Ion-selective Sensors Research Articles

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.

Lipophilic Fluorescent Dye Liquids: Förster Resonance Energy Transfer-Based Fluorescence Amplification for Ion Selective Optical Sensors Based on a Solvent Polymeric Membrane.

Optical sensors based on solvent polymeric membranes have the potential to measure analytes present in an aqueous solution through the development of a tailored method for a specific target. However, limits in the concentrations of the component dyes have prevented improvements in sensitivity. We propose a Förster resonance energy transfer (FRET)-based fluorescence amplification system for ion-selective optical sensors using a highly fluorescent liquid material composed of a lipophilic phosphonium cation and a pyrene modifying sulfonate anion ([P66614][HP-SO3]), as both the plasticizer and donor, in addition to a combination of the lipophilic phosphonium cation and the fluorescein dodecyl ester anion ([P66614][12-FL]) as the fluorescent sensing dye acceptor. For ion extraction-based sensing, the donor and acceptor were retained in the plasticized PVC membrane with negligible leaching upon exposure to acidic and basic aqueous solutions. Systematic investigation of the donor and acceptor ratios clarified the effect of the amplification factor and the sensitivity of the sensor. At an acceptor doping level of 0.5 mol % (vs donor), an approximately 22-fold higher sensitivity was obtained compared to that of a conventional PVC membrane optical sensor. During ion measurement based on the coextraction of protons and anions, selectivity following the Hofmeister order was observed, which was controlled by the addition of ionophores. The proposed FRET system based on a lipophilic fluorescent liquid material has the potential to significantly improve the sensitivities of optical sensors using solvent polymeric membranes with high selectivities for various target analytes.

Real-time monitoring of rhizosphere nitrate fluctuations under crops following defoliation

BackgroundManagement regime can hugely influence the efficiency of crop production but measuring real-time below-ground responses is difficult. The combination of fertiliser application and mowing or grazing may have a major impact on roots and on the soil nutrient profile and leaching.ResultsA novel approach was developed using low-cost ion-selective sensors to track nitrate (NO3−) movement through soil column profiles sown with the forage crops, Lolium perenne and Medicago sativa. Applications of fertiliser, defoliation of crops and intercropping of the grass and the legume were tested. Sensor measurements were compared with conventional testing of lysimeter and leachate samples. There was little leaching of NO3− through soil profiles with current management practices, as monitored by both methods. After defoliation, the measurements detected a striking increase in soil NO3− in the middle of the column where the greatest density of roots was found. This phenomenon was not detected when no NO3− was applied, and when there was no defoliation, or during intercropping with Medicago.ConclusionMowing or grazing may increase rhizodeposition of carbon that stimulates soil mineralization to release NO3− that is acquired by roots without leaching from the profile. The soil columns and sensors provided a dynamic insight into rhizosphere responses to changes in above-ground management practices.

Enantioselective high performance new solid contact ion-selective electrode potentiometric sensor based on sulphated γ-cyclodextrin‑carbon nanofiber composite for determination of multichiral drug moxifloxacin

Multiple chiral centered drugs not only pose greater risk than single center in asymmetric medium of human bodies but also beneficial to them in many ways. Therefore, online monitoring and rapid chiral sensing method is always desirable for both isomers as well as their impurities. In the present paper, we have developed a new solid-contact ion-selective electrode (SC-ISE) for enantioselective recognition of RR and SS moxifloxacin (RR-MX/SS-MX) based on chiral nanocomposite of sulphated γ-cyclodextrin (Sγ-CD) and carbon nanofibers (CNF) incorporated into a plasticized poly vinyl chloride (PVC) employing potentiometry. CNF are used for the first time to fabricate SC-ISE as the intermediate layer between an ionophore-doped polymeric membrane and a glassy carbon electrode (GC) for MX enantiomers. The host-guest interaction takes place between γ-CD and RR/SS isomer in the polymeric membrane of the solid-contact electrode forming 1:1 chelate complex where enantioselectivity is achieved in the terms of stability constant (SS-MX = 1786 M−1 and RR-MX = 390 M−1 and Gibbs free energy employing square wave voltammetry (SWV). The new electrode displays a Nernstian slope (60.10 ± 0.25 mV/decade) with the linear range obtained was 1 × 10−2 to 6.5 × 10−7 M and the detection limit of 1.5 ± 0.16 × 10−7 M. The developed solid-contact electrode shows very small drift in potential (EΔ/tΔ = 154 μVh−1) and fast response time of less than 5 s throughout the linear range. The assay of SS-MX in the presence of its antimer RR-MX was carried out using different ratios of both enantiomers, recovery of SS-MX in the presence of RR clearly demonstrate the enantioselectivity and stereospecificity of the proposed SC-ISE. The practical analytical utility of developed chiral potentiometric sensor was demonstrated by measurement of SS-MX in pharmaceutical formulations, urine and blood serum samples. Surface characterization of solid-contact electrode was performed using Frequency Response Analyzer (FRA), Scanning electron microscopy (SEM) and the effect of the interfacial water film was evaluated using potentiometric water layer test.

Integrated all-solid-state sulfite sensors modified with two different ion-to-electron transducers: rapid assessment of sulfite in beverages.

An integrated all-solid-state screen-printed ion-selective potentiometric sensor for rapid assessment of sulfite ion in beverages, based on analytical transduction, is described. The constructed potentiometric cell incorporates a polymeric membrane sulfite ion-selective electrode based on cobalt(ii) phthalocyanine (CoPC) as a recognition material and an Ag/AgCl reference electrode with a polyvinyl butyral reference membrane. Two different solid-contact transducers, namely multi-walled carbon nanotubes (MWCNTs) and polyaniline (PANI) were used for a comparative study. The presented sensors exhibited a rapid Nernst response across the concentration ranges from 2.0 × 10−6 to 2.3 × 10−3 M and from 5.0 × 10−6 to 2.3 × 10−3 M with detection limits equal to 1.1 × 10−6 M and 1.5 × 10−6 M for sensors based on MWCNTs and PANI, respectively. The proposed sensors manifested high selectivity and sensitivity, enhanced stability and low cost that provides a wide number of potential applications for food analysis. Good performance characteristics were obtained for the proposed method after applying the validation requirements. Method precision, accuracy, bias, trueness, repeatability, reproducibility, and uncertainty are examined. These analytical capabilities support the rapid and direct determination of sulfite in different beverage samples. The analytical results were verified and compared with the standard iodometric method.

Photonic microresonator based sensor for selective nitrate ion detection

Sensing nitrate concentrations in soil with high sensitivity and selectivity using field-deployable compact sensor platforms is a sought-after goal for environment and agriculture applications. This study demonstrates a new optically based nitrate sensing platform based on ion-selective membrane (ISM) functionalized chip-scale photonic micro-ring resonators. Our approach relies upon measurements of resonance shifts in the micro-resonators and leverages the excellent, though little studied, optical properties of ISMs. Using a high-quality micro-ring resonator, a nitrate ion-selective photonic sensor exhibits a detection limit down to 0.1 parts per million (ppm) and enables nitrate concentration measurements in the 1−100 ppm level, appropriate for soil science and agriculture. Importantly, the sensor also shows high selectivity over other competing anions in soil, such as Cl− and NO2−. We argue that this chip-scale approach can be incorporated into compact sensor platforms.

Improving selectivity of ion-sensitive membrane by polyethylene glycol doping

Hydrophobic ions can generate considerable interference to ion detection in a complex analyte with membrane-based ion-selective sensors, due to the hydrophobic interaction. In this paper, we demonstrate that the interference from the hydrophobic interaction to the sensors can be significantly reduced by incorporating hydrophilic polyethylene glycol (PEG) into the membrane. The sensor is a silicon nanowire field-effect transistor (SiNWFET) with its surface functionalized with an ionophore-doped mixed-matrix membrane (MMM), where the ionophore is either a commercial Na-ionophore Ⅲ or a novel synthetic metal-organic supercontainer. The incorporation of PEG suppresses the partitioning of hydrophobic ions into the MMM and thus reduces their interference to the detection of target ions. This is evidenced with an improvement in selectivity for Na+ detection in the presence of interfering methylene blue (MB+) ion by more than an order of magnitude. It further enables detection of Na+ and MB+ using a SiNWFET sensor array in a multiplexed manner with controlled susceptivity to cross-interference and a greatly expanded dynamic range.

An integrated all-solid-state screen-printed potentiometric sensor based on a three-dimensional self-assembled graphene aerogel

An integrated all-solid-state screen-printed ion-selective potentiometric sensor for the determination of Cu2+ is proposed. The whole-cell potentiometric sensor incorporates a polymeric membrane copper ion-selective electrode (Cu2+-ISE) as an indicator electrode and an Ag/AgCl reference electrode with a polyvinyl butyral reference membrane. The three-dimensional (3D) self-assembled porous graphene aerogel (PGA) can be conveniently and rapidly electrodeposited on the electrode substrate surface. Due to its interior 3D interconnected porous structures, the PGA has a large electrical double layer capacitance and fast charge transfer capability, which make it promising to be used as solid contact for the fabrication of the Cu2+-ISE. The developed potentiometric sensor shows a good Nernstian response over a range from 10−6 to 10−3 M with a detection limit of 10−6.5 M. In addition, the sensor exhibits a stable potential response with the absence of an undesirable water layer at the ion-selective membrane/PGA interface.

An Integrated Paper-Based Microfluidic Device for Real-Time Sweat Potassium Monitoring

Wearable electrochemical sensors have attracted tremendous attention in recent years. Here, an integrated three-dimensional paper-based microfluidic electrochemical device (3D-PMED) with flexible wireless circuits is demonstrated for real-time monitoring of sweat potassium. The paper-based microfluidic pad is fabricated by printing wax patterns on cellulose paper and then folding the pre-patterned paper four times to form a five-layer stacked structure: sweat collector, vertical channel, transverse channel, electrode layer, and sweat evaporator. Also, we have discussed the different properties with three swear collector types. The sweat monitoring device is realized by integrating a screen-printed potassium ion-selective sensor on the PET substrate with the fabricated paper microfluidic pad. The sweat flow in 3D-PMED is modeled with red ink to generate the flow pathway of sweat and the capability of sweat storage. The detection range of the potassium ion-selective sensor is 1-32 mM, and the electrode response potential is 61.79 mV per decade of K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> concentration. The device has a small size that is suitable for everywhere on the body, and also have shown good selectivity for both anion and cation, and a stable performance within 1 week. This 3D-PMED has provided a simple, low-cost way for real-time dynamic sweat potassium monitoring when exercising.

PH-dependent distribution of the indicator dye tetrabromophenolphthalein ethyl ester between aqueous solution and plasticized polymeric phase: Predicting the lifetime of ion-selective optical sensors

The pH-dependent distribution of the indicator dye tetrabromophenolphthalein ethyl ester (TBPE, chromoionophore VIII) between plasticized polymeric phase and aqueous solution is studied. The commonly utilized algorithms for partition properties calculation are evaluated experimentally in terms of their suitability for the ionized species. The physical-chemical characteristics of TBPE that determine its applicability for use in chemical sensors, namely, the lipophilicity and acidity constant are estimated in the hydrophobic polymeric phase for the first time. The distribution coefficients of the neutral (protonated) and ionized (deprotonated) forms of TBPE are determined in plasticized PVC/water biphase system as 7.2 and 3.8, respectively (logk, ionic strength 1 M, 25 °C). The acidity constant of TBPE in plasticized PVC membrane, pKaPVC−DOS, is estimated spectrophotometrically as 6.1 ± 0.2 log units. The results can be used for developing optical chemical sensors based on TBPE (chromoionophore VIII), in particular for predicting the sensor lifetime, optimization of the sensor operating range and measuring conditions.

Indirect Nano-sensing approach: A universal potentiometric silver ion selective sensor for inline quantitative profiling of the kinetics and thermodynamics of formation and decay of silver nanoparticles

Indirect Nano-sensing are indispensable chemical sensory points that make use of the unique properties of nanoparticles to derive information about it to our macroscopic world. Precious Silver nanoparticles have become more attractive in many areas of healthcare and life sciences leading to massive industrial production and increase of environmental exposure which may lead to Nanotoxicity accompanied by the release of Ag+ ions. A reversible silver selective screen-printed electrode was fabricated, optimized, and validated. A wide linearity range of 1 × 10−6 – 1 × 10−2 M was obtained, with a LOD that reaches 1.5 × 10−7 M and a typical slope of monovalent cationic compounds of 59.6 mV/decade. It showed high selectivity towards the cationic Ag+ ion activity in presence of the negatively charged citrate capped silver nanoparticles (Cit-AgNPs). The fabricated sensor has been used for tracking the decrease of Ag+ activity during the reduction of AgNO3 with tri-sodium citrate during the Bottom-up synthesis of Cit-AgNPs at different temperature (60, 70 and 80 °C). The kinetic parameters (Activation energy (Ea) and Reaction rate (K)) and the thermodynamic characteristics (free activation energy (ΔG), entropy (ΔS), enthalpy (ΔH)) have been calculated. Furthermore, it has been used for tracking the release of Ag+ during the spontaneous and stimulated decay of Cit-AgNPs. The present work could be a junction between nanotechnology and recent advances in design of a reproducible, portable real-time analyzer for in-process monitoring of the production of Cit-AgNPs and its environmental hazards with many advantages in comparison to the reported techniques in terms of portability, simplicity, cost-efficient, fast inline tracking, no sampling, real-time profiles at high temperatures and it does not need professional operators.

Polymeric nanofiber-based ion-selective sensors

Abstract Ion-selective sensors are established tools of chemical analysis used in both electrochemical and optical sensing modes. They allow insight into ion concentrations in various samples, offering reliable performance. One of the ways of improving this class of devices is to explore the benefits of nanoscale receptor layers. In this respect, nanofibers seem to be a highly attractive option because of unique properties related to the geometry of this class of nanomaterials. This paves the way to explore alternative approaches to design ion-selective receptors architecture, to benefit from receptor molecules that are not compatible with classical ion-selective membranes.

Investigation of Highly Sensitive Cadmium Ion Selective FET Sensors with AC Impedance Analysis

In this study, we developed a cadmium ion selective sensor which can detect cadmium ion in water, in the convenience of home/office. The ion selective membrane (ISM) FET sensor combines novel extended gate FET structure and cadmium ion selective membrane. The AC impedance measurement result is also analyzed in this research. There is an electrode pair on the epoxy substrate. One is the reference electrode (RE) and another one is the extended electrode (EE). Gate voltage is applied on the reference electrode and the extended electrode is connected to the gate of the FET. The voltage change caused by ions will be amplified by the FET. The cadmium ISM is immobilized on the electrode pair. A narrow gap between the two electrodes leads to the high sensitivity and, as well as the high gate voltage. Figure 1 shows the electrical characteristic of Cd-ISFET. From the figure we can find out that as the cadmium ion concentration increases, the drain current will also increase. The response time of the Cd-ISFET sensor only needs 15 minutes and detection limit can reach 10-11M which is comparable with laboratory based instrument like ICP-MS. This Cd-ISFET sensor has high sensitivity (71 mV/ decade [Cd2+]) which is beyond ideal Nernst sensitivity (29 mV /decade [Cd2+]). A portable device is developed in this research and makes the operation method easy, friendly and convenient in contrast with ICP-MS. We first demonstrate the methodology of our sensor and we will apply our sensor on drinking water, tea, Chinese herbal medicine, and milk etc. Figure 1

Improved Sensing Capability of Hg-Ion Selective Membrane(ISM)-Coated FET Sensors with PBS Conditioning

In this work, phosphate buffered saline (PBS) conditioned PVC-based mercury ion selective membranes (Hg-ISM) were used to fabricate ion-selective extended gate FET mercury ion sensor. At pH 7.4 phosphate buffer solution, a detection limit below 10-12M and a linear response ranging from 10-12M to 10-7M were obtained. The excellent selectivity of the PBS-conditioned mercury ion selective membrane were demonstrated by the selectivity experiment of the membrane. It has been shown that PBS-conditioned mercury ion selective membrane possesses superb selectivity toward Pb and Cd. X-ray photoelectron spectroscopy were successfully applied in the surface characterization of the mercury ion selective membrane coated extended gate field effect transistor. The X-ray photoelectron spectroscopy confirmed that mercury ion were captured in the membrane structure after testing with mercury standard solution. This PBS-conditioned mercury ion selective membrane coated extended gate FET provides the detection limit lower than the conventional ion-selective electrode (10-6M), and the detection limit is comparable to the laboratory-based instrument such as ICP-MS. Our sensor can enable us to conduct facile, instant and accurate test of the mercury ion in the daily diet. Figure 1

Developing an Ion-Selective Electrode Membrane Sensor to Detect Lead Levels in Drinking Water

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. This is particularly evident in houses built prior to 1986 when the United States Environmental Protection Agency (EPA) amended the Safe Drinking Water Act (SDWA) to prohibit the use of any lead-based pipe. Despite the legally established action limit of lead level of 15 parts-per-billion (ppb) in drinking water, incidents with disastrous consequences have occurred repeatedly (e.g. water crisis in Flint, Michigan). The objective of this research is to develop a polymeric ion-selective electrode (ISE) for the detection of lead levels at the EPA action level, or 10-9 molar concentration (M). Primarily, various ratios of sodium tetraphenylborate, resin powder, and lead-selective ionophore were considered and investigated to accomplish this goal. Two commercially available ionophores (Dibenzo-18-Crown-6 and Tert-Butylcalix(4)Arene-Tetrakis) were investigated as well as a synthesized poly (AN-co-HSA) copolyaniline ionophore. The commercially available ionophores were able to consistently achieve a limit of detection (LOD) of 10-6 M when used for the ISE electrode while the synthesized ionophore showed a less consistent LOD between 10-6 M and 10-9 M.

Printed Wearable Sensor Patch for Multi-Analytes Detection in the Sweat Range

Printed Wearable Sensor Patch for Multi-Analytes Detection in the Sweat Range

Investigation of Highly Sensitive Cadmium Ion Selective FET Sensors with AC Impedance Analysis

In this study, we developed a cadmium ion selective sensor which can detect cadmium ion in water, in the convenience of home/office. The ion selective membrane (ISM) FET sensor combines novel extended gate FET structure and cadmium ion selective membrane. With the unique structure and the methodology the sensitivity of Cd-ISFET is 71 mV/ decade [Cd2+] which is beyond ideal Nernst sensitivity and the detection limit is comparable with ICP-MS. The AC impedance measurement result is also analyzed in this research. Through the AC impedance results we can find out and investigate the mechanism of Cd-ISFET.

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 highly sensitive ion selective electrochemical sensor amplified with ionic liquid for determination of lanthanum ion in real water samples

ABSTRACT Lanthanum(La) has been utilised in various industries and entered water samples through the discharge of industrial wastewater. Exposure to La (III) ion can damage some human organisms, such as the nervous system and lungs, and increase the risk of lung cancer. Therefore, the measurement of lanthanum in water samples is very important to control its adverse effects. In this study, a new and cheap potentiometric sensor was developed to determine La(III) ion in real water samples. A carbon paste electrode (CPEs) as an indicator electrode was prepared using graphite powder, commercial ionic liquids as a binder, graphene oxide and a synthetic ligand as an ionophore. The complex reaction between the 2-((2-(5-amino-1, 3, 4-thiadiazol-2-yl)hydrazono)methyl)phenol Schiff base and La(III) ion has been explored by employing the density functional theory (DFT). The results of the theoretical were shown the complex formation La(III) is thermodynamically favourable and confirmed the obtained experimental results. The percentage of components present in La(III) ion electrode was optimised by an experimental design based on D-optimal mixture design, which reduces the cost and time of the electrode optimisation process. A Nernstian behaviour was observed by the electrode in a concentration range from 7.0 × 10−7 to 1.0 × 10−1 M to measure La(III) with a correlation coefficient of 0.9832. Also, a low LODs (5.16 × 10−8) and RSDs (2.05%) were obtained with the sensor. Application of the sensor for the real samples was indicated the La(III) sensor can be well utilised for the analyte determination with a suitable recovery (≥97.4).

Recent advances in voltammetric, amperometric and ion-selective (bio)sensors fabricated by microengineering manufacturing approaches

Summary Over the last few years, microengineering fabrication approaches, originating from the semiconductor manufacturing technology, have been increasingly used for the development of electrochemical (bio)sensors and analytical devices. The application of various microengineering technologies enables the rapid mass fabrication of low-cost and disposable sensors of small size with uniform and strictly controlled geometry and surface properties and provides wide scope for device miniaturization and integration. This work will focus on the latest developments of microfabricated voltammetric, amperometric and ion-selective sensors with representative applications to organic/gas analysis, ion detection, biosensing/wearable devices and electrochemical imaging/in-vivo sensing.