OH functionalized Multi-Walled Carbon Nanotube modified electrode as electrochemical sensor for the detection of Aceclofenac

ABSTRACT

The rapid electrochemical determination of Aceclofenac (ACF) has been employed by cyclic voltammetry (CV), differential pulse voltammetry (DPV) using developed OH-functionalised multiwalled carbon nanotube carbon paste electrode (OH-MWCNT/CPE). Modified electrode was characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), X-ray diffraction spectroscopy (XRD), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The ACF exhibits two oxidation peaks at +0.4 V, +0.66 V and one reduction peak at +0.3 V. The active surface area of the bare carbon paste electrode (BCPE) and modified electrode have been characterised by using K₃[Fe(CN)₆] solution containing 0.1 M KCl. In DPV mode, variation of ACF gave the limit of detection (LOD = 3s/m) 0.246 μM over the concentration range 1.0 to 190.0 μM (R² = 0.9994). The developed electrode has good stability, reproducibility and could be successfully validated for the detection of ACF in pharmaceutical samples and biological fluids.     

Functionalization of gold cysteamine self-assembled monolayer with ethylenediaminetetraacetic acid as a novel nanosensor

Electrochemical characterization of gold cysteamine self-assembled monolayer, in situ functionalized with ethylenediaminetetraacetic acid (Au-CA-EDTA SAM), is described by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Osteryoung square wave voltammetry (OSWV). The results obtained by EIS and CV, in the presence of [Fe(CN)₆]^3−/4− redox probe, show that EDTA is successfully grafted to the surface of Au-CA electrode. Reproducible and reversible variation of the R_ct and ΔEp as a function of solution pH show that Au-CA-EDTA SAM is stable in a wide range of pH and potentials. Accumulation of the Pb²⁺ and Cu²⁺ ions on the Au-CA-EDTA SAM electrode is investigated using faradaic currents or impedimetric effects measured by OSWV and EIS, respectively. These results reveal the presence of active complexing functional groups of EDTA on the surface, and thus, the formation of Au-CA-EDTA SAM electrode. The new sensor responds to the Pb²⁺ and Cu²⁺ separately and simultaneously in a wide linear range of concentrations.     

银纳米修饰电极的制备及电化学行为

金属纳米粒子由于其小的体积和大的比表面积而具有独特的电子、光学和异相催化特性,是目前表面纳米工程及功能化纳米结构制备的一种理想研究对象[1]。银纳米粒子可广泛应用于催化剂材料、电池的电极材料、低温导热材料和导电材料等,成为近年来人们研究的热点[2,3]。在电化学方面,银纳米粒子具有比其他纳米粒子更为优异的导电性能和电催化性能。因此,研究银纳米粒子修饰电极有重要的应用价值和前景[4]。1实验部分1.1仪器CHI660电化学工作站(USA);TU-1901型双光束紫外可见分光光度计(北京普析通用仪器公司);KQ-100型超声清洗器(昆山市超声…     

Determination of Paracetamol Based on 3-Amino-4H-1,2,4-triazole Coated Glassy Carbon Surface in Pharmaceutical Sample

In this present study, to determine paracetamol, an electroanalytical method is presented using differential pulse voltammetry (DPV) at 3-amino-4H-1,2,4-triazole (3AT) coated glassy carbon (GC) electrode. The electrochemical characterization and electron transfer behavior of this prepared electrode in the mixture of K₄[Fe(CN)₆]/K₃[Fe(CN)₆] contains 0.1 M KCl was confirmed by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. Furthermore, scanning electron microscopy (SEM) was used to observe morphological structures of the bare and modified surfaces. The effect of pH was studied on the redox reaction of paracetamol in phosphate buffer in the range of pH 3.0–9.0. The limit of detection was 0.043 μM (3 s/m) for 3AT-GC electrode. The developed electrode was successfully utilized in pharmaceutical samples.     

The Determination of Nonelectroactive Anticancer Drug 6‐Thioguanine on DNA‐Modified Gold Electrode

Abstract

A nonelectroactive anticancer drug 6‐thioguanine was determined by differential pulse stripping voltammetry on the DNA‐modified gold electrode. The electrode was prepared by the dry adsorptive method, which is simple and direct. Potassium ferricyanate [K₃Fe(CN)₆] was chosen as an appropriate electroactive indicator to probe and characterize the interaction since the 6‐thioguanine and DNA both are nonelectroactive over the potential range studied. The reductive peak current of K₃Fe(CN)₆ is linear with the concentration of 6‐thioguanine in the range of 2.0×10^?8～8.0×10^?7 mol L^?1. The detection limit is 6.0×10^?9 mol L^?1. The established method was successfully applied to determining trace 6‐thioguanine with the recoveries between 95.7% and 105.6%.     

Electrochemical characterization of the redox couple of Fe(III)/Fe(II) mediated by grafted polymer reference electrode (GPRE)

A grafted polymer reference electrode (GPRE) (polystyrene grafted with acrylonitrile as a monomer using gamma irradiation) was fabricated as a reference electrode using cyclic voltammetry (CV). The redox process of K₃Fe(CN)₆ during CV was studied. It was found that the redox current peaks of Fe(II)/Fe(III) in 0.1 M of KCl as supporting electrolyte is given the same oxidation–reduction current as in the Ag/AgCl reference electrode, indicating a good result of GPRE and, hence, it can be used for voltammetric analysis technique. The physical properties of GPRE include good hardness, insoluble in non-aqueous electrolytes (except dimethyl formamide and chloroform), and good stability at different solvents. In addition, the sensitivity under conditions of CV is significantly dependent on the scan rate (SR) and variation in concentration. At different SRs, redox peaks of K₃Fe(CN)₆ were observed in a reversible process: Fe(II)/Fe(III). Interestingly, the redox reaction of Fe(II)/Fe(III) solution using GCE versus GPRE remains constant even after 15 cyclings. It is therefore evident that the GPRE possesses some degree of stability. Also, the new reference electrode GPRE has improved the properties of electroanalysis of CV on the working electrode GCE in reliability with the relative standard deviation.     

Voltammetric Characterization of Grafted Polymer Modified with ZnO Nanoparticles on Glassy Carbon Electrode

In this study, a grafted polymer (GP) with ZnO nanoparticles (GP/ZnO NPs) was attached on the surface of glassy carbon electrode (GCE), in order to produce a new modified electrode (GP/ZnO NPs-GCE). The gamma irradiation method was used to grafted polystyrene (polymer) with acrylonitrile (monomer), while slow evaporation process was used to prepare the new modified electrode. The cyclic voltammetry (CV) of K₄[Fe(CN)₆] was used to study the electrochemical properties GP/ZnO NPs-GCE. The peak separation (ΔE_pa-c) was 500 mV between the redox peaks of Fe(II)/Fe(III) in an aqueous solution of 1 M KCl and the current ratio of redox current peaks (I_pa/I_pc) was ≈ 1 for the modified electrode. This indicated that the modified electrode has s good reversibility and conductivity, wherefore; it was applied in the voltammetric filed. It was found that the modified electrode GP/ZnO NPs-GCE have a reasonable solubility and stability at various pH medium. Additionally, the sensitivity of the electrochemical analysis by cyclic voltammetric (CV) method is extensively subjected to the pH medium and the scan rate (SR). A couple of redox current peaks of K₄[Fe(CN)₆] in KCl solution was observed with a reversible process: Fe³⁺/Fe²⁺. Finally a good diffusion coefficient of electroactive species (D) for the new modified electrode was found in this study by chronoamperometry method using Cottrell equation.     

A Novel Three‐Electrode System Fabricated on Polymethyl Methacrylate for On‐Chip Electrochemical Detection

A new strategy of three‐electrode system fabrication in polymer‐based microfluidic systems is described here. Standard lithography, hot embossing and UV‐assisted thermal bonding were employed for fabrication and assembly of the microfluidic chip. For the electrode design the gold working (WE) and counter electrodes (CE) are placed inside a main channel through which the sample solution passes. A silver reference electrode (RE) is embedded in a small side channel containing KCl solution that is continuously pushed into the main channel. In the present work, the overall electrochemical set up and its microfabrication is described. Conditions including silver ion concentration, cyclic voltammetry (CV) settings, and the flow rate of KCl solution in the RE channel were optimized. The electrochemical performance of the three‐electrode system was evaluated by CV and also by amperometric oxidation of ferro hexacyanide ([Fe(CN)₆]^4?) and ruthenium bipyridyl ([Ru(bipy)₃]²⁺) at 400 mV and 1200 mV, respectively. CV analysis using ferri/ferro hexacyanide showed a stable, quasi‐reversible redox reaction at the electrodes with 96 mV peak separation and an anodic/cathodic peak ratio of 1. Amperometric analysis of the electrochemical species resulted in linear correlation between analyte concentration and current response in the range of 0.5–15 µM for [Fe(CN)₆]^4?, and 0–1000 µM for [Ru(bipy)₃]²⁺. Upon the given experimental conditions, the limit of detection was found to be 3.15 µM and 24.83 µM for [Fe(CN)₆]^4? and [Ru(bipy)₃]²⁺, respectively. As a fully integrated three‐electrode system that is fabricated on polymer substrates, it has great applications in microfluidic‐based systems requiring stable electrochemical detection.     

Molecularly Imprinted Impedimetric Sensor for Determination of Mycotoxin Zearalenone

The mycotoxin zearalenone (ZEA) prompts reproductive toxicity due to its strong estrogenic effects. In this work, an electrochemical sensor for determination of ZEA was developed by electropolymerization of a molecularly imprinted poly (o‐phenylenediamine) (PPD) film on screen‐printed gold electrode (SPGE) surface. The sensor was examined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using K₃[Fe(CN)₆]/K₄[Fe(CN)₆] as redox probe. The molecularly imprinted polymer (MIP) sensor showed a wide determination range from 2.50 to 200.00 ngmL^?1 for ZEA. The Limit of detection (LOD) was calculated to be 0.20 ngmL^?1, based on the signal to noise (S/N) ratio equal to 3.0. The sensor displayed good repeatability, with RSD values≤4.6 %, and maintained 93.2 % of its initial response after storage for 10 days in air at room temperature. The developed method was successfully applied for the determination of ZEA in corn flakes with mean recoveries ranged from 96.2 % to 103.8 % and RSDs within the interval of 2.1 % to 3.8 %.     

Study of the Electrostatic Interaction of Lysine Monolayer on Glassy Carbon Electrodes Using the Electrochemical Method

A covalent modified glassy carbon electrode (GCE) with Lysine (Lys) has been fabricated via an electrochemical oxidation procedure. The electrostatic interaction of the monolayer has been investigated by cyclic voltammetry (CV) with Fe(CN)₆^3? redox probe in different concentrations of protons and different charged cations, respectively. The electrochemical method can be a new feasible method for the study of electrostatic interaction of the monolayer.     

An insight to the filtration mechanism of Pb(II) at the surface of a clay ceramic membrane through its preconcentration at the surface of a graphite/clay composite working electrode

The use of cyclic voltammetry (CV) and linear scan anodic stripping voltammetry (LSASV) to predict the selectivity of microfiltration ceramic membranes made from a lump of local clay towards Pb(II) ions filtration is described. The membranes were characterized by different techniques followed by CV analysis of the Fe(CN)₆^3-/Fe(CN)₆^4- redox couple and Pb(II) on bare graphite, raw clay, and clay-modified carbon paste electrode (clay-modified CPE). The effect of clay loading in the range of 1–10 % (w/w) on the electrodes is studied, where an enhanced peak current is observed for 5 % w/w clay. Moreover, a decrease in the peak current can be seen for bare graphite electrodes, suggesting that the clay mineral had played a substantial role in the sieving of heavy metal ions through the ceramic membrane. The electroactive surface area of 5% w/w raw clay towards Fe(II) ions was found to be in the order of 3.07 × 10^-2 cm² and higher than 5% w/w clay sintered to 1000 °C and bare graphite. CV analysis shows that both, 5 % w/w raw clay and 5 % w/w clay sintered to 1000 °C exhibited high peak currents towards Pb(II) ions. The mobility of the Pb(II) ions is found to increase when 5% w/w clay sintered to 1000 °C is utilized as membrane/electrode, leading to an increase in the amount of reduced Pb(II) ions on the surfaces of the clay membranes/electrodes. The study suggests successful filtration of Pb(II) ions through the proposed membrane/electrode and a much better accumulation than Fe(II) at the surface of the membrane/electrode before being subjected to filtration.     

Study on surface acid-base property of carboxylic acid-terminated self-assembled monolayers by cyclic voltammetry and electrochemical impedance spectroscopy

Cyclic voltammetry and electrochemical impedance spec-troscopy were used to study the surface acid-base property of carboxylic acid-terminated self-assembled monolayers(SAMs).A carboxylic acid-terminated thiol,such as thioctic acid(1,2-dithiolane-3-pentanoic acid),was self-assembled on gold electrodes.Electron transfer between the bulk solution and the SAM modified electrode was studied at different pH using Fe(CN)63-as a probe.The surface pka of thioctic acid was determined by cyclic voltammetry and electrochemical impedance spectroscopy to be 5.6 ±0.1 and 5.8±0.1,respectively.The method is compared with other methods of monolayer pKa measurement.     

An electrochemical immunosensor based on agarose hydrogel films for rapid determination of ractopamine

A novel label-free electrochemical immunosensor for rapid determination of ractopamine was constructed by incorporating ractopamine–bovine thyroglobulin antigen in agarose hydrogel films modified on a glassy carbon electrode. Cyclic voltammetry and differential pulse voltammetry were employed to investigate the electrochemical character of the immunosensor during different modified stages using a redox probe system of K₃Fe(CN)₆/K₄Fe(CN)₆. In the presence of polyclonal antibody against ractopamine, K₃[Fe(CN)₆] electron transfer is inhibited, presumably due to that antibody in solution could adsorb on the electrode surface modified antigen. A competitive immunoreaction system was applied to determinate the free ractopamine in phosphate buffer solution. The selected polyclonal antibody showed very high sensitivity and specificity for ractopamine, and was used for the detection and quantitative determination of trace amounts of ractopamine in spiked animal feeds.     

A highly selective and sensitive cocaine aptasensor based on covalent attachment of the aptamer-functionalized AuNPs onto nanocomposite as the support platform

Based on the conformational changes of the aptamer-functionalized gold nanoparticles (AuNPs) onto MWCNTs/IL/Chit nanocomposite as the support platform, we have developed a sensitive and selective electrochemical aptasensor for the detection of cocaine. The 5′-amine-3′-AuNP terminated aptamer is covalently attached to a MWCNTs/IL/Chit nanocomposite. The interaction of cocaine with the aptamer functionalized AuNP caused the aptamer to be folded and the AuNPs with negative charge at the end of the aptamer came to the near of electrode surface therefore, the electron transfer between ferricyanide (K₃Fe(CN)₆) as redox probe and electrode surface was inhibited. A decreased current of (K₃Fe(CN)₆) was monitored by differential pulse voltammetry technique. In an optimized condition the calibration curve for cocaine concentration was linear up to 11 μM with detection limit (signal-to-noise ratio of 3) of 100 pM. To test the selectivity of the prepared aptasensor sensing platform applicability, some analgesic drugs as the interferes were examined. The potential of the aptasensor was successfully applied for measuring cocaine concentration in human blood serum. Based on our experiments it can be said that the present method is absolutely beneficial in developing other electrochemical aptasensor.     

Preparation of Carbon Nanotubes/Neutral Red Composite Film Modified Electrode and Its Catalysis on Rutin

Neutral red was directly electropolymerized onto the carbon nanotubes modified electrode. A polymerized neutral red/carbon nanotubes composite film was characterized by scanning electron micrograph (SEM) and cyclic voltammetry (CV). Well‐defined voltammetric responses are observed for [Fe(CN)₆]^4?/3? on the composite film modified glassy carbon electrode. And it's found that this modified electrode has good catalysis on the redox of rutin. Differential pulse voltammetry method was used to determinate the concentration of rutin and obtain a linear equation between the current and concentration in a certain range. The modified electrode is satisfied with us for its good sensibility and stability.     

Electrochemical DNA impedance biosensor for the detection of DNA hybridization with polymeric film, single walled carbon nanotubes modified glassy carbon electrode

In this work, we report the fabrication of a sensitive electrochemical DNA impedance biosensor for the detection of sequence-specific target DNA. p-Aminobenzoic acid was first immobilized on the surface of the electrode modified with single walled carbon nanotubes with carboxylic acid groups (SWCNTs) by cyclic voltammetry (CV). A single-stranded DNA probe with a NH₂ group at the end (H₂N-ssDNA) was then covalently immobilized on the surface of polymeric film at room temperature. The impedance measurement was performed in a solution containing 5 mM K₃[Fe(CN)₆]/K₄[Fe(CN)₆]. The change of interfacial charge transfer resistance (R _CT) was confirmed the hybrid formation. The difference of R _CT was linear with the logarithm of complementary oligonucleotides concentrations in the range of 1.0 × 10^?12 to 1.0 × 10^?7 M, with a detection limit of 3.5 × 10^?13 M (S/N = 3).     

Research on electrochemical properties of nonaqueous ionic liquid microemulsions

The nonaqueous ionic liquid (IL) microemulsions composed of 1-butyl-3-methylimidazolium tetrafluoroborate, Triton X-100, and toluene were prepared and the electrochemical properties of the nonaqueous IL microemulsions were investigated in this paper. It is shown that characteristics of the nonaqueous IL microemulsions such as electrical conductivity, electrochemical window, and solubility are good, which indicate that the nonaqueous IL microemulsions can be used as electrolyte for electrochemical research. The electrochemical properties of the nonaqueous IL microemulsions were researched by cyclic voltammetry (CV) and electrochemical impedance spectroscopy methods using potassium ferricyanide as electroactive probe. It was found that the reversibility was better and the peak current densities of CV were higher for the [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ electrode reaction in the nonaqueous IL microemulsions than those in IL. However, the electrochemical behavior of the probe in the nonaqueous IL microemulsions with different microenvironments (oil-in-IL, IL-in-oil, and bicontinuous) was different. The electrochemical property of the probe in the oil-in-IL microemulsion was the best, which was studied in detail.     

Ferricyanide immobilized within organically modified MCM-41; application for electrocatalytic reduction of hydrogen peroxide

Carbon paste electrode modified with aminated Mobil Catalytic Material Number 41 (MCM-41) was prepared and used for immobilization of K₃[Fe(CN)₆] in acidic medium, and then electrochemical behavior of modified electrode containing ferricyanide was studied in detail, including pH-dependence and scan rate effect. Cyclic voltammetry studies showed that the electrode reaction is a surface-controlled process at the scan rate range from 5 to 60 mV s⁻¹. Also, the electrocatalytic behavior of modified electrode toward the reduction of H₂O₂ is reported and the effect of pH on catalytic peak current was discussed. According to experimental results, with increasing solution pH, the catalytic effect of this modified electrode is decreased. Catalytic reduction current of H₂O₂ increases linearly with its concentration. It has been demonstrated that ferricyanide immobilized on the aminated MCM-41 is a stable catalyst for the electrocatalytic reduction of H₂O₂.     

Voltammetric Studies on Graphite Impregnated Silicone Rubber Electrodes

Abstract

The voltammetric behaviour of iodide ions, K₄ Fe(CN)₆, K₃ Fe(CN)₆, quinone, hydroquinone, p-phenylenediamine and p-toluidine was studied with graphite impregnated silicone rubber electrodes. The electrode enables us to carry out the quantitative analysis of these compounds. The peak height of the voltammetric curves is proportional to the concentration. Data on the reproducibility of measured values are given.     

Amperometric sensor for hydrogen peroxide based on direct electron transfer of spinach ferredoxin on Au electrode

A protein-based electrochemical sensor for hydrogen peroxide (H₂O₂) was developed by an easy and effective film fabrication method where spinach ferredoxin (Fdx) containing [2Fe–2S] metal center was cross linked with 11-mercaptoundecanoic acid (MUA) on a gold (Au) surface. The surface morphology of Fdx molecules on Au electrodes was investigated by atomic force microscopy (AFM). Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were employed to study the electrochemical behavior of adsorbed Fdx on Au. The interfacial properties of the modified electrode were evaluated in the presence of Fe(CN)₆^3?/4? redox couple as a probe. From CV, a pair of well-defined and quasi-reversible redox peaks of Fdx was obtained in 10 mM, pH 7.0 Tris–HCl buffer solution at ?170 and ?120 mV respectively. One electron reduction of the [2Fe-2S]²⁺ cluster occurs at one of the iron atoms to give the reduced [2Fe-2S]⁺. The formal reduction potential of Fdx ca. ?150 mV (vs. Ag/AgCl electrode) at pH 7.0. The electron-transfer rate constant, k_s, for electron transfer between the Au electrode and Fdx was estimated to be 0.12 s^?1. From the electrochemical experiments, it is observed that Fdx/MUA/Au promoted direct electron transfer between Fdx and electrode and it catalyzes the reduction of H₂O₂. The Fdx/MUA/Au electrode displays a linear increase in amperometric current for increasing concentration of H₂O₂.The sensor calibration plot was linear with r² = 0.998 with sensitivity approximately 68.24 μAm M^?1 cm^?2. Further, the effect of nitrite on the developed sensor was examined which does not interfere with the detection of H₂O₂. Finally, the addition of H₂O₂ on MUA/Au electrode was observed which has no effect on amperometric current.