Nanodiamond Decorated with Silver Nanoparticles as a Sensitive Film Modifier in a Jeweled Electrochemical Sensor: Application to Voltammetric Determination of Thioridazine

Nanodiamond? graphite (NDG) decorated with Ag nanoparticles (AgNPs‐NDG) was prepared and used to construct a novel sensitive sensor for the voltammetric determination of thioridazine (TR). The results indicate a remarkable increase in the oxidation peak currents together with a negative shift in the oxidation peak potentials, in comparison to the bare pyrolytic graphite electrode. Remarkable enhancement in microscopic area of the electrode along with strong adsorption of TR on the surface of the modified electrode resulted in a considerable increase in the peak current of TR. The surface morphology and the nature of the composite film deposited on PGE were characterized by scanning electron microscopy, atomic force microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Experimental variables, such as the deposited amount of the modifier suspension, pH of the supporting electrolyte, the accumulation potential and time are optimized by monitoring the CV responses of TR. Under the optimal conditions, the modified electrode showed a wide linear response to the concentration of TR in the range of 0.08–100 µM with a detection limit of 0.01 µM. The prepared modified electrode showed several advantages: simple preparation method, high stability and uniformity in the composite film, high sensitivity, long‐term stability and remarkable voltammetric reproducibility in response to TR. The modified electrode can be successfully applied for accurate determination of trace amounts of TR in pharmaceutical and clinical preparations.     

Construction of an electrochemical sensor based on the electrodeposition of Au-Pt nanoparticles mixtures on multi-walled carbon nanotubes film for voltammetric determination of cefotaxime

Mixtures of gold-platinum nanoparticles (Au-PtNPs) are fabricated consecutively on a multi-walled carbon nanotubes (MWNT) coated glassy carbon electrode (GCE) by the electrodeposition method. The surface morphology and nature of the hybrid film (Au-PtNPs/MWCNT) deposited on glassy carbon electrodes is characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The modified electrode is used as a new and sensitive electrochemical sensor for the voltammetric determination of cefotaxime (CFX). The electrochemical behavior of CFX is investigated on the surface of the modified electrode using linear sweep voltammetry (LSV). The results of voltammetric studies exhibited a considerable improvement in the oxidation peak current of CFX compared to glassy carbon electrodes individually coated with MWCNT or Au-PtNPs. Under the optimized conditions, the modified electrode showed a wide linear dynamic range of 0.004-10.0 μM with a detection limit of 1.0 nM for the voltammetric determination of CFX. The modified electrode was successfully applied for the accurate determination of trace amounts of CFX in pharmaceutical and clinical preparations.     

Sensitive Voltammetric Determination of Baicalein at Thermally Reduced Graphene Oxide Modified Glassy Carbon Electrode

This work presents a sensitive voltammetric method for determination of the flavonoid baicalein by using a thermally reduced graphene oxide (TRGO) modified glassy carbon electrode (GCE) in 100 mM KCl‐10 mM sodium phosphate buffer solution (pH 7.40). The surface morphology and structure of TRGO investigated by atomic force microscopy, FT‐IR spectroscopy and Raman spectroscopy reveal that the TRGO prepared maintained as single or bilayer sheets and with significant edge‐plane‐like defect sites. The TRGO/GCE modified electrode shows more favorable electron transfer kinetics for potassium ferricyanide and potassium ferrocyanide probe molecules, which are important electroactive compounds, compared with bare GCE and GO/GCE electrodes. The electrochemical behaviors of baicalein at the TRGO/GCE were investigated by cyclic voltammetry, suggesting that the TRGO/GCE exhibits excellent electrocatalytic activity to baicalein. Under physiological conditions, the modified electrode showed linear voltammetric response from 10 nM to 10 µM for baicalein, with a detection limit of 6.0 nM. This work demonstrates that the graphene‐modified electrode is a promising tool for electrochemical determination of flavonoid drugs.     

Enhanced sensing of anthraquinone dyes using multiwalled carbon nanotubes modified electrode

The voltammetric behaviour of two anthraquinone dyes such as Alizarin Red S (ARS) and Reactive blue 4 (RB4) was investigated at plain glassy carbon electrode (GCE), multiwalled carbon nano tube modified GCE (MWCNT/GCE) and zeolite modified GCE (ZE/GCE) using cyclic voltammetry. Effects of pH, scan rate and concentration were studied. The surface morphology of the modified electrode in the absence and presence of dye molecules was characterized by scanning electron microscopy (SEM). A systematic study on the variation of experimental parameters with differential pulse stripping voltammetry (DPSV) was carried out and the optimized experimental conditions were arrived. MWCNT/GCE performed well among the three electrode systems and the limit of detection (LOD) was 0.036?µg?mL^?1 for ARS and 0.05?µg?mL^?1 for RB4 on this modified system. Suitability of the differential pulse stripping voltammetric method for the trace determination of textile dyes in effluents was also realized.     

Voltammetric Determination of Folic Acid Using Adsorption of Methylene Blue onto Electrodeposited of Reduced Graphene Oxide Film Modified Glassy Carbon Electrode

This work presents a sensitive voltammetric method for determination of folic acid by adsorbing methylene blue onto electrodeposited reduced graphene oxide film modified glassy carbon electrode (MB/ERGO/GCE) in 100 mM KCl‐10 mM sodium phosphate buffer solution (pH 7.40). The surface morphology of the MB/ERGO/GCE modified electrode was characterized using scanning electron microscopy, displays that both MB and ERGO distributed homogeneously on the surface of GCE. The MB/ERGO/GCE modified electrode shows more favorable electron transfer kinetics for potassium ferricyanide and potassium ferrocyanide probe molecules, which are important electroactive compounds, compared with bare GCE, MB/GCE, and ERGO/GCE. The electrochemical behaviors of folic acid at MB/ERGO/GCE were investigated by cyclic voltammetry, suggesting that the modified electrode exhibited excellent electrocatalytic activity towards folic acid compared with other electrodes. Under physiological condition, the MB/ERGO/GCE modified electrode showed a linear voltammetric response from 4.0 μM to 167 μM for folic acid, and with the detection limit of 0.5 μM (S/N=3). The stability, reproducibility and anti‐interference ability of the modified electrode were examined. The developed method has been successfully applied to determination of FA in tablets with a satisfactory recovery from 96 % to 100 %. The work demonstrated that the electroactive MB adsorbing onto graphene modified electrode showed an enhanced electron transfer property and a high resolution capacity to FA.     

Electrochemical Behavior and Voltammetric Determination of Curcumin at Electrochemically Reduced Graphene Oxide Modified Glassy Carbon Electrode

This work presents a sensitive voltammetric method for determination of curcumin by using a electrochemically reduced graphene oxide (ERGO) modified glass carbon electrode (GCE) in 100 mM KCl‐10 mM sodium phosphate buffer solution (pH 7.40). The electrochemical behaviors of curcumin at ERGO/GCE were investigated by cyclic voltammetry, suggesting that the ERGO/GCE exhibits excellent electrocatalytic activity towards curcumin, compared with bare GCE and GO/GCE electrodes. The electrochemical reaction mechanisms of curcumin, demethoxycurcumin and bisdemethoxycurcumin at the ERGO/GCE were also investigated and discussed systematically. Under physiological condition, the modified electrode showed linear voltammetric response from 0.2 μM to 60.0 μM for curcumin, with the detection limit of 0.1 μm. This work demonstrates that the graphene‐modified electrode is a promising strategy for electrochemical determination of biological important phenolic compounds.     

纳米银修饰电极差分脉冲伏安法测定盐酸金霉素

建立了快速测定盐酸金霉素(CTC)的方法。通过NaBH4还原法制备纳米银(AgNPs)溶胶,并利用X射线衍射和紫外-可见光谱进行表征。将制备好的AgNPs滴涂到玻碳电极表面制备修饰电极(AgNPs/GCE),研究了CTC在AgNPs/GCE上的电化学行为及伏安法测定,优化了缓冲溶液和pH等检测条件。结果表明,CTC在pH 3.3的柠檬酸-NaOH-HCl缓冲溶液中检测效果最佳。CTC在AgNPs/GCE上发生2个电子和2个质子的不可逆电化学氧化反应,且反应受吸附控制。最佳条件下,CTC的氧化峰电流与其浓度呈现良好的线性关系,线性范围为0.5~100μmol/L,检出限为0.14μmol/L。该修饰电极可用于河水样品检测。     

基于纳米银/碳纳米纤维复合材料的增强效应电化学测定多贝斯

将银纳米粒子(AgNPs)电沉积在碳纳米纤维(CNFs)修饰玻碳电极表面制备纳米银/碳纳米纤维修饰玻碳电极(AgNPs/CNFs/GCE).采用扫描电镜考察其表面形态,在K3[Fe(CN)6]-K4[Fe(CN)6]体系中用循环伏安法和电化学阻抗法研究AgNPs/CNFs/GCE的电化学行为.采用循环伏安法和方波伏安法...     

CuO Nanostructures Based Electrochemical Sensor for Simultaneous Determination of Hydroquinone and Ascorbic Acid

A simple, sensitive and reliable electrochemical sensor has been developed based on CuO nanostructures modified glassy carbon electrode for simultaneous determination of hydroquinone (HQ) and ascorbic acid (AA). The CuO nano material was synthesized by aqueous chemical growth method using different sources of OH. The characterization of nano material was performed by Fourier transform infrared spectroscopy, X‐ray diffraction, field emission scanning electron microscopy and energy dispersive X‐ray spectroscopy. The glassy carbon electrode was modified by CuO nano material using drop cast method and studied by cyclic voltammetry. The CuO/GCE exhibited excellent electrocatalytic activity towards the oxidations of HQ and AA in borate buffer solution (pH 8.0) and the corresponding electrochemical signals have appeared as two well resolved oxidation peaks with significant peak potential differences of (0.21V vs. Ag/AgCl). Differential pulse voltammetry was used for simultaneous determination of HQ and AA using the CuO/GCE. At the optimum conditions, for simultaneous determination by synchronous change of the analyte concentrations, the linear response ranges were between 0.0003–0.355 mM for HQ and 0.0001–0.30 mM for AA respectively. Furthermore, CuO/GCE was successfully applied for the independent determination of AA in fruit juices as well as for the simultaneous determination of HQ and AA in cosmetic samples.     

Voltammetric Determination of Nifedipine on Carbon Nanotubes‐Modified Glassy Carbon Electrode: A new Application to Dissolution Test Studies

We report the adsorptive voltammetric determination of nifedipine on multiwalled carbon nanotubes (MWCNT)‐modified glassy carbon electrode (GCE). Nifedipine was adsorbed on the MWCNT and then reduced using linear sweep and cyclic voltammetry (LSV and CV). Parameters such as pH and accumulation time were tested. The MWCNT‐modified GCE showed enhanced currents and good signal‐to‐noise characteristics in comparison with the bare GCE. Consecutive measurements with the modified electrode were highly repeatable and reproducible. The MWCNT/GCE was used for the determination of nifedipine and is recommended for quantitation in dissolution test studies. In this study we have tested normal and extended‐release pharmaceutical formulations of nifedipine using USP apparatus 2 and tracking the released drug in solution by the proposed voltammetric method. The main advantage of the voltammetric determination is the feasibility to detect the drug in‐situ avoiding tedious intermediate steps such as filtration, collection and replenishment of sample solutions. This work seeks to demonstrate the feasibility of applying voltammetric techniques in dissolution test studies.     

Biomimetic Sensor for Dobutamine Employing Nano‐ TiO2/Nafion/Carbon Nanoparticles Modified Electrode

A novel voltammetric biosensor based on nano‐TiO₂/nafion/carbon nanoparticles modified glassy carbon electrode (TiO₂/N/CNP/GCE) was developed for the determination of dobutamine (DBA). Characterization of the surface morphology and property of TiO₂/N/CNP layer was carried out by the scanning electron microscopy and atomic force microscopy. The electrochemical performance of the modified electrode was investigated by means of the cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy techniques. Effective experimental variables, such as the scan rate, pH of the supporting electrolyte, drop size of the casted modifier suspension and accumulation conditions of DBA on the surface of TiO₂/N/CNP/GCE were optimized. Under the optimized conditions, a significant electrochemical improvement was observed toward the electro‐oxidation of DBA on the surface of TiO₂/N/CNP/GCE compared to the bare GCE. Under the optimized conditions, a wide linear dynamic range (6 nM–1 µM) with a low detection limit of 2 nM for DBA was resulted. The prepared modified electrode shows high sensitivity, stability and good reproducibility in the determination of DBA concentrations. Satisfactory results were obtained for DBA analysis in the pharmaceutical and clinical preparations using TiO₂/N/CNP/GCE.     

Nanocellulose/Carbon Nanoparticles Nanocomposite Film Modified Electrode for Durable and Sensitive Electrochemical Determination of Metoclopramide

A novel electrochemical sensor based on nanocellulose‐carbon nanoparticles (NC‐CNPs) nanocomposite film modified glassy carbon electrode (GCE) is developed for the analysis of metoclopramide (MCP). Atomic force microscopy, scanning electron microscopy and electrochemical impedance spectroscopy were used to characterize the roughness, surface morphology and performance of the deposited modifier film on GCE. SEM image demonstrated that modifier nanoparticles are uniformly deposited on GCE, with an average size of less than 50 nm. The electrochemical behavior of MCP and its oxidation product is studied using linear sweep and cyclic voltammetry over a wide pH range on NC‐CNPs modified glassy carbon electrode. The results revealed that the oxidation of MCP is an irreversible and pH‐dependent process that proceeds in an adsorption‐controlled mechanism and results in the formation of a main oxidation product, which adsorbs on the surface of NC‐CNPs/ GCE. The modified electrode showed a distinctive anodic response towards MCP with a considerable enhancement (49 fold) compared to the bare GCE. Under the optimized conditions, the modified electrode exhibited a wide linear dynamic range of 0.06–2.00 µM with a detection limit of 6 nM for the voltammetric determination of MCP. The prepared modified electrode showed several advantages such as simple preparation method, high stability, reproducibility, and repetitive usability. The modified electrode is successfully applied for the accurate determination of trace amounts of MCP in pharmaceutical and clinical preparations.     

Fabrication of an electrochemical sensor based on the electrodeposition of Pt nanoparticles on multiwalled carbon nanotubes film for voltammetric determination of ceftriaxone in the presence of lidocaine, assisted by factorial-based response-surface methodology

A glassy carbon electrode (GCE) is modified with platinum nanoparticle (PtNPs) decorated multiwalled carbon nanotube (MWCNT). The modified electrode is applied for the determination of ceftriaxone (CFX) in the presence of lidocaine. Different methods were used to characterize the surface morphology of the modified electrode. The electrochemical behavior of CFX was investigated at GCE, MWCNT/GCE and PtNPs/MWCNT/GCE. A factorial-based response-surface methodology was used to find out the optimum conditions with minimum number of experiments. Under the optimized conditions, oxidation peak currents increased linearly with CFX concentration in the range of 0.01–10.00 μM with a detection limit of 9.01 nM. The results prove that the modified electrode is also suitable for the determination of CFX in pharmaceutical and clinical preparations.     

Simultaneous Voltammetry Determination of Dihydroxybenzene Isomers by Nanogold Modified Electrode

A convenient electrochemical deposition method to prepare nanogold/glassy carbon modified electrode (nano‐Au/GCE) is adopted. In 0.1 mol/L HAc‐NaAc buffer solution (pH 4.61), the nano‐Au/GCE shows an excellent electrocatalytical behavior for the redox of dihydroxybenzene. A simple, rapid and highly selective voltammetry for simultaneous determination of dihydroxybenzene isomers, hydroquinone, catechol, and resorcinol, is developed using the nano‐Au/GCE. This method has been applied to the direct determination of the three dihydroxybenzene isomers in artificial wastewater.     

金纳米粒子/碳纳米管修饰电极对4 壬基酚的电催化氧化及检测研究

制备了金纳米粒子/碳纳米管修饰玻碳电极(AuNPs-CNTs/GCE),采用循环伏安法和线性扫描伏安法研究了4-壬基酚在修饰电极上的电化学行为,并建立了一种灵敏简便地检测4-壬基酚的电化学方法。优化了pH值、扫描速率、富集时间等测定参数,并计算出pH值与氧化峰电压、扫描速率与氧化峰电流之间的数量关系。在pH 10.0的BR缓冲溶液中,4-壬基酚在AuNPs-CNTs/GCE上出现灵敏的氧化峰,氧化电位为0.51 V。与裸玻碳电极(GCE)和单一碳纳米管修饰电极(CNTs/GCE)相比,AuNPs-CNTs/GCE明显提高了4-壬基酚的氧化电流。在优化实验条件下,4-壬基酚的浓度分别在0.05～4μmol/L和6～14μmol/L范围内与氧化峰电流呈良好的线性关系,检出限为0.023μmol/L,对于实际样品测定的回收率为95%～104%。该修饰电极具有良好的重现性和稳定性,可用于环境样品中4-壬基酚的直接检测。     

A Selective Simultaneous Determination of Levodopa and Serotonin Using a Glassy Carbon Electrode Modified with Multiwalled Carbon Nanotube/Chitosan Composite

A glassy carbon electrode (GCE) modified with carbon nanotube/chitosan (MWCNTs‐CHT/GCE) was used for the sensitive voltammetric determination of levodopa (Lev) and serotonin (Ser). The measurements were carried out using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CA). Under the optimum conditions the electrode provides a linear response versus Lev and Ser concentrations in the range of 2.0–220.0 µM and 0.5–130.0 µM, respectively, using DPV. The modified electrode was satisfactorily used for determination of Lev and Ser in human serum and urine with satisfactory results.     

Electroanalysis of some common pesticides using conducting polymer/multiwalled carbon nanotubes modified glassy carbon electrode

The cyclic voltammetric behaviour of three common pesticides such as isoproturon (ISO), voltage (VOL) and dicofol (DCF) was investigated at glassy carbon electrode (GCE), multiwalled carbon nanotubes modified GCE (MWCNTs/GCE), polyaniline (PANI) and polypyrrole (PPY) deposited MWCNT/GCE. The modified electrode film was characterized by scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The electroactive behaviour of the pesticides was realized from the cyclic voltammetric studies. The differential pulse voltammetric principle was used to analyze the above-mentioned pesticides using MWCNT/GCE, PANI/MWCNT/GCE and PPY/MWCNT/GCE. Effects of accumulation potential, accumulation time, Initial scan potential, amplitude and pulse width were examined for the optimization of stripping conditions. The PANI/MWCNT/GCE performed well among the three electrode systems and the determination range obtained was 0.01-100 mgL(-1) for ISO, VOL and DCF respectively. The limit of detection (LOD) was 0.1 microgL(-1) for ISO, 0.01 microgL(-1) for VOL and 0.05 microgL(-1) for DCF on PANI/MWCNT/GCE modified system. It is significant to note that the PANI/MWCNT/GCE modified system results in the lowest LOD in comparison with the earlier reports. Suitability of this method for the trace determination of pesticide in spiked samples was also realized.     

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.     

Rapid and Sensitive Determination of Dinotefuran Residue Based on Electrochemical Enhancement of β‐cyclodextrin‐Graphene Composite

A rapid method for sensitive voltammetric determination of dinotefuran residue was reported. The proposed method was based on the electrocatalytic reduction of dinotefuran on β‐cyclodextrin‐graphene composite modified glassy carbon electrode (β‐CD‐rGO/GCE), giving rise to a higher reduction signal to dinotefuran relative to the bare (GCE) and graphene modified electrode (rGO/GCE). Moreover, a further signal enhancement was observed when the modified electrode incubated in solution at low temperature (0 °C) for a short time. The reduction mechanism and binding affinity were also discussed. The external standard calibration curve was obtained from linear sweep voltammetry in the range of 0.5 to 16.0 μM with a detection limit of 0.10 μM. In addition to optimization of pretreatment, this electrochemical method has been applied to the dinotefuran residue determination in millet samples with the detection limit of 0.01 mg kg^?1 and compared with an high performance liquid chromatography method. The proposed electrode and analysis methods were proven to be sensitive, accurate and rapid under the used conditions.     

Synthesis and characterisation of Ag-nanoparticles immobilised on ordered mesoporous carbon as an efficient sensing platform: application to electrocatalytic determination of hydrazine

In this study, a new strategy for the preparation of a modified glassy carbon electrode (GCE) based on a novel nano-sensing layer for the electrocatalytic oxidation of hydrazine was suggested. The suggested nano-sensing layer was prepared with the immobilisation of silver nanoparticles (AgNPs) on ordered mesoporous carbon. The morphology and properties of the prepared nanocomposite on the surface of GCE were characterised by scanning electron microscopy, transmission electron microscopy, N₂ adsorption-desorption, X-ray powder diffraction and electrochemical impedance spectroscopy. The electrochemical response characteristics of the modified electrode towards the target analyte were investigated by cyclic voltammetry. Under optimal experimental conditions, the suggested modified GCE showed excellent catalytic activity towards the electro-oxidation of hydrazine (pH = 7.5) with a significant increase in anodic peak currents in comparison with the unmodified GCE. By differential pulse voltammetry and amperometric methods, the suggested sensor demonstrated wide dynamic concentration ranges of 0.08–33.8 µM and 0.01–128 µM with the detection limit (S/N = 3) of 0.027 and 0.003 µM for hydrazine, respectively. The suggested hydrazine sensor was successfully applied for the highly sensitive determination of hydrazine in different real samples with satisfactory results.