Potentiometric Sensor Research Articles

Metal-organic frameworks as sensitisers for potentiometric sensors

As an example for a metal-organic framework (MOF) sorbent acting as sensitiser in a potentiometric sensor, we introduce the metal–organic framework (MOF) UiO-66-NH2 into a bridged extended-gate field effect transistor (EGFET) design. The sensitised EGFET detects residue of the insecticide imidacloprid with a limit of detection more than 3 orders of magnitude smaller than the EU ‘Maximum Residue Limit’ (MRL) for imidacloprid. This allows decisions on MRL compliance of water at a much lower experimental footprint than with chromatographic methods. To apply the sensor to food samples, we account for possible interference from legitimate food ingredients. Interference is small or moderate for fruit juices, moderate for ‘red’ juice (containing anthocyanin dyes), and small for others. Interference is strong for tea, probably from caffeine. We propose a test protocol to make ‘accept/reject’ decisions with respect to imidacloprid residue even in the presence of small or moderate interference. The present agar-bridged EGFET design enables the wider use of MOF sorbents in potentiometric sensors.

A New Planar Potentiometric Sensor for In Situ Measurements.

A new construction of a potentiometric sensor was introduced for the first time. It relies on the use of two membranes instead of one, as in the well-known coated-disc electrode. For this purpose, a new electrode body was constructed, including not one, but two glassy carbon discs covered with an ion-selective membrane. This solution allows for the sensor properties to be enhanced without using additional materials (layers or additives) on the membrane. The new construction is particularly useful for in situ measurements in environmental samples. Two ion-selective polymeric membranes were used, namely H+ and K+-selective membranes, to confirm the universality of the idea. The tests conducted included chronopotentiometric tests, electrochemical impedance spectroscopy, and potentiometric measurements. The electrical and analytical parameters of the sensors were evaluated and compared for all tested electrodes to evaluate the properties of the planar electrode versus previously known constructions. Research has shown that the application of two membranes instead of one allows for the resistance of an electrode to be lowered and for the electrical capacitance to be elevated. Improving the electrical properties of an electrode resulted in the enhancement of its analytical properties. The pH measurement range of the planar electrode is 2-11, which is much wider in contrast to that of the single-membrane electrode. The linear range of the K+-selective planar electrode is wider than that of the coated-disc electrode and equals 10-6 to 10-1 M. The response time turned out to be a few seconds shorter, and the potential drift was smaller due to the application of an additional membrane in the electrode construction. This research creates a new opportunity to design robust potentiometric sensors, as the presented construction is universal and can be used to obtain electrodes selective to various ions.

PVC plasticized membranes modified with Fe3O4 nanoparticles for potentiometric sensing of sulfate

Potentiometric sensing is one of the most wide spread platforms for analysis of aqueous solutions. The development of potentiometric sensors for hydrophilic anions such as sulfate, phosphate and bicarbonate is a challenging problem, since their high hydration energy results in a low affinity for non-polar polymer membranes – a standard material for potentiometric sensor production.In this study we propose a new type of polymeric sensor membranes for ion-selective sensors with pronounced selectivity to hydrophilic anions. The membranes are based on inorganic Fe3O4 nanoparticles (NP) embedded into plasticized poly(vinyl chloride). Six different formulations of membranes with various combinations of Fe3O4 nanoparticles and other membrane-active components were synthesized and characterized with a wide range of physico-chemical methods. Contact angle measurements, FTIR spectra, SEM and AFM imaging, magnetization hysteresis curves, ZFC/FC studies were performed. The obtained results proved the formation of nanocomposites and demonstrated a structure with “cavities” in membranes with embedded nanoparticles. Potentiometric sensitivity and selectivity of the developed sensors in aqueous solutions of SO42−, HPO42−, HCO3−, H2PO4−, NO3− and Cl−anions were studied. The developed sensors showed high sensitivity to sulfate ion (-22 mV/dec in the concentration range from 10−5 to 10−3 M) and low sensitivity to the typical interfering anions – chloride and nitrate (-14 mV/dec). The optimized sensor membrane composition demonstrated sulfate selectivity higher than that of commercially available ion-selective sensor formulations. The novel sensors were tested for quantification of SO42− in real samples of natural mineral water and the obtained content of sulfate was in a good agreement with the reference data (relative error < 3 %)

SPOOC (Sensor for Periodic Observation of Choline): An Integrated Lab-on-a-Spoon Platform for At-Home Quantification of Choline in Infant Formula.

Choline is an essential micronutrient for infants' brain development and health. To ensure that infants receive the needed daily dose of choline, the U.S. Food and Drug Administration (FDA) has set requirements for choline levels in commercialized infant formulas. Unfortunately, not all families can access well-regulated formulas, leading to potential inadequacies in choline intake. Economic constraints or difficulties in obtaining formulas, exacerbated by situations like COVID-19, prompt families to stretch formulas. Accurate measurement of choline in infant formulas becomes imperative to guarantee that infants receive the necessary nutritional support. Yet, accessible tools for this purpose are lacking. An innovative integrated sensor for the periodic observation of choline (SPOOC) designed for at-home quantification of choline in infants' formulas and milk powders is reported. This system is composed of a choline potentiometric sensor and ionic-liquid reference electrode developed on laser-induced graphene (LIG) and integrated into a spoon-like device. SPOOC includes a micro-potentiometer that conducts the measurements and transmits results wirelessly to parents' mobile devices. SPOOC demonstrated rapid and accurate assessment of choline levels directly in pre-consuming infant formulas without any sample treatment. This work empowers parents with a user-friendly tool for choline monitoring promoting informed nutritional decision-making in the care of infants.

New use of an Ag electrode and a potentiodynamic method to control the presence of chlorides in porous media like concrete

Chloride detection in porous materials is important for the soil characterisation and the durability control of reinforced concrete structures. Chloride content in soil can affect soil fertility, and the presence of chlorides in reinforced concrete structures can trigger the corrosion of reinforcement, which leads to structure failure.In both cases, the material in which chlorides are detected is a porous medium. Traditionally in this type of materials, chlorides have been controlled by means of tedious laboratory tests, in which specimens of the material are used, as are passive sensor systems like potentiometric sensors. In the former, tests are usually costly and do not allow effective control in real time. In the latter, as the sensor is not excited, overlapping reactions occur on its surface that can lead to errors when estimating chloride content.In aqueous media, chloride detection is efficiently carried out by electrochemical sensors using potentiodynamic techniques. However, they have hardly been employed in porous media, in which the porous network contains the so-called "pore solution". The present work aims to evaluate the feasibility of using an Ag electrode together with a triangular sweep potentiodynamic signal using concretes of different porosities as a porous medium. This opens up a new study field in electrochemical sensor technology.

A High‐Performance Phosphate Potentiometric Sensor Based on Cobalt Nanoparticles Electroplated on Hierarchically Porous Laser‐Induced Graphene

AbstractPhosphate is an important fertilizer in agriculture and electrochemical sensors based on cobalt (Co) are promising for measurement of phosphate. The deposition of Co onto conductive substrates to form a nano/microstructured Co layer with rich active sites is a typical strategy to improve detection performances. However, the widely used substrates show smooth surfaces, which cannot provide extra active sites. Herein, a high‐performance phosphate sensor is fabricated by generating Co nanoparticles (NPs) on a hierarchically porous laser‐induced graphene (LIG) matrix with a large surface area. Specifically, a Co layer is first electroplated on the LIG matrix. Nevertheless, the pores of LIG will be blocked by the dense Co layer so the performances of the fabricated LIG‐Co sensor exhibit limited enhancements. Therefore, a “nearly all etching (NAE)” technique is developed to transform the dense Co layer to dispersive Co NPs and re‐expose the pores of LIG, both increasing the active sites. Compared to the LIG‐Co sensor, the LIG‐Co NP sensor displays overall superiority. The response time, sensitivity, and linearity are enhanced from ≈60 to ≈10 s, from 0.012 to 0.069 V dec−1, and from 0.973 to 0.998, respectively. The LIG‐Co NP sensor also shows a decent anti‐interference capability.

Development of cobalt-carbon-based potentiometric phosphate sensors using cyclic voltammetry with potential scan rate variations

Phosphate sensor development is still needed because there are not many available in the field offering fast detection on environment, medicine, and agriculture. Herein, this study reported the potentiometric sensing of phosphate ions using a cobalt-carbon electrode. Cobalt was electrodeposited in the surface of carbon-producing cobalt-carbon electrodes using cyclic voltammetry at various scan-rate using Ag|AgCl as reference electrode and assisted by ionic strength adjustor 0.0025 M at pH 4. The electrode was characterized based on morphology and crystallinity. Then, the potentiometric sensing performance was evaluated using a Cobalt carbon electrode as a working electrode for phosphate ions in various concentrations. The results showed the homogeneous particle size observed at a scan rate of 5 mV/s. Besides, all the scan-rate variations produced an amorphous structure. The greatest potentiometric slope was −34.2 mV/decade on the electrode produced at a scan rate of 1 mV/s. The electrode reproducibility test produced the highest coefficient of variation value of 0.77 %.

Development of a Highly Selective Chloride Ion Potentiometric Sensor Utilizing a Novel N, N-Ethylene-bis-(Salicylideneaminato) Zinc (II) Molecule for Clean Environment

The present study focuses on the advancement of a chloride ion potentiometric sensor that exhibits high selectivity. This sensor employs a novel molecule, namely N, N-Ethylene-bis-(Salicylideneaminato) zinc (II), in order to achieve accurate measurements in the pursuit of maintaining a clean environment. N, N′-Ethylenebis( salicylideneaminato) nickel (II) ionophore has been generated as well as evaluated using analysis of NMR, IR and C, H, N. Subsequently, membranes incorporating the ionophore (I) were developed utilizing poly(vinyl chloride) (PVC) as a matrix, with plasticizing solvent mediators including Dioctyl phthalate (DOP), chloronapthalene (CN), Dibutyl phthalate (DBP), and tri-n-butylphosphate (TBP). Additionally, catalyzed cation discriminator, hexadecyltrimethylammonium bromide (HDTMA) was employed to enhance membrane formation. This sensor performed better than all other variants. Its membrane composition was 5 mg ionophore, 32 mg PVC, 60 mg DBP, and 3 mg HDTMA. Notably, the sensor exhibited an extended operational range of 2.0×10−6 to 1.0×10−1 M, in addition to Nernstian compliance (58.8 mV/Decade) within pH span of 2.3–9.3, and an impressive response time of 19 s. A detection range as low as 1.64×10−6 was attained, indicative of its high sensitivity. Furthermore, the sensor exhibited remarkable selectivity for chloride ions, as confirmed by selectivity coefficient measurements obtained through fixed interference technique (FIM). The sensor demonstrated a satisfactory three-month shelf life and acceptable repeatability. In practical application, the sensor demonstrated effectiveness in quantifying chloride ions in wastewater samples. This work addresses important sustainability issues while contributing to an improved comprehension of the underlying concepts of self-assembled behavior and setting up an option for the generation of efficient sensors with potential uses in photonics and microelectronics.

Environmentally friendly anti-biofouling polymeric membrane potentiometric sensors based on imprinted receptors

Polymeric membrane potentiometric sensors using molecularly imprinted polymer (MIP) receptors are an ideal tool for determination of organic ionic species. However, their applications in complicated samples are very limited because of occurrence of sensor biofouling. Herein, for the first time, we describe a simple but environmentally friendly strategy to improve anti-biofouling performance of MIP-based potentiometric sensors. The non-toxic, environmentally friendly anti-fouling agent is doped into the polymeric membrane. The released organic biocidal agent from the polymeric membrane can kill the microorganisms adhered to the sensing membrane surface, and the formation of biofilms can thus be prevented. As a proof-the-concept experiment, an all-solid-state MIP-based potentiometric ceftiofur sensor is selected as a model. Capsaicin, a naturally occurring alkaloid derived from chillis, is chosen as a non-toxic biocide agent. Another widely used biocide agent 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) with low toxicity is also used as a comparison. Compared to the undoped electrode, the capsaicin-doped MIP sensor exhibits remarkably improved anti-biofouling abilities in terms of the low survival rates and the low adhesion rates of the bacterial cells and microalgae. Especially, the capsaicin-based electrode displays similar anti-fouling and response properties to the DCOIT-based one. It can be anticipated that such anti-fouling strategy may lay the foundation for development of “green” anti-fouling sensors, which are urgently required in marine monitoring and clinical diagnosis.

Inkjet Printed Potentiometric Sensors for Nitrate Detection Directly in Soil enabled by a Hydrophilic Passivation Layer

AbstractAgricultural intensification has increased the use of chemical fertilizers, promoting plant growth and crop yield. Excessive use of nitrogen fertilizers leads to nutrient loss and low nitrogen use efficiency. Management of nitrogen fertilizer input requires close to real‐time information about the soil nitrate concentration. While there is extensive work developing nitrate ion sensing solutions for liquid media, few allow for in‐soil measurements. This study introduces inkjet‐printed potentiometric sensors, containing 2 electrodes, the reference electrode (RE) and the nitrate‐selective film‐encapsulated working electrode (WE). The interaction between the nitrate‐sensitive membrane and soil nitrate ions causes a change in potential across the RE and WE. Additionally, a hydrophilic Polyvinylidene Fluoride (PVDF) layer ensures the long‐term functionality of the sensor in wet soil environments by protecting it from charged soil particles while simultaneously allowing water to flow from the soil toward the sensor electrodes. The sensors are tested in sand and silt loam soil, demonstrating their versatility across soil types. The potential change can be related to the nitrate concentration in soil, with typical sensitivities of 45–55 mV decade−1. Overall, the use of the PVDF layer allows for direct sensing in moist soil environments, which is critical for developing soil nitrate sensors.

Controllable Fabrication of Polypyrrole Nanopillar/Hair Arrays by Oxygen Plasma Treatment and Their Applications as Antibacterial Flexible pH Sensors

AbstractFlexible pH sensors have attracted a great deal of attention in numerous applications, such as wearable healthcare devices, smart wound bandages, and other pH monitor sensors for chemical and bioprocess control. Herein, a facile approach to fabricate conducting polymer polypyrrole nanopillar arrays is proposed, and its potential as an advanced pH sensing interface is shown. Using oxygen plasma treatment as the etching tool, polypyrrole nanopillar/hair arrays can be prepared after etching 3D polypyrrole network structures. Conductive polypyrrole nanopillar arrays possessed unique advantages in sensing: their featured nanopillars has enhanced antibacterial properties; their structures showed excellent hydrophilicity and are favorable for interaction with analytes in small‐volume liquids. A flexible polypyrrole nanopillar array‐based potentiometric pH sensor integrated with a solid‐state reference electrode is further designed and fabricated. Superior performance with a near‐Nernstian response of 60.1±1.0 mV pH−1, excellent repeatability, high stability, and reproducibility is verified in the physiological pH range. The reliabilities of flexible and small‐volume sample testing, as well as the applicability for artificial sweat sample pH sensing, are examined. Provided with the advantages of antibacterial properties and hydrophilicity, the proposed flexible pH sensor is promising for trace analysis in biological, medical, and healthcare applications.

Quality-by-design ecofriendly potentiometric sensor for rapid monitoring of hydroxychloroquine purity in the presence of toxic impurities

Hydroxychloroquine (HCQ) is prescribed to treat malaria and certain autoimmune diseases. Recent studies questioned its efficiency in relieving COVID-19 symptoms and improving clinical outcomes. This work presents a quality-by-design approach to develop, optimize, and validate a potentiometric sensor for the selective analysis of HCQ in the presence of its toxic impurities (key starting materials), namely 4,7-Dichloroquinoline (DCQ) and hydroxynovaldiamine (HND). The study employed a custom experimental design of 16 sensors with different ion exchangers, plasticizers, and ionophores. We observed the Nernstian slopes, correlation coefficients, quantification limit, response time, and selectivity coefficient for DCQ and HND. The computer software constructed a prediction model for each response. The predicted responses strongly correlate to the experimental ones, indicating model fitness. The optimized sensor achieved 93.8% desirability. It proved a slope of 30.57 mV/decade, a correlation coefficient of 0.9931, a quantification limit of 1.07 × 10–6 M, a detection limit of 2.18 × 10–7 M, and a fast response of 6.5 s within the pH range of 2.5–8.5. The sensor was successfully used to determine HCQ purity in its raw material. The sensor represents a potential tool for rapid, sensitive, and selective monitoring of HCQ purity during industrial production from its starting materials.

Development of a dual sensitive N,N,N’,N’,N”,N”-hexa-n-octylnitrilotriacetamide (HONTA) based potentiometric sensor for direct thorium(IV) estimation

A dual sensitive, simple, and rapid membrane-based potentiometric sensor was developed to determine thorium (Th) ion in nuclear fuel samples which does not require any prior chemical separation of other matrix elements. Sensor was prepared by incorporating N,N,N’,N’,N”,N”-hexa-n-octylnitrilotriacetamide (HONTA) in a polyvinyl chloride (PVC) matrix in presence of 2-nitrophenyl octyl ether (NPOE) and sodium tetraphenyl borate (NaTPB). The optimum membrane composition was found to be 14.1% HONTA, 3.2% NaTPB, 54.9% NPOE, 27.8% PVC, which showed a dual sensitive linear region in the calibration plot with sub-Nernstian and super-Nernstian slopes of 12.1 ± 0.4 mV/decade and 71.7 ± 3.5 mV/decade, respectively, with the corresponding linear dynamic ranges of 2.0 × 10−5 to 5.3 × 10−4 M and 3.8 ×10−3 to 1.4 × 10−2 M, respectively. The super-Nernstian sensitivity exhibited by the sensor increases with Th(IV) as well as HONTA concentrations in the membrane and can be thought to be due to micelle-mediated selective adsorption (MMSA) sensing of the metal ion. Solution speciation of Th(IV) in acetate buffer was determined by laser desorption/ionization mass spectrometry (LDI-MS) and Medusa software. Pristine and used membranes were characterized by Fourier transform infrared (FTIR), scanning electron microscopy–energy dispersive x–rays (SEM-EDS) and small angle neutron scattering (SAXS). Thorium was measured in an actual (Th–U) mixed solution and in a synthetic advance heavy water reactor (AHWR) fuel sample. The present study describes a new approach for the detection of Th(IV) ion through MMSA in an ion selective electrode (ISE).

Highly sensitive on-skin flexible Sb2O3/Sb thin film pH sensor for real-time sweat sensing

This study presents a significant advancement in the application of a freestanding potentiometric pH sensor patch made of PDMS, incorporating a sensing electrode of Sb2O3/Sb thin film and a reference electrode of AgIO3/Ag thin film. The pH sensing electrodes of Sb2O3/Sb/Au/Ni and AgIO3/Ag/Au/Ni thin films were deposited over the PDMS/cellulose acetate/Si substrate using the ECR/RF sputtering technique. The pH sensor prepared on the PDMS/cellulose acetate/Si substrate displayed excellent sensitivity (−58.24 to −60.84 mV/pH, n = 4) and a robust linear response (R2 ∼ 0.99) in a wider pH range (1.68–9.18). The flexible on-skin wearable pH sensors were obtained by peeling off the pH sensor-assisted PDMS sheet from the Si substrate, which exhibited a remarkable sensitivity of -54.29 mV/pH and a linear pH response (R2 ∼ 0.99). Real-time sweat sensing experiments confirmed the accuracy of the developed flexible on-skin wearable pH sensors in monitoring pH levels at different body parts.

Machine learning-based prediction of seasonal hypoxia in eutrophic estuary using capacitive potentiometric sensor

A hypoxia occurred in eutrophic estuary was predicted using long short-term memory (LSTM) model with prediction time steps (PTSs) of 0, 1, 12, and 24 h. A capacitive potential (CP), which provides quantitative information on dissolved oxygen (DO) concentration, was used as a predictor along with precipitation, tide level, salinity, and water temperature. First, annual changes in DO concentration were clustered in three phases of annual DO trends (oversaturation, depletion, and stable) using k-means clustering. CP was the most influential variable in clustering the DO phases. The LSTM was implemented to predict the DO phases and hypoxia occurrences. In the simultaneous prediction of the depletion phase and hypoxia occurrence with a 12 h PTS, the accuracy was 92.1% using CP along with other variables; it was 3.3% higher than that achieved using variables other than CP. In the case of predicting the depletion phase and hypoxia non-occurrence using CP along with other variables, the accuracy was 61.1%, which was 5.5% higher than that when CP was not used. When using CP along with other variables, the total accuracy was highest for all PTS. Overall, the utilization of CP and machine learning techniques enables accurate predictions of both short-term and long-term hypoxia occurrences, providing us with the opportunity to proactively respond to disasters in aquaculture and environmental management due to hypoxia.

Actively Driven Light-Addressable Sensor/Actuator System for Automated pH Control for the Integration in Lab-On-A-Chip (LoC) Platforms.

The miniaturization of microfluidic systems usually comes at the cost of more difficult integration of sensors and actuators inside the channel. As an alternative, this work demonstrates the embedding of semiconductor-based sensor and actuator technologies that can be spatially and temporally controlled from outside the channel using light. The first element is a light-addressable potentiometric sensor, consisting of an Al/Si/SiO2/Si3N4 structure, that can measure pH changes at the Si3N4/electrolyte interface. The pH value is a crucial factor in biological and chemical systems, and besides measuring, it is often important to bring the system out of equilibrium or to adjust and control precisely the surrounding medium. This can be done photoelectrocatalytically by utilizing light-addressable electrodes. These consist of a glass/SnO2:F/TiO2 structure, whereby direct charge transfer between the TiO2 and the electrolyte leads to a pH change upon irradiation. To complement the advantages of both, we integrated a light-addressable sensor with a pH sensitivity of 41.5 mV·pH-1 and a light-addressable electrode into a microfluidic setup. Here, we demonstrated a simultaneous operation with the ability to generate and record pH gradients inside a channel under static and dynamic flow conditions. The results show that dependent on the light-addressable electrode (LAE)-illumination conditions, pH changes up to ΔpH of 2.75 and of 3.52 under static and dynamic conditions, respectively, were spatially monitored by the light-addressable potentiometric sensor. After flushing with fresh buffer solution, the pH returned to its initial value. Depending on the LAE illumination, pH gradients with a maximum pH change of ΔpH of 1.42 were tailored perpendicular to the flow direction. In a final experiment, synchronous LAE illumination led to a stepwise increase in the pH inside the channel.

Potentiometric detection of apomorphine in human plasma using a 3D printed sensor

Apomorphine is a dopamine agonist that is used for the management of Parkinson's disease and has been proven to effectively decrease the off-time duration, where the symptoms recur, in Parkinson's disease patients. This paper describes the design and fabrication of the first potentiometric sensor for the determination of apomorphine in bulk and human plasma samples. The fabrication protocol involves stereolithographic 3D printing, which is a unique tool for the rapid fabrication of low-cost sensors. The solid-contact apomorphine ion-selective electrode combines a carbon-mesh/thermoplastic composite as the ion-to-electron transducer and a 3D printed ion-selective membrane, doped with the ionophore calix[6]arene. The sensor selectively measures apomorphine in the presence of other biologically present cations – sodium, potassium, magnesium, and calcium – as well as the commonly prescribed Parkinson's pharmaceutical, levodopa (L-Dopa). The sensor demonstrated a linear, Nernstian response, with a slope of 58.8 mV/decade over the range of 5.0 mM–9.8 μM, which covers the biologically (and pharmaceutically) relevant ranges, with a limit of detection of 2.51 μM. Moreover, the apomorphine sensor exhibited good stability (minimal drift of just 188 μV/hour over 10 h) and a shelf-life of almost 4 weeks. Experiments performed in the presence of albumin, the main plasma protein to which apomorphine binds, demonstrate that the sensor responds selectively to free-apomorphine (i.e., not bound or complexed forms). The utility of the sensor was confirmed through the successful determination of apomorphine in spiked human plasma samples.

Improvement of the selectivity of a molecularly imprinted polymer-based potentiometric sensor by using a specific functional monomer

Potentiometric sensors based on the molecularly imprinted polymers (MIPs) as the receptors have been successfully developed for determination of various organic and biological species. However, these MIP receptors may suffer from problems of low selectivity. Especially, it would be difficult to distinguish the target analyte from its structurally similar interferents. In this work, we propose a novel strategy that using specific functional monomer to fabricate MIP with high selectivity towards the target molecule. The density functional theory calculations are used to investigate the interactions between the template and the functional monomer. The binding energy between the template and functional monomer can be used as the criterion for identifying the optimal monomer. As a proof-of-concept experiment, bisphenol A (BPA) is chosen as the template and the MIP is synthesized by the precipitation polymerization method using the specific allyl-β-cyclodextrin (allyl-β-CD) with high affinity towards BPA as the functional monomer. The high-affinity MIP is employed as the receptor for the construction of the potentiometric sensor. The proposed potentiometric sensor based on the MIP using allyl-β-CD as the functional monomer shows an improved response performance in terms of selectivity and sensitivity compared to the conventional potentiometric sensor based on the MIP with the common monomer (i.e., methacrylic acid). This allyl-β-CD MIP-based potentiometric sensor shows a detection limit of 0.29 μM for BPA, which is about one order of magnitude lower than that obtained by the conventional MIP-based potentiometric sensor. We believe that utilizing a functional monomer with specific recognition ability towards target in the fabrication of MIP could provide an appealing way to construct highly selective MIP-based electrochemical and optical sensors.

Hydrophilic redox buffers for textile-based potentiometric sensors

One of the barriers to the more widespread use of ion-selective electrodes (ISEs) in resource-limited areas is the need for frequent recalibration of such devices. The incorporation of a redox buffer to minimize the effect of redox-active impurities in the system has previously been shown to significantly improve reproducibility. To date, however, there have been no examples of redox buffers compatible with anion-sensing polymeric sensing membranes that can be incorporated into the inner filling solution of an ISE. Here, we introduce a novel hydrophilic redox buffer, cobalt(II/III) bis(terpyridine), and show the improvement of the standard deviation of E0 of chloride sensors from 2.7 to 0.3 mV upon introduction of the redox buffer into the inner filing solution of conventional, rod-shaped electrodes. The redox buffer is also compatible with a textile-based sensing platform, which was shown by incorporation into a textile-based platform with embedded ion-sensing and reference membranes. As only a surprisingly small number of hydrophilic redox buffers have been reported in the literature, the cobalt(II/III) bis(terpyridine) redox buffer may also find applications outside of the field of ISEs.

Rapid measurement of bacterial contamination in water: A catalase responsive-electrochemical sensor

The present study describes the development of a potentiometric sensor for microbial monitoring in water based on catalase activity. The sensor comprises a MnO2-modified electrode that responds linearly to hydrogen peroxide (H2O2) from 0.16 M to 3.26 M. The electrode potential drops when the H2O2 solution is spiked with catalase or catalase-producing microorganisms that decompose H2O2. The sensor is responsive to different bacteria and their catalase activities. The electrochemical sensor exhibits a lower limit of detection (LOD) for Escherichia coli at 11 CFU/ml, Citrobacter youngae at 12 CFU/ml, and Pseudomonas aeruginosa at 23 CFU/ml. The sensor shows high sensitivity at 3.49, 3.02, and 4.24 mV/cm2dec for E. coli, C. youngae, and P. aeruginosa, respectively. The abiotic sensing electrode can be used multiple times without changing the response potential (up to 100 readings) with a shelf-life of over six months. The response time is a few seconds, with a total test time of 5 min. Additionally, the sensor effectively tested actual samples (drinking and grey water), which makes it a quick and reliable sensing tool. Therefore, the study offers a promising water monitoring tool with high sensitivity, stability, good detection limit, and minimum interference from other water contaminants.