Solid-state Ion-selective Electrodes Research Articles

Pinecone derived hierarchical carbon nanostructure as a transducer in a solid-state ion-selective electrode for in vivo analysis of calcium ion

Monitoring extracellular calcium ion (Ca2+) chemical signals in neurons is crucial for tracking physiological and pathological changes associated with brain diseases in live animals. Potentiometry based solid-state ion-selective electrodes (ISEs) with the assist of functional carbon nanomaterials as ideal solid-contact layer could realize the potential response for in vitro and in vivo analysis. Herein, we employ a kind of biomass derived porous carbon as a transducing layer to prompt efficient ion to electron transduction while stabilizes the potential drift. The eco-friendly porous carbon after activation (APB) displays a high specific area with inherit macropores, micropores, and large specific capacitance. When employed as transducer in ISEs, a stable potential response, minimized potential drift can be obtained. Benefiting from these excellent properties, a solid-state Ca2+ selective carbon fiber electrodes (CFEs) with a sandwich structure is constructed and employed for real time sensing of Ca2+ under electrical stimulation. This study presents a new approach to develop sustainable and versatile transducers in solid-state ISEs, a crucial way for in vivo sensing.

Paper-Based Analytical Device Based on Potentiometric Transduction for Sensitive Determination of Phenobarbital.

In medicine, barbiturates are a class of depressive medications used as hypnotics, anticonvulsants, and anxiolytics. For the treatment of specific forms of epilepsy and seizures in young children in underdeveloped countries, the World Health Organization recommends phenobarbital (PBAR), a barbiturate drug. This review describes the fabrication and characterization of a paper-based analytical apparatus for phenobarbital detection that is straightforward, affordable, portable, and disposable. All of the solid-state ion-selective electrodes (ISEs) for PBAR as well as a Ag/AgCl reference electrode were constructed and optimized on a nonconductive paper substrate. Using carbon nanotube ink, the sensors were made to function as an ion-to-electron transducer and to make the paper conductive. A suitable polymeric membrane is drop-cast onto the surface of the carbon ink orifice. The pyrido-tetrapeptide and pyrido-hexapeptide derivatives, which were recently synthesized, functioned as distinct ionophores in the PBAR-membrane sensor, enabling its detection. With a detection limit of 5.0 × 10-7 M, the manufactured analytical device demonstrated a Nernstian response to PBAR anions in 50 mM phosphate buffer, pH 8.5, over a linear range of 1.0 × 10-6 to 1.0 × 10-3 M. The PBAR-based sensors showed quick (less than 5 s) response times for PBAR ion detection. The modified separate solution method was utilized to evaluate the selectivity pattern of these novel ionophores with respect to PBAR ions in comparison to other common anions. The analytical instrument that was exhibited on paper had good precision both within and between days. The suggested technology assisted in the detection of trace amounts of PBAR in real pharmaceutical samples. A comparison was made between the data acquired using the HPLC reference method and the information obtained by the recommended potentiometric approach. The described paper-based analytical device may be a good choice for point-of-care PBAR determination because it is cheap and easy to find and can self-pump (especially when combined with potentiometric detection).

Solid-state ion-selective electrodes for the first potentiometric determination of the anti-COVID 19 drug Remdesivir in human plasma; A comparative study

Establishing sensitive and targeted analytical methodologies for drug identification in biological fluids as well as screening of treatments that can counteract the most severe COVID-19 infection-related side effects are of utmost importance. Here, first attempts have been made for determination of the anti-COVID drug Remdesivir (RDS) in human plasma using four potentiometric sensors. Calixarene-8 (CX8) was used as an ionophore applied to the first electrode (Sensor I). The second had a layer of dispersed graphene nanocomposite coating (Sensor II). (Sensor III) was fabricated using nanoparticles of polyaniline (PANI) as ion-to–electron transducer. A reverse-phase polymerization using polyvinylpyrrolidone (PVP) was employed to create a graphene-polyaniline (G/PANI) nanocomposite electrode (Sensor IV). Surface morphology was confirmed by Scanning Electron Microscope (SEM). UV absorption spectra and Fourier Transform Ion Spectrophotometry (FTIR) also supported their structural characterization. The impact of graphene and polyaniline integration on the functionality and durability of the manufactured sensors was examined using the water layer test and signal drift. In the ranges of concentration of 10−7 to 10−2 mol/L and 10−7 to 10−3, sensors II & IV exhibited linear responses; respectively while sensors I & III displayed linearity within 10−6 to 10−2 mol/L. The target drug was easily detectable using LOD down to 100 nmol/L. The developed sensors satisfactorily offered sensitive, stable, selective and accurate estimate of Remdesivir (RDS) in its pharmaceutical formulation as well as spiked human plasma with recoveries ranging from 91.02 to 95.76 % with average standard deviations less than 1.85. The suggested procedure was approved in accordance with ICH recommendations.

Novel fabricated potentiometric sensors for selective determination of carbinoxamine with different greenness evaluation perspectives

Electrochemical sensors, such as ion-selective electrodes (ISEs) is one of the promising green analytical techniques with significant advances that opens up new frontiers of its application. In this contribution, we developed and validated novel potentiometric sensing method for selective monitoring of carbinoxamine maleate (CRX) in presence of the co-formulated drugs. A comparative potentiometric study was employed using a dual design of ISEs; a classical liquid inner-contact and solid-contact sensors. Herein, a full investigation of the opportunities and challenges offered by the two ISEs assemblies and configurations were discussed. Taking into consideration the impressive added values of solid-contact ISEsover the conventional ones, including: being eco-friendly, real-time analyzers, portable, disposal, maintenance-free, easily miniaturized, and compatible with microfabrication technologies. The backbone of the solid contact electrode is the incorporation of ionophore (2-hydroxypropyl-β-cyclodextrin) as supramolecular element and a network of multi-walled carbon nanotubes as ion-to-electron transducer in a single-piece nanocomposite membrane. Besides, the fabrication of solid-state ISEs was performed via simple one-step drop casting of the ion sensing mixture on surface of microfabricated electrode.Furthermore, the morphological and structural features of the obtained membrane were characterized using Raman spectroscopy and scanning electron microscopy (SEM) techniques. The suggested sensors were successfully applied for quantitation of CRX in its pure and dosage form. Performances of fabricated sensors were assessed as per IUPAC recommendations. The outcomes of the proposed method were statistically benchmarked to the official approach, where no significant difference was found. Moreover, a comprehensive greenness evaluation of the investigated method was performed via various green-metrics, namely, GAM, Eco-Scale, GAPI and AGREE algorithm which is utilized 12 principles of green analytical chemistry. Finally, studying the whiteness degree of the established method was conducted using the recently introduced RGB12 model.

The New Reliable pH Sensor Based on Hydrous Iridium Dioxide and Its Composites

The new reliable sensor for pH determination was designed with the use of hydrous iridium dioxide and its composites. Three different hIrO2-based materials were prepared and applied as solid-contact layers in pH-selective electrodes with polymeric membrane. The material choice included standalone hydrous iridium oxide; composite material of hydrous iridium oxide, carbon nanotubes, and triple composite material composed of hydrous iridium oxide; carbon nanotubes; and poly(3-octylthiophene-2,5-diyl). The paper depicts that the addition of functional material to standalone metal oxide is beneficial for the performance of solid-state ion-selective electrodes and presents the universal approach to designing this type of sensors. Each component contributed differently to the sensors' performance-the addition of carbon nanotubes increased the electrical capacitance of sensor (up to 400 µF) while the addition of conducting polymer allowed it to increase the contact angle of material changing its wetting properties and enhancing the stability of potentiometric response. Hydrous iridium oxide contacted electrodes exhibit linear response in wide linear range of pH (2-11) and stable potentiometric response (the lowest potential drift of 0.036 mV/h is attributed to the electrode with triple composite material).

Solid-State Ion-Selective pH Sensor

pH sensors are widely used in various applications such as agriculture, wastewater monitoring, and biomedical engineering. Solid-state ion-selective electrodes (ISEs) have been developed to enable the miniaturization of pH sensors. This paper evaluated the pH sensing electrodes based on hydrogen ionophores or pH-sensitive emeraldine-polyaniline. A miniaturized leak-free reference electrode was integrated with pH sensing electrodes. A multiple-channel electromotive force recording unit was built to facilitate the measurement of multiple ISEs. The sensitivity and dynamic range were assessed using the pH solutions from pH 1.3 to pH 10. The conductance and capacitance of different ISEs were measured and compared. We evaluated the longevity and stability of the emeraldine-polyaniline-based pH sensor, and the drifting was less than 4 mV/day.

Calibration-free Solid-State Ion-Selective Electrode Based on a Polarized PEDOT/PEDOT-S-Doped Copolymer as Back Contact.

Solid-contact ion-selective electrodes (ISEs) have the inherent advantage of being miniaturized in addition to maintaining high selectivity and sensitivity of the ionophore-based ISE. The major disadvantage of ISEs is the necessity of performing a calibration curve (varying the intercept in the linear calibration curve equation) each time before running experiments, which limits their application as one-time disposable sensors or for use in remote water sample analysis. To overcome these challenges, we designed a unique back contact made of 3,4-ethylenedioxythiophene (EDOT) and 4-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl-methoxy)-1-butanesulfonic acid, sodium salt (EDOT-S). The calibration-free ISEs showed near Nernstian responses of 57.2 ± 0.2 mV/log [K+] and 28.5 ± 0.3 mV/log [Ca2+], while maintaining their respective selectivity against major interfering ions. The detection limits for Ca2+ and K+ ISEs were 0.45 ± 0.01 and 1.68 ± 0.18 μM, respectively. The charging cycles of the PEDOT: PEDOT-S back contact allowed us to fix the background potential at a desired fixed intercept value across different ionophores (K+, Ca2+). This protocol was used to determine the K+ and Ca2+ contents in creek water samples. The activity and concentration of [Ca2+] and [K+] in a local creek was found to be 257 ± 7.3 and 28.1 ± 1.1 μM, respectively.

Electrospraying Zwitterionic Copolymers as an Effective Biofouling Control for Accurate and Continuous Monitoring of Wastewater Dynamics in a Real-Time and Long-Term Manner.

Long-term continuous monitoring (LTCM) of water quality can provide high-fidelity datasets essential for executing swift control and enhancing system efficiency. One roadblock for LTCM using solid-state ion-selective electrode (S-ISE) sensors is biofouling on the sensor surface, which perturbs analyte mass transfer and deteriorates the sensor reading accuracy. This study advanced the anti-biofouling property of S-ISE sensors through precisely coating a self-assembled channel-type zwitterionic copolymer poly(trifluoroethyl methacrylate-random-sulfobetaine methacrylate) (PTFEMA-r-SBMA) on the sensor surface using electrospray. The PTFEMA-r-SBMA membrane exhibits exceptional permeability and selectivity to primary ions in water solutions. NH4+ S-ISE sensors with this anti-fouling zwitterionic layer were examined in real wastewater for 55 days consecutively, exhibiting sensitivity close to the theoretical value (59.18 mV/dec) and long-term stability (error <4 mg/L). Furthermore, a denoising data processing algorithm (DDPA) was developed to further improve the sensor accuracy, reducing the S-ISE sensor error to only 1.2 mg/L after 50 days of real wastewater analysis. Based on the dynamic energy cost function and carbon footprint models, LTCM is expected to save 44.9% NH4+ discharge, 12.8% energy consumption, and 26.7% greenhouse emission under normal operational conditions. This study unveils an innovative LTCM methodology by integrating advanced materials (anti-fouling layer coating) with sensor data processing (DDPA).

Research Progress of Miniaturized Solid State Ion Selective Electrode

Compared with the traditional liquid junction ion selective electrode, the all-solid-state ion selective electrodes have the advantages of miniaturization, miniaturization. The all-solid-state ion-selective electrode have been applied to on-site rapid detection in environmental testing, industrial analysis, and clinical testing. This paper focuses on the application of screen printing technology, paper chip technology and microfluidic technology in the miniaturization of solid-state ion selective electrodes, and looks forward to the future development trend.

The New Ion-Selective Electrodes Developed for Ferric Cations Determination, Modified with Synthesized Al and Fe-Based Nanoparticles.

The solid-state ion-selective electrodes presented here are based on the FePO4:Ag2S:polytetrafluoroethylene (PTFE) = 1:1:2 with an addition of (0.25–1)% microwave-synthesized hematite (α-Fe2O3), magnetite (Fe3O4), boehmite [γ-AlO(OH)], and alumina (Al2O3) nanoparticles (NPs) in order to establish ideal membrane composition for iron(III) cations determination. Synthesized NPs are characterized with Fourier-Transform Infrared (FTIR) spectroscopy, Powder X-Ray Diffraction (PXRD), and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS). The iron oxides NPs, more specifically, magnetite and hematite, showed a more positive effect on the sensing properties than boehmite and alumina NPs. The hematite NPs had the most significant effect on the linear range for the determination of ferric cations. The membrane containing 0.25% hematite NPs showed a slope of −19.75 mV per decade in the linear range from 1.2∙10−6 to 10−2 mol L−1, with a correlation factor of 0.9925. The recoveries for the determination of ferric cations in standard solutions were 99.4, 106.7, 93.6, and 101.1% for different concentrations.

Ionic Liquid-Multiwalled Carbon Nanotubes Nanocomposite Based All Solid State Ion-Selective Electrode for the Determination of Copper in Water Samples

A new copper sensitive all solid-state ion-selective electrode was prepared using multiwalled carbon nanotubes-ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) nanocomposite as an additional membrane component. The effect of nanocomposite content in the membrane on the electrode parameters was investigated. The study compares, among others, detection limits, sensitivity, and the linearity ranges of calibration curves. Content 6 wt.% was considered optimal for obtaining an electrode with a Nernstian response of 29.8 mV/decade. An electrode with an optimal nanocomposite content in the membrane showed a lower limit of detection, a wider linear range and pH range, as well as better selectivity and potential stability compared to the unmodified electrode. It was successfully applied for copper determination in real water samples.

Comparative study of nitrate all solid state ion-selective electrode based on multiwalled carbon nanotubes-ionic liquid nanocomposite

Carbon nanotubes have enjoyed unflagging popularity in recent years. They are successfully used in many fields of science, including potentiometry for the construction of ion selective electrodes with solid contact. A new type of SC-ISEs sensitive to nitrate(V) ions using multiwalled carbon nanotubes-ionic liquid nanocomposite was prepared. The effect of the kind of carbon nanotubes on the parameters of SC-ISEs was investigated. The study compares, among others, detection limits, sensitivity and linearity ranges of characteristic curves, and stability of the potential measured for the tested electrodes. Electrochemical impedance spectroscopy and chronopotentiometric techniques were also used as research methods. It was found that the type of carbon nanotubes included in the nanocomposite influences both the metrological and electrical parameters of the obtained solid contact nitrate ion-selective electrode.

UV-Ozone Treated Modified Laser-Induced Graphene Based Electrochemical Sweat Sensor

Recent studies shows laser-induced graphene (LIG) based electrodes can be very effective for electrochemical sensing applications. In this work, we aim to develop a stable ion selective membrane (ISM) based sweat sensor using laser-induced graphene (LIG) as the electrode material. However, the surface of pristine LIG is hydrophobic. Hence, coating these hydrophobic LIG films with ISM produces low sensitivity in sensing applications. In this study, UV-Ozone irradiated laser-induced graphene (LIG) based electrodes were explored for sensing biomarkers like ion in sweat. Solid-state ion-selective electrodes (ISEs) sensitive to ions were fabricated by a two-step drop-coating process of polyvinyl chloride solution containing plasticizer, ionophore, and ion-exchanger on the LIG electrode. We found the ozone treatment process significantly increased the electrochemical active surface area (EASA) and porosity of the pristine LIG. Hydrophobic to hydrophilic transition induced by UV-Ozone treatment reduced the contact angle (CA), resulting in better permeation of the ion-selective membrane (ISM) into the ozonized LIG film. Raman spectroscopy and IR absorption studies indicate physisorption of ozone on LIG. The concentration of the ISM solution has a great influence on attachment to the O-LIG film. Here, we report the applicability of O-LIG as an electrochemical sensor towards the detection of sodium ion () using the open circuit potential (OCP) method. The performance of ozonized LIG (O-LIG) electrodes was much better than pristine LIG and screen printed carbon electrodes. The sensitivity of 60.2 ± 0.9 mV/ decade to Na+ ions and a lower limit of detection of 1 × 10-6 M was achieved using O-LIG based ISEs. Response time of the O-LIG based electrodes were around 1 min. The current study demonstrates that the LIG-based electrodes can be used as a flexible electrochemical sensing platform and is suitable for future wearable sensing devices. Keywords Laser-induced graphene; ion-selective electrode; wearable sensors; electrochemical sensor; sweat sensor.

Printed-Circuit-Board (PCB) Based Multiplex Sensor for Ion Sensing

Combining electrochemical sensing with microfluidic system presents an attractive approach for in vitro study of physiology and pathophysiology (e.g. organ-on-chip platform) [1] and for inline monitoring of environmental parameters (e.g. water quality) [2]. Ion-selective electrodes (ISE) are potentiometric sensors that measure activities of ions. They offer a simpler analytical method compare to voltammetric sensors or ISFETs. Solid-state ISEs differ from conventional ISEs in that the inner filling solution is replaced by a solid contact material. The removal of liquid compartment can make such sensor more durable and flexible, enabling it to be integrated with microfluidic device. In this work, we fabricated and evaluated a multiplex ion sensing platform by modifying the printed circuit board with solid-state ISEs. The choice of PCB platform allows straightforward multiplexing of electrodes and interfacing with downstream electronics by leveraging standardized PCB technology, which can also be cost effective in terms of fabrication. ISEs for potassium (K+) and nitrate (NO3-) approximately 1.5 mm in diameter were prepared by coating polymeric membrane and mesoporous carbon layers as the solid contact on a pre-patterned transfer tape. The electrode response was significantly stabilized by casting the membrane away from the underlying metal pads. The stabilizing effect was attributed to the increase of effective surface area of mesoporous carbon between membrane and conducting metal. The multiplex sensor was further integrated with a 3D printed microchamber for onchip analysis (Figure 1A). The K+ and NO3- electrodes displayed near-Nernstian slopes of 53 and -50 mV/dec (vs. Ag/AgCl/0.01 M Cl- reference) in KNO3 solutions, respectively. Despite some noise and baseline drift, both electrodes showed reasonable stability and reversibility upon switching solution (Figure 1B). The sensor can be stored dry between measurements. The slope of K+ electrode decayed over time, while NO3- electrode maintained sensitivity for at least one week. The slope decrease was likely due to the diffusion of ion-exchanger (tetraphenylborate) into the surrounding adhesive tape. During integration with the microchamber, the K+ electrode was also found subject to the bonding adhesive between the chamber and transfer tape, where possible reaction and/or degradation of the ion exchanger has caused complete loss of electrode response. Nevertheless, with further improvement, the PCB based multiplex ISEs provides a promising tool for ion sensing in many biomedical and environmental applications.

Stable Solid-State Microfabricated Potentiometric Sensor Based on Chitosan- Prussian Blue Nanocomposite Film for Amlodipine Selective Detection

Solid state ion-selective electrodes have a grown importance in advanced detection techniques especially with exploiting different solid contact transducing substances. Nowadays, various approaches focus on producing simple, sensitive, durable and significantly stable electrodes. Lower cost of production could be achieved by employing simple, economical and efficient materials in their fabrication. Herein, a solid state microfabricated copper electrode was firstly designed from a reasonably priced and easily fabricated copper printed circuit boards followed by applying chitosan-Prussian blue nanocomposite layer. Finally, amlodipine sensing membrane was added resulting in construction of an amlodipine sensing microfabricated solid-state electrode. The designed electrode was characterized by being miniaturized, durable, portable, easily fabricated, affordable and highly stable over 60 d with a potential drift value of 600 μV h−1. The microfabricated electrode revealed promising results upon the direct analysis of amlodipine besylate and the responses showed a good linear Nernstian pattern in the dynamic range of 1.0 ×10−5.5 to 1.0 ×10−3 mol l−1 with a slope of 55.1 mV/decade. The detection limit was found to be 2.0 ×10−6 mol l−1. Selective determination of the drug was successfully achieved in presence of its degradation product without any sample preparation steps.

Potentiometric ion-selective sensors based on UV-ozone irradiated laser-induced graphene electrode

Disposable devices for sensing biomarkers like Na+ ion in sweat was developed using UV-Ozone irradiated laser-induced graphene (LIG) based electrodes. Solid-state ion-selective electrodes (ISEs) sensitive to Na+ ions were fabricated by a two-step drop-coating process of polyvinyl chloride solution containing plasticizer, ionophore and ion-exchanger on LIG electrode. Hydrophobic to hydrophilic transition induced by UV-Ozone treatment reduced the contact angle, resulting in better permeation of the ion-selective membrane into the ozonized LIG film. Raman spectroscopy and IR absorption studies indicate physisorption of ozone on LIG. Performance of ozonized LIG (O-LIG) electrodes was much better than pristine LIG and screen-printed carbon electrodes. Sensitivity of 60.2 ± 0.9 mV/ decade to Na+ ions and a lower limit of detection of 1 × 10−6 M was achieved using O-LIG based ISEs. Response time of the devices were around 1 min.

Electrochemical Detection of Electrolytes Using a Solid-State Ion-Selective Electrode of Single-Piece Type Membrane.

This study aimed to develop simple electrochemical electrodes for the fast detection of chloride, sodium and potassium ions in human serum. A flat thin-film gold electrode was used as the detection electrode for chloride ions; a single-piece type membrane based solid-state ion-selective electrode (ISE), which was formed by covering a flat thin-film gold electrode with a mixture of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and ion-selective membrane (ISM), was developed for sodium and potassium ions detection. Through cyclic voltammetry (CV) and square-wave voltammetry (SWV), the detection data can be obtained within two minutes. The linear detection ranges in the standard samples of chloride, sodium, and potassium ions were 25–200 mM, 50–200 mM, and 2–10 mM, with the average relative standard deviation (RSD) of 0.79%, 1.65%, and 0.47% and the average recovery rates of 101%, 100% and 96%, respectively. Interference experiments with Na+, K+, Cl−, Ca2+, and Mg2+ ions demonstrated that the proposed detection electrodes have good selectivity. Moreover, the proposed detection electrodes have characteristics such as the ability to be prepared under relatively simple process conditions, excellent detection sensitivity, and low RSD, and the detection linear range is suitable for the Cl−, Na+ and K+ concentrations in human serum.

All-in-one, wireless, fully flexible sodium sensor system with integrated Au/CNT/Au nanocomposites

Abstract Advancements in functional nanomaterials and wearable electronics have demonstrated the use of solid-state ion-selective electrodes (SS-ISEs) for human health applications. Existing devices, however, still rely on separate and multiple components of flexible sensors, interconnectors, and rigid data acquisition units, which limits the wearability of the entire system on the skin for continuous analyte monitoring. Here, this paper introduces an all-in-one, wireless, fully flexible, sodium detection system that integrates gold-carbon nanotube-gold (Au/CNT/Au) sensors and flexible thin-film circuits, together on a soft elastomeric membrane. The nanocomposite sensor includes electrochemically deposited Au nanoparticles on a CNT transducer to improve the conductivity, capacitance, and interfacial contact between materials. A set of experimental electrochemical analysis confirms the high stability of the SS-ISE based on Au/CNT/Au nanocomposites. At the same time, the thin-film system shows mechanical robustness and reliability, even with repetitive bending up to 500 cycles. The fully flexible, sensor-circuit integrated system demonstrates stable sodium measurements when mounted on the skin with minimized motion artifacts. The measured sensitivity of the sodium sensor is 55.5 ± 0.3 mV/decade, along with less than 3% change when the entire device is mounted on the skin with continuous movements. Overall, the presented comprehensive study, including nanomaterials, nano-microfabrication, electrochemistry, and electronics, shows the enormous potential of the wireless all-in-one sensor system for seamless integration with various types of skin-mounted wearable health monitors.

Toward Long-Term Accurate and Continuous Monitoring of Nitrate in Wastewater Using Poly(tetrafluoroethylene) (PTFE)-Solid-State Ion-Selective Electrodes (S-ISEs).

Long-term accurate and continuous monitoring of nitrate (NO3-) concentration in wastewater and groundwater is critical for determining treatment efficiency and tracking contaminant transport. Current nitrate monitoring technologies, including colorimetric, chromatographic, biometric, and electrochemical sensors, are not feasible for continuous monitoring. This study addressed this challenge by modifying NO3- solid-state ion-selective electrodes (S-ISEs) with poly(tetrafluoroethylene) (PTFE, (C2F4)n). The PTFE-loaded S-ISE membrane polymer matrix reduces water layer formation between the membrane and electrode/solid contact, while paradoxically, the even more hydrophobic PTFE-loaded S-ISE membrane prevents bacterial attachment despite the opposite approach of hydrophilic modifications in other antifouling sensor designs. Specifically, an optimal ratio of 5% PTFE in the S-ISE polymer matrix was determined by a series of characterization tests in real wastewater. Five percent of PTFE alleviated biofouling to the sensor surface by enhancing the negative charge (-4.5 to -45.8 mV) and lowering surface roughness (Ra: 0.56 ± 0.02 nm). It simultaneously mitigated water layer formation between the membrane and electrode by increasing hydrophobicity (contact angle: 104°) and membrane adhesion and thus minimized the reading (mV) drift in the baseline sensitivity ("data drifting"). Long-term accuracy and durability of 5% PTFE-loaded NO3- S-ISEs were well demonstrated in real wastewater over 20 days, an improvement over commercial sensor longevity.

Simultaneous Quantification of Nine Major Water-Soluble Inorganic Ions Using a Potentiometric Electronic Tongue in Cheese Samples

This study presents the applicability of a new potentiometric electronic tongue (ET) for simultaneous quantification of nine ions (Na+, K+, Ca2+, Mg2+, Cl−, PO43−, SO42−, NO3−, and NH4+) in various kind of commercial cheese samples. A sensor array comprising 12 solid-state ion-selective electrodes was employed; whose recognition elements were various selectophores with specific and generic responses. A Bayesian regularization algorithm was applied in the topology of the selected artificial neural networks (ANNs) with 12 inputs, 3 and 9 neurons in the hidden and output layers, respectively. A train set of 30 solution standards were set up to establish the model. For evaluation of the model validation, 10 external test solutions were applied and the model accurately predicted the concentration of all ions in these synthetic solutions. The results of a paired student’s t-test indicated no significant variation between nominal and obtained concentrations in the validation set, confirming the applicability of proposed ET for simultaneous quantitative analyses of ions. Finally, Mineral ion content of 18 commercial cheese samples was determined by ET. The results showed an improvement from 65.0% to less than 12.5%) according to ion chromatography reference method (for all relative errors in comparison with ion-selective electrodes individually. It is believed that the proposed ET system can be potentially applied as a suitable device for multiple determinations of common mineral ions in the food industry.