 × 10−1 mol. L−1. The electrode was found to be usable within the pH range of 3.5–8.0 and exhibited a fast response time, limit of detection (LOD) (1 × 10−7 mol. L−1), limit of quantification (LOQ) (3.33 × 10−7 mol. L−1), long lifetime and good stability. The matched potential method (MPM) was applied to determine the selectivity coefficient. The isothermal temperature coefficient (dEo/dt) of the electrode was calculated. The electrode was successfully applied for the determination of Bi(III) ion in different authentic samples. By comparing the current results with those obtained using inductively coupled plasma optical emission spectrometry, the nominated Bi(III) screen-printed ion-selective electrode has attained acceptable and efficient performance. [ABSTRACT FROM AUTHOR]

Abstract 2,4,6‐trichlorophenol (TCP) is regarded as a very harmful persistent organic pollutant. It is prohibited by the US EPA due to its stability, possible toxicity, and substantial carcinogenicity, which could result in long‐term harm to both the environment and living things. A novel solid‐contact electrode (SCE) is fabricated and characterized for potentiometric determination of 2,4,6‐trichlorophenol (2,4,6‐TCP). Molecularly imprinted trichlorophenol polymer (MIP) beads are used as a recognition receptor for potentiometric determination of this persistent organic pollutant. The MIPs are synthesized using 4‐vinyl pyridine (4‐VP) and N,N′‐Methylene bis(acrylamide) (N,N‐MBAA) as functional monomer and cross‐linking agent, respectively. They are embedded in a selective polyvinyl chloride (PVC) membrane on the top of multi‐walled carbon nanotubes (MWCNTs), which is used as an ion to electron transducer. The SCE exhibits a Nernstian response with a slope of −55.4±2.1 mV/decade (R2=0.999) over the concentration range of 8.0×10−6 to 1.0×10−4 M, a detection limit of 5.0×10−7 M (0.98 μg/mL), and a response time of

Sweat analysis by means of minimally invasive wearable sensors is considered a potentially disruptive method for assessing clinical parameters, with exciting applications in early medical diagnostics and high-performance sports. Electrochemical sensors and biosensors are especially attractive because of the possibility of the electronic integration of wearable devices. In this article, we review several aspects regarding the potentialities and present limitations of electrochemical sweat (bio)sensors, including: the main target analytes and their relationships with clinical conditions; most usual electrochemical techniques of transduction used according to the nature of the target analytes; issues connected to the collection of representative sweat samples; aspects regarding the associated, miniaturized electronic instrumentation used for signal processing and communication; and signal processing by machine learning. [ABSTRACT FROM AUTHOR]

• Ni-HAB MOF sensor array provides exceptionally low drift in electrochemical sensors. • MOF-modified solid-contact sensors improve hydroponic nutrient monitoring. • K+, pH, and NO 3 - monitoring in a portable system enables long-term agricultural use. In agricultural contexts, the demand for continuous and precise measurement of multiple ions is crucial. While arrays of solid-contact ion-selective electrodes (SCEs) have been developed previously, there has been limited emphasis on their continuous and long-term monitoring of ions. Addressing this gap, our work introduces an innovative sensor array utilizing Ni-HAB MOF as an ion-to-electron transducer, enabling real-time detection of nitrate, potassium, and pH levels. The sensors exhibit exceptional stability, eliminating the need for frequent recalibration. For instance, the K+-selective sensor displays an unprecedentedly low potential drift of 0.05 µV/h, surpassing existing solid-contact sensors by two orders of magnitude. Similarly, the pH sensor demonstrates a drift of 0.3 µV/h, outperforming competitors by a factor of 100. The NO 3 --selective sensor shows minimal drift at 0.5 µV/h, surpassing comparable sensors by a factor of ten. Additionally, the K+-selective sensor features a sensitivity of 57.8 mV/dec and a LOD of 1.9 µM, while the NO 3 --selective sensor offers a sensitivity of 56.8 mV/dec and a LOD of 6.23 µM. Integrated into a portable array with wireless data transmission, this system enables real-time water quality monitoring in remote areas. Rigorous testing of the developed sensor array in a tailored complex agricultural solution confirms its selective response to target ions even in the presence of interfering ions. Importantly, pH fluctuations do not compromise the precision of the K+ and NO 3 -- selective sensors, highlighting the system's robustness in real-world agricultural settings. [ABSTRACT FROM AUTHOR]

The ion‐sensitive field effect transistors (ISFETs), proposed little over 50 years ago, today make the most promising devices for lab‐on‐a‐chip, implantable, and point‐of‐care (POC) diagnostics. Their compatibility with CMOS (Complementary Metal Oxide Semiconductor) technology and the low cost through mass production have been the driving factors so far. Nowadays, they are also being developed in flexible form factors for new applications such as wearables and to improve the effective usage in existing applications such as implantable systems. In this regard, the CMOS ultra‐thin chip (UTC) technology and the bonding by printing are the noteworthy advances. This paper comprehensively reviews such new developments in the CMOS‐compatible ISFETs, along with their theory, readout circuitries, circuit‐based techniques for compensation of the ISFET's instabilities, such as the offset, flicker noise, and drift. The sensing mechanisms and the properties of interface between the electrolyte under test and the metal‐oxide based ion‐sensitive electrodes have been discussed along with a brief overview of the metal‐oxide based pH sensors. An overview of the reported mechanically flexible pH sensors, including ISFETs, is provided and the history of ISFET applications are also covered. Finally, established models that can be used to design flexible circuits are presented, and possible opportunities to use circuit techniques to compensate for mechanical deformation are discussed. [ABSTRACT FROM AUTHOR]

Recently, there has been rapid development of electrochemical sensors, and there have been numerous reports in the literature that describe new constructions with improved performance parameters. Undoubtedly, this is due to the fact that those sensors are characterized by very good analytical parameters, and at the same time, they are cheap and easy to use, which distinguishes them from other analytical tools. One of the trends observed in their development is the search for new functional materials. This review focuses on potentiometric sensors designed with the use of various metal oxides. Metal oxides, because of their remarkable properties including high electrical capacity and mixed ion-electron conductivity, have found applications as both sensing layers (e.g., of screen-printing pH sensors) or solid-contact layers and paste components in solid-contact and paste-ion-selective electrodes. All the mentioned applications of metal oxides are described in the scope of the paper. This paper presents a survey on the use of metal oxides in the field of the potentiometry method as both single-component layers and as a component of hybrid materials. Metal oxides are allowed to obtain potentiometric sensors of all-solid-state construction characterized by remarkable analytical parameters. These new types of sensors exhibit properties that are competitive with those of the commonly used conventional electrodes. Different construction solutions and various metal oxides were compared in the scope of this review based on their analytical parameters.

[Display omitted] • Optimization of electropolymerized PANI as a solid inner contact. • PANI layer thickness affects its structure and electrical properties. • PANI with optimal thickness inhibits water layer formation on the PANI/PVC interface. • Sensor with optimized PANI solid contact exhibits lower LOD and higher selectivity. • Detection of paralytic shellfish toxins in mussel extracts used as a case study. The present study optimized the properties of the electropolymerized polyaniline (PANI) solid inner contact for a potentiometric chemical sensor by varying the thickness of the polymer layer. A potentiometric sensor for detecting one of the paralytic shellfish toxins, decarbamoyl saxitoxin (dcSTX), in mussel extracts was selected as a case study. The plasticized PVC membrane composition, developed in previous work for the detection of this toxin, was used. The structure and electrical properties of PANI layers of different thicknesses were studied using scanning electron microscopy and electrochemical impedance spectroscopy. The effect of PANI solid contact thickness on the characteristics of the potentiometric sensor, including sensitivity, detection limit, and selectivity to dcSTX in buffer solutions and mussel extracts, was evaluated. The formation of a water layer at the inner solid contact and PVC membrane interface was investigated using electrochemical impedance spectroscopy and a water test. PANI layer thickness 1.1 µm was found to be optimal for solid inner contact for potentiometric sensor with PVC membrane providing highest sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

We present and validate an equilibrium model based on the Poisson-Boltzmann equations that includes the main ingredients to simulate ion-sensitive membranes in the context of electrochemical potentiometric sensors with and without ionophores. With respect to phase boundary models, our model includes spatial resolution of the electrostatic potential and concentrations. The model enables the study of Nernstian and non-Nernstian equilibrium responses, helps improving the detection range and investigating selectivity and cross-sensitivity issues related to interferent ions in the sample solution. Therefore, the model is a useful support for the design of potentiometric microelectronic sensors and helps optimizing relevant membrane features such as ionic sites and ionophore concentration for best sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

We present an approach to simulate ion’s drift and diffusion in chemical sensors based on ion-selective-membranes (ISMs) in either ion-selective electrode structures or coupled to field-effect transistors. The model is used to analyze the sensitivity, selectivity, and transient response of ISMs in non-equilibrium conditions upon real-time concentration changes. Our simple implementation combines advanced features from semiconductor theory and analytical electrochemistry, such as the Schafetter-Gummel discretization scheme and Chang-Jaffé boundary conditions for ions at the interfaces, thus allowing to perform simulations beyond sensing. The results are in agreement with experimental transient responses reported in the literature. As relevant case studies, we examine the ISM preconditioning in miniaturized sensors and the electrostatic interaction between the FET channel and ISMs. In the first case, simulations reveal that calibration curves performed on incomplete ISM conditioning can lead to hysteretical responses when the ion affinity in the electrolyte and ISM is similar (e.g., with organic ions). In the second case, we find that the gate oxide field in contact with the ISM affects the device characteristics such that the ion concentrations not only change the FET threshold voltage but also the slope of its IV curve. This effect can be minimized by working in the subthreshold regime or using extended gates. [ABSTRACT FROM AUTHOR]

Two new potentiometric sensors were created for the quantification of bisoprolol fumarate and alverine citrate in bulk pharmaceutical dosage forms and human serum. Bisoprolol and alverine sensors were manufactured by combining potassium tetrakis (p-chlorophenyl) borate ion pairs to serve as electroactive substances, plasticized poly (vinyl chloride) matrix membranes, and o-nitrophenyl octyl ether. They demonstrated high responses over the concentration ranges of 1.0×10−6 to 1.0×10−2 mol L−1 bisoprolol and alverine with close to Nernstian cationic slopes of 52 and 56 mV decade−1, respectively. The detection limits for bisoprolol and alverine were 2.6×10−6 and 1.75×10−6 mol L−1, respectively. For both medications, the response time was instantaneous (2.0 s). The working pH ranges for bisoprolol and alverine were 4.50–8.50 and 2.00–8.80, respectively. For both sensors, the life cycle was long (3 months). The sensors were used in pharmaceutical dosage types for the assay of bisoprolol and alverine, recording average recoveries of 99.40% and 99.98% respectively and were also successfully used for estimating the two drugs in human serum with an average recovery of 99.60% for both drugs. For all multiple staged interfering materials, the reported latest potentiometric sensor methods displayed high selectivity. The current sensor obtained a high percentage recovery and an excellent relative standard deviation compared with those obtained from previously published methods.

Developing chemical sensors with pronounced sensitivity towards lanthanides is a very important task related to the analytical control of industrial processes in nuclear industry. Various diamides of organic acids were shown to be very effective for such sensing applications when employed as ligands in plasticized polymeric membranes of potentiometric sensors. The chemical structures of some of these ligands (diamides of diglycolic acid) are very similar to those suggested in 80's as Ca(II) ionophores that were later commercialized. We have hypothesized that commercial ionophores ETH 129 (N,N,N′,N′-tetra[cyclohexyl] diglycolic acid diamide) and ETH 5234 (N,N-dicyclohexyl-N′,N′-dioctadecyl-diglycolic diamide) originally intended for calcium detection can provide noticeable potentiometric sensitivity towards lanthanides. To confirm this hypothesis a series of PVC-plasticized sensor membranes containing ETH 129 and ETH 5234 were prepared. The sensing properties of these membranes in aqueous solutions of rare earth metals were studied and compared to earlier developed lanthanide sensors based on diamide ligands. It was found that commercial calcium ionophores indeed provide pronounced sensitivities towards lanthanides, scandium, and yttrium, while the selectivities in presence of calcium ions are in the favor of Ca(II). [ABSTRACT FROM AUTHOR]

Potentiometric multisensor systems were shown to be very promising tools for the quantification of numerous analytes in complex radioactive samples deriving from spent nuclear fuel reprocessing. Traditional multivariate calibration for these multisensor systems is performed with partial least squares regression—an intrinsically linear regression method that can provide suboptimal results when handling potentiometric signals from very complex multi-component samples. In this work, a thorough investigation was performed on the performance of a multisensor system in combination with non-linear multivariate regression models for the quantification of analytes in the PUREX (Plutonium–URanium EXtraction) process. The multisensor system was composed of 17 cross-sensitive potentiometric sensors with plasticized polymeric membranes containing different lipophilic ligands capable of heavy metals, lanthanides, and actinides binding. Regression algorithms such as support vector machines (SVM), random forest (RF), and kernel-regularized least squares (KRLS) were tested and compared to the traditional partial least squares (PLS) method in the simultaneous quantification of the following elements in aqueous phase samples of the PUREX process: U, La, Ce, Sm, Zr, Mo, Zn, Ru, Fe, Ca, Am, and Cm. It was shown that non-linear methods outperformed PLS for most of the analytes. [ABSTRACT FROM AUTHOR]

Sweat analysis by means of minimally invasive wearable sensors is considered a potentially disruptive method for assessing clinical parameters, with exciting applications in early medical diagnostics and high-performance sports. Electrochemical sensors and biosensors are especially attractive because of the possibility of the electronic integration of wearable devices. In this article, we review several aspects regarding the potentialities and present limitations of electrochemical sweat (bio)sensors, including: the main target analytes and their relationships with clinical conditions; most usual electrochemical techniques of transduction used according to the nature of the target analytes; issues connected to the collection of representative sweat samples; aspects regarding the associated, miniaturized electronic instrumentation used for signal processing and communication; and signal processing by machine learning.

Unmodified and modified solid-contact potentiometric sensors based on associates of alkyl sulfates with copper(II)–organic reagent complex compounds and alkylpyridinium alkyl sulfates for the determination of synthetic anionic surfactants are considered. The electroanalytical properties of the sensors are compared. The introduction of compounds of alkyl sulfates with cationic complexes of copper(II) with pyridine, 2,2'-dipyridyl, 1,10-phenanthroline, N,N '-bis(salicylidene)ethylenediamine (ionophores) into the composition of plasticized polyvinyl chloride membranes made it possible to create sensors for anionic surfactants (ASs) with improved electroanalytical characteristics (analytical range 1 × 10–2–2 × 10–7 М, сmin = 1 × 10–7 М, response time 8–9 s, potential drift 2–3 mV/day in solutions with concentrations of at least 1 × 10–4 М, service life 12 months). The considered compounds are poorly soluble (Ks = n × 10–22–n × 10–20) and thermally stable (80–90°C). As ionophores of membranes for sensors for nonionic surfactants (NSs), tetraphenylborate associates with barium(II)–polyethoxylate complexes with different numbers of oxyethyl groups (n = 10–100). On the basis of electrode, dynamic, transport, selective properties, cross-sensitivity parameters of AS and NS sensors, their use in the multisensor determination of homologous sodium alkyl sulfates, polyoxyethylated nonylphenols in model mixtures, natural waters, and technical preparations is justified. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simplified 'universal' design of EGFET sensors for insecticide imidacloprid in water. • UiO66-NH 2 MOF confirmed as sensitiser for the detection of 'imidacloprid' residue in food and water samples. • The limit- of- detection is more than 3 orders- of- magnitude smaller than the EU 'Maximum Residue Limit' (MRL) for imidacloprid. • pH and common salts do not interfere with the detection of imidacloprid. As an example for a metal-organic framework (MOF) sorbent acting as sensitiser in a potentiometric sensor, we introduce the metal–organic framework (MOF) UiO-66-NH 2 into a bridged extended-gate field effect transistor (EGFET) design. The sensitised EGFET detects residue of the insecticide imidacloprid with a limit of detection more than 3 orders of magnitude smaller than the EU 'Maximum Residue Limit' (MRL) for imidacloprid. This allows decisions on MRL compliance of water at a much lower experimental footprint than with chromatographic methods. To apply the sensor to food samples, we account for possible interference from legitimate food ingredients. Interference is small or moderate for fruit juices, moderate for 'red' juice (containing anthocyanin dyes), and small for others. Interference is strong for tea, probably from caffeine. We propose a test protocol to make 'accept/reject' decisions with respect to imidacloprid residue even in the presence of small or moderate interference. The present agar-bridged EGFET design enables the wider use of MOF sorbents in potentiometric sensors. [ABSTRACT FROM AUTHOR]

One of the barriers to the more widespread use of ion-selective electrodes (ISEs) in resource-limited areas is the need for frequent recalibration of such devices. The incorporation of a redox buffer to minimize the effect of redox-active impurities in the system has previously been shown to significantly improve reproducibility. To date, however, there have been no examples of redox buffers compatible with anion-sensing polymeric sensing membranes that can be incorporated into the inner filling solution of an ISE. Here, we introduce a novel hydrophilic redox buffer, cobalt(II/III) bis(terpyridine), and show the improvement of the standard deviation of E 0 of chloride sensors from 2.7 to 0.3 mV upon introduction of the redox buffer into the inner filing solution of conventional, rod-shaped electrodes. The redox buffer is also compatible with a textile-based sensing platform, which was shown by incorporation into a textile-based platform with embedded ion-sensing and reference membranes. As only a surprisingly small number of hydrophilic redox buffers have been reported in the literature, the cobalt(II/III) bis(terpyridine) redox buffer may also find applications outside of the field of ISEs. [Display omitted] • Introduction of a novel hydrophilic redox buffer, cobalt(II/III) bis(terpyridine) • The redox buffer is compatible with a textile-based ion-selective electrodes • The redox buffer enables calibration-free sensing of chloride. [ABSTRACT FROM AUTHOR]

Solid-contact ion-selective electrodes (SC-ISEs) exhibit great potential in the detection of routine and portable ions which rely on solid-contact (SC) materials for the transduction of ions to electron signals. Carbon-based materials are state-of-the-art SC transducers due to their high electrical double-layer (EDL) capacitance and hydrophobicity. However, researchers have long searched for ways to enhance the interfacial capacitance in order to improve the potential stability. Herein, three representative carbon-based SC materials including nitrogen-doped mesoporous carbon (NMC), reduced graphene oxide (RGO), and carbon nanotubes (CNT) were compared. The results disclose that the NMC has the highest EDL capacitance owing to its mesopore structure and N-doping while maintaining high hydrophobicity so that no obvious water-layer effect was observed. The Ca2+-SC-ISEs based on the SC of NMC exhibited high potential stability compared with RGO and CNT. This work offers a guideline for the development of carbon-material-based SC-ISEs through mesoporous and N-doping engineering to improve the interfacial capacitance. The developed NMC-based solid-contact Ca2+-SC-ISE exhibited a Nernstian slope of 26.3 ± 3.1 mV dec−1 ranging from 10 μM to 0.1 M with a detection limit of 3.2 μM. Finally, a practical application using NMC-based SC-ISEs was demonstrated through Ca2+ ion analysis in mineral water and soil leaching solutions.

Sitagliptin, an oral antidiabetic drug, is an effective medication for lowering blood glucose level either as monotherapy or in combination with other antidiabetic drugs. This work aims for the fabrication of a potentiometric sensor for sitagliptin detection. The sensor was designed by doping the polyvinyl chloride polymeric ion-selective membrane with calix[4]arene as an ionophore which highly improved the linearity range (1 × 10−6—1 × 10−2 M), sensitivity, selectivity and limit of detection (6.3 × 10−7 M) compared to ionophore-free membrane. The method was then validated according to the International Council for Harmonization (ICH) guidelines. The sensor was successfully employed to determine sitagliptin in bulk and pharmaceutical dosage form without any pre-treatment steps. Moreover, to demonstrate the deployability of the proposed sensor; it has been applied for the dissolution testing of sitagliptin by in-line continuous monitoring of sitagliptin release as a function of time from the pharmaceutical dosage form into the dissolution medium. This in-line dissolution monitoring has many advantages such as there is no need for the frequent sampling followed by the complicated procedures of samples treatment. Finally, the proposed potentiometric method was evaluated using the analytical eco-scale and has proved to be excellent green analysis in which solvent consumption and pre-treatment of samples were not necessary for its application. [ABSTRACT FROM AUTHOR]

Here, two screen-printed electrodes modified with multi-walled carbon nanotubes alone (electrode III) or along with a triazole-based ionic liquid (electrode VII) were developed for sensitive uranium(VI) determination. The electrodes exhibited calibration slopes of 25.10 ± 1.35 and 29.93 ± 0.88 mV decade−1 over the concentration ranges of 1.0 × 10–5–1.0 × 10–1 and 4.7 × 10–7–1.0 × 10–1 mol L−1 for electrodes III and VII, respectively. The electrodes showed fast response times with a service life exceeding 5 months. The electrodes revealed good thermal stability and fairly high uranium(VI) selectivity over many cations and anions. The electrodes were successfully employed for sensitive detection of uranium(VI) in different water samples. [ABSTRACT FROM AUTHOR]

This paper firstly reports a general and powerful approach to evaluate the power spectral density (PSD) of the surface charge fluctuations, so-called “chemical noise”, from a generic set of reactions at the sensing surface of potentiometric sensors such as, for instance, Ion-Sensitive Field Effect Transistors (ISFETs). Starting from the master equation, the spectral noise signature of a reaction set is derived as a function of the reaction kinetic parameters and of the interface concentration of the ionic species. Secondly, we derive an equivalent surface admittance, whose thermal noise PSD produces a noise PSD equal to that of the surface charge fluctuations. We also show how to expand this surface admittance into stair-case RC networks, with a number of elementary cells equal to the number of surface reactions involved. This admittance can be included in circuit simulations coupled with a SPICE compact model of the underlying FET, to enable the physically based modelling of frequency dispersion and noise of the sensing layer when simulating the sensor and the read-out. Validation with existing models and literature results as well as new application examples are provided. The proposed methodology to compute the PSD from rate equations is amenable to use in different contexts where fluctuations are generated by random transitions between discrete states with given exchange rates. [ABSTRACT FROM AUTHOR]

Wearable sensors reflect the real–time physiological information and health status of individuals by continuously monitoring biochemical markers in biological fluids, including sweat, tears and saliva, and are a key technology to realize portable personalized medicine. Flexible electrochemical pH sensors can play a significant role in health since the pH level affects most biochemical reactions in the human body. pH indicators can be used for the diagnosis and treatment of diseases as well as the monitoring of biological processes. The performances and applications of wearable pH sensors depend significantly on the properties of the pH–sensitive materials used. At present, existing pH–sensitive materials are mainly based on polyaniline (PANI), hydrogen ionophores (HIs) and metal oxides (MOx). In this review, we will discuss the recent progress in wearable pH sensors based on these sensitive materials. Finally, a viewpoint for state–of–the–art wearable pH sensors and a discussion of their existing challenges are presented.

Novel cost-effective screen-printed potentiometric platforms for simple, fast, and accurate assessment of Fluoxetine (FLX) were designed and characterized. The potentiometric platforms integrate both the FLX sensor and the reference Ag/AgCl electrode. The sensors were based on the use of 4′-nitrobenzo-15-crown-5 (ionophore I), dibenzo-18-crown-6 (ionophore II), and 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) (ionophore III) as neutral carriers within a plasticized PVC matrix. Multiwalled carbon nanotubes (MWCNTs) were used as a lipophilic ion-to-electron transducing material and sodium tetrakis [3,5-bis(trifluoromethyl)phenyl] borate (NaTFPB) was used as an anionic excluder. The presented platforms revealed near-Nernstian potentiometric response with slopes of 56.2 ± 0.8, 56.3 ± 1.7 and 64.4 ± 0.2 mV/decade and detection limits of 5.2 × 10−6, 4.7 × 10−6 and 2.0 × 10−7 M in 10 mM Tris buffer solution, pH 7 for sensors based on ionophore I, II, and III, respectively. All measurements were carried out in 10 mM tris buffer solution at pH 7.0. The interfacial capacitance before and after insertion of the MWCNTs layer was evaluated for the presented sensors using the reverse-current chronopotentiometry. The sensors were introduced for successful determination of FLX drug in different pharmaceutical dosage forms. The results were compared with those obtained by the standard HPLC method. Recovery values were calculated after spiking fixed concentrations of FLX in different serum samples. The presented platforms can be potentially manufacturable at large scales and provide a portable, rapid, disposable, and cost-effective analytical tool for measuring FLX.

In this study, molecularly imprinted polymer (MIP) was prepared and used in the preparation of carbon paste electrode (CPE) for the quantification of bisoprolol fumarate (BF) in pure, pharmaceutical formulation and biological fluids. The selective MIP for BF was synthesized from methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross‐linker in dimethyl sulfoxide solution, BF as the template molecule and 2, 2‐azobisisobutyronitrile (AIBN) as the initiator. The non‐imprinted polymer (NIP) was synthesized by the same procedure, but in the absence of the template molecule then incorporated in the paste of the carbon paste electrodes (CPEs). The prepared MIP for BF and its corresponding NIP were well characterized using scanning electron microscopy (SEM), Fourier transform infrared spectrometer, and thermal gravimetric analysis (TGA). The MIP and NIP based CPEs were further used for the determination of BF and the obtained results indicated that the sensor modified by the MIP have much higher recognition power for the BF molecules than the NIP based sensor where the MIP based CPE exhibited a Nernstian response 29.50±0.55 mV decade−1 within a concentration range of 1.0×10−7–1.0×10−2 mol L−1and pH independence in the range 3.50–7.15. The proposed sensor has high selectivity over several possible interfering compounds. The obtained results by the proposed sensor were satisfactory with excellent percentage recovery and relative standard deviation and were comparable with those obtained from HPLC reported method. [ABSTRACT FROM AUTHOR]

Three new modified electrodes based on a well‐characterized Al(III)‐Dicloxacillin complex (Dicloxacillin: penicillin antibiotic) in the form of carbon‐paste, PVC and coated graphite were fabricated and investigated for determination of Al(III) ions in multivitamin syrup, tap water and soda cans. The developed sensors showed excellent sensitives to Al(III) ions with slopes in the range of 16.77–20.00 mV/concentration decade and detection limits of 4.04×10−4–3.16×10−7 mol L−1 as well as fast response time of 10–20 s. The electrodes were effectively applied as indicators in the potentiometric titration of Al(III) with disodium hydrogen phosphate. [ABSTRACT FROM AUTHOR]

Molecular imprinted polymers (MIPs) are tailor made from synthetic polymers and designed to mimic the recognition properties of natural biological affinity molecules. MIPs incorporate binding motifs complementary to target organic molecule shape and functional groups in order to mimic the complex binding surfaces of natural macromolecules. This confers selectivity and specificity, with the added advantage of artificial MIP polymer stability and ready adaptability to the fabrication and creation of miniaturised affinity interfaces for electrochemical sensing and extra‐laboratory testing. Their generic capability as robust sorbent phases for drug extraction and concentration allows for targeted, interfacial interrogation by the active electrochemical surface. A wide range of electrochemical sensing strategies has also been advanced in recent years, which is covered by this review. The review covers MIP functional principles, examples of MIP preparative routes and final assay outcomes for the measurement of small molecule drugs of biomedical, and also of potential environmental relevance. Some small molecules as examples of toxin and contaminant measurement are also given. A historic background to MIP development is provided, but the review mainly focuses on electrochemical sensor advances in the last five years. [ABSTRACT FROM AUTHOR]

Hybrid materials based on perfluorinated sulfonic acid Nafion-type membranes and poly-3,4-ethylenedioxythiophene (PEDOT) with a gradient distribution of the latter along the film length were synthesized by in situ oxidative polymerization. The initial monomer concentration (0.01 and 0.002 M) and the concentration ratio of the monomer to the oxidant (1/1.25 and 1/2.5) were varied. We studied the effect of the equilibrium and transport properties of the obtained materials on the characteristics of cross-sensitive DP-sensors (analytical signal is the Donnan potential) in aqueous solutions of procaine, lidocaine, and bupivacaine hydrochlorides, including those containing sodium chloride, in a concentration range from 1.0 × 10–4 to 1.0 × 10–2 M and pH from 2 to 6. The relative error in determining the active substance in the Novokain preparation using a DP-sensor based on the Nafion/PEDOT membrane (0.002 M, 1/2.5) was 0.4%. An array of DP-sensors based on Nafion and Nafion/PEDOT (0.002 M, 1/1.25) membranes was used to determine bupivacaine hydrochloride and sodium chloride in the Markain® Spinal preparation with an error of 11 and 6%, respectively. [ABSTRACT FROM AUTHOR]

The development of novel ionophores for ion‐selective sensors is a time‐consuming and tedious process requiring synthesis of candidate substances, preparation of plasticized polymeric membranes, and their thorough characterization with traditional protocols to assess sensitivity, selectivity and detection limits for target ions. The vast amount of literature data accumulated on various ion‐selective sensors allows for significant facilitation of the development through in silico experiments. In this report, we performed the feasibility study on the prediction of potentiometric Mg2+/Ca2+ selectivity for various amide ligands using quantitative structure‐property relationship (QSPR) modeling. The approach proved to be promising for ionophore screening purposes with achieved precision in prediction of the selectivity coefficient logK(Mg2+/Ca2+) of 0.5 in the range from −1.7 to +2.3. The study also shows a route for prediction of new potential ionophores with high selectivity values. [ABSTRACT FROM AUTHOR]