Search Results (86)

This work presents an idea for a new reliable potentiometric sensor for nitrate ion determination. The paper provides the optimized procedure for the preparation and maintenance of single-piece nitrate-selective electrodes with carbon black nanoparticles. The optimal carbon black amount was selected based on the electrical properties of the designed sensors. The 5% addition of carbon nanomaterial to the polymeric membrane ensured the highest electrical capacitance (of 610 µF) and the lowest resistance (of 421 kΩ); therefore, this amount was further applied to design single-piece sensors. The influence of carbon black incorporation into the membrane on the analytical performance of the nitrate-selective electrodes was investigated, focusing on parameters such as sensitivity, selectivity, detection limit, and potential stability. Carbon black-modified nitrate-selective sensors exhibit a near-Nernstian response in a wide range of nitrate ion concentrations (with a detection limit of 7 × 10⁻⁷). Remarkable potential stability, ensured by the hydrophobic properties of the modified membrane, was evaluated during the water-layer test and the calculated potential drift equaled 0.052 mV/h. Full article

An implantable multi-ion image sensor equipped with magnesium ion (Mg²⁺)-and calcium ion (Ca²⁺)-sensitive membranes was fabricated for the selective measurement of extracellular Mg²⁺ in the brain, and the sensor performance was evaluated. This sensor complements the low selectivity of the Mg²⁺-sensitive membrane for Ca²⁺ by depositing a Ca²⁺-sensitive membrane in addition to the Mg²⁺-sensitive membrane on a CMOS (Complementary Metal Oxide Semiconductor)-based potentiometric sensor array with 5.65 × 4.39 µm² pitch, enabling selective measurement of Mg²⁺ and Ca²⁺. Characterization of the sensor confirmed a Ca²⁺ sensitivity of 26.5 mV/dec and Mg²⁺ sensitivity of 19 mV/dec. Based on validation experiments with varying concentrations of Mg²⁺ and Ca²⁺, selective Ca²⁺ and Mg²⁺ measurements were successfully achieved. Furthermore, real-time imaging of Mg²⁺ and Ca²⁺ and quantification of their concentration changes were performed. The developed sensor may be successfully applied for extracellular multi-ion imaging of Mg²⁺ and Ca²⁺ in the living brain. Full article

This paper presents a methodology for the preparation of a new active component for ion-selective membranes, based on a di-substituted sulfonium derivative of the closo-decaborate anion at the apical vertices with the octadecylalkyl substituents 1,10-B₁₀H₈(S(C₁₈H₃₇)₂)₂. This approach is characterized by physicochemical methods of analysis (11B, 1H, 13C NMR spectroscopy, IR spectroscopy and elemental analysis). The compound obtained is used as an active component of a PVC membrane selective to terbinafine hydrochloride. The sensor developed is highly selective to the drug to be detected, has a linearity range of 4.0 × 10⁻⁸–1.0 × 10⁻² and a detection limit of 1.0 × 10⁻⁸, and can detect terbinafine hydrochloride in the pH range of 3 to 6. Full article

Due to their mechanical robustness and chemical resistance, composite electrospun membranes based on polyvinyl chloride (PVC) are suitable for sensor applications. Aiming to improve the electrical characteristics of these membranes, this work investigated the effects of the addition of carbon nanotubes (CNTs) to PVC electrospun membranes, in terms of morphology and thermal and impedance behavior. Transmission electron microscopy images evidenced that most of the nanotubes were encapsulated within the fibers and oriented along them, while field-emission scanning electron micrographs revealed that the membranes consisted of uniform fibers with an average diameter of 339 ± 31 nm, regardless of the addition of the carbon nanotubes. With respect to the neat resin, the addition of nanotubes caused a significant lowering of the glass transition temperature (up to 20 °C) and a marked change in the second degradation step of PVC. Nyquist plots from electrical impedance spectra showed a charge transfer resistance (R_CT) of 38 and 40 MΩ for neat PVC and PVC/CNT 3 wt.% membranes, respectively, indicating that, in the dry state, the encapsulation of CNTs in the fibers and the high porosity of the membranes prevented the formation of a percolation network, increasing the electrical resistance. In the wet state, however, there was a greater change in the impedance behavior, decreasing the resistance R_CT to 4.5 and 1.1 MΩ, for neat PVC and PVC/CNT 3 wt.% membranes, respectively. The results of this study, showing a significant variation in impedance behavior between dry and wet membranes, are relevant for the development of various types of sensors based on PVC composites. Full article

Carbon nanomaterials were introduced into this research as modifiers for polymeric membranes for single-piece electrodes, and their properties were studied for the case of nitrate-selective sensors. The use of graphene, carbon black and carbon nanotubes is shown to significantly improve the potentiometric response, while no redox response was observed. The use of carbon nanomaterials results in a near-Nernstian response (54 mV/pNO₃⁻) towards nitrate ions over a wide linear range (from 10⁻¹ to 10⁻⁶ M NO₃⁻). The results obtained by chronopotentiometry and electrochemical impedance spectroscopy reveal little resistance, and the capacitance parameter is as high as 0.9 mF (for graphene-based sensor). The high electrical capacity of electrodes results in the good stability of the potentiometric response and a low potential drift (0.065 mV/h). Introducing carbon nanomaterials into the polymetric membrane, instead of using them as separate layers, allows for the simplification of the sensors’ preparation procedure. With single-piece electrodes, one step of the procedure could be omitted, in comparison to the procedure for the preparation of solid-contact electrodes. Full article

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. Full article

In this study, a novel highly sensitive and selective fluorescent optode membrane aimed at the determination of Pb(II) ion is proposed by incorporating N-(3-(1,4-dioxa-7,13-dithia-10-azacyclopentadecan-10-yl)propyl)-5-(dimethylamino)naphthalene-1-sulfonamide (L) as fluoroionophore in polyvinyl chloride (PVC) containing 2-nitrophenyl octylether (NPOE) as a plasticizer. In addition to high stability and reproducibility, the proposed optosensor showed a unique selectivity toward Pb(II) ion, with a wide linear range of molar concentrations (1.0 × 10⁻⁹–1.0 × 10⁻³ M) and a low detection limit of 7.5 × 10⁻¹⁰ M in solution at pH 5.0. The formation constants of the Pb(II) complexes with the fluoroionophore were evaluated by fitting the fluorescence data with a nonlinear least-squares curve-fitting program, and further information about the structures of the complexes were evaluated based on hybrid-DFT calculations. The optosensor exhibited a fast response time of less than three min, being easily regenerated by exposure to a solution of dithiothreitol. The sensor was applied to the determination of Pb(II) in real samples (canned tuna fish), and it provided satisfactory results comparable to those obtained via atomic absorption spectrometry (AAS). Full article

Gemcitabine is a chemotherapeutic agent used to treat various malignancies, including breast and bladder cancer. In the current study, three innovative selective gemcitabine hydrochloride sensors are developed using 4-tert-butylcalix-[8]-arene (sensor 1), β-cyclodextrin (sensor 2), and γ-cyclodextrin (sensor 3) as ionophores. The three sensors were prepared by incorporating the ionophores with o-nitrophenyl octyl ether as plasticizer and potassium tetrakis(4-chlorophenyl) borate as ionic additive into a polyvinyl chloride polymer matrix. These sensors are considered environmentally friendly systems in the analytical research. The linear responses of gemcitabine hydrochloride were in the concentration range of 6.0 × 10⁻⁶ to 1.0 × 10⁻² mol L⁻¹ and 9.0 × 10⁻⁶ to 1.0 × 10⁻² mol L⁻¹ and 8.0 × 10⁻⁶ to 1.0 × 10⁻² mol L⁻¹ for sensors 1, 2, and 3, respectively. Over the pH range of 6–9, fast-Nernst slopes of 52 ± 0.6, 56 ± 0.3, and 55 ± 0.8 mV/decade were found in the same order with correlation regressions of 0.998, 0.999, and 0.998, respectively. The lower limits of detection for the prepared sensors were 2.5 × 10⁻⁶, 2.2 × 10⁻⁶, and 2.7 × 10⁻⁶ mol L⁻¹. The sensors showed high selectivity and sensitivity for gemcitabine. Validation of the sensors was carried out in accordance with the requirements established by the IUPAC, while being inexpensive and easy to use in drug formulation. A statistical analysis of the methods in comparison with the official method showed that there was no significant difference in accuracy or precision between them. It was shown that the new sensors could selectively and accurately find gemcitabine hydrochloride in bulk powder, pharmaceutical formulations, and quality control tests. The ionophore-based sensor shows several advantages over conventional PVC membrane sensor sensors regrading the lower limit of detection, and higher selectivity towards the target ion. Full article

The monitoring of potassium ion (K⁺) levels in human sweat can provide valuable insights into electrolyte balance and muscle fatigue non-invasively. However, existing laboratory techniques for sweat testing are complex, while wearable sensors face limitations like drift, fouling and interference from ions such as Na⁺. This work develops printed electrodes using β-cyclodextrin functionalized reduced graphene oxide (β-CD-RGO) for selective K⁺ quantification in sweat. The β-CD prevents the aggregation of RGO sheets while also providing selective binding sites for K⁺ capture. Electrodes were fabricated by screen printing the β-CD-RGO ink onto conductive carbon substrates. Material characterization confirmed the successful functionalization of RGO with β-CD. Cyclic voltammetry (CV) showed enhanced electrochemical behavior for β-CD-RGO-printed electrodes compared with bare carbon and RGO. Sensor optimization resulted in a formulation with 30% β-CD-RGO loading. The printed electrodes were drop-casted with an ion-selective polyvinyl chloride (PVC) membrane. A linear range from 10 μM to 100 mM was obtained along with a sensitivity of 54.7 mV/decade. The sensor showed good reproducibility over 10 cycles in 10 mM KCl. Minimal interference from 100 mM Na⁺ and other common sweat constituents validated the sensor’s selectivity. On-body trials were performed by mounting the printed electrodes on human subjects during exercise. The K⁺ levels measured in sweat were found to correlate well with serum analysis, demonstrating the sensor’s ability for non-invasive electrolyte monitoring. Overall, the facile synthesis of stable β-CD-RGO inks enables the scalable fabrication of wearable sensors for sweat potassium detection. Full article

A heterocyclic compound of S and N with cyclic structures, like Furans, thiophenes and related azole analogs, is important as a ligand because of it is readily available, stable and easily functionalized. Various types of heterocyclic molecules quinazolines and their derivatives contain important chromophores with desirable electrochemical properties to be applied in the sensor field. Metal complexes of these compounds have demonstrated significant electrochemical properties as ionophore or electroactive materials for the fabrication of ISEs with different polymeric membranes. R. Selva Kumar et al. 2019 reported the use of dibutyl(8-hydroxyquinolin-2-yl)methylphosphonate as ionophore in a PVC matrix for the fabrication of a potentiometric thorium(IV) ion-selective electrode These quinazoline-based membranes with other additives and plasticizers are very useful for the development of a potential difference across the membrane at membrane-solution interface in the required proportions . Analytes, such as Butralin, Hydroxylamine, and Nitrite, and heavy metal ions, like Fe³⁺ and Th⁴⁺, have also been determined using quinazoline-based membrane sensors. ISE-based electrochemical sensors are very useful in the analysis of food products, drinking water, beverages, fertilizers, soil industrial effluents, etc. They also are applied in potentiometric titration as indicator electrodes. Full article

Supramolecular gemifloxacin (GF) sensors have been developed. Supramolecular chemistry is primarily concerned with noncovalent intermolecular and intramolecular interactions, which are far weaker than covalent connections, but they can be exploited to develop sensors with remarkable affinity for a target analyte. In order to determine the dose form of the quinolone antibacterial drug gemifloxacin, the current study’s goal is to adapt three polyvinylchloride (PVC) membrane sensors into an electrochemical technique. Three new potentiometric membrane sensors with cylindric form and responsive to gemifloxacin (GF) were developed. The sensors’ setup is based on the usage of o-nitrophenyl octyl ether (o-NPOE) as a plasticizer in a PVC matrix, β-cyclodextrin (β-CD) (sensor 1), γ-cyclodextrin (γ-CD) (sensor 2), and 4-tert-butylcalix[8]arene (calixarene) (sensor 3) as an ionophore, potassium tetrakis (4-chlorophenyl) borate (KTpClPB) as an ion additive for determination of GF. The developed method was verified according to IUPAC guidelines. The sensors under examination have good selectivity for GF, according to their selectivity coefficients. The constructed sensors demonstrated a significant response towards to GF over a concentration range of 2.4 × 10⁻⁶, 2.7 × 10⁻⁶, and 2.42 × 10⁻⁶ mol L⁻¹ for sensors 1, 2, and 3, respectively. The sensors showed near-Nernstian cationic response for GF at 55 mV, 56 mV, and 60 mV per decade for sensors 1, 2, and 3, respectively. Good recovery and relative standard deviations during the day and between days are displayed by the sensors. They demonstrated good stability, quick response times, long lives, rapid recovery, and precision while also exhibiting good selectivity for GF in various matrices. To determine GF in bulk and dose form, the developed sensors have been successfully deployed. The sensors were also employed as end-point indicators for titrating GF with sodium tetraphenyl borate. Full article

Supramolecular fexofenadine sensors have been constructed. Although noncovalent intermolecular and intramolecular interactions, which are far weaker than covalent contacts, are the main focus of supramolecular chemistry, they can be used to create sensors with an exceptional affinity for a target analyte. The objective of the current research study is to adapt two PVC membrane sensors into an electrochemical approach for the dosage form determination of histamine H1-receptor antagonists: fexofenadine. The general performance characteristics of two new modified potentiometric membrane sensors responsive to fexofenadine hydrochloride were established. The technique was based on the employment of γ-cyclodextrin (CD) (sensor 1), 4-tert-butylcalix[8]arene (calixarene) (sensor 2) as an ionophore, potassium tetrakis (4-chlorophenyl) borate (KTpClPB) as an ion additive, and (o-NPOE) as a plasticizer for sensors 1 and 2. The sensors showed fast responses over a wide fexofenadine concentration range (1 × 10⁻² to 4.5 (4.7) × 10⁻⁶ M), with detection limits of 1.3 × 10⁻⁶ M and 1.4 × 10⁻⁶ M for sensors 1 and 2, respectively, in the pH range of 2–8. The tested sensors exhibit the fexofenadine near-Nernstian cationic response at 56 and 58 mV/decade for sensors 1 and 2, respectively. The sensors exhibit good stability, fast response times, accuracy, precision, and longer life for fexofenadine. Throughout the day and between days, the sensors exhibit good recovery and low relative standard deviations. Fexofenadine in its pure, dose form has been identified with success using the modified sensors. The sensors were employed as end-point indications for the titration of fexofenadine with NaTPB. Full article

In this work, the stability, electrical conductivity, and versatility of graphite-based inks were taken advantage of to fabricate a nitrate potentiometric sensor. One other key property that was exploited for the design of an ion-selective electrode was the hydrophobicity of graphite. This prevented the formation of a water layer between the solid contact and the polymeric selective membrane. Moreover, given the use of printing technologies for electrode fabrication, it was possible to easily miniaturize the sensors and achieve lower fabrication costs. In this article, a printed sensor, composed of a graphite working electrode and a Ag/AgCl reference electrode, is presented and thoroughly characterized. The working electrode was modified with a well-known PVC-ionophore membrane, and the reference electrode was protected with a PVB-NaCl saturated membrane. It showed almost-Nernstian sensitivity of −(55.4 ± 0.7) mV/dec to NO₃⁻, stability of up to 25 days of operation, limit of detection of 0.204 ± 0.009 mM, and repeatability of 99.02 % (N = 3). Coupled with its high selectivity compared with other anions, this low-cost, mass-producible sensor is a great alternative for environmental and industrial applications. Full article

Background: The remarkable properties of nickel oxide (NiO) and cerium oxide (CeO₂) nanostructures have attracted considerable interest in these nanocomposites as potential electroactive materials for sensor construction. Methods: The mebeverine hydrochloride (MBHCl) content of commercial formulations was determined in this study using a unique factionalized CeO₂/NiO-nanocomposite-coated membrane sensor. Results: Mebeverine-phosphotungstate (MB-PT) was prepared by adding phosphotungstic acid to mebeverine hydrochloride and mixing with a polymeric matrix (polyvinyl chloride, PVC) and plasticizing agent o-nitrophenyl octyl ether. The new suggested sensor showed an excellent linear detection range of the selected analyte at 1.0 × 10⁻⁸–1.0 × 10⁻² mol L⁻¹ with regression equation E_mV = (−29.429 ± 0.2) log [MB] + 347.86. However, the unfunctionalized sensor MB–PT displayed less linearity at 1.0 × 10^−5–1.0 × 10⁻² mol L⁻¹ drug solution with regression equation E_mV = (−26.603 ± 0.5) log [MB] + 256.81. By considering a number of factors, the applicability and validity of the suggested potentiometric system were improved following the rules of analytical methodological requirements. Conclusion: The created potentiometric technique worked well for determining MB in bulk substance and in medical commercial samples. Full article

A new sensing material, Pt(II)-5-(4-carboxyphenyl)-10,15,20-tris(4-phenoxyphenyl)-porphyrin (Pt(II)-COOH-TPOPP), was synthesized and characterized. Polymeric membranes containing the porphyrin and three different plasticizers were used as an electroactive material for a new anion-selective sensor. The best composition of the membrane was the one plasticized with dioctylsebacate (DOS), the obtained sensor being citrate-selective in a linear range of 5 × 10⁻⁷–1 × 10⁻¹ M citrate. The slope was Nernstian (19.73 mV/decade) with good selectivity towards a number of interfering anions and a lifetime of five weeks. Full article