Amperometric acetylcholine sensor catalyzed by nickel anode electrode

An amperometric method was using a nickel catalytic electrode in aqueous base solution for detecting acetylcholine (ACh). A sensing mechanism was developed in which ACh was hydrolyzed in base aqueous solution to produce the acetic anion and choline. The alcohol group of choline was oxidized to the corresponding carboxylic acid by Ni(OH)2/NiOOH catalytic system. The amperometric response resulted from the current generated by ACh oxidation in response to step changes in ACh concentration. The potential window of limiting current of ACh anodic oxidation at the Ni interface was determined in NaOH electrolyte. The effect of NaOH electrolyte concentration on sensitivity was also discussed. At the optimum operating condition, the method exhibits a good linear relationship between the response current and the ACh concentration. The response time of the ACh sensing system was 10 s. Scanning electrochemical microscopy (SECM) with platinum micro-tips was used to investigate the diffusion layer thickness of Ni electrode.     

Highly sensitive sensor for picomolar detection of insulin at physiological pH, using GC electrode modified with guanine and electrodeposited nickel oxide nanoparticles

The electrochemical behavior of insulin at glassy carbon (GC) electrode modified with nickel oxide nanoparticles and guanine was investigated. Cyclic voltammetry technique has been used for electrodeposition of nickel oxide nanoparticles (NiOx) and immobilization of guanine on the surface GC electrode. In comparison to glassy carbon electrode modified with nickel oxide nanoparticles and bare GC electrode modified with adsorbed guanine, the guanine/nickel oxide nanoparticles/modified GC electrode exhibited excellent catalytic activity for the oxidation of insulin in physiological pH solutions at reduced overpotential. The modified electrode was applied for insulin detection using cyclic voltammetry or hydrodynamic amperometry techniques. It was found that the calibration curve was linear up to 4muM with a detection limit of 22pM and sensitivity of 100.9pA/pM under the optimized condition for hydrodynamic amperometry using a rotating disk modified electrode. In comparison to other electrochemical insulin sensors, this sensor shows many advantages such as simple preparation method without using any special electron transfer mediator or specific reagent, high sensitivity, excellent catalytic activity at physiological pH values, short response time, long-term stability and remarkable antifouling property toward insulin and its oxidation product. Additionally, it is promising for the monitoring of insulin in chromatographic effluents.     

Cobalt hydroxide nanoparticles modified glassy carbon electrode as a biosensor for electrooxidation and determination of some amino acids

The electrochemical behavior of some amino acids was investigated on cobalt hydroxide nanoparticles modified glassy carbon (CHM-GC) electrode in alkaline solution. The process of oxidation and its kinetics were established by using cyclic voltammetry, chronoamperometry techniques, and steady-state polarization measurements. The results revealed that cobalt hydroxide promotes the rate of oxidation by increasing the peak current, so these bimolecular reactions are oxidized at lower potentials. Cyclic voltammograms and chronoamperometry indicate a catalytic EC′ mechanism to be operative with electrogeneration of Co(IV) as the electrochemical process. Also, the process is diffusion controlled and the current-time responses follow Cottrellian behavior. This result was confirmed by steady-state measurements. The rate constants of the catalytic oxidation of amino acids and the electron transfer coefficients are reported.     

Hydroxyurea Could Be a Good Clinically Relevant Iron Chelator

Our previous study showed a reduction in serum ferritin of β-thalassemia patients on hydroxyurea therapy. Here we aimed to evaluate the efficacy of hydroxyurea alone and in combination with most widely used iron chelators like deferiprone and deferasirox for reducing iron from experimentally iron overloaded mice. 70 BALB/c mice received intraperitonial injections of iron-sucrose. The mice were then divided into 8 groups and were orally given hydroxyurea, deferiprone or deferasirox alone and their combinations for 4 months. CBC, serum-ferritin, TBARS, sTfr and hepcidin were evaluated before and after iron overload and subsequently after 4 months of drug therapy. All animals were then killed. Iron staining of the heart and liver tissue was done using Perl’s Prussian Blue stain. Dry weight of iron in the heart and liver was determined by atomic absorption spectrometry. Increased serum-ferritin, TBARS, hepcidin and dry weight of iron in the liver and heart showed a significant reduction in groups treated with iron chelators with maximum reduction in the group treated with a combination of deferiprone, deferasirox and hydroxyurea. Thus hydroxyurea proves its role in reducing iron from iron overloaded mice. The iron chelating effect of these drugs can also be increased if given in combination.     

A cyclodextrin host-guest recognition approach to an electrochemical sensor for simultaneous quantification of serotonin and dopamine

An electrochemical sensor for simultaneous quantification of serotonin (5-hydroxytryptamine, 5-HT) and dopamine (DA) using a β-cyclodextrin/poly(N-acetylaniline)/carbon nanotube composite modified carbon paste electrode has been developed. Synergistic effect of multi-walled carbon nanotube (MWCNT) in addition to the pre-concentrating effect of β-cyclodextrin (β-CD) as well as its different inclusion complex stability with 5-HT and DA was used to construct an electrochemical sensor for quantification of these important neurotransmitters. The overlapping anodic peaks of 5-HT and DA at 428 mV on bare electrode resolved in two well-defined voltammetric peaks at 202 and 363 mV vs. Ag/AgCl respectively. The oxidation mechanism of 5-HT and DA on the surface of the electrode was investigated by cyclic voltammetry and it was found that the electrode processes are pH dependent and electrochemical oxidation of 5-HT is totally irreversible while the electrode gave a more reversible process to DA. Under optimized conditions, linear calibration curves were obtained in the range of about 4-200 μM with a detection limits down to sub-μM levels (S/N=3) after 20-s accumulation, for both. The proposed sensor was shown to be remarkably selective for 5-HT and DA in matrices containing different species including ascorbic acid and uric acid. The suitability of the developed method was tested for the determination of 5-HT and DA in the Randox Synthetic Plasma samples and acceptable recoveries were obtained for a set of spiked samples.     

Inhibited enzyme electrodes. Part 2: The kinetics of the cytochrome oxidase system

An inhibition enzyme electrode to measure toxic gases can be constructed using the respiratory enzyme cytochrome oxidase. The rate of enzyme turnover is followed by reducing cytochrome c on a gold electrode modified with the mediator bis(4-pyridyl) disulphate. The kinetics and mechanism of the system have been measured. The electrochemical kinetics for the oxidation of cytochrome c have been studied by rotating disc voltammetry and are shown to obey the Koutecky-Levich equation. The standard electrochemical rate constant is found to be 3 x 10(-3) cms-1. At ambient oxygen concentration the orders of the current with respect to the concentration of cytochrome oxidase, cytochrome c and oxygen are found to be 1/2, 1/2 and zero respectively. These orders are consistent with the rate limiting step being the turnover of the enzyme under saturated conditions in a thin reaction layer close to the electrode. At lower oxygen concentrations a good fit between the experimental results and a theoretical model further confirms the assignation of the mechanism. The rate constants describing the oxidation and reduction of the enzyme have been measured. The pH dependence of the current has been studied.     

Voltammetric detection of anti-HIV replication drug based on novel nanocomposite gold-nanoparticle–CaCO<Subscript>3</Subscript> hybrid material

A novel bionanocomposite, horse radish peroxidase- gold-nanoparticle–Calcium carbonate (HRP-AuNPs-CaCO₃), hybrid material was encapsulated by silica sol on a glassy carbon electrode (GCE). The fabricated modified electrode was used as a novel voltammetric sensor for electrochemical sensing of anti-HIV replication drug i.e. deferiprone. The surface morphology of the modified electrode was characterized by scanning electron microscopy (SEM). Results obtained from the voltammetric measurements show that HRP-AuNPs-CaCO₃ modified GCE offers a selective and sensitive electrochemical sensor for the determination of deferiprone. Under experimental conditions, the proposed voltammetric sensor has a linear response range from 0.01 to 10,000 μM with a detection limit of 0.01 μM. Furthermore, the fabricated sensor was successfully applied to determine deferiprone level in spiked urine and serum samples.     

Nano nickel oxide/nickel incorporated nickel composite coating for sensing and estimation of acetylcholine

Pure nickel electrodes can be used as biosensors especially for sensing and estimating acetylcholine neurotransmitter. In the present work, a good electrochemical sensor was developed by electroplating nano nickel oxide reinforced nickel on graphite substrate. The morphology of the working electrode surface was studied by using a scanning electron microscope (SEM). The electrochemical and biological performance of the modified electrode was characterized by polarization studies in different media. The present modified electrode showed good sensing performance with a response time as low as 8s during sensing and estimation of acetylcholine. The sensitivity of the modified electrode was 34.88 microA/(microM cm(2)).     

Oxidation of arsenopyrite by Thiobacillus ferrooxidans detected by a mineral electrode

Summary A new electrochemical study of arsenopyrite biooxidation was based on process detection by arsenopyrite electrode. The rate of reaction was evaluated as the exchange current density calculated from polarization curves. Obtained data were used for determination of released electrons from mineral and for evaluation of reaction mechanism of its oxidation.     

Chelation of chromium(VI) by combining deferasirox and deferiprone in rats

The present research is aimed to characterize the potential efficiency of two chelators after chromium(VI) administration for 60 days following two doses of 15 and 30 mg/kg chromium(VI) per body weight daily to male rats. However, the hypothesis that the two chelators might be more efficient as combined therapy than as single therapy in removing chromium(VI) from rat organs was considered. In this way, two known chelators deferasirox and deferiprone were chosen and given orally as a single or combined therapy for a period of 1 week. Chromium(VI) and iron concentrations in tissues were determined by flame atomic absorption spectroscopy. The combined chelation therapy results show that deferasirox and deferiprone are able to remove chromium(VI) ions from various tissues while iron concentration returned to normal levels and symptoms also decreased.     

A novel system combining biocatalytic dephosphorylation of L-ascorbic acid 2-phosphate and electrochemical oxidation of resulting ascorbic acid

An enzyme electrode was prepared with acid phosphatase (ACP) for development of a new electric power generation system using ascorbic acid 2-phosphate (AA2P) as a fuel. The properties of the electrode were investigated with respect to biocatalytic dephosphorylation of AA2P and electrochemical oxidation of resulting ascorbic acid (AA). The enzyme electrode was fabricated by immobilization of ACP through amide linkage onto a self-assembled monolayer of 3-mercaptopropionic acid on a gold electrode. AA2P was not oxidized on a bare gold electrode in the potential sweep range from -0.1 to +0.5 V vs. Ag/AgCl. However, the enzyme electrode gave an oxidation current in citric buffer solution of pH 5 containing 10 mM of AA2P. The oxidation current began to increase at +0.2V, and reached to 5.0 μA cm(-2) at +0.5 V. The potential +0.2 V corresponded to the onset of oxidation of ascorbic acid (AA). These results suggest that the oxidation current observed with the enzyme electrode is due to AA resulting from dephosphorylation of AA2P. The oxidation current increased with increasing concentration of AA2P and almost leveled off at around the concentration of 5mM. Thus the enzyme electrode brought about biocatalytic conversion of AA2P to AA, followed by electrochemical oxidation of the AA. The oxidation current is likely to be controlled by the biocatalytic reaction.     

Electrochemical immunosensor of platelet-derived growth factor with aptamer-primed polymerase amplification

A new method for the determination of platelet-derived growth factor BB (PDGF-BB) was developed using an electrochemical immunosensor with an aptamer-primed, long-strand circular detection probe. Rabbit anti-human PDGF-B polyclonal antibody was immobilized on the electrode to serve as the capture antibody. The detection probe was synthesized via polymerase extension along a single-stranded circular plasmid DNA template with a primer headed by the anti-PDGF-B aptamer. In the presence of the analyte, the aptamer-primed circular probe was captured on the electrode via the formation of an antibody/PDGF-BB/aptamer sandwiched complex. The electroactivity indicator methylene blue was adsorbed on the electrode surface via the analyte-sandwiched complex with long-strand circular DNA, thus yielding a strong electrochemical signal for the quantification of PDGF-BB. This strategy allowed electrochemical detection with enormous signal amplification arising from the long-strand localized circular probe. The oxidation peak current of methylene blue in square wave voltammetric measurements showed a linear dependence on the concentration of PDGF-BB in the range from 50 to 500 ng mL⁻¹, with a detection limit as low as18 pg mL⁻¹.     

Electrochemical bioreactor with regeneration of NAD+ by rotating graphite disk electrode with PMS adsorbed.

Kinetic constants were compared among p-quinone, 2,6-dichlorophenolindophenol, phenazine methosulfate (PMS), methylene blue, and FAD in the oxidation of NADH. Among those, PMS was selected for its highest rate constant as a mediator for the electrochemical oxidation of NAD. The PMS could be stably immobilized on a graphite electrode surface by adsorption. The PMS adsorbed and that in the solution showed distinctly separated peaks in the cyclic voltammogram. The immobilized PMS functioned as an immobilized mediator to reduce the overpotential in the electrochemical oxidation of NAD so that the electrode could be used as an NAD regenerator. For the construction of an electrochemical bioreactor, a specially designed rotating disk graphite electrode was used. In spite of its extraordinarily large surface area, the behavior of the rotating disc electrode was described well by the Levich law. The NAD oxidation system of the rotating graphite disk electrode with PMS adsorbed was combined with glucose-6-phosphate dehydrogenase reaction, which reduced NAD with the consumption of glucose-6-phosphate. The electrochemical bioreactor system worked well with recycling of NAD at a high current efficiency.     

Novel electrochemical catalysis as signal amplified strategy for label-free detection of neuron-specific enolase

A label-free electrochemical immunoassay for neuron-specific enolase (NSE), a kind of lung cancer marker, was developed in this work via novel electrochemical catalysis for signal amplification. The new amplified strategy was based on the electrochemical catalysis of nickel hexacyanoferrates nanoparticles (NiHCFNPs) in the presence of dopamine (DA). NiHCFNPs, which were assembled on the porous gold nanocrystals (AuNCs) modified glassy carbon electrode (GCE), could exhibit a distinct pair of redox peaks corresponding to anodic and cathodic reactions of hexacyanoferrate (II/III). Subsequently, gold nanoparticles functionalized graphene nanosheets (Au-Gra) were coated on the surface of NiHCFNPs/AuNCs film. Then an enhanced amount of neuron-specific enolase antibody (anti-NSE) could be loaded to obtain a sensitive immunosensor of anti-NSE/Au-Gra/NiHCFNPs/AuNCs/GCE due to the strong adsorption capacity and large specific surface area of Au-Gra. More importantly, the oxidation peak current can be enormously enhanced towards the electrocatalytic oxidation of DA based on NiHCFNPs, resulting in the further improvement of the immunosensor sensitivity. Under optimal conditions, the electrochemical immunosensor exhibited a linear range of 0.001-100 ng/mL with a detection limit of 0.3 pg/mL (S/N=3). Thus, the proposed immunosensor provides a rapid, simple, and sensitive immunoassay protocol for NSE detection, which may hold a promise for clinical diagnosis.     

Fine steps of electrocatalytic oxidation and sensitive detection of some amino acids on copper nanoparticles

The electrocatalytic oxidation of five amino acids—glycine, aspartic acid, cysteine, glutamic acid, and tyrosine—on two copper-based electrodes comprising copper microparticle-modified carbon paste electrode (m-CPE) and copper nanoparticle-modified CPE (n-CPE) was investigated. In the voltammograms recorded using m-CPE, a single anodic peak related to the oxidation of amino acids appeared and was related to the electrocatalytic oxidation of the amino acids via the electrogenerated Cu(III) species. Using n-CPE, however, two overlapped anodic peaks in the voltammograms appeared and were related to two fine tunable steps of the oxidation process. The currents of the two peaks were controlled by diffusion and were confirmed by chronoamperometric measurements. The amino acids were oxidized on n-CPE at higher rates and at lower potentials compared with m-CPE. This was attributed to the nanosize of copper nanoparticles. Some primary linear-chain amines and primary branched-chain amines were oxidized on the copper-based electrodes as markers. The catalytic rate constants, the transfer coefficients, and the diffusion coefficients for the amino acids are reported. Simple, sensitive, and time-saving sensing procedures in both batch and flow systems were developed for the analysis of the amino acids, and the corresponding analytical parameters are reported.     

Electrochemical behavior of L-cysteine and its detection at carbon nanotube electrode modified with platinum

The electrochemical behavior of L-cysteine (CySH) on platinum (Pt)/carbon nanotube (CNT) electrode was investigated by cyclic voltammetry. CNTs used in this study were grown directly on graphite disk by chemical vapor deposition. Pt was electrochemically deposited on the activated CNT/graphite electrode by electroreduction of Pt(IV) complex ion on the surface of CNTs. Among graphite, CNT/graphite, and Pt/CNT electrodes, improved electrochemical behavior of CySH oxidation was found with Pt/CNT electrode. On the other hand, a sensitive CySH sensor was developed based on Pt/CNT/graphite electrode. A linear calibration curve can be observed in the range of 0.5 microM-0.1 mM. The detection limit of the Pt/CNT electrode is 0.3 microM (signal/nose=3). Effects of pH, scan rate, and interference of other oxidizable amino acids were also investigated and discussed. Additionally, the reproducibility, stability, and applicability of the Pt/CNT electrode were evaluated.     

Characterization and electrocatalytic properties of Prussian blue electrochemically deposited on nano-Au/PAMAM dendrimer-modified gold electrode

Gold electrode was modified with 3-mercaptopropionic acid (MPA) and further reacted with poly(amidoamine) (PAMAM) dendrimer (generation 4.0) then attached the nano-Au to obtain films on which Prussian blue (PB) was electrochemically deposited to afford much wider pH adaptive range, much better electrochemical stability and excellent electrochemical response. The microstructure and electrochemical behavior of Au/MPA/PAMAM/nano-Au/PB electrode were investigated by scanning electron microscopy (SEM) and cyclic voltammetry. The electrochemical response of the Au/MPA/PAMAM/nano-Au/PB-modified electrode for the electrocatalytic reduction of hydrogen peroxide was investigated, and it was found that the sensitivity as well as the corresponding detection limits were improved as compared to the voltammetric response of a Au/PB-modified electrode and Au/MPA/PAMAM/PB electrode. Based on this, a new electrochemical sensor for determination of hydrogen peroxide has been developed.     

Prospect and Reality of Ni‐Rich Cathode for Commercialization

The layered nickel‐rich cathode materials are considered as promising cathode materials for lithium‐ion batteries (LIBs) due to their high reversible capacity and low cost. However, several significant challenges, such as the unstable powder properties and limited electrode density, hindered the practical application of the nickel‐rich cathode materials with the nickel content over 80%. Herein, important stability issues and in‐depth understanding of the nickel‐rich cathode materials on the basis of the industrial electrode fabrication condition for the commercialization of the nickel‐rich cathode materials are reviewed. A variety of factors threatening the battery safety such as the powder properties, thermal/structural stability are systemically investigated from a material point of view. Furthermore, recent efforts for enhancing the electrochemical stability of the nickel‐rich cathode materials are summarized. More importantly, critical key parameters that should be considered for the high energy LIBs at an electrode level are intensively addressed for the first time. Current electrode fabrication condition has a difficulty in increasing the energy density of the battery. Finally, light is shed on the perspectives for the future research direction of the nickel‐rich cathode materials with its technical challenges in current state by the practical aspect.     

Chelator-facilitated removal of iron from transferrin: relevance to combined chelation therapy

Current iron chelation therapy consists primarily of DFO (desferrioxamine), which has to be administered via intravenous infusion, together with deferiprone and deferasirox, which are orally-active chelators. These chelators, although effective at decreasing the iron load, are associated with a number of side effects. Grady suggested that the combined administration of a smaller bidentate chelator and a larger hexadentate chelator, such as DFO, would result in greater iron removal than either chelator alone [Grady, Bardoukas and Giardina (1998) Blood 92, 16b]. This in turn could lead to a decrease in the chelator dose required. To test this hypothesis, the rate of iron transfer from a range of bidentate HPO (hydroxypyridin-4-one) chelators to DFO was monitored. Spectroscopic methods were utilized to monitor the decrease in the concentration of the Fe-HPO complex. Having established that the shuttling of iron from the bidentate chelator to DFO does occur under clinically relevant concentrations of chelator, studies were undertaken to evaluate whether this mechanism of transfer would apply to iron removal from transferrin. Again, the simultaneous presence of both a bidentate chelator and DFO was found to enhance the rate of iron chelation from transferrin at clinically relevant chelator levels. Deferiprone was found to be particularly effective at 'shuttling' iron from transferrin to DFO, probably as a result of its small size and relative low affinity for iron compared with other analogous HPO chelators.     

Voltammetry of tobacco mosaic virus and its isolated protein at the graphite electrode

The electrochemical behaviour of tobacco mosaic virus (TMV) and its isolated protein was studied using differential pulse (DP) voltammetry at a graphite electrode and by direct current (DC) polarography in Brdicka solution. TMV and its isolated protein were found to be electrooxidized at the graphite electrode in the adsorbed state. Both species yielded two oxidation peaks on DP voltammograms. The first, more negative peak, corresponded to electrooxidation of tyrosine residues, whereas the other, more positive, peak corresponded to electrooxidation of tryptophan residues. DC polarography was used to detect degradation of TMV and denaturation of TMV-protein induced by an increased pH and by the addition of urea, respectively. These structural transformations resulted in increased DP voltammetric oxidation currents as recorded using a graphite working electrode. It has been suggested that the higher oxidation currents were due to an increase in the number of tyrosine and tryptophan residues accessible to the reaction at the graphite electrode. The results of these electrochemical investigations were in a good agreement with the estimation of the accessibility of tyrosine and tryptophan residues based on the well-explored three-dimensional structure of TMV and its isolated protein.