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In this research, a novel manganese dioxide nanorod-anchored graphene oxide (MnO2 NRs/GO) composite was synthesized by a simple hydrothermal method for electrochemical sensing application. A highly sensitive electrochemical sensor for dopamine (DA) was constructed by modifying glassy carbon electrode (GCE) with MnO2 NRs/GO. The morphology and performance of the composite material and modified GCEs were investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and cyclic voltammetry (CV), respectively. The resultant MnO2 NRs/GO composite has a large electroactive area and shows excellent electrochemical activity toward DA. Under the optimal conditions, the DA sensor shows a linear response in the DA concentration ranges of 0.1 μM–0.08 mM and 0.08–0.41 mM with a low detection limit of 0.027 μM and a high sensitivity of 602.4 μA·mM−1·cm−2. The MnO2 NRs/GO composite provides a promising platform for the construction of a highly sensitive and selective sensor of DA. [ABSTRACT FROM AUTHOR]

A cage-like PbS nanostructure was functionalized with platinum nanoparticles, and the resulting material (PtNP@PbS) was deposited on a glassy carbon electrode in order to study the direct electron transfer to FADH in glucose oxidase (GOx) and further to construct a glucose biosensor. The PtNP@PbS nanostructure and the biosensor were characterized using scanning electron microscopy, UV-vis and electrochemical impedance spectroscopy, and by cyclic voltammetry. Compared to the use of cage-like PbS alone, the PtNP@PbS nanostructure shows much higher electrochemical activity and an enhanced direct electron transfer rate. The GOx loaded onto the nanostructure displays good enzymatic activity and an apparent electron transfer rate constant of 3.0 s. The glucose biosensor is operated best at −0.4 V (vs. SCE) and then exhibits a linear range that extends from 4 μM to 1.1 mM, with a detection limit as low as 1 μM (at an S/N ratio of 3). The biosensor is selective, acceptably repeatable and stable. It was applied to the determination of glucose in human serum samples. [ABSTRACT FROM AUTHOR]

We describe a sensitive photoelectrochemical (PEC) sensor for the determination of the herbicide clethodim. The PEC sensor was constructed by using amino-MIL-125/TiO (MIL stands for Materials from Institute Lavoisier), an amino-functionalized metal-organic framework (MOF) modified with TiO. The amino-MIL-125/TiO was synthesized by a simple one-step solvothermal method and placed on a glassy carbon electrode where it displays photoelectrocatalytic activity. Scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and X-ray diffractometry (XRD) were used to characterize the amino-MIL-125/TiO. In the sensing process, amino-MIL-125/TiO is illuminated by visible light to produce electrons. These excited electrons are delivered to the glassy carbon electrode, leaving positively charged holes (h) on the surface of the amino-MIL-125/TiO. The holes react with HO to generate hydroxy radicals (•OH). Clethodim rapidly attacks the hydroxy radicals and improves the efficiency of charge separation, this leading to an enhanced photocurrent. Under the optimal experimental conditions, this photoelectrochemical method enables clethodim to be quantified in the concentration range from 0.2 to 25 μmol L, with a detection limit (3 S/N) of 10 nmol L. The assay was applied to the determination of clethodim in soil samples, and results were in acceptable agreement with data obtained by liquid chromatography/mass spectrometry. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We describe a highly sensitive electrochemical enzymatic glucose biosensor. A glassy carbon electrode was modified with cylinder-shaped titanium dioxide nanorods (TiO-NRs) for the immobilization of glucose oxidase. The modified nanorods and the enzyme biosensor were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The glucose oxidase on the TiO-NRs displays a high activity and undergoes fast surface-controlled electron transfer. A pair of well-defined quasi-reversible redox peaks was observed at −0.394 and −0.450 V. The TiO-NRs provide a good microenvironment to facilitate the direct electron transfer between enzyme and electrode surface. The biosensor has two linear response ranges, viz. from 2.0 to 52 μM, and 0.052 to 2.3 mM. The lower detection limit is 0.5 μM, and the sensitivity is 68.58 mA M cm. The glucose biosensor is selective, well reproducible, and stable. In our perception, the cylindrically shaped TiO-NRs provide a promising support for the immobilization of proteins and pave the way to the development of high-performance biosensors. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

An electrochemical non-enzymatic glucose sensor was fabricated by electrodeposition of copper nanoparticles (CuNPs) onto a poly( o-phenylenediamine) (PoPD) film-modified glassy carbon electrode (CuNPs/PoPD/GCE). We had studied some factors such as the pH value of supporting electrolyte, the amount of PoPD and applied potentials and optimize the experiment conditions. Under the optimum conditions, the as-obtained sensor for glucose sensing had achieved a wide linear range, low detection limit, and fast response time. The current response of the as-obtained sensor towards electrochemical oxidation of glucose was linear with the concentration of glucose in the range of 5.0 μM to 1.6 mM ( R = 0.998) in the solution of 0.1 M NaOH at the applied potential of 0.5 V. The detection limit is 0.25 μM and the fast response achieves within 1 s. The sensor exhibits good sensitivity, selectivity, and reproducibility. The proposed non-enzymatic glucose was successfully employed to determine glucose in blood samples. [ABSTRACT FROM AUTHOR]

Biomorphic calcium phosphate (CaP) microspheres with hierarchical porous structure were synthesized using natural cole pollen grains as templates and were further employed for the immobilization of horseradish peroxidase (HRP). Scanning electron microscopy and Fourier transform infrared spectroscopy revealed (a) the porous structure of the CaP microspheres, (b) the effective immobilization, and (c) the retention of the conformation of HRP on CaP. The immobilized HRP was placed on a glassy carbon electrode where it underwent a direct, fully reversible, and surface-controlled redox reaction with an electron transfer rate constant of 1.96 s. It also exhibits high sensitivity to the reduction of HO The response to HO is linear in the 5.00 nM to 1.27 μM concentration range, and the sensitivity is 30357 μA⋅mM⋅cm. The detection limit (at an SNR of 3) is as low as 1.30 nM. The apparent Michaelis-Menten constant ( K) of the immobilized enzyme is 0.92 μM. This new CaP with hierarchical porous structure therefore represents a material that can significantly promote the direct electron transfer between HRP and an electrode, and is quite attractive with respect to the construction of biosensors. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Urchin-like InS nanostructures were functionalized with multi-walled carbon nanotubes (MWCNTs) and deposited on a glassy carbon electrode (GCE) to obtain a new kind of sensor for dopamine (DA). The new electrode was characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, cyclic voltammetry and differential pulse voltammetry. It is found that the current response toward DA is significantly enhanced compared to that of a bare GCE or a GCE modified with MWCNTs. The peak separation between DA and ascorbic acid (AA) is up to 225 mV. The new electrode also has improved selectivity for DA over AA compared to the bare electrode. The new DA sensor has a wide linear range (0.5-300 μM), high sensitivity (594.9 μA mM cm) and low detection limit (0.1 μM). CNTs wrapped on urchin-like nanostructures remarkable improve its electrocatalytic activity and thus provide a promising strategy to develop excellent composite materials for electrochemical sensing. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The voltammetric behavior of dopamine was studied at a glassy carbon electrode modified by cysteic acid, based on electrochemical oxidation of L-cysteine. The modified electrode showed strong electrocatalytic activity towards dopamine and good selectivity. In a phosphate buffer solution (pH 7.4), the anodic peak current obtain from the differential pulse voltammetry of dopamine was linearly dependent on its concentration in the range of 5×10-9 to 4.0×10-6mol · L-1, with a detection limit of 2×10-9mol · L-1. The low-cost modified electrode had been applied to the determination of dopamine in human serum and urine samples with satisfactory results. [ABSTRACT FROM AUTHOR]

A method for determination of paracetamol is established by the differential pulse voltammetry (DPV) using a pumice mixed carbon paste electrode with the pumice weight percent of 6% (m/m) in 0.1 mol1[SUP-1] H[SUB2]SO[SUB4]. The anodic peak potential is ca. 0.640V (vs. SCE). There is a good linear relationship between the peak current and paracetamol concentration in the range of 6.0 × 10[SUP-8] -1.0 × 10-[SUP-6]mol1[SUP-1], and 2.0 × 10[SUP-6] -9.8 × 10[SUP-5] mo1l[SUP-1] with the detection limit of 2.0 × 10[SUP-8] mol 1[SUP-1]. Compared with the carbon paste electrode, the detection limit of this method decreases two orders of magnitude. This method is rapid, simple, accurate and highly sensitive. Satisfactory results for determination of paracetamol in pharmaceutical preparations and urine are obtained. [ABSTRACT FROM AUTHOR]

Abstract: An electrochemical method has been successfully demonstrated for sensitive determination of Metronidazole (MTZ) with graphene (Gr)-room temperature ionic liquid (IL) of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) composite modified glassy carbon electrode (GCE). The cyclic voltammetric results indicate that Gr-IL/GCE can remarkably enhance electrocatalytic activity towards the reduction of MTZ in neutral solutions. MTZ produce a cathodic peak at about −0.69V at this electrode. The electrochemical parameters of MTZ in the composite film were carefully calculated with the results of the charge transfer coefficient (α) as 0.625 and the number of electron transferred (n) as 4. The electrocatalytic behavior was further exploited as a sensitive detection scheme for the MTZ determination by differential-pulse voltammetry (DPV). Under optimized conditions, the concentration range and detection limit were 1.0×10−7–2.5×10−5 molL−1 and 4.7×10−8 molL−1 (S/N =3), respectively for MTZ. The method was successfully applied assay of the drug in the pharmaceutical dosage forms. [Copyright &y& Elsevier]

Abstract: A new petentiometric method to determine peroxide hydrogen and glucose had been studied. This method had been applied on the petentiometric determination of peroxide hydrogen and glucose in the total ionic strength adjustment buffer (TISAB) (pH 7.5) solution with the glassy electrode modified by the calix[4]arene. The glassy carbon electrode covered with the calix[4]arene depended on the H2O2 concentration in the range of log[H2O2] from −3.3 to −1.2 in the solution of TISAB (pH 7.5) with nearly Nernstian slope of about 65.6±3mV and the detection limit of peroxide hydrogen was 4.0×10−5 molL−1. The glassy carbon electrode covered with the calix[4]arene depended on the glucose concentration in the range of log[glucose] from −3.6 to −2.8 in the solution of TISAB (pH 7.5) with nearly Nernstian slope of about 50.2±2mV and the detection limit of glucose was 2.0×10−5 molL−1. The electrode had the good selectivity, sensitivity, stability and repeatability. [Copyright &y& Elsevier]

In this work, an ultrasensitive electrochemiluminescence (ECL) method was established for the detection of trace amount of Ag ions (Ag + ). In sulfuric acid medium, Ag(II), the electro-oxidized product of Ag(I), oxidizes manganese ions (Mn 2+ ) to produce permanganate (MnO 4 - ) by using a pair of graphite catheters as electrodes. While permanganate and luminol can produce strong chemiluminescence, based on the catalytic effect of Ag(II) on Mn 2+ oxidation, there is a good linear relationship between the concentration of Ag + and luminescence intensity. Under optimized conditions, the linear range of this method for Ag + is from 0.2 to 150 nM with a detection limit of 0.06 nM. The method was applied for determination of Ag + in various water samples with satisfactory results. [ABSTRACT FROM AUTHOR]

Using a facile and efficient method, two-dimensional (2D) ultra-thin MnO 2 nanosheets were successfully prepared. Due to the large specific surface area and mesoporous structure, MnO 2 nanosheet is a good candidate for use as an enhanced electrochemical sensing material. MnO 2 nanosheets were immobilized onto glassy carbon electrodes with Nafion film to construct a H 2 O 2 electrochemical nonenzymatic sensor. Amperometric study showed MnO 2 nanosheets exhibited very high electrocatalytic activity towards H 2 O 2 reduction. A very low detection limit (5 nM) was reached with a wide linear range (25 nM–2 μM and 10–454 μM) and a high sensitivity of 3261 mA M −1 cm −2 . The fabricated H 2 O 2 sensor also exhibited excellent selectivity, good reproducibility and long-time stability. Furthermore, the constructed high sensitive sensor was successfully applied to perform real-time monitoring trace concentration of H 2 O 2 released by SP2/0 cells, indicating that MnO 2 nanosheets provide a new platform for developing high performance electrochemical sensors in biological applications. [ABSTRACT FROM AUTHOR]

An electrochemical sensor based on multi-walled carbon nanotubes and chitosan-nickel complex (MWCNTs/CTS-Ni) was fabricated by self-assembly technique for sensitive determination of metronidazole. The electroanalytical performance of the proposed MWCNTs/CTS-Ni modified electrode was intensively evaluated. The experimental results indicated that the MWCNTs/CTS-Ni modified glassy carbon electrode exhibited excellent electrocatalytic activity towards metronidazole. The proposed sensor revealed linear response to metronidazole in the concentration range of 0.1 to 150 μmol L − 1 , with a low detection limit of 0.025 μmol L − 1 . Moreover, the sensor also showed good selectivity, reproducibility and stability. The proposed method could be successfully applied for the sensitive determination of metronidazole in pharmaceutical and biological samples. [ABSTRACT FROM AUTHOR]

A simple and sensitive electrochemical sensor based on the formation of heteropoly blue at poly- l -lysine (PLL)-functionalized graphene (GR) modified glassy carbon electrode (GR-PLL/GCE) was developed to detect sulfate in the presence of cetyltrimethylammonium bromide (CTAB). This method was based on the oxidation currents of the blue complex formed via 40 s electrolysis of Mo (VI)–acetone–HCl solution containing sulfate at 0.1 V vs. SCE and sulfate concentration. The structure and morphology of GR, PLL and GR-PLL were examined by Raman, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The fabricated sensor was further characterized using cyclic voltammetry (CV). Under optimum conditions, the sensor displayed a wide linear range of 0.8–1000 μM for sulfate concentration with the coefficient of determination of 0.9996 and a detection limit of 0.26 μM. The proposed sensor was further employed to detect sulfate in fine particles (PM 2.5 , particulates with aerodynamic diameters <2.5 μm). The results obtained were in good agreement with those of using ion chromatography (IC), which indicates that this novel voltammetric sensor has promising applications for the detection of sulfate in environmental fields. [ABSTRACT FROM AUTHOR]

A glassy carbon electrode modified with nano TiO 2 and multi-walled carbon nanotubes composites dispersed in a novel cationic surfactant was described for the determination of trace mercury(II) by linear anodic stripping voltammetry. Under optimal experimental conditions, the linear sweep anodic stripping peak current was linear with the concentration of Hg(II) in the range of 0.1–100 μmol L −1 with a detection limit of 0.025 μmol L −1 . The sensitivity was found to be 3.7014 A/mol L −1 . The proposed electrode also showed a high selectivity for mercury in the presence of common potential interfering metal ions. Moreover, the proposed electrode revealed good reproducibility and stability. The proposed method was successfully applied for the determination of Hg(II) in river water and industrial wastewater samples. [ABSTRACT FROM AUTHOR]

Highlights: [•] The first example of sensor construction based on NH2-MIL-125. [•] Photo-oxidization ability of NH2-MIL-125. [•] Mn2+ detection based on photooxidation and electrochemistry. [•] The method has low detection limit and wide linearity. [Copyright &y& Elsevier]

Abstract: An electrochemical sensor based on a copolymer poly(4-vinylpyridine)-co-poly(acrylonitrile), P4VP-co-PAN, and Fe2O3 nanoparticle film modified glassy carbon electrode was developed for the determination of glucose. We studied the response of glucose with the proposed electrode, and determined the optimum conditions by changing the potential, pH and P4VP-co-PAN. The current response measurements were performed in PBS (c=0.1M) with a potential of 0.7V. The current response of this glucose sensor showed a linear relationship with the concentration in the range of 2.5μM–0.58mM (r=0.997). The experimental results demonstrate that this method has such merits as simple operation, low cost, high sensitivity, long term stability and good reproducibility, with satisfactory results. [Copyright &y& Elsevier]

Abstract: In this work, we have developed a novel approach that fabricating carbon nanoelectrode ensembles (carbon NEEs) with the pores of 50–120nm in radii by self-assembling a copolymer [poly(acrylonitrile-co-acrylic acid)]. Only conventional, inexpensive electrochemical instrument is required for this procedure, which is simple and fast. The electrochemical behavior of AA and UA at this carbon NEEs has been studied by CV and differential pulse voltammetry (DPV). The carbon NEEs can suppress the response of ascorbic acid (AA) drastically and resolve the overlapping voltammetric response of uric acid (UA) and AA into two well-defined peaks with a large anodic peak difference (ΔE pa) of about 330mV. Meanwhile, the carbon-based electrodes have the weak absorption and fast electron transfer. The reaction of UA and AA take place in the different micro-environment in the presence of the carboxylic functional groups in the nanopores. The sensor offers the peak current that was linearly dependent on the UA concentration in the range from 5.0×10−7 mol/L to 5.0×10−5 mol/L at neutral pH (PBS, pH 6.86) with a correlation coefficient of 0.998, and the detection limit was 1.0×10−7 mol/L (S/N=3). The carbon NEEs shows excellent sensitivity and selectivity and has been used for the determination of UA in real serum and urine samples with satisfied results. [Copyright &y& Elsevier]

Abstract: Metal–organic framework (MOF) is a relatively new group of interesting materials for specific electrochemical sensing because of its electrocatalytic activity and large surface area. Here, a Zn4O(BDC)3 (MOF-5; BDC2− =1,4-benzenedicarboxylate) modified carbon paste electrode for lead detection was developed. The electroanalytical procedure comprised two steps: chemical accumulation of the adsorbed metal ions at the modified electrode surface, followed by electrochemical detection of the pre-concentrated species using differential pulse stripping voltammetry. It was found that the MOF-5 was capable of adsorbing lead ions from aqueous solutions and could determine the ions prominently at optimum experimental conditions. Many important parameters to acquire the best electrochemical response were carried out, including the amount of MOF-5, different electrolyte solutions, pH, deposition potential, deposition time, and interferences due to other ions. Finally, a calibration graph was obtained with a linear range from 1.0×10−8 to 1.0×10−6 molL−1 (R 2 =0.9981) and detection limit was found to be 4.9×10−9 molL−1. The relative standard deviation (for n =11) was 3.4% at 1.0×10−7 molL−1 of lead level. The proposed method was used for the determination of lead in the real water samples and standard reference materials. [Copyright &y& Elsevier]

Abstract: A novel urchin-like In2O3–chitosan modified glassy carbon electrode (GCE) is for the first time prepared. The direct electrochemistry of glucose oxidase (GOD) immobilized on the surface of modified GCE and biosensing are studied. The urchin-like In2O3 nanostructure-based matrix has large specific surface area and provides a favorable and biocompatible microenvironment for promoting the direct electron transfer between proteins and electrode surface. The properties of different modified electrode are characterized by scanning electron microscopy (SEM), electrochemical impedance spectra (EIS), UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR) and cyclic voltammetry, respectively. The constructed glucose biosensor shows wide linear range (5.0×10−6 to 1.3×10−3 M), low detection limit (1.9×10−6 M), a Michaelis–Menten constant of 0.37mM. The proposed biosensor has good sensitivity, excellent selectivity, good reproducibility and stability. This urchin-like In2O3–chitosan matrix provides a new approach and efficient matrix for the direct electrochemistry of proteins and developing novel types of biosensors. [Copyright &y& Elsevier]

Abstract: A sequential injection lab-on-valve (LOV) unit, integrating a miniaturized electrochemical flow cell (EFC), has been constructed for the determination of trace amounts of Se (IV) by employing cathodic stripping voltammetry (CSV) technique. The procedure is carried out on a mercury film coated glassy carbon electrode. The analyte solution and electrolyte solution were continuously aspirated and merged in the holding coil (HC) by using a single syringe pump, which were afterwards pushed into the EFC, where the peak current was generated during the subsequent deposition/stripping procedure and measured as the basis of quantification. Assay parameters were optimized in order to achieve the best analytical performance, including mercury film preparation, supporting electrolyte composition, deposition potential and deposition time, and flow variables in the LOV. By loading a sample volume of 500μL, a linear calibration graph was derived within 1–600μgL−1, and a detection limit (3б) of 0.11μgL−1 was achieved along with a sampling frequency of 20h−1. By integrating the EFC into the LOV unit, the assembling system not only minimized the sample/reagent consumption and waste generation, but also enhanced the sampling frequency. The work itself extended the applications of electrochemical detection techniques and provided a good platform for Se (IV) electrochemical analysis. [Copyright &y& Elsevier]

Abstract: Amidosulfonic acid was electropolymerized by cyclic voltammetry onto the surface of glassy carbon electrode (GCE) to fabricate the chemically modified electrode, which showed high stability, good selectivity and reproducibility for determination of isoniazid. The modified electrode showed an excellent electrocatalytical effect on the oxidation of isoniazid. Under the optimum conditions, there was a good linear relationship between anodic peak current and isoniazid concentration in the range of 5.0 × 10−8– 1.0 × 10−5 M, and a detection limit of 1.0 × 10−8 M (S/N = 3) was obtained after 120 s at the accumulation potential of − 0.2 V (vs. SCE). This developed method had been applied to the direct determination of isoniazid in injection and tablet samples with satisfactory results. [Copyright &y& Elsevier]

Abstract: Carbon nanotubes (CNTs) and cysteic acid based on electrochemical oxidation of l-cysteine (CySH) to form a novel composite thin film material at a glassy carbon electrode (GCE) for electroanalytical determination of nimesulide. The determination of nimesulide at the composite modified electrode with strong accumulation of nimesulide was studied by differential pulse voltammetry (DPV). The peak current obtained at +1.251V (versus SCE) from DPV was linearly dependent on the nimesulide concentration in the range of 1.0×10−7–1.0×10−5 M in 0.05M H2SO4 solution with a correlation coefficient of 0.997. The detection limit (S/N=3) was found to be 5.0×10−8 M. The low-cost modified electrode showed good sensitivity, selectivity, stability and had been applied to the determination of nimesulide in pharmaceutical formulation and human serum samples with satisfactory results. [Copyright &y& Elsevier]

Abstract: A new and simple method for fabricating controllable insulted nanometer-sized carbon electrodes is presented. Electrochemical etching of carbon fibers is employed, and then a repeated process of cycle voltammetric deposition of electrophoretic paint and heat cure for film shrink is followed which controls effectively the size of nanoelectrodes. This technique allows complete insulation of the whole body of the carbon fiber etched except for the very tip with the film shrink during heat curing of the film, leaving an electrochemical active area with effective diameters of nanometers. The process overcomes the pinhole formation resulted from the electrophoretic paint deposition process. The fabricated electrodes show ideal steady-state voltammetric behaviors from which the effective areas of nanoelectrodes are measured. The effective radius of the nanoelectrodes prepared ranges from tens of nanometer to hundreds of nanometer. [Copyright &y& Elsevier]