Electrocatalytic detection of insulin at RuOx/carbon nanotube-modified carbon electrodes

A bilayer surface coating, prepared by electrodepositing ruthenium oxide (RuOx) onto a carbon nanotube (CNT) layer, offers dramatic improvements in the stability and sensitivity of voltammetric and amperometric measurements of insulin compared to the individual (CNT or RuOx) coated electrodes. The enhanced electrocatalytic activity towards insulin is indicated from lowering the potential of the oxidation process (starting around 0.35 versus Ag/AgCl) and the substantially higher sensitivity over the entire potential range. A wide linear dynamic range (10-800 nM) was achieved with a detection limit of 1 nM. The marked electrocatalytic activity of the RuOx/CNT coating towards insulin is coupled with a greatly enhanced stability. For example, the insulin amperometric response of the RuOx/CNT-coated electrodes is highly stable, with 97% of the initial activity remaining after 60 min stirring of 2 × 10⁻⁶ M solution (compared to significantly faster current diminutions at the RuOx- or CNT-coated surfaces). The results suggest great promise for miniaturized sensors and detectors for monitoring insulin.     

A nickel nanoparticle/carbon nanotube-modified carbon fiber microelectrode for sensitive insulin detection

A nickel nanoparticle (NiNP)/carbon nanotube (CNT)-modified carbon fiber microelectrode (NiNPs/CNTs/CFME) was fabricated using a two-step electroless plating/chemical vapor deposition method. The morphology of the NiNPs/CNTs composite structure was characterized by scanning electron microscopy, and its elemental composition was characterized by an energy dispersive spectrometer. The electrochemical behavior of the NiNPs/CNTs/CFME in aqueous alkaline solutions of insulin was investigated by cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance spectroscopy in sequence. CV curves show that the NiNPs/CNTs/CFME displays a high oxidation peak current, a fast electron transfer rate, and good electrocatalytic activity towards insulin, compared to a bare CFME and a pure NiNP-modified CFME. In the chronoamperometry tests, the NiNPs/CNTs/CFME demonstrates an excellent analytical performance in detecting low concentrations of insulin, including good sensitivity (1.11 nA μM^?1) and a low detection limit (270 nM). Moreover, this microelectrode exhibits great reproducibility in successive potential cycling and satisfactory long-term stability after storage at room temperature for approximately 8 weeks.     

Electro-oxidation and determination of trazodone at multi-walled carbon nanotube-modified glassy carbon electrode

A simple and rapid electrochemical method was developed for the determination of trace-level trazodone, based on the excellent properties of multi-walled carbon nanotubes (MWCNTs). The MWCNT-modified glassy carbon electrode was constructed and the electrochemical behavior of trazodone was investigated in detail. The cyclic voltammetric results indicate that MWCNT-modified glassy carbon electrode can remarkably enhance electrocatalytic activity towards the oxidation of trazodone in neutral solutions. It leads to a considerable improvement of the anodic peak current for trazodone, and allows the development of a highly sensitive voltammetric sensor for the determination of trazodone. Trazodone could effectively accumulate at this electrode and produce two anodic peaks at about 0.73 V and 1.00 V. The electrocatalytic behavior was further exploited as a sensitive detection scheme for the trazodone determination by differential-pulse voltammetry. Under optimized conditions, the concentration range and detection limit are 0.2-10 μM and 24 nM, respectively for trazodone. The proposed method was successfully applied to trazodone determination in pharmaceutical samples. The analytical performance of this sensor has been evaluated for detection of analyte in urine as a real sample.     

Electrocrystallized platinum nanoparticle on carbon substrate

Platinum nanoparticles were electrocrystallized on a 4-aminophenyl monolayer-grafted carbon substrate. These Pt-modified surfaces were characterized by scanning tunneling microscopy (STM). The characterization by STM revealed that the platinum nanoparticles obtained had good size monodispersity and were well separated from one another on HOPG surfaces.     

Electrochemical reduction of tartrazine at multi-walled carbon nanotube-modified pyrolytic graphite electrode

Electrochemical reduction of tartrazine on multi-walled carbon nanotube-modied pyrolytic graphite electrode is investigated. A simple, sensitive and inexpensive method for determination of tartrazine in drinks is proposed. The accuracy and reproducibility of the determination method for various known amounts of tartrazine were evaluated. This method was satisfactorily applied for the determination of tartrazine in drinks. The reduction peak currents were proportional to tartrazine concentrations over two intervals in the range from 2.0 to 70.0 mg l⁻¹ and from 70.0 to 230.0 mg l⁻¹, and the detection limit for tartrazine is 0.5 mg l⁻¹.     

Direct electrochemical conversion of bilirubin oxidase at carbon nanotube-modified glassy carbon electrodes

We report on direct electron transfer reactions of bilirubin oxidase at multi-walled carbon nanotube (MWCNT) modified glassy carbon electrodes (GCE). The bioelectrocatalytic oxygen reduction was recorded using linear sweep voltammetry (LSV) with BOD in solution, adsorbed and covalently linked to the nanotubes. The MWCNT modification of GC electrodes strongly enhances the oxygen reduction compared to the signals at unmodified GCE. Under anaerobic conditions with a high protein concentration in solution a pair of redox peaks with a formal potential of 450 ± 15 mV vs Ag/AgCl, 1 M KCl (pH 7.4) was found with cyclic voltammetry. The redox conversion is indicated to be surface-controlled and pH-dependent (54.5 mV/pH). The quasi-reversible redox reaction might be attributed to the trinuclear T2/T3 cluster of BOD.     

Electrooxidation of catecholamines at carbon nanotube-modified indium tin oxide electrodes

In this study, we prepared carbon nanotube (CNT)/Nafion-modified ITO electrodes and investigated their electrochemical behavior. The CNTs were dissolved in a solution of the ionic polymer Nafion and then CNT/Nafion composite films were deposited onto ITO electrodes through spin-coating of this homogeneous solution. We studied the effects of chemical pretreatment of the CNTs and the pH of the buffer on the electroanalytical behavior of the CNT/Nafion-modified ITO electrodes toward catecholamines. The modified electrodes enhanced the peak current and lowered the overpotentials. We observed high electrooxidative performance for the modified ITO electrodes: the oxidative currents of the catecholamines were up to 125-fold higher than those obtained using bare ITO electrodes.     

Electrochemical detection of phenolic estrogenic compounds at carbon nanotube-modified electrodes

The use of a carbon nanotube-modified glassy carbon electrode (CNT-GCE) for the LC-EC detection of phenolic compounds with estrogenic activity is reported. Cyclic voltammograms for phenolic endocrine disruptors and estrogenic hormones showed, in general, an enhancement of their electrochemical oxidation responses at CNT-GCE attributable to the electrocatalytic effect caused by CNTs. Hydrodynamic voltammograms obtained under flow injection conditions lead to the selection of +700 mV as the potential value to be applied for the amperometric detection of the phenolic estrogenic compounds, this value being remarkably less positive than those reported in the literature using other electrode materials. Successive injections of these compounds demonstrated that no electrode surface fouling occurred. A mobile phase consisting of a 50:50 (v/v) acetonitrile:0.05 mol l⁻¹ phosphate buffer of pH 7.0 was selected for the chromatographic separation of mixtures of these compounds, with detection limits ranging between 98 and 340 nmol l⁻¹. Good recoveries were obtained in the analysis of underground well water and tap water samples spiked with some phenolic estrogenic compounds at a 14 nmol l⁻¹ concentration level.     

基于多壁碳纳米管/壳聚糖多层膜修饰玻碳电极邻苯二酚的测定

改进了碳纳米管在壳聚糖溶液中的分散方法,制备了多壁碳纳米管/壳聚糖多层膜修饰玻碳电极,对比了不同修饰层数膜电极的循环伏安和电化学阻抗行为,5层多壁碳纳米管/壳聚糖膜修饰玻碳电极的电化学性能优良.在最优实验条件下,该修饰玻碳电极对邻苯二酚(CAT)有灵敏的响应,CAT浓度在3.99×10-6～9.09×10-4mol/L范围内与氧化峰电流呈良好的线性关系,检出限为2.39×10-6mol/L(S/N=3).该修饰玻碳电极性能稳定,测定4×10-5mol/LCAT溶液,RSD(n=10)为2.1%;15周后,该电极的响应值仅降低1.9%.     

Electrodeposition and electrocatalytic properties of platinum nanoparticles on multi-walled carbon nanotubes: effect of the deposition conditions

Platinum (Pt) nanoparticles were electrochemically deposited on multi-walled carbon nanotubes (MWCNTs) through a three-step process, including an electrochemical treatment of MWCNT, electro-oxidation of PtCl₄ ²⁻ to Pt(IV) complex, and an electro-conversion of Pt(0) on MWCNT. The effect of formation conditions for Pt(IV) complexes on the Pt nanoparticals transformed was investigated. The structure and elemental composition of the resulting Pt/MWCNT electrode were characterized by transmission electron micrograph (TEM) and energy dispersive X-ray spectroscopy (EDX). The electrocatalytic properties of the resulting Pt/MWCNT electrode for methanol oxidation have been investigated. The high electrocatalytic activity and good stability of Pt/MWCNT electrode may be attributed to the high dispersion of platinum nanoparticles and the particular properties of the MWCNT supports.     

Electro-deposition of platinum nanoparticles on 4-mercaptobenzene-functionalized multi-walled carbon nanotubes

A new method to electro-deposit platinum nanoparticles on the surface of multi-walled carbon nanotubes (MWNTs) functionalized with 4-mercaptobenzene has been described. X-ray photoelectron spectroscopy results reveal that 4-mercaptobenzene was attached to the surface of MWNTs. Transmission electron microscope and X-ray diffraction analysis confirm that platinum nanoparticles were highly dispersed on the surface of MWNTs, and the average size of the platinum particle is 4.2 nm. The electrocatalytic properties of the Pt/MWNT composite electrode for methanol oxidation were investigated by cyclic voltammetry, and the results show that the fabricated composites exhibit high catalytic activity and good long-term stability. The study provides a feasible approach to fabricate Pt/MWNT composite electrode for direct methanol fuel cell.     

Poly(brilliant green)/carbon nanotube-modified carbon film electrodes and application as sensors

Poly(brilliant green) (PBG) films were formed on carbon film electrodes (CFE) by electropolymerisation of brilliant green monomer using potential cycling or at fixed potential from different pH solutions. The modified electrodes, PBG/CFE, were characterised by cyclic voltammetry (CV) in electrolytes of different pH by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). In order to increase the stability of the polymer film and enhance the response, multi-walled carbon nanotubes (MWCNTs) were first deposited on CFE and then PBG was formed on top, PBG/CNT/CFE. The modified electrodes were applied to the amperometric determination of ascorbic acid (AA) in phosphate buffer pH?7.0 at 0.0 V vs. saturated calomel electrode (SCE) and the results were compared, the presence of CNT leading to a significant increase in sensitivity. An interference study was carried out and good separation between AA and dopamine (DA) peaks was achieved that led to the successful determination of DA without interferences. Other interferents: aspirin, acetaminophen, salicylic acid and uric acid exhibited no response on the PBG/CNT/CFE. Determination of AA in pharmaceutical samples was successfully performed.     

Kinetics of rhenium dioxide deposition on columnar structured platinum electrodes

The kinetics concerning the early stage of the electrodeposition of rhenium dioxide on columnar-structured platinum electrodes from acid aqueous containing perrhenate ions was studied. The results demonstrate a zero-order kinetics obtained by holding the potential at two different values.     

Influence of carbon shell structure on electrochemical performance of multi-walled carbon nanotube electrodes

Core/shell nanostructures have received considerable attention due to the synergistic effect of their combination of materials. In this work, core/shell carbon/multi walled carbon nanotubes (MWNTs) (C-MWNTs) composed of core MWNTs and carbon shells were prepared to obtain a new type of carbon electrode materials. Carbon shells containing nitrogen groups were prepared by coating polyaniline (PANI) onto the MWNTs by in situ polymerization and subsequent carbonization at 850 °C. After carbonization, the C-MWNTs contained 5.84% nitrogen and showed a hollow structure and crystallinity like that of pristine MWNTs. In addition, the C-MWNTs exhibited electrochemical performance superior to that of pristine MWNTs, and the highest specific capacitance (231 F g⁻¹) of the C-MWNTs was obtained at a scan rate of 0.1 A g⁻¹, as compared to 152 F g⁻¹ for pristine MWNTs. This superior performance is attributed to the maintenance of high electrical conductivity by the π–π interaction between the carbon layer and the MWNTs, increased specific surface area of C-MWNTs, and the presence of nitrogen groups formed on the carbon electrode after the carbonization of the shell PANI.     

Fabrication of nanometre-sized platinum electrodes by controllable electrochemical deposition

A new and simple method for fabricating controllable insulated nanometer-sized platinum electrodes is presented. Electrochemical etching of platinum wire is employed, and then a repeated process of cycle voltammetric deposition of electrophoretic paint and heat curing for shrink film follows which effectively controls the size of the nanoelectrodes, which is different from previous DC electrolysis deposition. This technique allows complete insulation of the whole body of the etched platinum wire, except for the very tip with the shrink film during heat curing of the film, leaving an electrochemical active area with effective diameters of nanometers. The process overcomes the pinhole formation resulting from the electrophoretic paint deposition process. The size of the platinum electrodes and the thickness of the deposed paint for insulation can be properly controlled and reproduced. The fabricated electrodes show ideal steady-state voltammetric behaviors from which the effective areas of the nanoelectrodes are measured. The effective radius of the prepared nanoelectrodes ranges from 3.1 nm to hundreds of nanometers.     

Electrochemical parameters of ethamsylate at multi-walled carbon nanotube modified glassy carbon electrodes

In this paper, some electrochemical parameters of ethamsylate at a multi-walled carbon nanotube modified glassy carbon electrode, such as the charge number, exchange current density, standard heterogeneous rate constant and diffusion coefficient, were measured by cyclic voltammetry, chronoamperometry and chronocoulometry. The modified electrode exhibits good promotion of the electrochemical reaction of ethamsylate and increases the standard heterogeneous rate constant of ethamsylate greatly. The differential pulse voltammetry responses of ethamsylate were linearly dependent on its concentrations in a range from 2.0 x 10(-6) to 6.0 x 10(-5) mol L(-1), with a detection limit of 4.0 x 10(-7) mol L(-1).     

Three-dimensional nanostructured carbon nanotube array/PtRu nanoparticle electrodes for micro-fuel cells

We have fabricated three-dimensional (3D) nanostructured carbon nanotube (CNT) array/PtRu nanoparticle (with the average molar percentage (26%) of Ru) electrodes using anodic aluminum oxide (AAO) templates for micro-fuel cells. 3D nanostructured CNT array was used to support PtRu nanoparticles to enhance the utilization efficiency of Pt. The 3D nanostructured CNT array/PtRu electrodes show the excellent catalytic activity and electrochemical stability of electro-oxidation of methanol. Their anodic current density is 10 times as high as that of PtRu thin-films, which could be explained in terms of the high specific surface area of 3D nanostructured CNT array supporting films and the uniform distribution of PtRu nanoparticles.     

Electrocrystallized Ag nanoparticle on functional multi-walled carbon nanotube surfaces for hydrazine oxidation

4-Aminobenzoic acid was covalently grafted on multi-walled carbon nanotubes (MWNTs) by amine cation radical formation in the electrooxidation process of the amino-containing compound. Then, silver (Ag) nanoparticles were electrocrystallized on 4-aminobenzoic acid monolayer-grafted MWNTs by a potential-step method. The structure and nature of the resulting Ag/MWNT composites were characterized by transmission electron microscopy and X-ray diffraction. The electrocatalytic properties of the Ag/MWNT electrode for hydrazine oxidation have been investigated by cyclic voltammetry, high electrocatalytic activity of the Ag/MWNT electrode can be observed. This may be attributed to the small particle size of the silver particles. The results imply that the Ag/MWNT composites have a good application potential in fuel cells.