Ion-selective Sensors Research Articles

Probe anchored porous organic polymer monolithic architectures as optical sensor for ultra-trace analysis of Hg2+ in water samples

In this article, we have demonstrated an effective strategy to detect and remove the toxic Hg2+ by an ion-selective optical sensor using chromoionophoric receptor that is homogenously dispersed onto the surface of porous organic polymer (POP) template. Herein, we present a detailed summation of the synthesis of different POPs by employing various kinds of monomers and crosslinkers to discover excellent structural property materials that could cater to the needs of an optical sensor. The resultant POP from the bulk polymerization of N,N-dimethyl allylamine (DMA), and trimethylolpropane triacrylate (TMPTA), i.e., poly(DMA-co-TMPTA), manifested a higher surface area with pore size, thus has been utilized as the substrate material for the fabrication of the sensor. Further, the chromoionophoric coordinating ligand, i.e., 7-4(diethylamino)phenyldiazenyl quinolin-8-ol (DPDQ), is immobilized as receptor molecules onto the POP template for ultra-trace detection of Hg2+. The surface dispersed receptor forms stable 1:1 charge-transfer complexes [Hg2+-DPDQ] with a striking naked-eye color transition from pale orange to bright reddish-brown. The developed optical sensor offers an ultra-fast, selective response for Hg2+ with a lower detection limit of 0.1 μg/L (ppb) in the linear range of 0–100 μg/L. The regeneration of the sensor is envisaged with 0.02 M HCl and can be reused for up to six sensing cycles. Actual water samples from different geographical locations of India are tested using the developed sensor, and the method proved effective for real-time monitoring of Hg2+.

All-electrical antibiotic susceptibility testing within 30 min using silicon nano transistors

Rapid and reliable antibiotic susceptibility testing (AST) platform is highly desired to select the right antibiotics to treat infectious disease at early stage. Here, we demonstrate rapid ASTs using nanoscale silicon ion-selective field-effect transistor sensors. Our sensors profile bacterial metabolic kinetics by monitoring the metabolism induced acidification in the growth media with the absence and the presence of different antibiotics. Rapid AST results could be determined from the metabolic profiles with a total assay time less than 30 min for different bacterial strains. In addition, the sensors could also distinguish the bactericidal mechanisms for antibiotics with different modes of actions. Furthermore, the initial bacterial concentration in an unknown sample, a key parameter to determine its clinic relevance, could be estimated based on the metabolic profiles. Our demonstrated AST method is all-electrical, label-free and silicon technology compatible, and holds great promise for the development of a high-throughput and low-cost point-of-care device.

Synthesis, Reactivity, and Applications of 4-Amino-3-Thioxo/Hydrazino-6-Substituted-1,2,4-Triazin-5-Ones and Their Derivatives: A Review

Triazine derivatives have attracted increasing attention due to their diverse applications in medicinal chemistry. They have been reported to be remarkably effective compounds regarding their bioactivities. Therefore, the synthesis and identification of new triazine-derived compounds are of interest for their therapeutic effects. Various approaches have been developed to synthesize triazine derivatives. In this review, a considerable number of studies on the synthesis of 1,2,4-triazine derivatives are investigated with 4-amino-3-thioxo-6-substituted-1,2,4-triazin-ones and 4-amino-3-hydrazino-6-substituted-1,2,4-triazin-5-ones as starting materials. Different types of chemical reactions have been applied to the efficient synthesis of 3-thioxo/hydrazino-6-substituted-1,2,4-triazin-5-ones, such as alkylation, acylation, aroylation, elimination, substitution, acidic/basic hydrolysis, oxidation, cyclocondensation, cycloaddition, phosphorylation, and complexation reactions. Interestingly, a set of compounds is identified to possess various biological activities, such as anticancer antibacterial, antifungal, acaricidal, and molluscicidal properties. Also, some 4-amino-3-thioxo-6-substituted-1,2,4-triazin-5-one derivatives are found to form metal complexes, be used as inhibitor probes for mild steel corrosion, prepare a selective sensor for the determination of gadolinium (III) ions in the soil and sediment samples, and demonstrate antibacterial activities. Finally, 4-amino-3-hydrazino-6-methyl-1,2,4-triazin-5-one was used as an ionophore to develop a chromium (III) ion-selective sensor beside the formation of silver complexes.

Teer and Voltammetric Ion Selective Transwell-Integrated Sensors System for Caco-2 Cell Model

Teer and Voltammetric Ion Selective Transwell-Integrated Sensors System for Caco-2 Cell Model

Laser-Induced Graphene as Wearable Epidermal Ion-Selective Sensors for Noninvasive Multiplexed Sweat Analysis

Laser-Induced Graphene as Wearable Epidermal Ion-Selective Sensors for Noninvasive Multiplexed Sweat Analysis

Highly Stable Potentiometric (Bio)Sensor for Urea and Urease Activity Determination.

There is growing interest for bioanalytical tools that might be designed for a specific user, primarily for research purposes. In this perspective, a new, highly stable potentiometric sensor based on glassy carbon/polyazulene/NH4+-selective membrane was developed and utilized for urease activity determination. Urease–urea interaction studies were carried out and the Michaelis–Menten constant was established for this enzymatic reaction. Biofunctionalization of the ammonium ion-selective sensor with urease lead to urea biosensor with remarkably good potential stability (drift coefficient ~0.9 mV/h) and short response time (t95% = 36 s). The prepared biosensor showed the Nernstian response (S = 52.4 ± 0.7 mV/dec) in the urea concentration range from 0.01 to 20 mM, stable for the experimental time of 60 days. In addition, some insights into electrical properties of the ion-to-electron transducing layer resulting from impedance spectroscopy measurements are presented. Based on the RCQ equivalent circuits comparison, it can be drawn that the polyazulene (PAz) layer shows the least capacitive behavior, which might result in good time stability of the sensor in respect to response as well as potential E0. Both the polyazulene-based solid-contact ion selective electrodes and urea biosensors were successfully used in trial studies for determination of ammonium ion and urea in human saliva samples. The accuracy of ammonium ion and urea levels determination by potentiometric method was confirmed by two reference spectrophotometric methods.

Enhancing long-term accuracy and durability of wastewater monitoring using electrosprayed ultra-thin solid-state ion selective membrane sensors

Current membrane deposition approaches (e.g., drop-casting, spin-coating) for solid-state ion selective membrane (S-ISM) sensors suffer from problems including sensor material waste, uncontrollable membrane thickness (100–200 μm), loose contact between sensing membrane and electrode surface, long response time (e.g., >20 s) and poor reading stability (e.g., >3 mV/h). This study addressed these challenges by depositing ISM through electrospray printing technology and enabling accurate and continuous monitoring in water and wastewater. Specifically, the final droplet size and the splash diameter of the electrosprayed droplets deposited a particularly tunable, high resolution and ultra-thin (thickness: ∼1 μm) membrane on the electrode surface, which immensely shortened the sensor response time (9.2 s), strengthened the adhesion between the ISM and the electrode surface, mitigated the formation of water layer in the S-ISM sensor entity, and ultimately enhanced the sensor reading stability (reading drifting <0.66 mV/h). Additionally, the ion diffusion model developed in this study confirmed that fast ion diffusion in the electrosprayed S-ISM polymer matrix effectively shortened the response time of sensors. Electrosprayed S-ISM sensors without anti-fouling protection exhibited high stability and accuracy with an error of less than 2.9 mg/L after continuously monitoring wastewater for 10 days, revealing a great potential for further enhancement.

All-Solid-State Ion-Selective Electrodes: A Tutorial for Correct Practice

The research on ion-measuring devices has seen a rapid expansion in the last years as a consequence of the growing interest in wearable sensors for biofluids analysis and in portable devices for remote or in-line water and food quality monitoring. As a result, an increasing number of researchers is approaching the field of ion-selective sensors. Despite the apparently simple transduction principle, the theory behind their working mechanism is far from trivial and a correct understanding is necessary for an optimal exploitation of the technology. In current literature, imprecise characterization procedures lead to the definition of misleading sensors parameters, which cannot be effectively used for comparisons. In fact, some unique definitions and procedures applies to this category of sensors, which significantly differ from the traditional ones applied in sensing research. This tutorial aims at highlighting the basic thermodynamic theory and the correct experimental practice for the accurate and reproducible characterization of potentiometric ion-sensors. The most important requirements and design considerations on hardware and software interfaces will also be discussed to give a complete overview of the various aspects of current technology to people approaching this promising area of sensing.

Cubosome Based Ion-Selective Optodes-Toward Tunable Biocompatible Sensors.

We report here on a new generation of optical ion-selective sensors benefiting from cubosomes or hexosomes–nanostructural lipid liquid phase. Cubosome as well as hexosome optodes offer biocompatibility, self-assembly preparation, high stability in solution, and unique, tunable analytical performance. The temperature trigger reversibly changes the lipid nanoparticle internal structure–changing analyte access to the bulk of the probe and ultimately affecting the response pattern. Thus, cubosome or hexosome optodes are highly promising alternatives to conventional polymeric based optical nanoprobes.

Developing potentiometric sensors for scandium

Scandium is a rare earth element that is not very abundant on Earth, however in recent years due to the employment of scandium in various high-tech fields the interest in the analytical chemistry of this metal is growing. Currently, the methods for scandium quantification are mainly based on inductively coupled plasma atomic emission and mass-spectrometry and to the best of our knowledge no potentiometric sensors for scandium detection were reported so far. This study is devoted to the development of simple and cost-effective ion-selective sensors for quantification of Sc3+ in aqueous media. Employing the variety of lipophilic ligands suggested in liquid extraction for separation of lanthanides and actinides we synthesized a series of plasticized polymeric sensor membranes that have shown pronounced sensitivity to Sc3+ in acidic aqueous solutions, reaching in some cases super-Nernstian values around 30 mV/dec. The selectivity of the sensors was studied with respect to transition metals, lanthanides and yttrium and it was found that most of the developed sensors are selective towards scandium. The real-life applicability of the sensors was demonstrated in quantification of scandium in industrial solutions – hydrolytic sulfuric acid obtained from pigment titanium dioxide production. We believe these sensors can be considered as a promising alternative to conventional analytical methods in technological process monitoring task.

Laser-induced graphene electrodes for electrochemical ion sensing, pesticide monitoring, and water splitting.

Laser-induced graphene (LIG) has shown to be a scalable manufacturing route to create graphene electrodes that overcome the expense associated with conventional graphene electrode fabrication. Herein, we expand upon initial LIG reports by functionalizing the LIG with metallic nanoparticles for ion sensing, pesticide monitoring, and water splitting. The LIG electrodes were converted into ion-selective sensors by functionalization with poly(vinyl chloride)-based membranes containing K+ and H+ ionophores. These ion-selective sensors exhibited a rapid response time (10-15s), near-Nernstian sensitivity (53.0mV/dec for the K+ sensor and - 56.6mV/pH for the pH sensor), and long storage stability for 40days, and were capable of ion monitoring in artificial urine. The pesticide biosensors were created by functionalizing the LIG electrodes with the enzyme horseradish peroxidase and displayed a high sensitivity to atrazine (28.9nA/μM) with negligible inference from other common herbicides (glyphosate, dicamba, and 2,4-dichlorophenoxyacetic acid). Finally, the LIG electrodes also exhibited a small overpotential for hydrogen evolution reaction and oxygen evolution reaction. The oxygen evolution reaction tests yielded overpotentials of 448mV and 995mV for 10mA/cm2 and 100mA/cm2, respectively. The hydrogen evolution reaction tests yielded 35mV and 281mV for the corresponding current densities. Such a versatile LIG platform paves the way for simple, efficient electrochemical sensing and energy harvesting applications.

Highly stable potentiometric sensor with reduced graphene oxide aerogel as a solid contact for detection of nitrate and calcium ions

• 3D reduced graphene oxide aerogel (rGOA) was synthesised through self-assembly of graphene oxide via heat treatment. • The sensor exhibited outstanding response, due to the large surface area and excellent electrical conductivity of rGOA. • Long-term stability of the sensor improved owing to the hydrophobicity of rGOA. • NO 3 – and Ca 2+ were detected in perilla leaves using the proposed sensor, and this result was in good agreement with the ICP and IC analysis results. Numerous reports have elucidated the importance of detecting of NO 3 − and Ca 2+ ions for monitoring their levels to optimize crop growth. Herein, we prepared a reduced graphene oxide aerogel (rGOA) as a promising solid-contact material for manufacturing a highly stable solid contact ion-selective electrode (SC-ISE) for monitoring to NO 3 − and Ca 2+ . The rGOA was synthesized through self-assembly of graphene oxide via heat treatment. Cyclic voltammetry and chronopotentilmetry were employed to demonstrate the fast charge transfer and large double layer capacitance of the rGOA layer modified electrode. The sensor comprising rGOA exhibited excellent Nernstian responses (59.1 mV/log [NO 3 − ] and 28.4 mV/log [Ca 2+ ]) and ion detection limits (759 nM for NO 3 − and 186 nM for Ca 2+ ) due to its outstanding electrical conductivity and large surface area of rGOA. The Ag/AgCl electrode with a polyvinyl butyral (PVB) film was used as the reference electrode. Water layer tests and potentiometry confirmed that the long-term stability of the electrode improved owing to the hydrophobicity of rGOA. Furthermore NO 3 − and Ca 2+ ions were detected in perilla leaf using the proposed ion-selective sensor, which was in agreement with the results of ion chromatography and inductively coupled plasma analyses. Thus, the proposed sensor provides an excellent sensing platform for the detection of inorganic ions in plant sap.

Akriloil Grup İçeren Schiff Bazlarının Potansiyometrik İyon-Seçici Sensörlerde İyonofor Olarak Kullanımının Araştırılması

Bu çalışmada, yeni sentezlenen iyonoforlar kullanılarak tümüyle katı-hal krom (III)-seçici potansiyometrik polivinil klorür (PVC) membran sensör geliştirildi. Bu amaçla yeni sentezlenen akriloil grup içeren (E)-4-(4-Nitro fenilimino) metil fenil akrilat (A1), (E)-4-(4-kloro fenilimino) metil fenil akrilat (A2) ve (E)-4-(4-hidroksibenzil dimino) benzoik asit akrilat (A3) schiff bazları iyonofor olarak kullanıldı. En uygun potansiyometrik özelliklere sahip membran bileşimi farklı oranlarda iyonoforlar (A1, A2 ve A3), plastikleştiriciler (o-nitrofeniloktil eter (o-NPOE)), bis (2-etilheksil) sebekat (DOS), dibutil ftalat (DBP) dioktil ftalat (DOP) ve PVC kullanılarak belirlendi. Ayrıca, potasyum tetrakisparaklorofenil borat (KTpClPB) ve sodyum tetrafenil borat (NaTPB) elektrotlarının doğrusal çalışma aralığına ve eğimine her onkat’lık iyon aktivitesi değişimine karşı etkisi de araştırıldı. Geliştirilen krom (III)-seçici sensör için % 1,0 A2 bileşiği, % 67,0 (a/a) o-NPOE ve % 32,0 (a/a) PVC oranları en uygun membran bileşimi olarak belirlendi. Geliştirilen krom (III)-seçici sensör pH 3,50’de 1,3×10-7−1,0×10-1 M konsantrasyon aralığında standart krom (III) iyon çözeltisine karşı doğrusal cevap sergiledi (R2= 0,9938). Sensör ile doğrusal çalışma aralığındaki her onkat’lık standart krom (III) konsantrasyon değişiminin ortalaması 27,12±0,81 mV’luk eğim değeri, tekrarlanabilir potansiyeller elde edildi. Geliştirilen tümüyle katı-hal krom (III)-seçici potansiyometrik PVC membran sensörün tayin limiti 6,3×10-8 M ve cevap süresi ≤10 s olarak belirlendi. Yaygın bazı katyon türlerinin geliştirilen sensör üzerindeki girişim etkileri incelendi. Önerilen sensörün analitik olarak kullanılıp kullanılamayacağını araştırmak için, gerçek numunelerde krom (III) iyonunun potansiyometrik tayini gerçekleştirildi. Elde edilen sonuçlar indüktif olarak eşleştirilmiş kütle spektrometresi (ICP-MS) metodu ile elde edilen verilerle istatiksel olarak karşılaştırıldı.

Exploitation of 2D Cu-MOF nanosheets as a unique electroactive material for ultrasensitive Cu(II) ion estimation in various real samples

Herein, hybrid carbon sensor has been developed with graphite sheets as a matrix, tricresyl phosphate (TCP) as a plasticizer and nanosheets of 2D Cu-MOF (metal-organic framework) as an electroactive material for the ultrasensitive Cu(II) ion detection in various real samples. Where, the present study proves the efficiency of 2D Cu-MOF as a promising sensing material for the development of Cu(II) ion selective carbon sensor. The developed 2D Cu-MOF nanosheets based sensor containing 2D Cu-MOF: TCP: graphite in the ratio of 2.67: 30.54: 66.79 (% wt/wt) displayed unique Nernstian behavior over two linearity ranges of 1.0 × 10−11-1.0 × 10−9 and 1.0 × 10−5-1.0 × 10−1 mol L−1 with slopes of 29.5 ± 0.25 and 29.6 ± 0.13 mV decade−1, respectively. The fabricated carbon sensor achieved a widely pH independency, fast response time and superior thermal stability with highly selective and ultrasensitive performance. Moreover, It has been efficiently applied for the Cu(II) ion potentiometric estimation in human hair, sesames seeds, two different tea infusions and tap water real samples.

Light-driven ion extraction of polymeric membranes for on-demand Cu(II) sensing

The modulation of the ion-fluxes across a polymeric membrane is important for designing attractive methodologies. As an alternative to the commonly used dynamic electrochemistry approaches, light can be used as an external stimulus and provides a very convenient way to manipulate ions release and/or extraction into a polymeric membrane. Herein, we designed a solid-contact polymeric membrane ion-selective sensor that exhibits dynamic response by light irradiation at 375 nm. The electrode membrane contains a light-sensitive lipophilic salt (bis(4-tert-butylphenyl)iodonium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (R+-R-, BTDT-TFPB) instead of traditional ion exchanger. Under light illumination, the decomposition of the lipophilic cation makes the membrane with ion-exchange properties. The solid-contact ion-selective electrodes based on potentiometry and constant potential coulometry have been explored for direct ion sensing. Copper was selected as a mode analyte and can be determined at micromole levels. The proposed dynamic ion sensors show promise for on-demand ion sensing.

A rapid cadmium determination based on ion selective membrane potentiometric sensor by bis (salicylaldehydo)ethylenediimine as carrier

An ion selective potentiometric electrode (IPE) was prepared based on salen material (bis(salicylaldehydo)ethylenediimine) as a suitable carrier for determination of cadmium ions. An acceptable response for cadmium ions obtained over a linear range 8 × 10−7 to 1.0 × 10−2 M with a slope of 29.8 ± 0.8 mV per decade of activity and a detection limit of 3.2 × 10−7 M for Cd (II) ions in water and liquid samples. It has a response time less than 10 s and can be used for at least 2.5 months without any measurable divergence in potential. The ion selective electrode can be used based on potential and potential changes in the pH range 3.5 to 6.5, so, the cadmium determination was obtained at independent pH. Moreover, the selectivity of proposed method in presence of interference ions was studied. The results showed that the other cations do not interfere significantly in response electrode at optimized pH. This electrode was successfully used for the determination of cadmium ions in aqueous samples. The validation was obtained based on ICP analyzer and certified reference material in water samples (CRM, NIST).

Prototyping of a Low-Cost Ion-Selective Electrode Sensor Unit for Determination of Lead Ions in Aqueous Samples

Exposure to lead via drinking water is a substantial health hazard. The current common practice of measuring lead levels in drinking water is to use analytical chemical analysis that involves sophisticated laboratory instruments. As lead contamination in drinking water is often a close-to-home contamination caused by corroded lead service pipes connecting households to main lines or lead-based pluming within the households, a low-cost and portable device that can be conveniently deployed to individual households to monitor lead levels in drinking water would offer consumers the opportunity to obtain first-hand information about the lead levels in their drinking water. The main objective of this study is to develop and prototype a portable low-cost device for detecting lead levels in drinking water. The lead-detecting device consists of two primary components: lead ion-selective electrode (ISE) sensing membrane and a microcontroller-based measuring unit. ISE membrane has proven to show low detection limits, good selectivity, low cost and great potential to be integrated in a miniature device. The ISE membrane in this study utilized polymeric membrane as the matrix with lead-selective ionophores embedded in the matrix. Hydroxyl type Vinyl Chloride-vinyl Acetate Terpolymer was used to create polymeric membrane matrix and allowed for all components to be housed in the membrane. The selected ionophore was Tert-Butylcalix(4)Arene-Tetrakis with its primary function is to differentiate and transport a specific ion (in this case, Pb2+ ions) through a membrane. A limit of detection of 1.0 ´ 10-8 M was achieved along with a linear Nernstian response over a lead concentration range from 1.0 ´ 10-8 M to 1.0 ´ 10-4 M. Durability test of the membrane showed a lifetime close to 30 days. A low-cost printed circuit board (PCB) was custom designed and created as an amplification unit to measure the ISE’s electromotive force (EMF). The custom-built device was able to capture the limit of detection (LOD) of the ISE sensing membrane and showed reasonably good consistency in comparison to measurements from commercial potentiostat.

A Highly Stable and Flexible Ca2+ Ion-Selective Sensor Based on Treated PEDOT:PSS Transducing Layer

In this work, a highly stable Ca <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ion-selective sensor was successfully developed by depositing a poly(3,4-ethylenedioxythiophene): poly(styrene-sulfonate) (PEDOT:PSS) layer on top of a carbon paste electrode as an ion-electron transducing layer. The PEDOT:PSS was treated by a co-solvent of ethylene glycol (EG) using the bath-sonication technique to enhance electrical and electrochemical characteristics, and finally coated with Ca <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ion-selective membrane cocktail. The developed Ca <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ion-selective electrode (Ca <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> -ISE) showed excellent electrochemical properties by much-improved charge transfer kinetics with remarkable electric conductivity. The fabricated Ca <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> -ISE exhibited an excellent sensitivity of 37.7 mV/decade (n = 4) in the range from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> M with a rapid response (< 20 seconds). Moreover, the EG-treated PEDOT:PSS (PEDOT:PSS-EG) based ISE showed negligible responses for primary interfering ions of human biofluid samples, proving significant potential selectivity. Furthermore, the negligible drift of open circuit potential ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.78~ { \mu }\text{V}$ </tex-math></inline-formula> /s) proved the stability of the PEDOT:PSS-EG compared to pristine PEDOT:PSS( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10.63~{ \mu }\text{V}$ </tex-math></inline-formula> /s) based ISE. Based on these analyses, it can be expected that the organic solvent treatment on PEDOT:PSS will pave the way for long-term monitoring of other biochemical compounds.

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.

Development of Flexible Ion-Selective Electrodes for Saliva Sodium Detection.

Saliva can be used for health monitoring with non-invasive wearable systems. Such devices, including electrochemical sensors, may provide a safe, fast, and cost-efficient way of detecting target ions. Although salivary ions are known to reflect those in blood, no available clinical device can detect essential ions directly from saliva. Here, we introduce an all-solid-state, flexible film sensor that allows highly accurate detection of sodium levels in saliva, comparable to those in blood. The wireless film sensor system can successfully measure sodium ions from a small volume of infants’ saliva (<400 µL), demonstrating its potential as a continuous health monitor. This study includes the structural characterization and error analysis of a carbon/elastomer-based ion-selective electrode and a reference electrode to confirm the signal reliability. The sensor, composed of a pair of the electrodes, shows good sensitivity (58.9 mV/decade) and selectivity (log K = −2.68 for potassium), along with a broad detection range of 5 × 10−5 ≈ 1 M with a low detection limit of 4.27 × 10−5 M. The simultaneous comparison between the film sensor and a commercial electrochemical sensor demonstrates the accuracy of the flexible sensor and a positive correlation in saliva-to-blood sodium levels. Collectively, the presented study shows the potential of the wireless ion-selective sensor system for a non-invasive, early disease diagnosis with saliva.