Sensitive and Green Method for Determination of Chemical Oxygen Demand Using a Nano‐copper Based Electrochemical Sensor

Copper nanoparticles (nano‐Cu) were electrodeposited on the surface of glassy carbon electrode (GCE) potentiostatically at −0.6 V vs. Ag/AgCl for 60 s. The developed nano‐copper modified glassy carbon electrode (nano‐Cu/GCE) was optimized and utilized for electrochemical assay of chemical oxygen demand (COD) using glycine as a standard. The surface morphology and chemical composition of nano‐Cu/GCE were investigated using scanning electron microscope (SEM) and energy dispersive X‐ray spectrometer (EDX), respectively. The electrochemical behavior was investigated using linear sweep voltammetry (LSV) which is characterized by a remarkable anodic peak at ∼0.6 V, compared to bare GCE. This indicates that nano‐Cu enhances significantly the electrochemical oxidation of glycine. The effect of different deposition parameters, such as Cu²⁺ concentration, deposition potential, deposition time, pH, and scan rate on the response of the developed sensor were investigated. The optimized nano‐Cu/GCE based COD sensor exhibited a linear range of 15 to 629.3 ppm, and a lower limit of detection (LOD) of 1.7 ppm (S/N=3). This developed method exhibited high tolerance level to chloride ion (0.35 M chloride ion has minimal influence). The analytical utility of the prepared COD sensor was demonstrated by investigating the COD recovery (99.8±4.3) and the assay of COD in different water samples. The results obtained were verified using the standard dichromate method.     

Pulsed Deposited Manganese and Vanadium Oxide Film Modified with Carbon Nanotube and Gold Nanoparticle: Chitosan and Ionic Liquid‐based Biosensor

Present study describes the synthesis of mixed oxide films of manganese and vanadium by electrochemical pulsed deposition technique on a glassy carbon electrode (GCE) modified with multiwall carbon nanotubes (MWCNT). The film was further decorated with gold nanoparticles to enhance the reduction signal of dissolved oxygen in pH 5.17 acetate buffer solution. All of the electrochemical synthesized modified electrodes have been characterized with Scanning electron microscopy(SEM), High‐resolution transmission electron microscopy (HRTEM), X‐Ray photoelectron spectroscopy (XPS), X‐Ray diffraction (XRD) techniques. The electrode obtained (AuNPs/MnOx?VOx/CNT/GCE) was utilized as a platform for glucose biosensor where the glucose oxidase enzyme was immobilized on the composite film with the aid of chitosan and an ionic liquid. The electrochemical performance of the biosensor was investigated by cyclic voltammetry and the relative parameters have been optimized by amperometric measurements in pH 5.17 acetate buffer solution. The developed biosensor exhibited a linear range for glucose between 0.1–1.0 mM and the limit of detection was calculated as 0.02 mM.     

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.     

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.     

Electrochemical Studies of Oxidation of Lomefloxacin and Interaction with Calf Thymus DNA at Nano‐SnO2/DHP Modified Electrode

A nanoparticle thin film modified electrode has been constructed using a glassy carbon electrode (GCE) coated with a nano‐tin oxide/dihexadecylphosphate (nano‐SnO₂/DHP). In pH 6.0 phosphate buffer solutions (PBS), lomefloxacin (LMF) appeared as an anodic peak with peak potential of 1.35 V at nano‐SnO₂/DHP modified electrode. In comparison with a bare GCE or a nano‐SnO₂ modified electrode, the nano‐SnO₂/DHP modified electrode exhibited an enhanced effectiveness for the oxidation of LMF. Cyclic voltammetry (CVs) coupled with fluorescence and UV/vis absorbance spectra techniques were used to study the interaction of LMF with Calf thymus DNA (ctDNA) in phosphate buffer solutions (PBS). The interaction of LMF and ctDNA could result in a considerable decrease in the peak currents and positive shift in the peak potential, as well as changes of fluorescence, UV/vis adsorption spectra and gel electrophoresis. All the acquired data showed that the new adduct between LMF and ctDNA was formed. Electrochemistry coupled with spectroscopy techniques could provide a relatively easy way to obtain useful information about the molecular mechanism of LMF‐ctDNA interactions.     

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.     

Modification of the Electrode Surface by Ag Nanoparticles Decorated Nano Diamond‐graphite for Voltammetric Determination of Ceftizoxime

A modified glassy carbon electrode with a film of nano diamond? graphite nano mixture decorated with Ag nanoparticles (AgNPs? NDG/GCE) was constructed and used for sensitive voltammetric determination of ceftizoxime (CFX). Morphology of AgNPs? NDG/GCE has been examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Experimental variables such as deposited amount of the modifier suspension, pH of the supporting electrolyte and accumulation potential and time were optimized by monitoring of CV and LSV responses of CFX. The results illustrate that AgNPs? NDG/GCE exhibits an excellent electrocatalytic effect in the electro‐oxidation of CFX that leads to a considerable improvement in the corresponding anodic peak current. This also allows the development of a highly sensitive voltammetric sensor for the determination of CFX in pharmaceutical and clinical samples. Under the optimum conditions, the modified electrode showed a linear response to the concentration of CFX in the range of 0.02–7 µM with detection limit of 6 nM. The prepared modified electrode has some remarkable electrochemical properties such as simple preparation, high sensitivity, excellent repeatability and reproducibility and long‐term stability.     

Preparation of Novel Arrays Silver Nanoparticles Modified Polyrutin Coat‐Paraffin‐Impregnated Graphite Electrode for Tyrosine and Tryptophan's Oxidation

A novel array silver nanoparticles and Rutin complex film modified paraffin‐impregnated graphite electrode was proposed in this work (denoted as Ag/Rutin/WGE). The characteristics were investigated by the field emission scanning electron microscopy (FE‐SEM), infrared spectra (IR), UV‐visible (UV), X‐ray photoelectron spectroscopy (XPS) and electrochemical techniques. Silver ions were gradually chelated by polyrutin film at 4′‐oxo‐5′‐OH and 5‐OH‐4‐oxo sites accompanying adsorption, then. Silver nanoparticles were highly‐dispersed electrodeposited on polyrutin film. The electrochemical behaviors of tyrosine (Tyr) and tryptophan (Trp) were studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The Ag/Rutin/WGE electrode shows overlapping catalysis for the oxidation of Tyr and Trp. The linear response of Tyr and Trp were 0.3–10.0 and 0.7–70.0 μM with detection limit of 0.07 and 0.1 μM in a signal‐to‐noise ratio of 3.     

Electrodeposition of Copper Oxide Nanoparticles on Precasted Carbon Nanoparticles Film for Electrochemical Investigation of anti‐HIV Drug Nevirapine

This work describes the development of a novel electrochemical sensor based on electrodeposition of copper oxide nanoparticles onto carbon nanoparticle (CNP) film modified electrode for the analysis of the anti‐HIV drug, nevirapine (NEV). The electrochemical experiments were performed using linear sweep and cyclic voltammetry. Atomic force microscopy was applied for surface characterization of the deposited modifier film (CuO‐CNP) on glassy carbon electrode (GCE). No oxidation peak was observed for NEV on the bare GCE, but both CNP‐GCE and CuO‐CNP‐GCE showed a distinctive anodic response towards NEV with considerable enhancement (276‐fold and 350‐fold, respectively) compared to CuO‐GCE. The mechanism of the electrocatalytic process on the modified electrode surface was investigated by cyclic and linear sweep voltammetry at various potential sweep rates and pHs of the buffer solutions. The modified electrode exhibited linear dynamic range in three concentration intervals (0.1–0.8, 1–10 and 10–100 µM) with a detection limit of 66 nM. The stability, reproducibility, and repetitive usability exhibited by the proposed modified electrode are good enough to make it a suitable sensor for the determination of NEV in real samples with complex matrices such as human blood serum.     

还原氧化石墨烯-多壁碳纳米管复合膜负载金纳米粒子修饰玻碳电极检测双酚A

以水合肼为还原剂,采用均相还原法制备还原氧化石墨烯-多壁碳纳米管复合材料(rGO-MWCNTs),通过滴涂法将其修饰到玻碳电极(GCE)表面.以此复合材料为载体,采用电化学方法制备了金纳米粒子-还原氧化石墨烯-多壁碳纳米管复合膜修饰电极(AuNPs-rGO-MWCNTs/GCE).通过扫描电镜(SEM)、EDS能谱技术和电化学方法对此电极进行了表征.研究了双酚A在修饰电极上的电化学行为.结果表明,此电极对双酚A的电极过程具有良好的电化学活性,在0.10 mol/L PBS溶液(pH 7.0)中,微分脉冲伏安法测定双酚A的线性范围为5.0 × 10-9~1.0 × 10-7 mol/L和1.0 × 10-7~2.0 × 10-5 mol/L,检出限为1.0 ×10-9 mol/L(S/N=3). 将此电极用于模拟水样和超市购物小票样品中双酚A含量的测定,加标回收率分别为97%~110%和98%~104%.     

Electroreduction of dioxygen on Aunano-DNA film electrode in acidic electrolyte

The colloidal Au nanoparticles-deoxyribonucleic acid (Au(nano)-DNA) film modified glassy carbon electrode (GCE) has been fabricated and the electrochemical reduction of dioxygen (O(2)) at this modified GCE has been studied in 0.2 mol/L air-saturated acetate buffer (pH=5.2) using cyclic voltammetry (CV), chronocoulometry (CC), linear scan voltammetry (LSV) and rotating disk electrode (RDE) as diagnostic techniques. The modified electrode shows excellent enhancement effect towards the reduction of dioxygen to hydrogen peroxide (H(2)O(2)), and the overpotential is lower than that at bare GCE. A well-defined dioxygen reduction peak appeared at about -0.24 V. Based on experimental results, a reaction mechanism is proposed and discussed.     

The Interaction of Iodide Film with Platinum Microparticles on Different Electrode Materials for Various Electrocatalytic Reactions

The electrochemical depositions of Pt microparticles and KI film were successfully carried out on glassy carbon electrodes (GCE), gold electrodes (GE), and indium tin oxide electrodes (ITO). The electrochemical studies of Pt micro/KI film on GCE show that the film was stable, active at pH 1.5 electrolyte solutions. The Pt microparticle/KI film modified ITO electrodes were examined by using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The SEM and AFM results show that the Pt particle sizes were in the range of 120 nm–1.4 μm, respectively. The proposed film on GCE shows efficient electrocatalysis for oxygen, Cr₂O reduction by using cyclic voltammetry. Further the electrochemical oxidation of sodium meta‐arsenite (As(III)), H₂O₂ were successfully carried out and the detection of H₂O₂ in real samples has been validated.     

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.     

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...     

Selective and Sensitive Nitrite Sensor Based on Glassy Carbon Electrode Modified by Silver Nanochains

Herein, we report a facile method for the synthesis of silver nanochains (Ag nanochains) using pyridine as growth directing agent and citrate ions as capping agents in alkaline medium. The characterization of the synthesized high aspect ratio Ag nanochains was accomplished with the help of Transmission Electron Microscopy (TEM) and High Resolution Transmission Electron Microscopy (HRTEM) which demonstrates the thickness below 100 nm. Crystalline nature of the synthesized Ag nanochains was investigated using X‐ray diffractrometry. A sensitive electrochemical nitrite sensor was assembled using synthesized Ag nanochains as electrode modifier. An improved cyclic voltammetric response for the oxidation of nitrite ions was witnessed at the modified GCE surface in comparison to bare GCE in Britton Robinson (BR) buffer (pH 4). The influence of pH on the oxidation peak current of nitrite ions was also examined using cyclic voltammetry. The electrocatalytic oxidation currents attained through amperometric measurements at Ag nanochains modified GCE were linearly dependent on the concentration of nitrite ions in the two ranges of 0.5–7.5 µM, 5–480 µM. Linear calibration plots of Ip vs. concentration of nitrite were also constructed at the proposed sensor using square wave voltammetry and differential pulse voltammetry. The proposed sensing strategy was successfully employed for the determination of nitrite in water samples with excellent recoveries.     

Electropolymerized Diphenylamine on Functionalized Multiwalled Carbon Nanotube Composite Film and Its Application to Develop a Multifunctional Biosensor

Diphenylamine (DPA) monomers have been electropolymerized on the amino‐functionalized multiwalled carbon nanotube (AFCNT) composite film modified glassy carbon electrode (GCE) by cyclic voltammetry (CV). The surface morphology of PDPA‐AFCNT was studied using field‐emission scanning electron microscopy (FE‐SEM). The interfacial electron transfer phenomenon at the modified electrode was studied using electrochemical impedance spectroscopy (EIS). The PDPA‐AFCNT/GCE represented a multifunctional sensor and showed good electrocatalytic behavior towards the oxidation of catechol and the reduction of hydrogen peroxide. Rotating‐disk electrode technique was applied to detect catechol with a sensitivity of 1360 µA mM^?1 cm^?2 and a detection limit of 0.01 mM. Amperometric determination of hydrogen peroxide at the PDPA‐AFCNT film modified electrode results in a linear range from 10 to 800 µM, a sensitivity of 487.1 µA mM^?1 cm^?2 and detection limit of 1 µM. These results show that the nano‐composite film modified electrode can be utilized to develop a multifunctional sensor.     

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.     

纳米金/双氢氧化物膜修饰电极制备及对肾上腺素的测定

研究了纳米金/双氢氧化物膜修饰玻碳电极(AuNPs/LDHs/GCE)的制备,通过循环伏安法、扫描电镜和电化学阻抗对修饰电极进行了表征;详细讨论了电极的性能,找出了制备该修饰电极的实验条件,并将此电极用于生物体系中肾上腺素(Adrenaline,AD)的电化学测定.在选定的实验条件下,修饰电极在磷酸盐缓冲溶液(pH=7.0)中进行循环伏安扫描时,氧化峰电流和肾上腺素浓度在9.0×10-8～1.0×10-4mol/L范围内呈良好的线性关系,相关系数为0.9982,其检出限(S/N=3)可达3.1×10-8 mol/L.据此建立了一种新的测定肾上腺素的分析方法,可用于实际样品的检测.     

Electrocatalysis of Hemoglobin in ZnO Nanoparticle/Ionic Liquid Composite Film Modified Glassy Carbon Electrode

A nanobiocompatible composite containing hemoglobin (Hb), ZnO nanoparticles (nano‐ZnO) and ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆) was fabricated and further modified on the glassy carbon electrode (GCE). The electrochemical behaviours of Hb in the composite film were carefully studied and a pair of quasi‐reversible redox peaks appeared in pH 7.0 phosphate buffer solution, which was attributed to the electrode reaction of Hb heme Fe(III)/Fe(II) redox couple. The presences of nano‐ZnO and BMIMPF₆ in the film can retain the bioactivity of Hb and greatly enhance the direct electron transfer of Hb. The immobilized Hb showed high stability and good electrocatalytic ability to the reduction of hydrogen peroxide and O₂.     

Direct Electrochemistry of Hemoglobin in Layer‐by‐Layer Films Assembled with DNA and Room Temperature Ionic Liquid

Based on electrostatic interaction and electrodeposition, poly‐anionic deoxyribonucleic acid (DNA), room temperature ionic liquid 1‐butyl‐3‐methyl‐imidazolium tetrafluoroborate (BMIMBF₄), hemoglobin (Hb) and Poly(diallyldimethylammonium chloride) (PDDA) were successfully assembled into Hb/IL/DNA/PDDA layer‐by‐layer complex films on the surface of ITO electrode. FTIR spectroscopy, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to characterize the composite film. The obtained results demonstrated that the Hb molecule in the film kept its native structure and showed its good electrochemical behavior. A pair of well‐defined redox peaks of Hb with the formal potentials (E°′) of ?0.180 V (vs. SCE) was appeared in phosphate buffer solution (PBS, pH 7.0). The Hb/IL/DNA/PDDA/ITO modified electrode also showed an excellent electrocatalytic behavior to the reduction of hydrogen peroxide (H₂O₂). Therefore, the IL/DNA/PDDA complex film as a novel matrix open up a possibility for further study on the direct electrochemistry of other proteins and the fabrication of the third‐generation electrochemical biosensors.