Preparation and characterization of nanofibrous cellulose as solid polymer electrolyte for lithium-ion battery applications

A novel bacterial cellulose (BC)-based nanofiber material has been utilized as an ionic template for the battery system solid polymer electrolyte (SPE). The effect of drying techniques such as oven and freeze-drying on the gel-like material indicate differences in both visual and porous structures. The morphological structure of BC after oven and freeze-drying observed by field-emission scanning electron microscopy indicates that a more compact porous structure is found in freeze-dried BC than oven-dried BC. After the BC-based nanofiber immersion process into lithium hexafluorophosphate solution (1.0 M), the porous structure becomes a host for Li-ions, demonstrated by significant interactions between Li-ions from the salt and the C O groups of freeze-dried BC as shown in the infrared spectra. X-ray diffraction analysis of freeze-dried BC after immersion in electrolyte solution shows a lower degree of crystallinity, thus allowing an increase in Li-ion movement. As a result, freeze-dried BC has a better ionic conductivity of 2.71 × 10⁻² S cm⁻¹ than oven-dried BC, 6.00 × 10⁻³ S cm⁻¹. Freeze-dried BC as SPE also shows a larger electrochemical stability window around 3.5 V, reversible oxidation/reduction peaks at 3.29/3.64 V, and an initial capacity of 18 mAHr g⁻¹ at 0.2C. The high tensile strength of the freeze-dried BC membrane of 334 MPa with thermal stability up to 250 °C indicates the potential usage of freeze-dried BC as flexible SPE to dampen ionic leakage transfer.

Nanofibrous cellulose as solid polymer electrolyte for lithium-ion battery applications.     

A study on the electrochemical behavior of hydroquinone at a nanometer cobalt/l-glutamate-modified electrode

A new electrochemical sensor for hydroquinone (HQ) was prepared. The electrochemical sensor was modified by electrodeposition and electrochemical polymerization to modify nanometer cobalt (nano-Co) and poly-l-glutamic acid (poly-l-glu) on the surface of a glassy carbon electrode (GCE). Then, the electrochemical behavior of hydroquinone on the electrochemical sensor was investigated by cyclic voltammetry (CV). The experimental conditions were optimized from the aspects of electrolyte type, concentration, acidity, enrichment time and scanning speed. The experimental results showed that under optimized conditions the oxidation peak current has a good linear relationship with the concentration of hydroquinone in the range of 3.85 × 10⁻⁶ to 1.30 × 10⁻³ mol L⁻¹ (R² = 0.9998). Moreover, there was a low detection limit of 4.97 × 10⁻⁷ mol L⁻¹. When the sensor was used for the analysis of hydroquinone in water samples, the recoveries with satisfactory results were in the range of 97.2–102.6%.

A new electrochemical sensor for hydroquinone (HQ) was prepared.     

Sensitive and selective detection of the highly toxic pesticide carbofuran in vegetable samples by a molecularly imprinted electrochemical sensor with signal enhancement by AuNPs

An imprinted electrochemical sensor was constructed for the detection of carbofuran with high sensitivity and selectivity. AuNPs were used as the electron wire for signal amplification, and molecularly imprinted polymer was used as the recognition element. The preparation process of the modified electrode was optimized, and the electrode was characterized using scanning electron microscopy, cyclic voltammetry and differential pulse voltammetry. The results proved that the prepared sensor can selectively detect carbofuran and the AuNPs can increase its sensitivity. The method validation included the systematic evaluation of the linearity, sensitivity, selectivity, reproducibility and stability. The optimized sensor showed a wide linear response to carbofuran in the range from 5.0 × 10⁻⁸ to 4.0 × 10⁻⁴ mol L⁻¹ with a low detection limit of 2.4 × 10⁻⁸ mol L⁻¹. The sensor also exhibited a high selectivity to carbofuran. The real sample analysis for vegetable samples suggested its potential application in the analysis of vegetable samples.

An imprinted electrochemical sensor was constructed for the detection of carbofuran with high sensitivity and selectivity.     

Phosphorus/nitrogen co-doped and bimetallic MOF-derived cathode for all-solid-state rechargeable zinc–air batteries

With the merits of high safety and energy density, all-solid-state zinc–air batteries possess potential applications in flexible and wearable electronic devices. Especially, the air cathodes with bifunctional catalytic activity, i.e. oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been received enormous attention. In this work, we provide a novel phosphorus/nitrogen co-doped and bimetallic metal–organic framework (MOF)-derived cathode configurated with phosphorus-doped bimetallic FeNi alloys and a nitrogen-doped porous carbon layer loaded on graphene (P–FeNi/NC@G). The P–FeNi/NC@G electrode exhibits a superior OER activity with an overpotential of 310 mV at 10 mA cm⁻² and an ORR performance with a half-wave potential of 0.81 V. With P–FeNi/NC@G as the air cathode, the integrated all-solid-state rechargeable zinc–air battery presents a high open-circuit voltage of 1.53 V, a high peak power density of 159 mW cm⁻², a small charge–discharge voltage gap of 0.73 V at 5 mA cm⁻², as well as excellent long-term stability up to 144 cycles. This work not only expands the air cathode materials database but also develops a new co-doped synthesis method that can be utilized to fabricate a cathode with promoted catalytic efficiency, resulting in improved performance for an all-solid-state zinc–air battery.

The bimetallic FeNi-MOFs are employed to fabricate P–FeNi and N–carbon co-doped bifunctional catalyst. Due to the enhanced catalytic performance, the peak power density of all-solid-state zinc–air battery is 159 mW cm⁻².     

Facile preparation of 3D porous agar-based heteroatom-doped carbon aerogels for high-energy density supercapacitors

The fabrication of heteroatom-doped porous carbon materials with high electrical conductivity and large specific surface area via an environmentally friendly route is critical and challenging. Herein, nitrogen and oxygen co-doped agar porous carbon (APC) was developed for supercapacitors via a one-step carbonization method with agar as the raw material and ammonia as the activator and nitrogen source. APC outperformed pectin porous carbon, tamarind porous carbon, and the previously reported carbon-based supercapacitors with a high capacitance retention of 72% even from 0.5 A g⁻¹ to 20 A g⁻¹ and excellent cycling stability in 6 M KOH solution (retained after 10 000 cycles) with a rate of over 98.5%. Furthermore, the APC electrode-based symmetric device exhibited an impressive energy density of 20.4 W h kg⁻¹ and an ultra-high power density of 449 W kg⁻¹ in 1 M Na₂SO₄ electrolyte together with excellent cycling stability (103.2% primary capacitance retentivity after 10 000 cycles). This study offers a novel method for the synthesis of nitrogen heteroatom-doped hierarchical porous carbon materials for performance-enhanced energy storage devices.

N and O co-doped agar porous carbon (APC) as electrode materials exhibit excellent performance. A respectable energy density of 20.4 W h kg⁻¹ and an ultra-high power density of 449 W kg⁻¹, as well as excellent cycle stability in 1 M Na₂SO₄ electrolyte.     

Nitrogen and phosphorus co-doped carbon modified activated carbon as an efficient oxygen reduction catalyst for microbial fuel cells

Activated carbon (AC) is an environmentally sustainable oxygen reduction reaction (ORR) catalyst and widely used in MFCs due to its intrinsic high specific surface area and mesoporous characteristics, but it shows relatively high ORR over-potential thus low electrocatalytic activity. In this study, a method of doped carbon modification was employed to decrease the over-potential and improve the ORR electrocatalytic activity of the AC catalyst. Nitrogen and phosphorus co-doped carbon modified AC (NPC@AC) was prepared by coating phytic acid doped polyaniline onto AC through in situ oxidative polymerization and subsequent high-temperature pyrolysis. The as-prepared NPC@AC possessed a large surface area of ∼649.3 m² g⁻¹ inherited from AC and a low ORR over-potential with a highly positive onset potential of +0.22 V vs. Ag/AgCl from NPC, thus showing an enhanced ORR electrocatalytic activity in neutral solution compared to the pristine AC, and even better than the pure NPC. The air-cathode MFC using the NPC@AC catalyst generated a much higher open circuit voltage of 0.753 V and two times higher power density of 1223 mW m⁻² than that using the pristine AC catalyst of about 0.432 V and 595 mW m⁻², respectively.

Nitrogen and phosphorus co-doped carbon modified activated carbon shows decreased ORR over-potential, thus enhanced ORR electrocatalytic activity in the air-cathode of microbial fuel cells compared to pristine AC.     

N/S co-doped coal-based porous carbon spheres as electrode materials for high performance supercapacitors

N/S co-doped porous carbon spheres (NSPCSs) were prepared by a simple ultrasonic spray pyrolysis (USP) using the mixed solution of coal oxide and l-cysteine, and without a subsequent activation process. The surface properties of carbon materials have been successfully modified by the concurrent incorporation of N and S. So the capacitive performance of NSPCSs was greatly enhanced. It is used as a supercapacitor electrode to achieve a high specific capacitance of 308 F g⁻¹ at a current density of 1 A g⁻¹ and 90.2% capacitance retention even after 10 000 cycles at 5 A g⁻¹. These numerical results show that the supercapacitors based on coal-based carbon materials have great potential in high performance electrochemical energy storage.

N/S co-doped porous carbon spheres were prepared using one step strategy for high performance supercapacitors.     

Determination of cesium ions in environmental water samples with a magnetic multi-walled carbon nanotube imprinted potentiometric sensor

A potentiometric sensor, based on the glassy carbon electrode (GCE) modified with a magnetic multi-walled carbon nanotubes/cesium ion-imprinted polymer composite (MMWCNTs@Cs-IIP), is introduced for the detection of cesium(i). The IIP was synthesized using cesium ions as the template ions, chitosan as the functional monomer and glutaraldehyde as the cross-linking agent. The membrane, which was coated on the surface of the GCE, was prepared using MMWCNTs@Cs(i)-IIP as the modifier, PVC as the neutral carrier, 2-nitrophenyloctyl ether as the plasticizer and sodium tetraphenylborate as the lipophilic salt. The proposed sensor exhibited a Nernstian slope of 0.05954 V dec⁻¹ in a working concentration range of 1 × 10⁻⁷ to 1 × 10⁻⁴ M (mol L⁻¹) with a detection limit of 4 × 10⁻⁸ M. The sensor exhibited high selectivity for cesium ions and was successfully applied for the determination of Cs(i) in real samples.

A Cs(i)-selective potentiometric microsensor based on the glassy carbon electrode (GCE) modified with a magnetic multi-walled carbon nanotubes/cesium ion-imprinted polymer has been developed.     

Selective and sensitive electrochemical sensors based on an ion imprinting polymer and graphene oxide for the detection of ultra-trace Cd(ii) in biological samples

New selective and sensitive electrochemical sensors were designed based on the deposition of a promising ion imprinted polymer (IIP) on the surface of glassy carbon electrode (GCE) for the detection and monitoring of Cd(ii) in different real samples. Herein, a highly selective Cd-imprinted polymer was successfully synthesized using a novel heterocyclic compound based on the benzo[f]chromene scaffold that acted as a complexing agent and a functional monomer in the presence of azobisisobutyronitrile (initiator) and ethylene glycol dimethacrylate (cross-linker). The characterization of the synthesized chelating agent and IIP was performed using FT-IR, SEM, ¹H-NMR, EIMS, and EDX analyses. After that, the voltammetric sensor was manufactured by introducing graphene oxide (GO) on the surface of GCE; then, the IIP was grown by a drop coating technique. The electrochemical characterization of the voltammetric sensor (IIP/GO@GCE) was performed by CV and EIS. For comparison, the potentiometric sensor was also prepared by embedding IIP in plasticized polyvinyl chloride and depositing it as one layer on the GCE surface. Anodic stripping voltammetry was used to construct the calibration graph; the IIP/GO@GCE exhibited a wider detection range (4.2 × 10⁻¹²–5.6 × 10⁻³ mol L⁻¹) and extremely low detection limit (7 × 10⁻¹⁴ mol L⁻¹) for Cd(ii). Meanwhile, the potentiometric sensor showed a linear calibration curve for Cd(ii) over a concentration range from 7.3 × 10⁻⁸ mol L⁻¹ to 2.4 × 10⁻³ mol L⁻¹ with a detection limit of 6.3 × 10⁻¹⁰ mol L⁻¹. Furthermore, both sensors offered outstanding selectivity for Cd(ii) over a wide assortment of other common ions, high reproducibility, and excellent stability.

New selective and sensitive electrochemical sensors were designed based on the deposition of a promising ion imprinted polymer (IIP) on the surface of glassy carbon electrode (GCE) for the detection and monitoring of Cd(ii) in different real samples.     

A novel molecularly imprinted electrochemiluminescence sensor based on cobalt nitride nanoarray electrode for the sensitive detection of bisphenol S

A substitute for bisphenol A (BPA), bisphenol S (BPS) has endocrine disruptive and toxic effects and could pose potential risk on human health and the environment. Herein, we fabricated a sensitive molecularly imprinted electrochemiluminescence (MIECL) sensor for the determination of BPS. CoN nanoarray with outstanding electrical conductivity was prepared and it directly served as the sensor platform. Especially, due to the high surface area of the porous CoN nanoarray, the ECL probe of Ru(bpy)₃²⁺ could be absorbed on the electrode. By means of the cation exchange of Nafion membrane and utilizing tripropylamine (TPrA) as co-reactant, boosted ECL signals were obtained. Meanwhile, by combining with molecularly imprinted polymers (MIPs), the constructed sensor achieved specific recognition of BPS. On the basis of the superior properties of the CoN nanoarray-based electrode, the ECL signal of the proposed sensor was linearly proportional to the BPS concentration from 2.4 × 10⁻⁹ to 5.0 × 10⁻⁵ mol L⁻¹ (R² = 0.9965) with a low limit of detection (LOD) of 8.1 × 10⁻¹⁰ mol L⁻¹ (S/N = 3). To test the accuracy of the proposed method, the HPLC method was adopted to analyze drinking water samples as a comparison. The t-test result proved that discrepancies between HPLC analysis and the method using the fabricated MIECL sensor were acceptable. The developed MIECL sensor with the sensitive, selective, reproducible, and stable analytical performance provides a potential pathway for the detection of BPS and other BPA substitutes in drinking water samples.

Sensitive molecularly imprinted ECL sensor for the determination of BPS based on the CoN nanoarray electrode directly used as the ECL sensing platform was fabricated for the first time.     

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.

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.     

Anti-corrosion porous RuO2/NbC anodes for the electrochemical oxidation of phenol

Efficient anode materials with porous structures have drawn increasing attention due to their high specific surface area, which can compensate for the slow reaction rate of electrochemical oxidation. However, the use of these materials is often limited due to their poor corrosion resistance. Herein, we report a facile scale-up method, by carbothermal reduction, for the preparation of porous niobium carbide to be used as an anode for the electrochemical oxidation of phenol in water. No niobium ions were detected when the anodes were under aggressive attack by sulfuric acid and under electrochemical corrosion tests with a current density less than 20.98 mA cm⁻². The porous niobium carbide was further modified by applying a ruthenium oxide coating to improve its catalytic activity. The removal rates of phenol and chemical oxygen demand by the RuO₂/NbC anode reached 1.87 × 10⁻² mg min⁻¹ cm⁻² and 6.33 × 10⁻² mg min⁻¹ cm⁻², respectively. The average current efficiency was 85.2%. Thus, an anti-corrosion, highly catalytically active and energy-efficient porous RuO₂/NbC anode for the degradation of aqueous phenol in wastewater was successfully prepared.

Efficient anode materials with porous structures have drawn increasing attention due to their high specific surface area, which can compensate for the slow reaction rate of electrochemical oxidation.     

Disposable gold nanoparticle functionalized and bare screen-printed electrodes for potentiometric determination of trazodone hydrochloride in pure form and pharmaceutical preparations

In the present study, screen-printed electrodes unmodified and chemically modified with gold nanoparticles were used as sensitive electrochemical sensors for the determination of trazodone hydrochloride. The sensors were based on the use of a tetraphenylborate ion association complex as an electroactive material in screen-printed electrodes with dioctyl phthalate (DOP) as a solvent mediator modified with gold nanoparticles which improve the electrode conductivity and enhance the surface area. The sensors displayed a stable response for 5, 6 and 7 months with a reproducible potential and linear response over the concentration range 1 × 10⁻⁵–1 × 10⁻² mol L⁻¹ at 25 ± 1 °C with Nernstian slopes of 57.50 ± 0.66, 58.30 ± 0.45 and 59.05 ± 0.58 mV per decade and detection limits of 7.9 × 10⁻⁶, 7.6 × 10⁻⁶ and 6.8 × 10⁻⁶ mol L⁻¹ for sensor 1, 2 and 3 respectively. The analytical performance of the screen printed electrodes in terms of selectivity coefficients for trazodone hydrochloride relative to the number of potentially interfering substances was investigated. The proposed method has been applied successfully for the analysis of the drug in its pure and dosage forms and there is no interference from any common pharmaceutical additives.

In the present study, screen-printed electrodes unmodified and chemically modified with gold nanoparticles were used as sensitive electrochemical sensors for the determination of trazodone hydrochloride.     

Label-free impedimetric sensing platform for microRNA-21 based on ZrO2-reduced graphene oxide nanohybrids coupled with catalytic hairpin assembly amplification

Herein, a sensitive electrochemical impedance sensor was constructed based on ZrO₂-reduced graphene oxide (RGO)-modified electrode coupled with the catalytic hairpin assembly signal amplification strategy. Electrochemical impedance spectroscopy (EIS) was used to detect microRNA (miRNA) using the change in electron transfer resistance (ΔR_et) originated from nucleic acid hybridization on the electrode surface. MiRNA-21 was used as a model to verify this strategy. The results indicated that ΔR_et exhibited a good linear relationship with the concentration of miRNA-21 in the range from 1.0 × 10⁻¹⁴ mol L⁻¹ to 1.0 × 10⁻¹⁰ mol L⁻¹ with a detection limit of 4.3 × 10⁻¹⁵ mol L⁻¹ (S/N = 3). Additionally, this sensor exhibited good selectivity, and it could be applied to detect miRNA-21 in human serum samples and measure the expression levels of miRNA-21 in human breast cancer cell lines (MCF-7); thus, this sensor has great potential in cancer diagnosis.

A label-free impedimetric sensor for highly sensitive detection of miRNA-21 based on ZrO₂-RGO nanocomposite and a catalytic hairpin assembly strategy.     

A thio-β-cyclodextrin functionalized graphene/gold nanoparticle electrochemical sensor: a study of the size effect of the gold nanoparticles and the determination of tetrabromobisphenol A

In this study, a novel tetrabromobisphenol A (TBBPA) sensor was fabricated based on a CTAB-capped gold nanoparticle (AuNPs)-thio-β-cyclodextrin (SH-β-CD)/graphene oxide modified glassy carbon electrode (GCE). The peak current of TBBPA was dramatically enhanced by the AuNPs with a diameter of 6.2 nm on the modified electrodes compared with the other sized particles (10.1 or 16.1 nm). To further improve the electrochemical performance of the modified electrode, the influence of pH of the buffer solution and the accumulation time on the determination were investigated. The optimum pH and accumulation time were 7.0 and 180 s, respectively. The developed sensor exhibited good reproducibility, and excellent sensitivity and selectivity, showing a low detection limit (1.2 × 10⁻⁹ mol L⁻¹) and a linear range from 1.5 × 10⁻⁸ to 7 × 10⁻⁶ mol L⁻¹. In addition, a possible oxidization mechanism of TBBPA was also discussed. Finally, this sensor was successfully applied to detect TBBPA in water samples, and the results were consistent with those acquired by high-performance liquid chromatography.

In this study, a novel tetrabromobisphenol A (TBBPA) sensor was fabricated based on a CTAB-capped gold nanoparticle (AuNP)-thio-β-cyclodextrin (SH-β-CD)/graphene oxide modified glassy carbon electrode (GCE).     

Enhanced mixed proton and electron conductor at room temperature from chemically modified single-wall carbon nanotubes

Remarkably high mixed proton and electron conduction arising from oxidized single-wall carbon nanotubes at room temperature is demonstrated. The respective proton and electronic conductivities are 1.40 and 8.0 × 10⁻² S cm⁻¹ in the in-plane direction, and 3.1 × 10⁻² and 1.1 × 10⁻³ S cm⁻¹ in the out-of-plane direction, indicating their potential in a wide range of solid electrolyte membranes.

A chemically modified single-wall carbon nanotube showing efficient mixed proton and electron conduction at room temperature is demonstrated.     

User-friendly lab-on-paper optical sensor for the rapid detection of bacterial spoilage in packaged meat products

A lab-on-paper colorimetric sensor for detection and quantification of bacterial meat spoilage is reported. Bromocresol purple (BCP) and bromothymol blue (BTB) were used for the construction of the proposed sensor. An Android application allowing fast detection and accurate quantification of bacteria in the spoiled chicken meat samples was developed. The sensor was applied to the determination of spoilage in real chicken-meat samples, at chiller and room temperatures, and can be used for producing smart meat-packaging films. Linearity ranges were found to be 11.2 × 10³ to 1.12 × 10⁶ and 38.0 × 10³ to 1.12 × 10⁶ CFU g⁻¹ for BTB and BCP, respectively. The calibration plots showed correlation coefficients (r) of 0.9998 (slope: 2.48 g CFU⁻¹) and 0.9999 (slope: 1.95 g CFU⁻¹) in case of bromothymol blue and bromocresol purple, respectively. The Android application uses standard images to plot a calibration curve for calculating the microbial count in the samples and relates it to the standard limits. Thereafter, the application shows a message with the product''s freshness degree ranging from excellent to poor.

A lab-on-paper colorimetric sensor for detection and quantification of bacterial meat spoilage is reported.     

Application of pyrite and chalcopyrite as sensor electrode for amperometric detection and measurement of hydrogen peroxide

The sensing performance of solid-state amperometric sensors based on natural sulfide minerals, i.e., pyrite and chalcopyrite, has been characterized for the detection and measurement of hydrogen peroxide (H₂O₂) in aqueous medium. The sensors showed a wide linear relationship range between response current and the concentration of H₂O₂ from 1.0 × 10⁻⁵ mol L⁻¹ to 1.0 × 10⁻² mol L⁻¹ and 1.0 × 10⁻⁴ mol L⁻¹ to 3.0 × 10⁻² mol L⁻¹ for pyrite and chalcopyrite, respectively. The limit of detection (LOD) was as low as 8.6 × 10⁻⁶ mol L⁻¹ and 5.2 × 10⁻⁵ mol L⁻¹ (S/N = 3), respectively. The electrodes exhibited great sensitivity, repeatability and short response time (less than 5 s). The results show that pyrite and chalcopyrite can be used as a natural, low cost, reliable and sensitive sensor for hydrogen peroxide detection, creating a new and high value application for the sulfide minerals.

The sensing performance of solid-state amperometric sensors based on natural sulfide minerals, i.e., pyrite and chalcopyrite, has been characterized for the detection and measurement of hydrogen peroxide (H₂O₂) in aqueous medium.     

Calixarene based portable sensor for the direct assay of indiscriminate ephedrine content of weight loss herbal preparations

A novel potentiometric sensor was developed and optimized for the quantitative analysis of ephedrine in non-prescribed herbal supplements used as adjunctive therapy for weight loss. An initial optimization study aimed to reach the optimum membrane composition, sensor assembly, and experimental conditions. The study evaluated the effect of several factors on the sensor performance including different ion-exchangers, plasticizers, ionophores, membrane thicknesses, soaking solution concentrations, soaking time intervals, and pH. The optimized polyvinyl chloride membrane included tungstophosphoric acid hydrate as a cation exchanger, tricresyl phosphate as a plasticizer, and calix[8]arene as an ionophore to enhance the sensitivity and selectivity of the developed sensor. The polyvinyl chloride membrane was drop-casted over a polyaniline modified glassy carbon electrode surface to form a solid-state sensor. The proposed membrane succeeded to quantify ephedrine over a linear range of 6 × 10⁻⁶ to 1 × 10⁻² M with a LOD of 3.60 × 10⁻⁶ M, acceptable selectivity, and fast response time. The IUPAC characterization of sensor response and International Conference on Harmonization validation parameters were calculated. The method successfully determined ephedrine concentration in spiked herbal mixtures and determined labeled and undeclared ephedrine content of weight loss herbal preparations.

Calixarene based solid-state potentiometric sensor for direct assay of indiscriminate ephedrine content in weight loss herbal products.     

Effective screen-printed potentiometric devices modified with carbon nanotubes for the detection of chlorogenic acid: application to food quality monitoring

All-solid state screen-printed electrodes were fabricated for chlorogenic acid (CGA) detection. The screen-printed platforms were modified with multi-walled carbon nanotubes (MWCNTs) to work as a lipophilic solid-contact transducer. The sensing-membrane was plasticized with a suitable solvent mediator and incorporating [Ni^II(bathophenanthroline)₃][CGA]₂ complex as a sensory material. In a 30 mM phosphate solution (buffer, pH 6), the sensor revealed a Nernstian-response towards CGA ions with a slope of −55.1 ± 1.1 (r² = 0.9997) over the linear range 1.0 × 10⁻⁷ to 1.0 × 10⁻³ (0.035–354.31 μg mL⁻¹) with a detection limit 7.0 × 10⁻⁸ M (24.8 ng mL⁻¹). It revealed a stable potentiometric response with excellent reproducibility and enhanced selectivity over several common ions. Short-term potential stability and the interfacial sensor capacitance was estimated using both electrochemical-impedance spectroscopy (EIS) and chronopotentiometry techniques. The presented electrochemical platform revealed the merits of design simplicity, ease of miniaturization, good potential-stability, and cost-effectiveness. It is successfully applied to CGA determination in different coffee beans extracts and juice samples. The data obtained were compared with those obtained by liquid chromatography reference method (HPLC).

All-solid state screen-printed electrodes were fabricated for chlorogenic acid (CGA) detection.