Construction and analytical characterization of Prussian-Blue-based carbon paste electrodes and their assembly as oxidase enzyme sensors

This paper reports on the development and characterization of Prussian Blue-modified carbon paste electrodes. New methods of matrix modification with Prussian Blue are reported. Two different carbon pastes have been prepared, using mineral oil or solid paraffin, thus obtaining different types of sensors whose behavior toward the electrochemical reduction of hydrogen peroxide has been fully characterized. Results obtained with Prussian Blue-modified electrodes showed a long operational lifetime, an excellent stability in a wide range of pH (3-9), a high sensitivity, and a fast response time. In addition, the coupling of solid carbon paste modified with Prussian Blue and the enzymes glucose oxidase and choline oxidase led to the assembling of biosensors that showed an optimum working range at alkaline pH.     

Modified carbon paste electrodes for Cu(II) determination

A new Cu²⁺ carbon paste electrode (CPE) using 2,2′-(1E,1′E)-1,1′-(2,2′-azanediylbis (ethane-2,1-diyl)bis(azan-1-yl-1-ylidene))bis(ethan-1-yl-1-ylidene)diphenol (ADEZEDP) has been prepared. The influence of variables including sodium tetraphenylborate (NaTPB), ionophore, and amount of multiwalled carbon nanotubes (MWCNT), CdO nanowires, CdS nanoparticles and palladium nanoparticles loaded on ADEZEDP and Nujol on the electrodes response were studied and optimized. At optimum values of all variables, for each nanomaterial the electrode response was linear in concentration range of 1.0 × 10^? 8 to 1.0 × 10^? 1 mol L^? 1 for ADEZEDP with Nernstian slope. The good performance of electrode viz. Wide applicable pH range (2.0–5.0), fast response time (≈ 6 s), and adequate life time (3 months) indicate the utility of the proposed electrodes for evaluation of Cu²⁺ ion content in various situations. Finally, these electrodes have been successfully applied for the determination of Cu²⁺ ions content in various real samples. The selectivity of proposed electrode was evaluated by separation solution method and fixed interference method.     

Carbon nanotube purification: preparation and characterization of carbon nanotube paste electrodes

Paste electrodes have been constructed using single-wall carbon nanotubes mixed with mineral oil. The electrochemical behavior of such electrodes prepared with different percentages of carbon nanotubes has been compared with that of graphite paste electrodes and evaluated with respect to the electrochemistry of ferricyanide with cyclic voltammetry. Carbon nanotubes were purified by a treatment with concentrated nitric acid, then oxidized in air. In addition, electrochemical pretreatments were carried out to increase the selectivity of carbon nanotube electrodes. Performances of carbon nanotube paste and carbon paste electrodes were evaluated by studying such parameters as current peak, deltaEp, anodic and cathodic current ratio, and charge density toward several different electroactive molecules. Data interpretation based on the carbon nanotubes and carbon surface area is presented. Carbon nanotube paste and carbon paste electrodes were tested as H2O2 and NADH probes, and several analytical parameters were evaluated. The oxidative behavior of dopamine was examined at these electrodes. The two-electron oxidation of dopamine to dopaminequinone showed an excellent reversibility in cyclic voltammetry that was significantly better than that observed at carbon paste electrodes.     

Some advantages of carbon paste electrodes in the morphological study of finely divided iron oxides

The electroreduction of finely divided trivalent iron oxides using a carbon paste electrode occurs according to a mechanism involving the dissolution of the solid and then the reduction of solvated Fe³⁺ ions into Fe²⁺ ions. The voltammetric curves exhibit two peaks. The first is due to the reduction of Fe³⁺ ions that come from dissolution of the smallest particles at the beginning of the experiment. The second is characteristic of reduction of the solid; its shape, position and amplitude are influenced by morphology. Theoretical aspects are considered. It appears that the use of a carbon paste electrode for the study of divided solids containing an electroreactive ion can easily give information either on the particle size distribution, if the dissolution kinetics of the compound are known, or on the dissolution kinetics of monodisperse solids or solids whose particle size distribution is well defined.     

Metal paste nanocomposite electrodes as a new generation of metallic electrodes

Fabrication of metal paste nanocomposite electrodes is introduced using metal nanostructures and ionic liquids. The combined application of unique properties of nanomaterials and ionic liquids in the design of these metal paste nanocomposites results in electrodes with interesting advantages compared to the conventional metal disk electrodes. In contrast to conventional metallic electrodes, which are usually prone to fouling effects and suffer from weak repeatability and reproducibility, these metal paste nanocomposite electrodes have very exciting advantages. Ease of electrode fabrication; cleaning and activating the electrode surface, together with high electrocatalytic activity; increased degree of active area and surface roughness; antifouling effect; good signal-to-noise ratio; low cost; and low weight are among the advantageous features of these electrodes. Compared to dropping mercury electrodes that have high toxicity, these metal paste nanocomposite electrodes have much less toxicity. Such abilities promote new opportunities for a wide range of electrochemical, sensing, and biosensing applications.     

Bioinorganic composites for enzyme electrodes

Sparingly soluble redox salts were combined with a model enzyme, glucose oxidase, in a host matrix of a biopolymer chitosan to form bioinorganic composite films on the surface of glassy carbon electrodes. Four redox salts, each containing the Ru(NH3)6(3+) cation and a selected anion, such as Ru(CN)6(4-), Fe(CN)6(4-), Co(CN)6(3-) or IrCl6(3-), were studied. The composition and catalytic properties of such composite materials toward glucose oxidation were investigated by spectroscopic and electrochemical methods. The composite films provided an oxygen-independent electrical communication between the enzyme's redox centers and a glassy carbon surface at a potential as low as -0.10 V vs Ag/AgCl(3 M Cl-). The nature of the electrical communication is discussed in terms of redox mediation by the Ru(NH3)6(3+)-containing ion pairs formed inside the biocomposites. The kinetic significance of the mediator's charge is considered by postulating that neutral ion pairs are more efficient redox mediators of the enzymatic reaction than those negatively charged. The low operating potential of enzyme electrodes based on the bioinorganic composites allows for an interference-free determination of glucose. The design of the biocomposites is generic and can incorporate oxidoreductase enzymes other than glucose oxidase to provide a host of biosensors for biologically and environmentally important analytes.     

Stearate-modified carbon paste electrodes for detecting dopamine in vivo: decrease in selectivity caused by lipids and other surface-active agents

Electrochemical characteristics of dopamine, ascorbic acid, and ferrocyanide measured with carbon-Nujol paste electrodes (CPEs) and stearate-modified carbon paste electrodes (SMEs) before and after treatment with either surfactant (Triton-X), lipid (phosphatidylethanolamine), or brain tissue indicate that the lipophilic nature of the brain destroys the selectivity of SMEs for dopamine by removing the hydrophobic elements from the electrode surface. Measurements of the degree and time-course of changes in surface capacitance of SMEs following contact with surface-active agents support this conclusion. The results suggest that SMEs cannot be used to detect dopamine unambiguously in vivo and emphasize the need to characterize electrochemical sensors in an environment similar to that of intended applications.     

Nitrogenated porous carbon electrodes for supercapacitors

Nitrogenated porous carbon materials, made by coating the pore surface with nitrogen functional groups from the pyrolysis of hexamine, were characterized and tested for supercapacitor applications. From X-ray photoelectron spectroscopy, the nitrogen content of the nitrogenated carbon sample was found to be 14?wt%. Electrochemical properties from potentiostatic and galvanostatic measurements, and open circuit voltage (OCV) were used to evaluate the effect of nitrogen in porous carbon electrodes. The nitrogenated carbon exhibits pseudocapacitive behavior and an increase in capacitance that is almost double that of plain porous carbon. The cyclic stability is also improved, as the sample retains its high capacitance even after extensive cycling. Also, the nitrogenated carbon shows battery-like characteristics with an initial OCV of ca. 0.4?V, and an OCV of ca. 0.3?V after cycling.     

Preparation and characterization of biocompatible carbon electrodes

Electron transfer in microbial fuel cell and biosensors could be facilitated through high conductive materials with enhanced active surface area and appropriate redox potential suited to microbial metabolism. In the first strategy based on bulk doping, graphite/epoxy composite electrode (GECE) bulk was modified with six types of metal ion which were prepared through a wet impregnation procedure. In the second strategy, immobilization of redox dye on carbon cloth and graphite sheet was carried out using N,N′-dicyclohexylcarbodiimide for surface modification. Crystallinity, morphology, surface chemistry and electrochemical properties of all modified electrodes were investigated. Influence of redox behavior of electrodes suited to microbial metabolism and conducive to biofilm formation have been examined. It was observed that the Fe³⁺ doped GECE surfaces exhibited significantly high biofilm formation of 1.10(±0.18) × 10⁷ CFU/cm² as compared to other dopants. The microbial growth on the carbon cloth electrode and carbon fiber reinforced plate were found to be less (2.6(±0.97) × 10⁴, 4.8(±1.8) × 10³ CFU/cm² respectively) compared to GECEs.     

ZnO-based FBAR resonators with carbon nanotube electrodes

Film bulk acoustic resonator (FBAR) devices with carbon nanotube (CNT) electrodes directly grown on a ZnO film by thermal chemical vapor deposition have been fabricated. CNT electrodes possess a very low density and high acoustic impedance, which reduces the intrinsic mass loading effect resulting from the electrodes? weight and better confines the longitudinal acoustic standing waves inside the resonator, in turn providing a resonator with a higher quality factor. The influence of the CNTs on the frequency response of the FBAR devices was studied by comparing two identical sets of devices; one set comprised FBARs fabricated with chromium/ gold bilayer electrodes, and the second set comprised FBARs fabricated with CNT electrodes. It was found that the CNTs had a significant effect on attenuating traveling waves at the surface of the FBARs' membranes because of their high elastic stiffness. Three-dimensional finite element analysis of the devices fabricated was carried out, and the numerical simulations were consistent with the experimental results obtained.     

Insulin oxidation and determination at carbon electrodes

The redox chemistry of insulin was investigated at glassy carbon (GC) electrodes that were coated with films of chitosan (CHIT) and multiwalled carbon nanotubes (CNT). While bare electrodes deactivated quickly during insulin oxidation, the GC electrodes coated with CHIT and CHIT-CNT films generated stable insulin currents. The GC/CHIT-CNT electrodes were used for investigating the electrooxidation process of insulin and amperometric determination of insulin. The mass spectrometric, electron paramagnetic resonance, and separation studies of electrolyzed insulin solutions suggested that the loss of 4 mass units upon insulin oxidation at CNT could be accounted for by the formation of two dityrosine cross-links intramolecularly. At a potential of 0.700 V and physiological pH 7.40, the GC/CHIT-CNT electrodes displayed a detection limit of approximately 30 nM insulin (S/N = 3), sensitivity of 135 mA M(-1) cm(-2), linear dynamic range from 0.10 to 3.0 microM (R2 = 0.995), and superior operational and long-term stability. The CNT-based electrodes are promising new insulin detectors for diabetes-related studies such as fast chromatographic analysis of therapeutic insulin formulations or evaluation of quality of pancreatic islets prior to their transplantation.     

Bismuth-coated carbon electrodes for anodic stripping voltammetry

Bismuth-coated carbon electrodes display an attractive stripping voltammetric performance which compares favorably with that of common mercury-film electrodes. These bismuth-film electrodes are prepared by adding 400 microg/L (ppb) bismuth(III) directly to the sample solution and simultanously depositing the bismuth and target metals on the glassy-carbon or carbon-fiber substrate. Stripping voltammetric measurements of microgram per liter levels of cadmium, lead, thallium, and zinc in nondeaerated solutions yielded well-defined peaks, along with a low background, following short deposition periods. Detection limit of 1.1 and 0.3 ppb lead are obtained following 2- and 10-min deposition, respectively. Changes in the peak potentials (compared to those observed at mercury electrodes) offer new selectivity dimensions. Scanning electron microscopy sheds useful insights into the different morphologies of the bismuth deposits on the carbon substrates. The in situ bismuth-plated electrodes exhibit a wide accessible potential window (-1.2 to -0.2 V) that permits quantitation of most metals measured at mercury electrodes (except of copper, antimony, and bismuth itself). Numerous key experimental variables have been characterized and optimized. High reproducibility was indicated from the relative standard deviations (2.4 and 4.4%) for 22 repetitive measurements of 80 microg/L cadmium and lead, respectively. Such an attractive use of "mercury-free", environmetally friendly electrodes (with a performance equivalent to that of mercury ones) offers great promise to centralized and decentralized testing of trace metals.     

炭气凝胶为电极的超级电容器的研究

采用低分子线性酚醛树脂-糠醛为原料通过溶液．溶胶-凝胶途径成功合成了炭气凝胶．探讨了结构对电化学性能的影响。采用直流循环法测定炭气凝胶为电极的超级电容器的电化学性能,结果表明,炭气凝胶电极在0．5mA充放电时电极的比电容为121F／g．充放电效率为95％．具有性能稳定、充放电效率高等优良性能。     

Enzymatic genosensor on streptavidin-modified screen-printed carbon electrodes

Voltammetric enzyme genosensors on streptavidin-modified screen-printed carbon electrodes (SPCEs) for the detection of virulence nucleic acid determinants of pneumolysin and autolysin genes, exclusively present on the genome of the human pathogen Streptococcus pneumoniae, were described. Alkaline phosphatase (AP) and 3-indoxyl phosphate were used as the enzymatic label and substrate, respectively. The oligonucleotide probes were immobilized on electrochemically pretreated SPCEs through the streptavidin/biotin reaction. The adsorption of streptavidin was performed by deposition of a drop of a streptavidin solution overnight at 4 degrees C on the surface of the SPCEs. After the hybridization reaction with FITC-labeled complementary targets, the enzyme is captured using an anti-FITC antibody conjugated to AP. In nonstringent experimental conditions, these genosensors can detect 0.49 fmol of 20-mer oligonucleotide target and discriminate between a complementary oligo and an oligo with a three-base mismatch. In the presence of 25% formamide in the hybridization buffer, a single-base mismatch on the oligonucleotide target can be detected.