Multiwalled Carbon Nanotubes/4,4′-Dihydroxybiphenyl Nanolayered Composite for Voltammetric Detection of Phenol

This paper reports the preparation of multiwalled carbon nanotubes/4,4′-dihydroxybiphenyl (MWCNTs-DHB) nanolayered composite as a new modifier for modification of carbon paste electrode (CPE/MWCNTs-DHB). CPE/MWCNTs-DHB shows linear responses for phenol in the concentrations range of 0.04–220 μM with a current sensitivity of 0.67 μA μM⁻¹ and a detection limit of 8.0 nM (S/N=3). The electrode shows high selectivity, good repeatability (RSD=4.1 %), excellent reproducibility (RSD=3.5 %), and acceptable stability (91.2 % over one-month storage). Moreover, the modified CPE exhibits appreciable recoveries (93.0–104.0 %) indicating its acceptable performance for determination of phenol in tap and river water samples.     

Highly Sensitive and Selective Measurement of Bismuth in Seawater and Drug with 1,2‐Phenylenedioxydiacetic Acid by Cathodic Adsorptive Stripping Voltammetry

A new method is presented for determination of bismuth based on cathodic adsorptive stripping of complex bismuth with 1,2‐phenylenedioxydiacetic acid (PDA) at a hanging mercury drop electrode (HMDE). The effect of various parameters such as pH, concentration of ligand, accumulation potential and accumulation time on the selectivity and sensitivity were studied. The optimum conditions for determination of bismuth include nitric acid concentration 0.01 M, 8.0×10^?4 M PDA and accumulation time 120 s, accumulation potential of ?200 mV. The limits of detection are 0.25 and 0.05 nM, and responses are linear 1–1000 and 0.1–400 nM at t_acc of 60 and 120 s, respectively. Many common anions and cations do not interfere in the determination of bismuth. The method was applied to the determination of bismuth in some real samples such as sea – and spring water and drug.     

Lab‐on‐a‐Chip Sensor with Evaporated Bismuth Film Electrode for Anodic Stripping Voltammetry of Zinc

In this work, we report on the development of a lab‐on‐a‐chip electrochemical sensor that uses an evaporated bismuth electrode to detect zinc using square wave anodic stripping voltammetry. The microscale electrochemical cell consists of a bismuth working electrode, an integrated silver/silver chloride reference electrode, and a gold auxiliary electrode. The sensor exhibits a linear response in 0.1 M acetate buffer at pH 6 with zinc concentrations in the 1–30 μM range and a calculated detection limit of 60 nM. The sensor successfully detected zinc in a bovine serum extract and the results were corfirmed by independent AAS measurements. Our results demonstrate the advantageous qualities of this lab‐on‐a‐chip electrochemical sensor for clinical applications, which include small sample volume (µL scale), reduced cost, short response time and high accuracy at low concentrations of analyte.     

Carbon Nanotubes‐Ionic Liquid and Chloropromazine Modified Electrode for Determination of NADH and Fabrication of Ethanol Biosensor

Potential cycling was used for oxidation of chloropromazine and producing an electroactive redox couples which strongly adsorbed on the electrode surface modified with carbon nanotubes and ionic liquid nanocomposite. The modified electrode shows excellent electrocatalytic activity toward NADH oxidation. The differential pulse voltammetry detection provided high sensitivity, 0.5835 A M^?1, low detection limit, 80 nM at concentration range up to 20 μM. An ethanol biosensor was also developed by immobilizing alcohol dehydrogenase enzyme onto nanocomposite. Differential pulse voltammetric detection of ethanol gives linear responses over the concentration range 40 μM–1.5 mM with detection limit 5 μM and sensitivity 1.97 μA mM^?1.     

Simultaneous Determination of Uric Acid and Ascorbic Acid Using Edge Plane Pyrolytic Graphite Electrodes

Edge plane pyrolytic graphite electrodes have been applied for the determination of uric acid and ascorbic acid. The separate determination of uric acid was found to produce three linear ranges from 100 nM to 3400 μM with a detection limit of 30 nM found to be possible. Uric acid detection was also explored in the presence of 200 μM ascorbic acid where a detection limit of 52 nM was found to be possible. The detection of ascorbic acid in the presence of uric acid was also explored over three linear ranges of ascorbic acid with a limit of detection of 80 nM. Last the simultaneous determination of both uric acid and ascorbic acid is investigated over the range 100 nM to 1000 μM where detection limits of 50 nM and 120 nM were obtained respectively. Analysis of uric acid in a growth tissue medium was found to be successful, confirming the applicability of the methodology to real matrices. This protocol is shown to provide low detection limits, easy handling (no electrode modification), good voltammetric peak separation of uric acid and ascorbic acid and a wide linear dynamic range.     

Rapid Determination of Phenolic Compounds in Water Samples: Development of a Paper‐based Nanobiosensor Modified with Functionalized Silica Nanoparticles and Potato Tissue

In this study, we present a fast, simple, low‐cost and disposable method for determination of phenolic content in water samples, using a paper based polyphenol oxidase biosensor. The propylamine functionalized silica nanoparticles was dropped onto a paper sheet. After drying at room temperature, the potato tissue extract including polyphenol oxidase was immobilized on the paper via physical and chemical adsorption. The modified paper was placed on the top of the graphite screen printed electrode. To construct of an electrochemical nanobiosensor, the electrochemical behavior of the modified electrode in different steps was investigated by cyclic voltammetry and electrochemical impedance spectroscopy methods. After being optimized the effective parameters, the changes in the biosensor electrochemical response vs. to the different concentrations of the substrate (phenol solution) were monitored by differential pulse voltammetry and amperometry methods. The linear relationships for phenol detection were obtained in the concentration ranges of 0.01–160 μM and 0.1–300 μM with a detection limit of 0.007 μM and 0.042 μM with DPV and amperometry methods, respectively. This method was successfully used in the voltammetric determination of the phenol content in the real samples, like the river water and the wastewater of wood factory.     

Potentiometric stripping analysis for bismuth(III) in seawater

Total bismuth(III) in seawater can be determined either directly after acidification with 0.1 M hydrochloric acid or after co-precipitation with magnesium hydroxide by means of pre-electrolysis for 8 min at —0.90 V vs. SCE at a rotated glassy carbon/mercury film electrode prior to potentiometric stripping analysis. The limits of detection (2σ) are 0.6 and 0.003 nM, respectively. Three Kattegatt surface seawater samples were found to contain bismuth(III) concentrations of 5–12 pM (l–2.5 ng l^-1).     

A Facile Fabrication of Poly-ethionine Film on Glassy Carbon Electrode for Simultaneous and Sensitive Detection of Dopamine and Paracetamol

An electrochemical sensor based on poly-ethionine (Poly-ET) film modified glassy carbon electrode was developed for sensitive and simultaneous sensing of dopamine (DA) and paracetamol (PA). The electropolymerization of ethionine monomer was carried out to modify the electrode. The modified electrode was characterized by using scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The Poly-ET/GCE exhibited excellent electrocatalysis towards the sensing of DA and PA. Poly-ET/GCE showed a linear increase of current response with increase concentration of DA and PA ranging from 0.1 μM–60 μM and 0.1 μM–180 μM, respectively. The LODs were found to be 7 nM and 18 nM (S/N=3) for DA and PA, respectively. This electrochemical sensor was successfully utilized for the detection of DA and PA in pharmaceutical samples.     

Disposable Bismuth Oxide Screen Printed Electrodes for the High Throughput Screening of Heavy Metals

We present a simplified approach for the trace screening of toxic heavy metals utilizing bismuth oxide screen printed electrodes. The use of bismuth oxide instead of toxic mercury films facilitates the reliable sensing of lead(II), cadmium(II) and zinc(II). A linear range over 5 to 150 μg L^?1 with detection limits of 2.5 and 5 μg L^?1 are readily observed for cadmium and lead in 0.1 M HCl, respectively. Conducting a simultaneous multi‐elemental voltammetric detection of zinc, cadmium and lead in a higher pH medium (0.1 M sodium acetate solution) exhibited a linear range between 10 and 150 μg L^?1 with detection limits of 5, 10 and 30 μg L^?1 for cadmium, lead and zinc respectively. The sensor is greatly simplified over those recently reported such as bismuth nanoparticle modified electrodes and bismuth film coated screen printed electrodes. The scope of applications of this sensor with the inherent advances in electroanalysis coupled with the negliable toxicity of bismuth is extensive allowing high throughput electroanalysis.     

Electrochemical Detection of Nitrite Using an Asymmetrically Substituted Cobalt Phthalocyanine Conjugated to Metal Tungstate Nanoparticles

This paper explores the synthesis and characterisation of an asymmetrical Co phthalocyanine (CoPc), and its covalent linking to two tungsten nanoparticles: bismuth tungsten oxide (Bi₂WO₆) and nickel tungsten oxide (NiWO₄). The nanoparticles were also mixed with the CoPc. The CoPc, nanoparticles and their respective conjugates were used as electrocatalysts in the electrochemical detection of nitrite. The electrocatalysts studied in this work had sensitivities ranging from 3–133 μA/mM while the limits of detection (LoDs) ranged between 0.063 μM and 1.7 μM. Bi₂WO₆ and its conjugate exhibited better LoD than corresponding NiWO₄ and conjugate.     

Enhanced Electrochemical Determination of Catechol and Hydroquinone Based on Pd Nanoparticles/Poly(Taurine) Modified Glassy Carbon Electrode

Here, Pd nanoparticles and poly(taurine) film was prepared on the glassy carbon electrode surface (Pd/Poly(TAU)/GCE) by the rapid electrochemical technique. The proposed composite surface was characterized by scanning electron microscopy(SEM), X‐ray photoelectron spectroscopy(XPS) and electrochemical impedance spectroscopy(EIS). Enhanced electron transfer ability and higher electroactive surface area were achieved at Pd/Poly(TAU)/GCE as compared to the bare GCE and polymer film electrode. The new and highly stable Pd/Poly(TAU)/GCE was employed for the individual and simultaneous determination of hydroquinone and catechol which were environmentally toxic. Under the optimized conditions, HQ and CC were individually determined by using the differantial pulse voltammetry in the linear ranges of 0.008–100 μM and 0.001–100 μM with the detection limits of (LOD) 2.1 nM and 0.68 nM, respectively. In case of simultaneous determination, LODs were found as 10 nM and 0.88 nM for HQ and CC, respectively. The content of both analytes in the real sample analysis was evaluated in the river water and tap water successfully.     

Dual Signals Electrochemical Biosensor for Point-of-Care Testing of Amino Acids Enantiomers

A highly sensitive electrochemical sensor based on both potential and current dual signals was constructed via polypyrrole-coated chiral carbon nanotubes (L/D-CNT@PPy) loaded with Pt nanoparticles (Pt NPs) and β-cyclodextrin (β-CD) hybrid. Using L/D-CNT and β-CD as chiral selectors, PPy and Pt NPs enhanced the conductivity and the sensors showed excellent performance for chiral recognition of tyrosine (Tyr) and tryptophan (Trp). The linear ranges of the D-CNT@PPy@Pt NPs@β-CD sensor were 3–30 μM (Tyr) and 19.6–196 μM (Trp), respectively, the detection limits were 0.107 nM (Tyr) and 0.133 nM (Trp), respectively, and the recoveries for L-Tyr were 96.56 %–106.32 %. This electrochemical sensor based on a dual-signal strategy of potential and current was expected to be used in the field of point of care testing (POCT).     

Magnetic loading of tyrosinase-Fe3O4/mesoporous silica core/shell microspheres for high sensitive electrochemical biosensing

A new protocol is proposed for magnetic loading and sensitive electrochemical detection of phenol via the tyrosinase cross-linked mesoporous magnetic core/shell microspheres. The mesoporous magnetic microspheres, characterized by transmission electron microscopy, N(2) adsorption/desorption isotherms, and magnetic curve displays high capacity for enzyme immobilization and strong magnetism to adhere to the magnetic electrode surface without any additional adhesive reagent. The biosensor exhibits a wide linear response to phenol ranging from 1.0×10(-9) to 1.0×10(-5) M, a high sensitivity of 78 μA mM(-1), a low detection limit of 1 nM, and a fast response rate (less than 5s). The proposed method is simple, rapid, inexpensive and convenient in electrode renewal, which is recommended as a promising experimental platform for wider applications in biosensing.     

Gold Nanoparticles/Biphenol–biphenoquinone for Ultra-trace Voltammetric Determination of Captopril

This study aims to synthesize gold nanoparticles/biphenol–biphenoquinone (AuNPs−BOH−BQ) and to study its application as a novel heterogeneous electron transfer mediator to modify carbon paste electrode (CPE/Au NPs−BOH−BQ) for ultra-trace determination of captopril (CP). Characterization results show well dispersed Au NPs with sizes in the range of 8.0–10.5 nm. Under optimized conditions, the calibration plot was linear from 1 to 5×10⁴ nM (two segments, 1–150 nM and 0.15–50.0 μM) and the detection limit was calculated to be 0.4 nM (S/N=3). Finally, the suggested sensor showed stable and reliable responses to CP in CP pharmaceutical tablet and urine samples.     

An Efficient Simultaneous Electrochemical Detection of Nanomolar Epinephrine and Uric Acid using Low Temperature Synthesized Nano-sized Copper Telluride

Herein we developed a simple, cost effective, electrochemical sensor based on nanosized copper telluride (nps-CuTe) for simultaneous detection of epinephrine (EP) and uric acid (UA). Voltammetric responses suggests dramatical improvement of electrocatalytic properties of both molecules by incorporating CuTe nps into unmodified graphite paste electrode (bare GP). Differential pulse voltammetric (DPV) measurement depicts large potential separation of 128 mV between EP and UA, allows their simultaneous determination from binary mixture. Under optimized condition, CuTe modified graphite paste electrode (CuTe/GP) manifested linear relationships of EP and UA in the range of 5–60 μM and 5–120 μM with detection limit (S/N=3) of 18 nM and 32 nM respectively. Moreover, CuTe/GP showed satisfactory response towards pharmaceutical and clinical samples for determining EP and UA concentrations.     

Organic Compounds In Cloud And Rain Water

Abstract

Cloud and rain water samples have been collected in spring 1991 in the Vosges mountains (France) and analyzed for aldehydes, phenols and polycyclic aromatic hydrocarbons (PAHs). Both passive and active cloud collectors have been employed. A mean concentration of formaldehyde of 197 μg/l (6.6 μM) has been found in cloud water while on the average only 100 μg/l (3.3 μM) were observed in rain water. The average phenol concentration was 3.5 μg/l (37 nM), but only 1.6 μg/l (17 nM) in rain water. Finally, the mean concentration of PAHs (only determined in cloud water) amounts to 0.37 μg/l. The PAH profile is similar to that observed for rain water sampled in Hannover (Germany).     

Acetylcholinesterase Biosensor Based on Reduced Graphene Oxide – Carbon Black Composite for Determination of Reversible Inhibitors

For the first time, acetylcholinesterase (AChE) biosensors based on mixed carbon nanomaterials (electrochemically reduced graphene oxide (ERGO) and carbon black (CB) particles) were described for the determination of antidementia drugs. Changes in the content of underlying layer allowed varying selectivity and sensitivity of the inhibitor determination. Appropriate limits of detection (LOD) varied in the range from 1 pM to 0.1 nM for donepezil, 5 nM–0.1 μM for berberine, 0.1–50 nM for huperzine A and 0.1–300 nM for galantamine. Variation in the inhibition measurement parameters can be used for increasing selectivity of the measurements.     

Comparison of Insulin Determination on NiNPs/chitosan‐ MWCNTs and NiONPs/chitosan‐MWCNTs Modified Pencil Graphite Electrode

The rising amount of patients suffering for diabetes mellitus increases the requirements for effective insulin sensors. Carbon materials are a suitable choice for the development of insulin sensors due to their electrochemical characteristics. Pencil graphite electrodes (PGE) represent the trade‐off between price and excellent conductive properties. The modification of PGE by NiO and Ni nanoparticles fixed by chitosan results in surface area enlargement and improved electrocatalytic properties. This paper is focused on the comparison of different properties of Ni and NiO nanoparticles and their effect on redox reaction mechanism of insulin and detection characteristics. The electrode modified by Ni nanoparticles displays linear range of 1 μM–5 μM (R² 0.80), limit of detection (LOD) of 4.34 μM and sensitivity of 0.12 μA/μM. On the other hand, the electrode modified by NiO nanoparticles displays enhanced electrochemical characteristics such as linear range of 0.05 μM–5 μM (R² 0.99), limit of detection of 260 nM and sensitivity of 0.64 μA/μM. These properties make the NiO nanoparticles modified PGE the appropriate candidate for insulin determination.     

Application of ion-exchange chromatography with an ion-selective electrode detector to iodine determination in natural waters

A system is described which uses a selective electrode for potentiometric detection of anions in natural waters after ion-exchange separation. With an iodide-selective electrode in the flow cell, a linear relationship exists between iodide concentration and potential in the sub-Nernstian range (0–100 μM). The limit of detection is 0.015 μM for an injection of 125 μl of sample. For optimum electrode performance, a constant iodide background of about 0.5 μM is required in the column effluent passing through the detector. This background is added uniformly through a short section of hollow-fibre dialysis tubing in a concentric-flow diffusion cell. The detector also responds to other anions which affect the solubility of silver ion. This can be used to advantage if chromatographic separation is sufficient. Preconcentration of iodide in fresh waters on an anion guard cartridge allows determination down to 1 nM concentrations. For sea-water samples, simple chemical pretreatment permits quantitation of different iodine species.     

Ultra‐sensitive Amperometric Hydrazine Sensing via Dimethyl Glyoxomat Derived NiO Nanostructures

Here we report the synthesis of NiO nanostructures via glyoxomat assisted precipitation protocol using hydrothermal route under the influence of ammonia followed by annealing at 450 ^oC. These nanostructures were characterized via Scanning Electron Microscopy (SEM) and X‐ray Diffraction (XRD) method. The morphological investigation of the finally prepared NiO revealed foam‐like porous nanostructures. These NiO nanostructures were immobilized onto glassy carbon electrode (GCE) with nafion as binding material and used as highly sensitive and selective sensor for determining hydrazine in the range of 100–500 nM and 600–1600 nM with a calculated limit of detection (LOD) equal to 5 nM. The as prepared sensor was tested for the presence of various interfering species such as Na⁺, Cu²⁺, uric acid, hydrogen peroxide and glucose in the presence of equimolar concentration of hydrazine and negligible interference was noticed. The sensor was further tested for hydrazine detection using square wave voltammetry (SWV) however it only worked in the range of 50–1200 μM. Finally the sensor was successfully implemented for hydrazine determination in real water samples using amperometric protocol.