Solid-contact Potentiometric Sensors Research Articles

New solid state contact potentiometric sensor based on a thiosemicarbazone derivative molecule for determination of copper(II) ions in environmental samples

Thiosemicarbazone derivative molecules have proven to be good sensor materials in studies using various analytical methods. In this study, new ion–selective sensors were prepared using 2–furaldehyde thiosemicarbazone and their potentiometric properties were then tested. The prepared sensors exhibited a very good selectivity towards copper(II) ions over various ions. Surface images and mappings of the prepared sensors were examined by scanning electron microscopy. Copper(II)–selective sensors had a Nernstian response of 28.5 ± 1.5 mV/decade, and a low detection limit of 6.89 × 10-6 mol L-1 over a wide concentration range of 1.0 × 10-5–1.0 × 10-1 mol L-1 (R2 = 0.9992). The newly prepared copper(II)–selective sensors were shown to be produced reproducibly, stable and economically. The sensors, which can operate in a wide pH range of 5.0–9.0 without being affected by pH changes, had a fast response time of 5 s. The newly developed copper(II)–selective sensors were used as indicator electrodes for the potentiometric titration of copper(II) ions with ethylenediaminetetraacetic acid and were successfully applied for the determination of copper(II) ion content in various environmental samples with very good performance. The data obtained with the developed sensor were compared with atomic absorption spectroscopy and it was determined that the results of both methods were compatible with each other.

Design and application of supramolecular based solid-contact ion-selective electrode for selective green determination of tenofovir disoproxil fumarate

This work describes the fabrication of solid-contact potentiometric sensor to determine the antiviral drug; tenofovir disoproxil fumarate. Screen-printed carbon electrodes have been selected as being a disposable substrate material. Ion sensing membrane is based on Polyvinyl chloride (PVC) polymer that was impregnated with calix [6] arene as being an ionophore for facilitating transferring the drug of interest from the sample phase into the membrane phase through decreasing Gibbs free energy of transfer. We applied a graphene nanocomposite interlayer between the carbon substrate and the polymeric membrane for overcoming potential drift, which is commonly encountered in solid-contact potentiometric sensors. As a result, the graphene nanocomposite layer enhanced the sensor performance and stabilized the potential signal as compared to the control sensor. The sensor performance characteristics were studied according to International Union of Pure and Applied Chemistry (IUPAC) recommendations, and linear range has been 0.01 M - 10 μM with limit of detection (LOD) 7.3 μM. We utilized the sensor for inline determination of the release of tenofovir disoproxil fumarate from its tablet pharmaceutical formulation without any separation or sample pre-treatment steps. In an attempt to be eco-friendly through evaluating the suggested method regarding its greenness, the method has been found to be excellent green according to the eco scale method.

Poly(vinyl chloride)/Nanocarbon Composites for Advanced Potentiometric Membrane Sensor Design.

Polymer nanocomposites filled with carbon nanoparticles (CNPs) are a hot topic in materials science. This article discusses the current research on the use of these materials as interfacial electron transfer films for solid contact potentiometric membrane sensors (SC-PMSs). The results of a comparative study of plasticized poly (vinyl chloride) (pPVC) matrices modified with single-walled carbon nanotubes (SWCNTs), fullerenes-C60, and their hybrid ensemble (SWCNTs-C60) are reported. The morphological characteristics and electrical conductivity of the prepared nanostructured composite films are reported. It was found that the specific electrical conductivity of the pPVC/SWCNTs-C60 polymer film was higher than that of pPVC filled with individual nanocomponents. The effectiveness of this composite material as an electron transfer film in a new potentiometric membrane sensor for detecting phenylpyruvic acid (in anionic form) was demonstrated. Screening for this metabolic product of phenylalanine in body fluids is of significant diagnostic interest in phenylketonuria (dementia), viral hepatitis, and alcoholism. The developed sensor showed a stable and fast Nernstian response for phenylpyruvate ions in aqueous solutions over the wide linear concentration range of 5 × 10-7-1 × 10-3 M, with a detection limit of 10-7.2 M.

Carbon fiber-based multichannel solid-contact potentiometric ion sensors for real-time sweat electrolyte monitoring

Solid-contact ion-selective electrodes (SC-ISEs) feature miniaturization and integration that have gained extensive attention in non-invasive wearable sweat electrolyte sensors. The state-of-the-art wearable SC-ISEs mainly use polyethylene terephthalate, gold and carbon nanotube fibers as flexible substrates but suffer from uncomfortableness, high cost and biotoxicity. Herein, we report carbon fiber-based SC-ISEs to construct a four-channel wearable potentiometric sensor for sweat electrolytes monitoring (Na+/K+/pH/Cl−). The carbon fibers were extracted from commercial cloth, of which the starting point is addressing the cost and reproducibility issues for flexible SC-ISEs. The bare carbon fiber electrodes exhibited reversible voltammetric and stable impedance performances. Further fabricated SC-ISEs based on corresponding ion-selective membranes disclosed Nernstian sensitivity and anti-interface ability toward both ions and organic species in sweat. Significantly, these carbon fiber-based SC-ISEs revealed high reproducibility of standard potentials between normal and bending states. Finally, a textile-based sensor was integrated with a solid-contact reference electrode, which realized on-body sweat electrolytes analysis. The results displayed high accuracy compared with ex-situ tests by ion chromatography. This work highlights carbon fiber-based multichannel wearable potentiometric ion sensors with low cost, biocompatibility and reproducibility.

Utilization of a TiO2-CuO Bimetallic/Polyaniline Nanocomposite as a Transducer in a Solid Contact Potentiometric Sensor for the Determination of Vildagliptin.

Current fundamental electrochemical research shows the potential of utilizing polymeric nanostructured materials as ion-to-electron transducers. In this paper, aniline was polymerized in the presence of TiO2 and CuO nanoparticles to yield a bimetallic/PANI nanocomposite. It was applied as a transducer in a carbon paste electrode for the potentiometric determination of vildagliptin in the presence of 18-crown-6-ether as a recognition element. The electrode's potentiometric performance was studied according to the IUPAC guidelines. It exhibited a wide linearity range of 1 × 10-2 M to 1 × 10-8 M, remarkable sensitivity (LOD of 4.5 × 10-9 M), and a fast response time of 10 s ± 1.3. The sensor did not show any potential drift due to the absence of the water layer between the carbon paste and the metallic conductor. This endowed the sensor with high stability and a long lifetime, as 137 days passed without the need to change the carbon paste surface. The electrode was utilized for the determination of the concentration of vildagliptin in bulk, pharmaceutical tablets, and human plasma, with average recovery ranging from 97.65% to 100.03%.

FAST (Flexible Acetylcholine Sensing Thread): Real-Time Detection of Acetylcholine with a Flexible Solid-Contact Potentiometric Sensor.

Acetylcholine (ACh) is involved in memory and learning and has implications in neurodegenerative diseases; it is therefore important to study the dynamics of ACh in the brain. This work creates a flexible solid-contact potentiometric sensor for in vitro and in vivo recording of ACh in the brain and tissue homogenate. We fabricate this sensor using a 250 μm diameter cotton yarn coated with a flexible conductive ink and an ACh sensing membrane that contains a calix[4]arene ionophore. The exposed ion-to-electron transducer was sealed with a 2.5 μm thick Parylene C coating to maintain the flexibility of the sensor. The resulting diameter of the flexible ACh sensing thread (FAST) was 400 μm. The FAST showed a linear response range from 1.0 μM to 10.0 mM in deionized water, with a near-Nernstian slope of 56.11 mV/decade and a limit of detection of 2.6 μM. In artificial cerebrospinal fluid, the limit of detection increased to 20 μM due to the background signal of ionic content of the cerebrospinal fluid. The FAST showed a signal stability of 226 μV/h over 24 h. We show that FAST can measure ACh dynamics in sheep brain tissue and sheep brain homogenate after ACh spiking. FAST is the first flexible electrochemical sensor for monitoring ACh dynamics in the brain.

Safinamide detection based on Prussian blue analogue modified Solid-contact potentiometric sensor

One of the most promising new avenues in eco-friendly analytical techniques is the creation of ion-selective electrodes (ISEs). Today, several techniques are being developed to create electrodes that are at once easy to use, very sensitive, long lasting, and remarkably stable. Here, an eco-friendly solid-state microfabricated copper electrode was constructed using readily available, low-cost copper printed circuit boards, and then a Prussian blue analogue (PBA) thin coating was applied for potentiometric determination of safinamide mesylate (SAF). The surface morphology, crystallinity and chemical structure of the produced PBA thin film were investigated using scanning electron microscopy (SEM), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS) respectively. The proposed sensor was effectively implemented for the quantification of SAF in pure and pharmaceutical dosage form. There was no statistically significant difference between the results obtained using the suggested technique and the results obtained using the reported one. Also, green-metrics (including GAPI and the AGREE algorithm, which relies on 12 principles of green analytical chemistry) were used to provide a full evaluation of the investigated method greenness. Finally, the newly announced RGB12 model was used to compare the whiteness degree of the proposed and reported methods.

Green Assay of Tolmetin Sodium Using Solid Contact Potentiometric Sensor Doped with Ionophore and Supported with Docking Study: Application to Human Plasma and Pharmaceutical Formulations

Tolmetin sodium (TOL) is a non-steroidal anti-inflammatory drug used to treat arthritis. Potentiometric ion selective electrodes (ISEs) bypass sample pre-treatment, high-tech apparatus, and toxic chemicals. The current study aimed to develop and validate a potentiometric analyser for the direct assay of TOL in pharmaceutical dosage form and human plasma. We designed an experimental approach to determine the factors that affect the performance of the developed sensor. A solid contact glassy carbon electrode was utilized as a support for the developed sensor. The interaction of TOL with several ionophore was studied using molecular docking. The optimized sensor was fabricated using dioctyl phthalate as plasticizer, tetra dodecyl ammonium bromide as anion exchanger, and β cyclodextrin as ionophore.The sensor achieved −58.78 Nernstian response within 1.00 × 10−2–2.00 × 10−6 mol l−1 linear range, 1.56 × 10−6 mol l−1 LOD, and fast response within 7 s. The greenness of the proposed method was assessed using the Analytical Eco-scale and the “Green Analytical Procedure Index” (GAPI) metric tools and compared with the reported methods and gained high scores. The proposed method has several advantages in encouraging quality control and clinical labs to routinely use the developed sensor in the assay of TOL in pharmaceutical dosage forms and human plasma.

Development of the New Sensor Based on Functionalized Carbon Nanomaterials for Promethazine Hydrochloride Determination

Promethazine hydrochloride (PM) is a widely used drug so its determination is important. Solid-contact potentiometric sensors could be an appropriate solution for that purpose due to their analytical properties. The aim of this research was to develop solid-contact sensor for potentiometric determination of PM. It had a liquid membrane containing hybrid sensing material based on functionalized carbon nanomaterials and PM ions. The membrane composition for the new PM sensor was optimized by varying different membrane plasticizers and the content of the sensing material. The plasticizer was selected based on calculations of Hansen solubility parameters (HSP) and experimental data. The best analytical performances were obtained using a sensor with 2-nitrophenyl phenyl ether (NPPE) as the plasticizer and 4% of the sensing material. It had a Nernstian slope (59.4 mV/decade of activity), a wide working range (6.2 × 10-7 M-5.0 × 10-3 M), a low limit of detection (1.5 × 10-7 M), fast response time (6 s), low signal drift (-1.2 mV/h), and good selectivity. The working pH range of the sensor was between 2 and 7. The new PM sensor was successfully used for accurate PM determination in a pure aqueous PM solution and pharmaceutical products. For that purpose, the Gran method and potentiometric titration were used.

Development of Solid-Contact Potentiometric Sensor Utilized Nanocarbon-filled Poly (vinyl chloride) Membrane as Ion-to-electron Transducing Layer

Current fundamental researches in the field of potentiometry demonstrate the perspectives of using polymeric nanostructured materials as ion-to-electron transducers in Solid-Contact Potentiometric Sensors (SCSs). This paper reports the preparation and comparative study of plasticized Poly(Vinyl Chloride) (PVC) membranes modified with fullerene C60, single-walled carbon nanotubes SWCNTs, multiwalled carbon nanotubes, and graphene oxide as the transducing layer in SCSs for the determination of a common local anesthetic drug – procaine hydrochloride (Pro·HCl). As an ion-sensitive (recognizing) layer, a PVC membrane containing highly lipophilic 2-[bis-octadecyl sulfo]-closo-decaborate anions was chosen. The results were discussed in relation to nanofiller’s type and content. The best potentiometric characteristics were obtained for the sensor with the transducing layer containing the hybrid nanofiller SWCNTs/C60. This new sensor of a double-layer PVC membrane configuration exhibited a Nernstian slope (59.2 ± 0.2 mV/decade) in the wide linear range (5×10-7– 1×10-2 M) with the low limit of detection (10-7.1 M), fast response time (≤ 7 s), and stable potentiometric response (drift potential ± 0.27 mV h-1 over 7 h of soaking in 1x10-5 M Pro·HCl solution).

Portable and green solid contact potentiometric sensor for the rapid and direct assay of clozapine in post-mortem rat liver and dosage forms: An analytical approach to forensic and pharmaceutical samples

This work is devoted to fabricating and validating a portable potentiometric sensor for in-site clozapine (CLZ) assay in tablets and post-mortem rat liver. The outcomes marking the overall sensor performance were defined to be (Nernstian slope, quantification limit, and correlation coefficients). A polyaniline-coated glassy carbon electrode was used as support for the sensors. The optimized sensor was composed of PVC (30.85 % w/w) plasticized with 2-nitrophenyl phenyl ether NPPE (64.32 % w/w) incorporating phosphotungstic acid PT (1.61 % w/w) as a cationic exchanger and calix-8-arene CX-8 (3.22 % w/w) as an ionophore, where the membrane thickness was 100 µm. The developed membrane works over the pH range of 2.3–6, providing a dynamic response time of 8 s. A computational docking approach was implemented, and the ionophore-CLZ complex interactions were studied to identify the best-fit complex. The docking study demonstrates that CX-8 is the optimum choice since it binds with CLZ+ by forming four bonds with −4.36 as binding free energy, reflecting the expected high stability of the developed complex. Validation of the proposed sensor illustrates that CLZ follows a linear response over the range of 1.8 × 10−5–1 × 10−2 M, yielding a correlation coefficient value of 0.9989 and a limit of detection LOD of 2.0 × 10−6 M. Moreover, the constructed membrane sensor proves to be of acceptable accuracy as reflected by the recovery percentage (97.48 %) and provides satisfactory precision as shown by the low relative standard deviation values; 0.114 for intermediate precision and 0.772 for repeatability. The greenness profile of the proposed method was assessed by the Green Analytical Procedure Index (GAPI), compared with the reported HPLC method, and found superior.

Potentiometric Sensor Based on Layered Pillar[6]arene—Copper Composite

A solid-contact potentiometric sensor has been developed on the basis of glassy carbon electrode covered with electropolymerized polyaniline and alternatively layered pillar[6]arene and Cu2+ ions films. The assembly of the surface layer was confirmed by surface plasmon resonance measurements. The number of deposited layers was selected to reach better analytical characteristics for Cu2+ determination. It was shown that better results were achieved by using five layers, the upper one consisting of the macrocycle. The addition of covering layers for polyelectrolytes (Nafion, poly(styrene sulfonate)) and Cu2+ ions did not improve sensor performance. The potentiometric sensor made it possible to determine Cu2+ ions in neutral and weakly acidic media with a linear range of the concentrations, from 3.0 μM to 10.0 mM (limit of detection 3.0 μM). The applicability of the sensor in real sample assays was confirmed by the determination of Cu2+ ions in copper vitriol, Bordeaux mixture, and polyvitamin-mineral pills of “Complivit” during an atomic emission spectroscopy analysis.

A portable solid-contact potentiometric sensor based on zeolite-carbon paste for assay of prucalopride succinate in tablet dosage form: Green profile assessment

A new, simple, highly sensitive potentiometric sensor was fabricated for the determination of Prucalopride succinate (Pru). The electrochemical sensor was based on the deposition of the ion exchanger (Prucalopride succinate-phosphotungstic acid (Pru-PTA) into the carbon paste which also was fabricated with zeolite particles and dibutyl phthalate to enhance its performance. The proposed sensor exhibits a Nernstian slope of 58.6589 ± 0.47 mV/decade over the linearity range 2 × 10-6 − 1 × 10-2 M Pru (0.1–4.5 × 102 µg/mL) and detection limit 1 × 10-6 M Pru with reasonable selectivity and thermal stability. The method was used for the determination of the studied drug in its pure form with an acceptable % recovery of 100.02 ± 1.3; it was successfully used for the determination of Pru in tablets. The proposed method was proven to be eco-friendly as assessed by two matrices; Analytical Eco-Scale and the recently developed Complementary green analytical procedure index (Complex-GAPI)

Electroanalytic properties of unmodified and modified solid contact potentiometric β-lactam sensors in aqueous and biological media

Results of a comparative study of the electroanalytic properties of solid contact sensors (tubular and planar) in cefuroxime (Cefur), cefotaxime (Ceftx), cefixim (Cefix), and amoxicillin (Amox) solutions are presented. Tetraalkylammonium associates — tetradecylammonium (TDA) and dimethyldistearylammonium (DMDSA) — with complex compounds silver (I) — β-lactam [Ag(β-lac)2] TAA; ZnO modifiers, polyaniline, and polyaniline nanotubes are used as electrode active components (EAC). The studied sensors based on [Ag(Cefur)2] TDA and [Ag(Amox)2] DMDSA in solutions of cefotaxime, cefuroxime, cefixime, and amoxicillin are characterized by a short response time: for tubular 20 – 25 sec (unmodified), 12 – 17 sec (modified); for planar – 20 – 25 sec (unmodified), 10 – 15 sec (modified). Modifiers stabilize electrode potential and perform a function of a mediator of electron transfer, which leads to improvement of electroanalytic characteristics of sensors. The linear range of electrode functions in antibiotic solutions is 1 × 10–4 – 1 × 10–2 M, the detection limit ranges between 2.5 × 10–5 – 8.9 × 10–5 M for unmodified and 5.6 × 10–6 – 7.5 × 10–5 M for modified sensors, and 4.2 × 10–5 – 7.2 × 10–5 M for planar sensors. The potential drift is 8 – 12 mV/day for unmodified and 5 – 7 mV/day for modified planar sensors; service life is 1.5 – 2 months. The advantage of planar sensors is the possibility of using them in microassay detection, which is relevant in the analysis of biological media. Application of solid-contact sensors for determination of the antibiotics under study in model aqueous solutions, medicinal preparations, oral fluid, blood serum in various infectious diseases is demonstrated.

Novel microfabricated solid-contact potentiometric sensors doped with multiwall carbon-nanotubes for simultaneous determination of bisoprolol and perindopril in spiked human plasma

The main concern when developing solid contact ion selective electrodes is the choice of ion sensing membranes while keeping in mind, cost effectiveness, simplicity, potential stability, and reproducibility of results. The main aim of this work is to design microfabricated solid contact ion selective electrodes (SC-ISEs) for the selective determination of bisoprolol (BIS) and perindopril (PER) either in their combined pharmaceutical formulation or simultaneously in human plasma. The obstacle was improving the detection limit of the proposed microfabricated sensors so they can determine the plasma peak concentrations of both drugs. Two factors were considered, namely the addition of ionophores and doping the ion sensing membranes with multiwalled carbon nanotubes (MWCNTs). Four sensors were developed for BIS while two other sensors were developed for PER, and their electrochemical performance was assessed. Selectivity of the sensors was determined in presence of some degradation products, impurities and metabolites of BIS and PER. Doping the ion sensing membranes with MWCNTs proved to interfere with the formation of water layer, resulting in more stable performance. Furthermore, addition of calix[6]arene (CX6) increased the sensitivity in case of BIS sensor. The optimum results for BIS were obtained with ion sensing membrane of potassium tetrakis(4-chlorophenyl)borate, CX6 and MWCNTs. Whereas an ion sensing membrane of tetradodecylammonium bromide and MWCNTs, showed best response in case of PER. The linearity range obtained in case of BIS was 8 × 10−9–1 × 10−2 M with an LOD of 1.74 × 10−9M. While for PER, the linearity range was 1 × 10−8–1 × 10−2 M with an LOD of 9.12 × 10−9 M.

Solid-contact potentiometric sensors based on silver nanoparticles in the supramolecular matrix for the determination of halogenide ions

Determination of halogenide ions in pharmaceuticals and various waters is an actual task for the modern analytical chemistry. In the current work, solid-contact potentiometric sensor, based on the glassy carbon electrode covered with the layer of electropolymerized polyaniline and suspension of silver nanoparticles in the matrix of thiacalix[4]arene derivative bearing terminal catechol groups, has been described. The suspension was obtained by the chemical reduction of silver ions with the thiacalix[4]arene and drop casted on the polyaniline layer. The sensor showed potentiometric response to chloride-, bromide and iodide ions. For the simultaneous determination of iodide and bromide ions, a multi-sensor system, consisting of four electrodes with the different volumes of the suspension placed on the polyaniline layer, has been developed. The possibility of the response prediction within the simple additive model was found for the set of the iodide and bromide mixtures. In a similar manner, simultaneous determination of both ions in the variable mixtures has been performed. The multi-sensor system was tested during the determination of iodides in iodine containing pharmaceuticals and the determination of iodide and bromide ions in the artificial mineral water samples. Ionic chromatography was chosen as the comparison method. Sensors made it possible to determine from 0.1 μM to10 mMiodide and bromide ions in mixtures. The proposed approach and solid-contact potentiometric sensors can be used in the analysis of ion content of the waters and in control of the production and storage conditions of pharmaceuticals.

Computational ionophore selection during optimization of a portable calixarene based sensor for direct assay of levamisole residues in livestock products

• Portable solid-state potentiometric sensor for rapid, direct assay of levamisole. • Experimental and computation optimization of the sensor composition. • Assay of levamisole residues in bovine milk, muscles, kidney, and liver samples. • Assessment of the entire method for greenness. Poor practices in the livestock industry include the misuse of veterinary drugs to promote production and enhance the feed transformation ratio. The drugs accumulate in the edible tissues and transfer to consumers imposing health hazards. For instance, levamisole (LVM) residues lead to health hazards (e.g. hematological toxicity and agranulocytosis). Accordingly, authorities have drawn strict limits for LVM residues in edible tissues. This work introduces the first portable solid-contact potentiometric sensor for direct LVM assay in multiple bovine products. The sensor included a drop-casted membrane cocktail over a polyaniline coated glassy-carbon substrate. An initial study optimized the membrane cocktail composition for maximum sensitivity and selectivity. Molecular docking supported the experimental results for ionophore selection. The optimized sensor engendered a Nernstian response with a LOD of 1.56 × 10 −6 M. The greenness of the developed method was assessed using the National Environmental Method Index pictogram. The method was officially validated; and successfully determined LVM in bovine milk, muscle, kidney, and liver samples. Quality control laboratories can use the portable sensor for LVM overuse surveillance.

Easy-to-Make Capillary-Based Reference Electrodes with Controlled, Pressure-Driven Electrolyte Flow.

As solid-contact potentiometric sensors based on novel materials have reached exceptional stabilities with drifts in the low μV/h range and long-term and calibration-free potentiometric measurements gain more and more attention, reference electrode designs that used to be satisfactory for most users do not satisfy the needs of new challenging applications. It is important that the interface between a reference electrode and the sample, often provided by a salt bridge, remains constant in ion composition over time. Excessive restriction of the flow of the bridge electrolyte, e.g., by using nanoporous frits or gelled reference electrolyte solutions, can result in contamination of the salt bridge with sample components and depletion of the reference electrolyte by diffusion into samples. This can be avoided by using salt bridges that flow freely into the sample. However, commonly used reference electrodes with free-flowing junctions often suffer either from experimental difficulties in assuring a minimum flow rate or from excessive flow rates that require frequent replenishing of the bridge electrolyte. To this end, we developed a reference electrode that contains a concentrated electrolyte contacting samples through a 10.2 μm capillary. By applying a minimal pressure of 10.0 kPa, a flow rate of 100 nL/h is achieved. This maintains a constant liquid junction potential at the interface with the sample and avoids contamination of the reference electrode, as evidenced by a potential stability of 6 ± 3 μV/h over 21 days. With such a minimal flow rate, there is no need to refill the reference electrode electrolyte for years.

Electrochemical sensors: From the bench to the skin

Sixty years have passed since Clark proposed the concept of glucose enzyme electrodes. Herein, we review major advances in such analyses based on electrochemical sensor systems over the past three decades that have paved the way to the leading role of wearable electrochemical sensing systems for non-invasive real-time chemical monitoring. These past developments of chemically modified electrodes, solid-contact potentiometric sensors, printable disposable electrodes, paper-based sensing devices, soft microfluidic detection systems, and miniaturized instrumentation along with the digital revolution and related advances in flexible electronics and material science have facilitated the evolution of wearable electrochemical sensors which have led to exciting possibilities for on-body analyses. Particularly, the introduction of non-invasive epidermal sensing platforms for monitoring health and wellness has been found fascinating and promising. Such skin-interfaced electrochemical sensors have shown to be extremely useful for continuous non-invasive biochemical monitoring of sweat and the interstitial fluid (ISF). A major driving force for these advances has been the large diabetes management market that has led to the introduction of self-testing glucose strips in the 1980s and continuous wearable glucose sensors in the 2000s. The current status of epidermal electrochemical sensors is discussed along with future prospects towards the broader scope and further integration and miniaturization towards the realization of complete lab-on-the-skin capable of multiplexed sensing of key biomarkers. Such use of wearable electrochemical sensors is expected to bring new opportunities in medical diagnostics, wellness, and nutrition, which will support the rapid changes from traditional, blood-centered diagnostics to decentralized personalized remote diagnostics.

Textile-based wearable solid-contact flexible fluoride sensor: Toward biodetection of G-type nerve agents

Rising global concerns posed by chemical and biological threat agents highlight the critical need to develop reliable strategies for the real-time detection of such threats. While wearable sensing technology is well suited to fulfill this task, the use of on-body devices for rapid and selective field identification of chemical agents is relatively a new area. This work describes a flexible printed textile-based solid-contact potentiometric sensor for the selective detection of fluoride anions liberated by the biocatalytic hydrolysis of fluorine-containing G-type nerve agents (such as sarin or soman). The newly developed solid-contact textile fluoride sensor relies on a fluoride-selective bis(fluorodioctylstannyl)methane ionophore to provide attractive analytical performance with near-Nernstian sensitivity and effective discrimination against common anions, along with excellent reversibility and repeatability for dynamically changing fluoride concentrations. By using stress-enduring printed inks and serpentine structures along with stretchable textile substrates, the resulting textile-based fluoride sensor exhibits robust mechanical resiliency under severe mechanical strains. Such realization of an effective textile-based fluoride-selective electrode allowed biosensing of the nerve-agent simulant diisopropyl fluorophosphate (DFP), in connection to immobilized organophosphorus acid anhydrolylase (OPAA) or organophosphorus hydrolase (OPH) enzymes. A user-friendly portable electronic module transmits data from the new textile-based potentiometric biosensor wirelessly to a nearby smartphone for alerting the wearer instantaneously about potential chemical threats. While expanding the scope of wearable solid-contact anion sensors, such a textile-based potentiometric fluoride electrode transducer offers particular promise for effective discrimination of G-type neurotoxins from organophosphate (OP) pesticides, toward specific field detection of these agents in diverse defense settings.