Hierarchically assembled ZnO nanosheets microspheres for enhanced glucose sensing performances

Nanostructures with higher surface specific area has great potential applications in sensing devices because higher surface specific area not only improve protein/enzyme immobilization efficiency, but also enhances charge transport and sensing performances. Herein, hierarchically assembled ZnO nanosheets microspheres (HAZNMs) were synthesized by facile one-pot solution process at low-temperature. Results showed that as-synthesized HAZNMs possessing higher specific surface area, significantly increased the enzyme loading efficiency which in turn improved the sensing performances. The as-fabricated biosensors showed a remarkably high sensitivity (210.8 μA/mM cm²) in the wide-linear response range of 0.05–23 mM, favorable stability for long-term storage, excellent anti-interference ability and high reliability for glucose detection in human blood serum samples. The improved sensing performances can be ascribed to the high glucose oxidase (GOx) enzyme immobilization on HAZNMs that provides a favorable microenvironment for the maintenance of GOx enzyme bioactivity.     

A hybrid photocatalytic and enzymatic process using glucose oxidase immobilized on TiO2/polyurethane for removal of a dye

A rectangular recycling photo-bioreactor using glucose oxidase (GOx) immobilized on TiO₂/polyurethane (PU) was developed as a novel coupling of photodegradation and enzymatic process. This method was tested for removal of Acid Orange 7 (AO7), as a model pollutant. High efficiency of decolorization (>99%) was achieved after 22 min using the GOx/TiO₂/PU photo-biocatalyst. Roles of various processes including photodegradation (TiO₂/PU), enzymatic process (GOx/PU) and a coupling of photocatalytic–enzymatic (GOx/TiO₂/PU) process were investigated in the presence and absence of UV light. All the experiments were performed in a circulation photoreactor equipped with a 6 W UV lamp with rate of 5 mL/min.     

Synthesis of highly dispersed titanium dioxide nanoclusters on reduced graphene oxide for increased glucose sensing

Highly dispersed titanium dioxide nanocluster (TDN) was synthesized on reduced graphene oxide (RGO) in a toluene–water system under microwave irradiation. The prepared RGO–TDN hybrids were used to modify glassy carbon electrode for loading glucose oxidase. The fabricated glucose biosensor exhibits excellent performance for glucose sensing including low work potential (−0.7 V), high sensitivity (35.8 μA mM⁻¹ cm⁻²), low detection limit (4.8 μM), wide linear range from 0.032 to 1.67 mM, small Michaelis–Menten constant (K_m) (0.81 mM), and short response time (10 s).     

Improvement of sensitive Ni(OH)2 nonenzymatic glucose sensor based on carbon nanotube/polyimide membrane

An improved nonenzymatic glucose sensor was fabricated of Ni(OH)₂ on carbon nanotube/polyimide (PI/CNT) membrane by a simple electrochemical method. Three different morphologies of Ni(OH)₂ have been formed by changing the conditions used in synthesis process. The formation mechanism for Ni(OH)₂ nanospheres was studied to provide a deep understanding of crystal growth. The electrochemical behaviors of different Ni(OH)₂ nanostructures were investigated by cyclic voltammetry and chronoamperometry in alkaline solution. At an applied potential of +0.60 V, the sensor based on PI/CNT–Ni(OH)₂ nanospheres shows a high sensitivity of 2071.5 μA mM⁻¹ cm⁻² and a detection limit of 0.36 μM (signal/noise = 3). The proposed sensor exhibits high sensitivity, long-term stability and good reproducibility, and performs well for detection of glucose in human blood serums. Therefore, this novel fabrication method for glucose sensor is promising for the future development of nonenzymatic glucose sensors.     

Electro-oxidation and determination of gemcitabine hydrochloride,an anticancer drug at gold electrode

Electrochemical behavior of an anticancer drug, gemcitabine hydrochloride (GMB) was studied in 10.4 pH with 0.2 M phosphate buffer solution as supporting electrolyte at 25 ± 0.1 °C at gold electrode (GE) using different voltammetric techniques. The electrochemical process was observed to be diffusion controlled, irreversible and involving one-electron oxidation. Under optimal conditions, the peak current was proportional to GMB concentration in the range of 0.1–15 μM with a detection limit of 0.06 μM by differential pulse voltammetry. The method was developed for the determination of GMB in pharmaceutical formulations and urine as a real sample.     

Boron-doped diamond electrochemical sensor for sensitive determination of nicotine in tobacco products and anti-smoking pharmaceuticals

A sensitive, selective and reliable electrochemical method for the determination of nicotine using differential pulse voltammetry on a bare boron-doped diamond electrode has been developed. Nicotine yielded a single oxidation peak at a highly positive potential of + 1.45 V (vs. Ag/AgCl/3 M KCl) in Britton–Robinson buffer solution at pH 8. The influence of supporting electrolyte, pH and scan rate on the current response of NIC was investigated. At optimized experimental conditions, a linear relation between peak current and concentration of nicotine was found for the range from 0.5 to 200 μM (0.08–32.9 mg L^− 1) with a detection limit of 0.3 μM (0.05 mg L^− 1) and a good repeatability (relative standard deviation of 2.1% at 25 μM concentration level, n = 10) was achieved without any electrode surface modification. The practical usefulness of the developed procedure was successfully demonstrated with the determination of nicotine in tobacco products and anti-smoking pharmaceuticals with results similar to those obtained by a high-performance liquid chromatography and to the contents declared by the manufacturer, respectively. Prior to analysis, the sample pretreatment includes only sonication and/or simple liquid–liquid extraction. The proposed sensor represents an effective electrochemical tool and a promising alternative for quality control analysis of products in tobacco and pharmaceutical industry.     

A mesoporous carbon nanofiber-modified pyrolytic graphite electrode used for the simultaneous determination of dopamine,uric acid,and ascorbic acid

A mesoporous carbon nanofiber-modified pyrolytic graphite electrode (MCNF/PGE) has been prepared and applied to the simultaneous electrochemical determination of dopamine (DA), uric acid (UA) and ascorbic acid (AA). The oxidation overpotentials of these biomolecules decrease significantly, the overlapping of these peaks in bare PGE is well resolved, and their anodic peak currents increase dramatically in MCNF/PGE due to the large amount of edge-plane-like defects, large surface area and especially the mesoporous structure of MCNFs. Using this method, anodic currents of DA, UA and AA are linear with their concentration in the range of 0.05–30 μM, 0.5–120 μM and 0.1–10 mM, respectively, with detection limits of 0.02, 0.2 and 50 μM. The good sensitivity and reproducibility of the proposed electrode make it be used as a good electrochemical sensor for the simultaneous determination of DA, UA and AA in real sample analysis.     

A kinetic study on hydrochloric acid leaching of nickel from Ni–Al2O3 spent catalyst

Hydrochloric acid leaching of nickel from spent Ni–Al₂O₃ catalyst (12.7% Ni, 39.2% Al and 0.68% Fe) has been investigated at a range of conditions by varying particle size (50–180 μm), acid concentration (0.025–2 M), pulp density (0.2–0.4%, w/v) and temperature (293–353 K). Nickel was selectively leached from the catalyst, irrespective of the different conditions. Under the most suitable conditions (1 M HCl, 323 K, stirring at 500 rpm, 50–71 μm particle size), the extent of leaching of Ni and Al after 2 h was 99.9% and 1%, respectively. The XRD pattern of the spent catalyst corresponded to crystalline α-Al₂O₃ along with elemental Ni. The peak due to elemental Ni was absent in the residue sample produced at the optimum leaching conditions, confirming the complete dissolution of Ni from the spent catalyst. The leaching results were well fitted with the shrinking core model with apparent activation energy of 17 kJ/mol in the temperature range of 293–353 K indicating a diffusion controlled reaction.     

Silan based paraoxon memories onto QCM electrodes

In this study, a novel quartz crystal microbalance (QCM) based on the modification of paraoxon-imprinted polymer onto a QCM with a high selectivity and sensitivity has been developed for the determination of paraoxon. The QCM sensor has characterized using AFM and ellipsometer. The performance of the QCM sensor has evaluated and presented good reproducibility, shorter response time (20 min), wider linear range (0.02–10 μM) and low detection limit (0.02 μM). The results have shown that the selectivity of QCM sensor has found as being very high in the presence of parathion which is similar in structure with paraoxon.     

A novel colorimetric chemosensor for multiple target ions in aqueous solution: simultaneous detection of Mn(II) and Fe(II)

We have synthesized a new Schiff base 1 having julolidine moiety, which detects Mn^2 + and Fe^2 + through naked eye in aqueous solution. The sensor 1 exhibited significant color changes from pale yellow to orange for Mn^2 + and to dark green for Fe^2 +. The complex formations were proposed to be 1:1 ratio, based on Job plot and ESI-mass spectrometry analysis. The detection limits of Mn^2 + and Fe^2 + were found to be 7.11 μM and 0.14 μM, respectively, which are below the WHO acceptable limits (manganese: 7.28 μM and iron: 5.36 μM) in drinking water.     

Electrochemical determination of adrenaline in human urine using a boron-doped diamond film electrode

A simple and sensitive square-wave voltammetric method for the determination of adrenaline on unmodified boron-doped diamond film electrode was developed. Adrenaline exhibited the quasi-reversible behavior with oxidation peak on the forward scan at + 0.75 V and smaller reduction peak on the reverse scan at − 0.10 V vs. Ag/AgCl electrode in 0.5 M HClO₄. The effect of supporting electrolyte, pH and scan rate on the current response of adrenaline was examined to select the optimum experimental conditions. At optimized square-wave voltammetric parameters (amplitude of 100 mV, frequency of 50 Hz and step potential of 5 mV), the linear concentration range from 0.7 to 60 μM (R² = 0.998, number of measurements n = 6), the excellent repeatability (relative standard deviation of 3.5% for n = 50) and the detection limit of 0.21 μM were achieved without any chemical modification and pretreatment of working electrode. The practical application of method was demonstrated in the determination of adrenaline in spiked human urine samples with satisfactory recoveries (98 to 102%).     

Electrochemical synthesis and characterization of a novel thiazole-based copolymer and its application in biosensor

A novel copolymer based on 2-aminothiazole (AT) and 2-amino-4-thiazoleacetic acid (ATA) is electrochemically synthesized and then characterized using UV–visible absorption spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and electrochemical techniques. The results confirmed that the obtained polymer was a copolymer rather than a blend or a composite of the respective homopolymers and could improve the electrochemical response of both positively and negatively charged analytes. Therefore, the copolythiazole film was applied to determine ascorbic acid (AA), dopamine (DA) and uric acid (UA). It is found that the peak separating degrees and peak currents of AA, DA and UA at copolythiazole modified electrode were much better than those at bare GCE. Under the optimum conditions, the linear calibration curves were obtained in the range of 10–2000 μM for AA, 1–150 μM for DA, 1–180 μM for UA. The detection limits of AA, DA and UA were 2, 0.04 and 0.4 μM, respectively (S/N = 3). The practical application of the modified electrode was demonstrated by the determination of UA in urine sample.     

Direct electron transfer in a mediator-free glucose oxidase-based carbon nanotube-coated biosensor

A novel biosensor was prepared by immobilizing glucose oxidase on multi-walled carbon nanotube (MWCNT)-coated electrospun gold fibers. Homogeneous coating of the electrospun gold fibers by MWCNTs was achieved by electrophoretic deposition at 20 V (40 V cm^?1), a deposition time of 30 s and a solution concentration of 0.25 mg mL^?1. Scanning electron microscopy confirmed the complete coverage of MWCNTs on the fiber surface. The carboxylated MWCNTs on the gold fibers provided an anchor for covalent immobilization of glucose oxidase (GOX). GOX covalently coupled to conductive carbon nanotubes demonstrated direct electron transfer between the enzyme and the electrode surface without the need for a redox active mediator. Electrochemical characterization of the fabricated sensor by cyclic voltammetry revealed that the immobilized GOX exhibited a surface-confined reversible two-electron and two-proton reaction, with an electron transfer rate constant, k_s, of 1.12 s^?1 and a surface coverage of 1.1 × 10^?12 mol cm^?2. The sensor produced a linear response to glucose concentration up to 30.0 mM with a sensitivity of 0.47 μA mM^?1 cm^?2 and a detection limit of 4 μM.     

Development of nonenzymatic hydrogen peroxide sensor based on catalytic properties of copper nanoparticles/Rutin/MWCNTs/IL/Chit

A new electrochemical sensor based on copper nanoparticles for detection of hydrogen peroxide has been developed. Copper nanoparticles/Rutin/Multiwall Carbon Nanotubes/Ionic liquid/Chitosan modified glassy carbon electrode (CuNPs/Rutin/MWCNTs/IL/Chit/GCE) prepared by consecutive coating of MWCNTs/IL/Chit nanocomposite and rutin on the GCE, followed by the electrodeposition of copper. Surface physical characteristics of modified electrode were studied by scanning electron microscopy (SEM). The electrochemical performance of the sensor for detection of H₂O₂ was investigated by cyclic voltammetry and chronoamperometry techniques. The modified electrode exhibits an enhanced electrocatalytic property, low working potential, high sensitivity, excellent selectivity, good stability, and fast amperometric sensing towards reduction of hydrogen peroxide. The response to H₂O₂ is linear in the range between 0.35 μM to 2500 μM, and the detection limit is 0.11 μM.     

Fabrication of a novel ZnO–CoO/rGO nanocomposite for nonenzymatic detection of glucose and hydrogen peroxide

Herein, a novel nanocomposite of binary ZnO–CoO nanoparticles loaded on the graphene nanosheets (ZnO–CoO/rGO) has been successfully constructed via a facile, economical and two–step process. The obtained ZnO–CoO/rGO hybrids with high electrical conductivity and abundant active sites, could be modified on a glassy carbon electrode to detect glucose and H₂O₂ multi–functionally. The fabricated biosensor exhibits wide linear range for glucose (10 μM to 11.205 mM) and H₂O₂ (25 μM to 11.1 mM), and their corresponding sensitivity are 168.7 μA mM^?1 cm^?2 and 183.3 μA mM^?1 cm^?2. The limits of detection are 1.3 μM and 0.44 μM for the oxidation of glucose and the reduction of H₂O₂, respectively. Furthermore, remarkable selectivity, long–term stability and outstanding reproducibility of the non–enzyme biosensor prove that ZnO–CoO/rGO hybrids are the promising candidate in practical applications.     

Rose-like CuO nanostructures for highly sensitive glucose chemical sensor application

This paper reports the synthesis, characterization and glucose chemical sensing applications of well-crystalline rose-like CuO nanostructures. The rose-like CuO nanostructures were synthesized by facile hydrothermal process at low-temperature and characterized in detail in terms of their morphological, compositional, structural, optical and sensing properties. The detailed characterizations revealed that the synthesized rose-like CuO nanostructures are nanocrystalline and possessing monoclinic structure. Further, the synthesized nanostructures were used as efficient electron mediator to fabricate non-enzymatic glucose sensor. The fabricated glucose chemical sensor shows a very high sensitivity of ~4.640 μA mM⁻¹ cm⁻² and an experimental detection limit of ~0.39 mM with correlation coefficient (R) of 0.9498. The observed linear dynamic range for the fabricated chemical sensor was from 0.78 mM to 100 mM. The presented work demonstrates that simply prepared CuO nanomaterials can efficiently be used to fabricate reliable and reproducible glucose chemical sensors.     

Elaboration of new tubular ceramic membrane from local Moroccan Perlite for microfiltration process. Application to treatment of industrial wastewaters

In this study, an original microfiltration tubular membrane (M1) made from local Moroccan Perlite was used to treat three wastewater types: effluents coming from beamhouse section of tannery (effluent A), textile effluent coming from jeans washing process (effluent B), and dicing wafer effluent generated by electronic industries (effluent C). The prepared membrane is composed of two layers of Perlite with two different granulometries: a macroporous support with a pore diameter centered near 6.6 μm and porosity of about 42%, and a microfiltration layer, performed by slip casting method, with a mean pore size of 0.27 μm. The water permeability determined of the membrane is 815 L/h m² bar. Tangential microfiltration using Perlite membrane proved to be effective in removing pollutants from the three effluents with almost the same efficiencies than that obtained with a commercial Alumina membrane (M2) with a pore diameter of 0.2 μm and a water permeability of 1022 L/h m² bar. Tangential microfiltration process operated at lower pressure (1 bar) was seen to remove turbidity from the three feeds completely. Perlite membrane allowed significant reduction of Chemical Oxygen Demand COD (50–54%) and Total Kjeldahl Nitrogen TKN (56%) of beamhouse effluent. It showed a significant decrease of COD (54–57%) and a complete discoloration of textile wastewater.     

Stereoselectivity of tyrosine enantiomers in electrochemical redox reactions on gold matrices

Electrochemical reduction of tyrosine (Tyr) enantiomers on gold matrices in chlorhydric acid (HCl) solutions (0.01 M, pH 2.00) was performed. The characteristics of the Tyr reductive product adsorbed onto the electrode surface were studied using cycle voltammetry (CV). A significant redox peak of Tyr was observed from 0.70 to 1.60 V potential ranges. The compared investigation about electrocatalytic ability of Tyr enantiomers used gold matrices (bare gold electrode and electrodepositive gold nanoparticles modified glassy carbon electrode (AuNPs-GCE)). The Scanning Electron Microscope (SEM) images have been utilized to discuss the surface morphous. And the redox degree of l-Tyr on gold matrices was obviously much larger than that of d-Tyr. The mechanism for stereoselectivity in redox reactions of Tyr enantiomers on gold matrices had been analyzed. In addition, the AuNPs-GCE was used to determine Tyr enantiomers. Both l-Tyr and d-Tyr presented a sensitivity of 1.30 μM (S/N = 3), with two linear ranges from 4.00 μM up to 1.00 mM. This method proposed the possibility of using a nanostructured surface to discriminate and determine the chiral molecules in bio-electroanalytical application.     

Preparation,characterisation and properties of sulphoxide modified polystyrene resins for solid-phase extraction of PtIV,RuIII and RuIV from hydrochloric acid

New sulphoxide modified resins were synthesized using poly(styrene-co-divinylbenzene) (PS-DVB) as matrix. Infrared spectroscopy and elemental analysis were used for characterisation. Solid-phase extraction of Pt^IV, Ru^III and Ru^IV from acidic chloride solutions was performed via batch experiments. Influence of spacer length between sulphoxide and matrix (ethylene, hexamethylene), substitution of sulphoxide (R¹: ethyl, hexyl, phenyl) and bead size of PS-DVB (spherical beads: d₅₀ < 155 μm, d₅₀ < 80 μm; powder: d₅₀ < 30 μm) on adsorption was investigated subjected to acidity. Experimental results showed that ethyl substituted sulphoxide immobilised onto ground PS-DVB and hexamethylene spacer exhibited best adsorption properties. Different kinetic models and isotherms were fitted to the experimental data to identify extraction mechanism. Pt^IV was quantitative sorbed at [HCl] ⩽ 0.1 mol/L whereas Ru^III and Ru^IV sorption ranged between 90% and 95% at [HCl] ⩾ 5 mol/L. Desorption was reached using a solution of 0.5 M thiourea (Tu) in 0.1 M HCl at 90 °C. Separation of Pt^IV and Ru^III occurred at [HCl] ⩽ 0.1 mol/L whereas Pt^IV was extracted and Ru^III remained in solution. A further separation was achieved by extracting Pt^IV and Ru^IV at 5 M HCl followed by sequential elution of Pt^IV with concentrated HCl and Ru^IV with 0.5 M Tu in 0.1 M HCl at 90 °C.     

Pre-concentration and determination of traces of nitrobenzene and 1,3-dinitrobenzene in water samples using anthracite adsorbent

This study introduces a novel analytical method for the determination of nitrobenzene (NB) and 1,3-dinitrobenzene (DNB) from an aqueous solution using high performance liquid chromatography (HPLC) and anthracite as adsorbent for pre-concentration. The method showed good linearity for determination of NB and DNB concentrations in the range of 0.10–200 μg L⁻¹ with regression coefficients better than 0.9995. Limits of detections (LOD) were 0.010 and 0.055 μg L⁻¹ for DNB and NB, respectively. Relative standard deviations (RSD) for 0.50 μg L⁻¹ and 150 μg L⁻¹ were in the range of 2.0–3.8% for (DNB) and 3.0–4.8% for (NB).