Electrocatalytic Oxidation of Cysteine at a CoSalophen/ n‐(butyl)4SiW12O40 Carbon Paste Electrode

In the present study, a novel mixture consisting of N,N′‐bis(salicylidene)‐1,2‐phenylenediamino cobalt (CoSalophen, CoSal) complex and (n‐butyl)₄SiW₁₂O₄₀ (SiW₁₂), have been used to chemically modify a carbon paste electrode (CPE) for sensitive determination of cysteine (CySH). The electrocatalytic effect of the newly developed modified CPE towards oxidation of CySH was evaluated by comparing cyclic and differential pulse voltammograms in the presence of cysteine at bare, CoSal, SiW₁₂ and CoSal/SiW₁₂ modified CPE. The differential pulse voltammetry method was applied as a sensitive method for quantitative detection of CySH trace amounts, the experimental conditions being optimized in order to evaluate the best analytical parameters of the sensor. Reproducibility and stability studies were also performed and the sensor was applied for the determination of CySH in a pharmaceutical sample and in human blood serum and urine samples.     

Analysis of Levodopa in the Presence of Vitamin B6 Using Carbon Paste Electrode Modified with 1‐Butyl‐3 methylimidazolium Hexafluorophosphate and CuO Nanoparticles

A carbon paste electrode modified with 1‐butyl‐3‐methylimidazolium hexafluorophosphate ionic liquid (BMIPF6) and CuO nanoparticles (CuO/NPs) (CPE/BMIPF₆/CuO/NPs) was fabricated and used for square wave voltammetric analysis of levodopa in the presence of vitamin B₆. The elemental analysis, SEM and XRD methods were used for characterization of synthesized CuO nanoparticle. CPE/BMIPF₆/CuO/NPs exhibited high electrical conductivity toward the electro‐oxidation of levodopa at a pH=7.0 as best experimental condition. Using CPE/BMIPF₆/CuO/NPs the levodopa and vitamin B₆ peaks are separated and oxidized at potentials of 0.565 V and 0.835 V, respectively; hence levodopa can be detected in the presence of vitamin B₆. The electrochemical response shows a linear relationship from concentration of levodopa and vitamin B₆ in the ranges of 0.06‐1000 μM and 0.1‐700.0 μM, respectively. Finally, CPE/BMIPF₆/CuO/NPs were applied as high performance tool for determination of levodopa and vitamin B₆ in real samples.     

Pt‐doped NiO Nanoparticle‐Ionic Liquid Modified Electrochemical Sensor: A Powerful Approach for Determination of Epinine in the Presence of Phenylephrine as two Blood Pressure Raising Drugs

A new and progressive electroanalytical sensor was made by the incorporation of Pt‐doped NiO nanoparticle (Pt‐NiO‐NPs) into carbon paste electrode (CPE) amplified with 1‐hexyl‐3‐methylimidazolium tetrafluoroborate (1H3MTFB) as a conductive binder. The Pt‐NiO‐NPs/1H3MTFB/CPE caused an extraordinary rise in the oxidation peak current of epinine (～4.6 times) and simultaneous reduction in the oxidation over‐potential of catecholamine drug (～120 mV). SWV method was employed to investigate the ability of Pt‐NiO‐NPs/1H3MTFB/CPE as an electroanalytical sensor in the determination of epinine in the presence of phenylephrine as two blood pressure raising drugs with ΔE=280 mV for the first time. Experimental results pertinent to SW voltammetric investigation reveal a linear relation between epinine and phenylephrine currents and drugs concentration in the rages 0.004–450 and 0.02–350 μM, respectively.     

Highly sensitive determination of promazine in pharmaceutical and biological samples using a ZnO nanoparticle-modified ionic liquid carbon paste electrode

In this work we describe the first report for the determination of promazine using a nanostructuremodified ionic liquid carbon paste electrode in aqueous solutions. To achieve this goal, a novel modified carbon paste electrode using ZnO nanoparticles and 1-methyl-3-butylimidazolium bromide as a binder(ZnO/NPs/ILs/CPE) was fabricated. The oxidation peak potential of promazine at the surface of the ZnO/NPs/ILs/CPE appeared at 685 m V, which was about 65 m V lower than the oxidation potential at the surface of CPE under similar conditions. Also, the peak current was increased to about 4.0 times higher at the surface of ZnO/NPs/ILs/CPE compared to that of CPE. The linear response range and detection limit were found to be 0.08–450 and 0.04 mmol/L, respectively. The modified electrode was successfully used for the determination of promazine in real samples with satisfactory results.     

A novel biosensor based on ZnO nanoparticle/1,3-dipropylimidazolium bromide ionic liquid-modified carbon paste electrode for square-wave voltammetric determination of epinephrine

The direct electrochemistry of epinephrine (EP) on a modified carbon paste electrode (CPE) was described. The electrode was modified with Zinc oxide (ZnO) nanoparticles and 1,3-dipropylimidazolium bromide as a binder. The oxidation peak potential of EP at the surface of the ionic liquid ZnO nanoparticle CPE (IL/ZnO/NP/CPE) appeared at 350 mV, which was about 80 mV lower than the oxidation peak potential at the surface of the traditional carbon CPE under a similar condition. On other hand, the oxidation peak current was increased for about three times at the surface of IL/ZnO/NP/CPE compared to CPE. The linear response range and detection limit were found to be 0.09–800 μmol L^?1 and 0.06 μmol L^?1, respectively. Other physiological species did not interfere in the determination of EP at the surface of the proposed sensor in the optimum condition. The proposed sensor was successfully applied for the determination of EP in real samples.     

Electrocatalytic and Simultaneous Determination of Ascorbic Acid,Nicotinamide Adenine Dinucleotide and Folic Acid at Ruthenium(II) Complex‐ZnO/CNTs Nanocomposite Modified Carbon Paste Electrode

This paper describes the development a novel ruthenium(II) complex‐ZnO/CNTs modified carbon paste electrode (Ru(II)/ZnO/CNTs/CPE) for the electrocatalytic determination of ascorbic acid (AA). The objective of this novel electrode modification was to seek new electrochemical performances for the detection of AA, nicotinamide adenine dinucleotide (NADH) and folic acid (FA). The peak potentials recorded were 170, 500 and 830 mV vs. Ag/AgCl/KCl_sat for AA, NADH and FA, respectively. The peak currents were linearly dependent on AA, NADH and FA concentrations using square wave voltammetry (SWV) method at the ranges of 0.008–251, 1.0–650, and 3.0–700 µmol L^?1, with detection limits of 0.005, 0.5, and 1.0 µmol L^?1, respectively.     

Investigation of Methanol Behavior at the Designed Electrochemical Sensor based on Ni(II) Complex and Graphene Nanosheets

In this work, the electrochemical oxidation of methanol was investigated by different electrochemical methods at a carbon paste electrode (CPE) modified with (N‐5‐methoxysalicylaldehyde, N´‐2‐hydroxyacetophenon‐1, 2 phenylenediimino nickel(II) complex (Ni(II)–MHP) and reduced graphene oxide (RGO), which is named Ni(II)‐MHP/RGO/CPE, in an alkaline solution. This modified electrode was found to be efficient for the oxidation of methanol. It was found that methanol was oxidized by the NiOOH groups generated by further electrochemical oxidation of nickel(II) hydroxide on the surface of the modified electrode. Under optimum conditions, some parameters of the analyte (MeOH), such as the electron transfer coefficient (α), the electron transfer rate constant) k_s), and the diffusion coefficient of species in a 0.1 M solution (pH = 13), were determined. The designed sensor showed a linear dynamic range of 2.0–100.0 and 100.0–1000.0 μM and a detection limit of 0.68 μM for MeOH determination. The Ni(II)‐MHP/RGO/CPE sensor was used in the determination of MeOH in a real sample.     

Highly Selective Sensing Platform Utilizing Graphene Oxide and Multiwalled Carbon Nanotubes for the Sensitive Determination of Tramadol in the Presence of Co‐Formulated Drugs

Novel insights into the strategy of highly precise, carbon‐based electrochemical sensors are presented by exploring the excellent properties of graphene oxide (GO) and multiwalled carbon nanotube composites (GO‐MWCNTs/CPE) for the sensitive determination of tramadol hydrochloride (TRH). Cyclic voltammetry, differential pulse voltammetry, chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) scanning electron microscopy, and X‐ray diffraction (XRD) techniques were used to characterize the properties of the sensor. The linear response obtained for TRH using the GO‐MWCNTs/CPE was found to be over the range of 2.0x10⁻⁹ to 1.1x10⁻³ M with a good linearity and high correlation (0.9996). The limits of detection and quantification were found to be 1.50x10⁻¹⁰ M and 4.99 x 10⁻¹⁰ M, respectively. The proposed sensor was applied for determination of TRH in the presence of presence of co‐formulated drugs ketorolac tromethamine (KTM) and paracetamol (PAR). The sensor was shown to successfully apply to the determination of TRH in plasma as real samples. Satisfactory recoveries of TRH from samples clearly revealed that the proposed sensor can be applied into clinical analysis, quality control and a routine determination of drugs in pharmaceutical formulations.     

Green synthesis,characterization, and biological activities of saffron leaf extract-mediated zinc oxide nanoparticles: A sustainable approach to reuse an agricultural waste

To increase the profitability and sustainability of agricultural waste, a facile green approach was established to synthesize zinc oxide nanoparticles (ZnO NPs) using saffron leaf extract as a reducing and stabilizing agent. Structural characteristics of NPs were investigated by X-ray diffraction (XRD), Fourier-transform infrared (FTIR), field emission scanning electron microscopy (FESEM), and UV–Visible (UV–Vis) spectroscopy. Characterization results revealed that ZnO NPs is highly crystalline with a hexagonal wurtzite structure and spherical particles with diameter less than 50 nm, as confirmed by XRD and FESEM techniques. UV–Vis absorption spectra depicted an absorption peak at 370 nm, which confirms the formation of ZnO NPs. FTIR spectral analysis confirmed the presence of functional groups and metal oxygen groups. The biological activities of ZnO NPs were also investigated. The antibacterial effect of ZnO NPs was investigated against selected food pathogens (Salmonella Typhimurium, Listeria monocytogenes, and Enterococcus faecalis). The study results prove that the green synthesized ZnO NPs show enhanced antibacterial activity against S. Typhimurium when compared with other strains. A dose-dependent free radical scavenging activity was observed for ZnO NPs in both 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) and fluorescence recovery after photobleaching (FRAP) assays. The ZnO NPs were evaluated for their photocatalytic activity during the degradation of methylene blue (MB) dye in aqueous solutions. The maximum removal of MB achieved was 64% with an initial ZnO NP concentration of 12 mg/mL under UV light. The present study revealed that the agricultural waste (saffron leaf) provides a simple and eco-friendly option to sustainably synthesize ZnO NPs for use as a photocatalyst. In addition, this is the first report on saffron leaf-mediated synthesis of ZnO NPs.     

Synthesis of CuS and ZnO/Zn(OH)2 nanoparticles and their evaluation for in vitro antibacterial and antifungal activities

In this study, the copper sulfide nanoparticles (CuS‐NPs) and the zinc oxide/zinc hydroxide nanoparticles ((ZnO/Zn(OH)₂‐NPs) were synthesized by a simple and low‐cost method, and the synthesized nanoparticles were characterized and identified by UV–Vis, field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The antimicrobial activity of the CuS‐NPs and the ZnO/Zn(OH)₂‐NPs were examined by broth dilution to determine the minimal inhibitory concentration (MIC) of antibacterial agent required to inhibit the growth of a pathogen and the minimum bactericidal concentration (MBC) required to kill a particular bacterium. Agar disc diffusion method was used to determine the zone of inhibition. The nanoparticles demonstrated potent antibacterial activity against Klebsiella pneumonia (ATCC 1827), Acinetobacter baumannii (ATCC 150504), Escherichia coli (ATCC 33218) and Staphylococcus aureus (ATCC 25293). Antifungal activity against Aspergillus oryzae (PTCC 5164) was also obtained. The data obtained from antimicrobial activities by broth dilution and agar disc diffusion methods exhibited the CuS‐NPs were more effective than the ZnO/Zn(OH)₂‐NPs. A good correlation was observed between the data obtained by both methods.     

MWCNTs/Ionic Liquid/Graphene Quantum Dots Nanocomposite Coated with Nickel‐Cobalt Bimetallic Catalyst as a Highly Selective Non‐enzymatic Sensor for Determination of Glucose

In this work, a glassy carbon electrode (GCE) was modified with multiwall carbon nanotubes/ionic liquid/graphene quantum dots (MWCNTs/IL/GQDs) nanocomposite. Then, the nanocomposite was decorated with nickel‐cobalt nanoparticles (Ni?Co NPs), and it was used as a non‐enzymatic glucose sensor. Field emission scanning electron microscopy, X‐ray diffraction spectroscopy, and energy dispersive spectroscopy were employed to prove the electrodeposition of the Ni?Co NPs on the surface of MWCNTs/IL/GQDs/GCE. Also, cyclic voltammetric and amperometric methods were utilized for the investigation of the electrochemical behaviour of the Ni?Co NPs/MWCNTs/IL/GQDs/GCE for glucose oxidation. The novel amperometric sensor displayed two linear ranges from 1.0 to 190.0 μmol L^?1 and 190.0 to 4910 μmol L^?1 with a low detection limit of 0.3 μmol L^?1 as well as fast response time (2 s) and high stability. Also, the sensor showed good selectivity for glucose determination in the presence of ascorbic acid, citric acid, dopamine, uric acid, fructose, and sucrose, as potential interference species. Finally, the performance of the proposed sensor was investigated for the glucose determination in real samples. Ni?Co NPs/MWCNTs/IL/GQDs/GCE showed good sensitivity and excellent selectivity.     

An Antibacterial Nonenzymatic Glucose Sensor Composed of Carbon Nanotubes Decorated with Silver Nanoparticles

A glucose sensor composed of silver nanoparticles decorated carbon nanotubes (Ag‐NPs/CNTs) prepared by ion implantation is described. Ag‐NPs with size of 2–4 nm are uniformly distributed in the CNTs after ion implantation. This process provides a strong combination between Ag‐NPs and CNTs and can effectively prevent the Ag‐NPs from aggregation. A linear range of 125 µM to 10 mM towards glucose determination was obtained. The Ag‐NPs/CNTs electrode shows minimal interferences from co‐existence species such as uric acid and ascorbic acid and an antibacterial rate of 94 % towards E. coli.     

A Cerium Hexacyanoferrate (III) Nanoparticle‐modified Carbon Paste Electrode: Voltammetric Characterization and Behavior in the Presence of Dopamine

This study describes a fast and simple methodology for the preparation of Cerium (III) Hexacyanoferrate (II) (CeHCF) nanoparticles (NPs). The NPs were characterized by fourier transform infrared (FTIR), x‐ray diffraction (XRD), scanning electron microscopy (SEM) and cyclic voltammetry (CV). The CeHCF cyclic voltammogram indicate a well‐defined redox pair assigned as Fe²⁺/Fe³⁺ in the presence of cerium (III), with a formal potential of E^θ′=0.29 V (v=100 mV s^?1, KNO₃; 1.0 mol/L, pH 7.0). The carbon paste electrode modified with CeHCF (CeHCF‐CPE) was applied to the catalytic electrooxidation of dopamine applying Differential Pulse Voltammetry (DPV). DPV showed linear response at two concentration ranges, from 9.0×10^?7 to 8.0×10^?6 and 9.0×10^?6 to 1.0×10^?4 mol/L, with an LOD of 1.9×10^?7 and 1.0×10^?5 mol/L, respectively. The CeHCF‐CPE exhibited selectivity against substances commonly found in biological samples, with redox potentials close to that of dopamine, such as urea and ascorbic acid (AA). Subsequently the CeHCF‐CPE was successfully applied to the detection of dopamine in simulated urine samples, with recovery percentages ranging between 99 and 103%.     

Electrodeposition of silver nanoparticles on a zinc oxide film: improvement of amperometric sensing sensitivity and stability for hydrogen peroxide determination

A strategy to fabricate a hydrogen peroxide (HP) sensor is developed by electrodepositing silver nanoparticles (Ag NPs) on a modified glassy carbon electrode (GCE) with a zinc oxide (ZnO) film. The Ag NPs/ZnO/GCE has been characterized by scanning electron microscopy, cyclic voltammetry, and chronoamperometry. It has been found that the Ag NPs synthesized in the presence of ZnO film provide an electrode with enhanced sensitivity and excellent stability. The sensitivity to HP is enhanced 3-fold by using Ag NPs/ZnO/GCE compared to Ag NPs/GCE. The HP sensor exhibits good linear behavior in the concentration range 2 µM to 5.5 mM for the quantitative analysis of HP with a detection limit of 0.42 µM (S/N?=?3).     

Electrocatalytic Determination of Hydroxylamine in the Presence of Thiosulfate in Water and Wastewater Samples Using a Nanostructure Modified Carbon Paste Electrode

In this research, we report the preparation of a high sensitive voltammetric sensor for electrocatalytic determination of hydroxylamine (HX) in the presence of thiosulfate (TS). We describe the synthesis and characterization of CdO nanoparticles (CdO/NPs) with transmission electron microscopy (TEM) and X‐ray diffraction (XRD) methods. At an optimum condition, the two peaks are separated ca. 0.58 and 0.92 V for HX and TS at the surface of the proposed sensor. Square wave voltammetry (SWV) of HX exhibited two linear dynamic ranges with a detection limit (3σ) of 0.06 µmol L^?1. The propose sensor was used for determination of HX in water samples.     

Structures,vibrational frequencies,topologies, and energies of hydrogen bonds in cysteine‐formaldehyde complexes

The hydrogen bonding interactions between cysteine (Cys) and formaldehyde (FA) were studied with density functional theory regarding their geometries, energies, vibrational frequencies, and topological features of the electron density. The quantum theory of atoms in molecules and natural bond orbital analyses were employed to elucidate the interaction characteristics in the Cys‐FA complexes. The intramolecular hydrogen bonds (H‐bonds) formed between the hydroxyl and the N atom of cysteine moiety in some Cys‐FA complexes were strengthened because of the cooperativity. Most of intermolecular H‐bonds involve the O atom of cysteine/FA moiety as proton acceptors, while the strongest H‐bond involves the O atom of FA moiety as proton acceptor, which indicates that FA would rather accept proton than providing one. The H‐bonds formed between the CH group of FA and the S atom of cysteine in some complexes are so weak that no hydrogen bonding interactions exist among them. In most of complexes, the orbital interaction of H‐bond is predominant during the formation of complex. The electron density (ρ_b) and its Laplace (?²ρ_b) at the bond critical point significantly correlate with the H‐bond parameter δR, while a linearly relationship between the second‐perturbation energy E(2) and ρ_b has been found as well. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

“Green Electrodes” Modified with Au Nanoparticles Synthesized in Glycerol,as Electrochemical Nitrite Sensor

A new environmentally friendly Au nanoparticles (Au NPs) synthesis in glycerol by using ultraviolet irradiation and without extra‐added stabilizers is described. The synthesis proposed in this work may impact on the non‐polluting production of noble nanoparticles with simple chemicals normally found in standard laboratories. These Au NPs were used to modify a carbon paste electrode (CPE) without having to separate them from the reaction medium. This green electrode was used as an electrochemical sensor for the nitrite detection in water. At the optimum conditions the green sensor presented a linear response in the 2.0×10^?7–1.5×10^?5 M concentration range, a good detection sensitivity (0.268 A L mol^?1), and a low detection limit of 2.0×10^?7 M of nitrite. The proposed modified green CPE was used to determine nitrite in tap water samples.     

MnO2‐TiO2 Nanocomposite and 2‐(3,4‐Dihydroxyphenethyl) Isoindoline‐1,3‐Dione as an Electrochemical Platform for the Concurrent Determination of Cysteine,Tryptophan and Uric Acid

A novel modified carbon paste electrode (CPE) based on an MnO₂‐TiO₂ nanocomposite and 2‐(3,4 dihydroxyphenethyl) isoindoline‐1,3‐dione (DPID) as the modifier for the simultaneous analysis of cysteine (Cys), tryptophan (Trp) and uric acid (UA), as three key biochemicals present in human body. The MnO₂/TiO₂ nanocomposite was synthesized through a chemical co‐precipitation approach and the resulting electrode (MnO₂‐TiO₂/DPID/CPE) was used for studying the electrochemical oxidation of cysteine (Cys), tryptophan (Trp) and uric acid. As opposed to conventional CPEs, the oxidation peak potential of cysteine on MnO₂‐TiO₂/DPID/CPE had a 600.0 mV decrease in overpotential and could be observed at 30.0 mV, and the signals were linear from 0.025 to 200.0 μM, and a lower detection limit of 0.013 μM was reached. The MnO₂‐TiO₂/DPID/CPE was satisfactorily used for the concurrent analysis of Cys, Trp and UA in pharmaceutical and biological samples.     

Antimicrobial,mechanical, optical and thermal properties of PVC/ZnO‐EDTA nanocomposite films

Covalent surface functionalization of synthesized ZnO nanoparticles (NP)s with ethylenediaminetetraacetic acid (EDTA) was successfully carried out. Modified ZnO‐EDTA NPs as a viable and inexpensive filler were incorporated into poly(vinyl chloride) PVC matrix after their chemical modification to investigate the agglomeration behavior. All prepared materials including modified NPs and PVC/ZnO‐EDTA nanocomposites (NC)s were analyzed by Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, thermogravimetric analysis, X‐ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. Fabricated PVC/ZnO‐EDTA NCs were reported to have high transparency and improved mechanical properties compared with PVC. Modified ZnO and the fabricated NCs were shown to exhibit excellent antibacterial activity against two bacteria species: Escherichia coli and Staphylococcus aureus. The obtained NCs could be considered as self‐extinguishing materials on the basis of the LOI values. Copyright © 2016 John Wiley & Sons, Ltd.