Ion-selective Membrane Sensor Research Articles

Micro-droplet printed ion-selective membrane sensors for in situ monitoring of marine heavy metal ions

Fast, accurate, and reliable techniques for marine toxic heavy metal ions (HMI) detection are critical for the ecological environment and human health. One of the fatal drawbacks of traditional ion selective electrochemical sensors is that the modification of electrode cannot be accurately quantified, resulting in poor repeatability of the detection electrode and large error between the multi-electrode detection results. In order to tackle this challenge, this study presents ultra-fine micro-droplet printed electrodes for the in-situ detection of Cd2+, a carcinogenic and toxic HMI commonly found in the ocean. The ion selective membrane casting liquid was dispersed into tiny droplets with a diameter of micron through microfluidic technology, and the microdroplets were precisely arranged on the electrode surface. As a result, the modification error of electrode was reduced to pL level (accurate to 10 pL), which greatly improved the repeatability between electrodes prepared in different batches. The results of experiments with pure electrolyte, interference ions and artificial seawater indicated that the micro-droplet printed sensors possessed excellent properties of accuracy, precision, repeatability, and anti-interference. This novel micro-droplet printed sensor has the potential to capture an accurate picture of nearshore HMI in heterogeneous environments under shock conditions.

Potentiometric determination of mebeverine hydrochloride antispasmodic drug based on molecular docking with different ionophores host-guest inclusion as a theoretical study.

The scientific community has continued to pay particular attention to potentiometric sensors based on ion-selective membrane sensors as an energy-efficient, easy-to-use method suitable for microfabrication. To this end, potentiometric ion-selective sensors were used as an alternative green analytical instrument. Three distinct sensors relying on various ionophores were built and assessed. A cationic exchanger, tetra phenyl borate, was used in the polyvinyl chloride polymeric plasticized matrix using di octyl phthalate, where α, β, and γ cyclodextrins were utilized as ionophores. A comparative potentiometric analysis was carried out using three ion-selective sensor designs: α, β, and γ cyclodextrins sensors. β-Cyclodextrin significantly reduced the detection limit and improved the discriminative performance of mebeverine hydrochloride (MBV) in the pharmaceutical dosage form over α- and γ-cyclodextrins in the presence of other interfering chemicals. Additionally, a significant connection was made between the practical perspective and a theoretical investigation based on computational research. Nernstian potentiometric results for the optimum sensor were obtained for MBV in the range of concentrations 1.0 × 10-2 to 1.0 × 10-6 M, its slope was -58.70 ± 0.12 mV per decade with lower detection limits 4.50 × 10-7 M. This computational molecular docking investigation clarified that the binding sites and modes were in good agreement with the experiment results. This investigation was applied to expect the interaction between MBV and the proposed sensors to ensure which ionophores were the best for MBV.

Development of a LoRaWAN IoT Node with Ion-Selective Electrode Soil Nitrate Sensors for Precision Agriculture

Crop productivity is highly dependent on the availability of soluble nitrogen (N), e.g. nitrate, in soil. When N levels are low, fertilisers are applied to replenish the soil's reserves. Typically the timing of these applications is based on paper-based guidance and sensor-based measurements of canopy greenness, which provides an indirect measure of soil N status. However this approach often means that N fertiliser is applied inappropriately or too late, resulting in excess N being lost to the environment, or too little N to meet crop demand. To promote greater N use efficiency and improve agricultural sustainability, we developed an Internet of Things (IoT) approach for the real-time measurement of soil nitrate levels using ion-selective membrane sensors in combination with digital soil moisture probes. The node incorporates state-of-the-art IoT connectivity using a LoRaWAN transceiver. The sensing platform can transfer real-time data via a cloud-connected gateway for processing and storage. In summary, we present a validated soil sensor system for real-time monitoring of soil nitrate concentrations, which can support fertiliser management decisions, improve N use efficiency and reduce N losses to the environment.

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.

Bionanopolymeric film for the electroanalytical detection of zinc, cadmium and lead ions

ABSTRACT An electrochemical gold nanoparticle sensor was developed for the detection of zinc, cadmium and lead ions, due to its electronic properties provided by the large surface/volume ratio and its easy surface modification. Linear ranges for Zn2+, Cd2+ and Pb2+ solutions were 0.469–3.051 µM, 3.968–68.970 µM and 7.937–137.900 µM, respectively. Sensitivity values were superior for electrode modified with chitosan, melamine and gold nanoparticles, and its microamperes/micromoles ratio were 5.7887 [µA/(µM)], 0.8915 [µA/(µM)] and 0.2221 [µA/(µM)], for Zn2+, Cd2+ and Pb2+ solutions, respectively. Synthetic sample solutions with concentrations higher than 1.481 µM Pb2+/L, 37.04 µM Cd2+/L and 74.07 µM Zn2+/L were analysed with high selectivity for the three ions in the mixed water samples. The results showed relevant enhancement of the electrochemical response signals for the ion-selective membrane sensor when the AuNPs added to the composite, a suitable resolution was reached leading to higher selectivity and better accuracy.

A non-optical multiplexed PCR diagnostic platform for serotype-specific detection of dengue virus

Viable point-of-care multi-target diagnostics requires single-sample multiplexed detection in a single PCR reactor with non-optical instruments. We report an integrated multiplexed PCR chip platform with a novel ion-selective membrane sensor array that eliminates the key selectivity and sensitivity issues for multiplexed PCR, such as primer dimerization and nonspecific amplification (mis-priming). The depletion action of the ion-selective membrane renders the sensor insensitive to pH and ionic strength variation or non-specific binding, which plague the current electrochemical sensor arrays. We validate the platform with robust, sensitive and selective detection of each of the four dengue virus (DENV) serotypes, even in the presence of misprimed non-target products, with plasma samples spiked with heterogeneous RNA populations that include all the serotypes. The assay time is ∼ 90 min with a detection sensitivity of DENV RNA template down to 100 copies per mL. By replacing the optical sensing technology of RT-PCR with the membrane sensor, the platform is scalable and can allow simultaneous screening for multiple viral infections in a single sample within a single PCR reactor chip for point-of-care applications.

Real-Time in Situ Monitoring of Nitrogen Dynamics in Wastewater Treatment Processes using Wireless, Solid-State, and Ion-Selective Membrane Sensors.

Real-time, in situ accurate monitoring of nitrogen contaminants in wastewater over a long-term period is critical for swift feedback control, enhanced nitrogen removal efficiency, and reduced energy consumption of wastewater treatment processes. Existing nitrogen sensors suffer from high cost, low stability, and short life times, posing hurdles for their mass deployment to capture a complete picture within heterogeneous systems. Tackling this challenge, this study presents solid-state ion-selective membrane (S-ISM) nitrogen sensors for ammonium (NH4+) and nitrate (NO3-) in wastewater that were coupled to a wireless data transmission gateway for real-time remote data access. Lab-scale test and continuous-flow field tests using real municipal wastewater indicated that the S-ISM nitrogen sensors possessed excellent accuracy and precision, high selectivity, and multiday stability. Importantly, autocorrections of the sensor readings on the cloud minimized temperature influences and assured accurate nitrogen concentration readings in remote-sensing applications. It was estimated that real-time, in situ monitoring using wireless S-ISM nitrogen sensors could save 25% of electric energy under normal operational conditions and reduce 22% of nitrogen discharge under shock conditions.

New Approach for Measuring Antioxidant Activity Via a Graphite Sensor

An ion selective membrane sensor from dioctyl phthalate as a plasticizer in a polymeric matrix of polyvinyl chloride (PVC) and �-cyclodextrin as an ionophore was constructed and evaluated according to IUPAC recommendations. Linear Nernstian response of DPPHwithin the concentration ranges of 10 �6 to 10 �2 mol L �1 was obtained with average recovery 99.87±0.617. Nernstian slope of 58.5 mV/decade with excellent selectivity over the pH range of 3-8 was observed. The suggested method was standardized using butylated hydroxyl anisole (BHA). The 50% radical scavenging activity (IC 50 ) determined by the proposed sensor correlated well with that of the common spectrophotometric method based on scavenging of 2,2-diphenyl-1- picrylhydrazyl (DPPH • ). An algorithm implemented in Microsoft Visual Basic ® 6.0 was used for calculating (IC 50 ) values which are 7.38 �g/mL ± 0.35, 89.98 �g/ mL ± 0.45 and 1.45 mg/ mL ± 1.50 for BHA, Paracetamol and Dipyridamole, respectively. The proposed sensor represents a simple and reproducible tool for measuring DPPH • scavenging activity of Paracetamol and Dipyridamole in bulk powder, pharmaceutical formulations and simulated intestinal fluid (SIF) without sophisticated separation techniques.

Synthesis, spectral characterization, thermal investigation and electrochemical evaluation of benzilbis(carbohydrazone) as Cd(II) ion selective electrode

Benzil bis(carbohydrazone) (BBC) has been synthesized and structurally characterized on the basis of IR, 1H NMR, mass, UV spectra and thermogravimetric analyses. BBC has been analysed electrochemically and explored as new N, N Schiff base. It plays the role of an excellent ion carrier in the construction of cadmium(II) ion selective membrane sensor. This sensor shows very good selectivity and sensitivity towards cadmium ion over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. The response mechanism was discussed in the view of UV-spectroscopy and Electrochemical impedance spectroscopy (EIS). The proposed sensor was successfully used for the determination of cadmium in different chocolate samples.

Spectral, thermal and electrochemical investigation of carbohydrazone derived ionophore as Fe(III) ion selective electrode

Dibenzoylmethane bis(carbohydrazone) (BMBC) has been synthesized and structurally characterized on the basis of IR, 1H NMR, mass, UV spectra and thermogravimetric analyses. BMBC has been analysed electrochemically and explored as new N, N Schiff base. It plays the role of an excellent ion carrier in the construction of iron(III) ion selective membrane sensor. This sensor shows very good selectivity and sensitivity towards iron ion over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. The response mechanism was discussed in the view of UV-spectroscopy and Electrochemical Impedance Spectroscopy (EIS). The proposed sensor was successfully used for the determination of iron in different samples.

A Co2+-Selective Poly(vinyl chloride) Membrane Electrode Based on a Newly Synthesized 3,3′-(Dodecylazanediyl)bis(N-(2-(2-aminoethylamino)ethyl)propanamide) Compound

A Co2+ ion-selective membrane sensor has been fabricated in a poly(vinyl chloride) matrix based on a recently synthesized 3,3′-(dodecylazanediyl)bis(N-(2-(2-aminoethylamino)ethyl)propanamide) (DAEP...

Comparative studies of ONNO-based ligands as ionophores for palladium ion-selective membrane sensors

Palladium sensors based on two neutral ionophores, N, N′-bis(acetylacetone) cyclohexanediamine ( L 1 ) and N, N′-bis( o-hydroxyacetophenone)-1,2-cyclohexanediamine ( L 2 ) for quantification of palladium ions are described. Effect of various plasticizers ( o-NPOE, DBP, DEP, DOP, TBP, and CN) and anion excluder, sodium tetra phenyl borate (NaTPB) has been studied. The best performance is obtained with a membrane composition of PVC: o-NPOE:ionophore ( L 1 ):NaTPB of 150:300:5:5 (%, w/w). The sensor exhibits significantly enhanced selectivity towards palladium ion over the concentration range 1.0 × 10 −8 to 1.0 × 10 −1 M with a lower detection limit of 4.0 × 10 −9 M and a Nernstian compliance (29.1 ± 0.3 mV decade −1 of activity) within pH range 2.0–6.0 and fast response time of 10 s. Influence of the membrane composition and possible interfering ions has also been investigated on the response properties of the electrode. Fast and stable response, good reproducibility and long-term stability of the sensor are demonstrated. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 4 months. Selectivity coefficients determined with fixed interference method (FIM) indicate high selectivity for palladium. The proposed electrode shows fairly good discrimination of palladium from other cations. The application of prepared sensor has been demonstrated in determination of palladium ions in spiked water sample.

Fabrication of an iron(III)-selective PVC membrane sensor based on a bis-bidentate Schiff base ionophore

A Fe3+ ion-selective membrane sensor was fabricated from polyvinyl chloride (PVC) matrix membrane containing bis-bidentate Schiff base (BBS) as a neutral carrier, sodium tetraphenyl borate (NaTPB) as anionic excluder, and o-nitrophenyloctyl ether (NPOE) as a plasticizing solvent mediator. The effects of the membrane composition, pH, and additive anionic influence on the response properties were investigated. The best performance was obtained with a membrane containing 32% PVC, 62.5% NPOE, 3% BBS, and 2.5% NaTPB. The electrode shows a Nernstian behavior (slope of 19.3 ± 0.6) over a very wide iron ion concentration range (1.0 × 10−7–1.0 × 10−2 M) and has a low detection limit (7.4 × 10−8 M). The potentiometric response of the sensor is independent of pH of the solution in the pH range 1.9–5.1. The proposed sensor has a very low response time (<15 s) and a good selectivity relative to a wide variety of other metal ions including common alkali, alkaline earth, heavy, and transition metal ions. The electrode can be used for at least 60 days without any considerable divergence in potentials. The proposed sensor was successfully applied as an indicator electrode for the potentiometric titration of 1.0 × 10−2 M Fe3+ ions with a 1.0 × 10−4 M EDTA and the direct determination of Fe3+ in mineral water and wastewater samples.

Highly selective and sensitive Th4+-PVC-based membrane sensor based on 2-(diphenylphosphorothioyl)-N′,N′-diphenylacetamide

A Th4+ ion-selective membrane sensor was fabricated from poly (vinyl chloride) (PVC) matrix membrane containing 2-(diphenylphosphorothioyl)-N′,N′-diphenyl acetamide (DPTD) as a neutral carrier, potassium tetrakis (p-chlorophenyl) borate (KTpClPB) as anionic excluder and o-nitrophenyloctyl ether (NPOE) as a plasticizing solvent mediator. The effects of the membrane composition, pH and additive anionic influence on the response properties were investigated. The sensor, comprising 30% PVC, 63% solvent mediator, 4% ionophore and 3% anionic additive demonstrates the best potentiometric response characteristics. It displays Nernstian behavior (15.2 ± 0.5 mV per decade) over the concentration range 1.0 × 10−2–1.0 × 10−6 M. The detection limit of the electrode is 6.3 × 10−7 M (∼140 ng/ml). The response time of the electrode is 30 s .The sensor can be used in the pH range 3.0–9.0 for about 6 weeks. The membrane sensor was used as an indicator electrode in the potentiometric titration of Th4+ ions with EDTA. It was successfully applied to the determination of thorium ions in binary mixture.

Sub-Micro Molar Monitoring of La3+ by a Novel Lanthanum PVC-Based Membrane Sensor Based on 3-Hydroxy-N'-(pyridin-2-ylmethylene)-2-naphthohydrazide

A La (III) ion-selective membrane sensor has been fabricated from poly vinyl chloride (PVC) matrix membrane, containing 3-hydroxy-N'-(pyridin-2-ylmethylene)-2-naphthohydrazide (HPMN) as a neutral carrier, potassium tetrakis (p-chlorophenyl) borate (KTpClPB) as an anionic excluder and ortho-nitrophenyloctyl ether (NPOE) as a plasticizing solvent mediator. The effects of membrane composition and pH as well as the influence of the anionic additive on the response properties were investigated. The sensor with 30% PVC, 62% solvent mediator, 6% ionophore and 2% anionic additive, shows the best potentiometric response characteristics. It displays a Nernstian behavior (19.2 mV per decade) across the range of M. The detection limit of the electrode is M (10 ng/mL) and the response time is 15 s from up to M and 30 s in the range of M. The sensor can be used in the pH values of 3.0-9.0 for about seven weeks. The membrane sensor was used as an indicator electrode in the potentiometric titration of lanthanum ions with EDTA. It was successfully applied to the lanthanum determination in some mouth wash preparations.

Cobalt(II)-selective electrode based on a newly synthesized macrocyclic compound

A cobalt(II) ion-selective membrane sensor has been fabricated in a poly(vinyl chloride) matrix based on a recently synthesized 2,3,4-pyridine-1,3,5,8,11,14-hexaazacyclohexadeca-2-ene as a neutral carrier. The electrode exhibits a Nernstian response over a wide concentration range (6.3 × 10 −6 to 1.0 × 10 −1 M) between pH 2.5 and 6.5. The response time of the sensor is about 15 s and it can be used over a period of 4 months without any divergence in potential. The proposed membrane sensor revealed good selectivity for Co(II) over a wide variety of other metal ions. The electrode has been used as an indicator electrode in potentiometric titration of Co(II) with EDTA and direct determination of Co(II) in wastewater of the electroplating industry.

A Potentiometric Rhodamine-B Based Membrane Sensor for the Selective Determination of Chromium Ions in Wastewater

The construction and performance characteristics of a novel chromate ion-selective membrane sensor are described and used for determining chromium(III) and chromium(VI) ions. The sensor is based on the use of a rhodamine-B chromate ion-associate complex as an electroactive material in a poly(vinyl chloride) membrane plasticized with o-nitrophenyloctyl ether as a solvent mediator. In a phosphate buffer solution of pH 6 - 7, the sensor displays a stable, reproducible and linear potential response over the concentration range of 1 x 10(-1) - 5 x 10(-6) mol l(-1) with an anionic Nernstian slope of 30.8 +/- 0.5 mV decade(-1) and a detection limit of 1 x 10(-6) mol l(-1) Cr(VI). High selectivity for Cr(VI) is offered over many common anions (e.g., I-, Br-, Cl-, IO4-, CN-, acetate, oxalate, citrate, sulfate, phosphate, thiosulfate, selenite, nitrate) and cations (e.g., Ag+, Ca2+, Sr2+, Co2+, Ni2+, Cu2+, Mn2+, Fe2+, Zn2+, Cd2+, Al3+, Cr3+). The sensor is used for determining Cr(VI) and/or Cr(III) ions in separate or mixed solutions after the oxidation of Cr(III) into Cr(VI) with H2O2. As low as 0.2 microg ml(-1) of chromium is determined with a precision of +/-1.2%. The chromium contents of some wastewater samples were accurately assessed, and the results agreed fairly well with data obtained by atomic absorption spectrometry.

Synthesis of a new oxime and its application to the construction of a highly selective and sensitive Co(II) PVC-based membrane sensor.

A cobalt(II) ion-selective membrane sensor has been fabricated from a poly vinyl chloride (PVC) matrix membrane containing a new oxime compound (oxime of 1-(2-oxocyclohexyl)-1,2-cyclohexanediol, OXCCD) as a neutral carrier, sodium tetraphenyl borate (NaTPB) as an anionic excluder and o-nitrophenyloctylether (o-NPOE) as a plasticizing solvent mediator. The membrane sensor exhibits a linear potential response in the concentration range of 1.0 x 10(-1) - 1.0 x 10(-6) M of Co2+. The electrode displays a Nernstian slope of 29.8 mV decade(-1) in the pH range of 3.5 - 8.0. The sensor also exhibits a fast response time of < 25 s. The detection limit of the proposed sensor is 9.0 x 10(-7) M (approximately 40 ng/ml), and it can be used over a period of two months. The selectivity of the sensor with respect to other cations (alkali, alkaline earth, transition and heavy metal ions) is excellent. The practical utility of the sensor has been demonstrated by using it as an indicator electrode in the potentiometric titration of Co2+ with EDTA and for the direct determination of Co(II) in wastewater of the electroplating industry.