Showing papers on "Amperometry published in 2005"

Highly Ordered Platinum‐Nanotubule Arrays for Amperometric Glucose Sensing

Abstract: Direct glucose sensing on highly ordered platinum-nanotubule array electrodes (NTAEs) is systematically investigated. The NTAEs are fabricated by electrochemical deposition of platinum in a 3-aminopropyltrimethoxysilane-modified anodic alumina membrane. Their structures and morphologies are then characterized using X-ray diffraction and scanning electron microscopy, respectively. Electrochemical results show that NTAEs with different real surface areas could be achieved by controlling the deposition time or by using anodic alumina membranes with different pore size. Electrochemical responses of the as-synthesized NTAEs to glucose in a solutions of either 0.5 M H2SO4, or phosphate-buffered saline (PBS, pH 7.4) containing 0.1 M KCl are discussed. Based on the different electrochemical reaction mechanisms of glucose and interferents such as p-acetamedophenol and ascorbic acid, their high roughness factor makes NTAEs sensitive, selective, and stable enough to be a kind of biosensor for the non-enzymatic detection of glucose. Such a glucose sensor allows the determination of glucose in the linear range 2–14 mM, with a sensitivity of 0.1 μA cm–2 mM–1 (correlation coefficient 0.999), and a detection limit of 1.0 μM glucose, with neglectable interference from physiological levels of 0.1 mM p-acetamedophenol, 0.1 mM ascorbic acid, and 0.02 mM uric acid.

Exploring the electrocatalytic sites of carbon nanotubes for NADH detection: an edge plane pyrolytic graphite electrode study

Abstract: The electrocatalytic properties of multi-walled carbon nanotube modified electrodes toward the oxidation of NADH are critically evaluated. Carbon nanotube modified electrodes are examined and compared with boron-doped diamond and glassy carbon electrodes, and most importantly, edge plane and basal pyrolytic graphite electrodes. It is found that CNT modified electrodes are no more reactive than edge plane pyrolytic graphite electrodes with the comparison with edge plane and basal plane pyrolytic graphite electrodes allowing the electroactive sites for the electrochemical oxidation of NADH to be unambiguously determined as due to edge plane sites. Using these highly reactive edge plane sites, edge plane pyrolytic graphite electrodes are examined with cyclic voltammetry and amperometry for the electroanalytical determination of NADH. It is demonstrated that a detection limit of 5 µM is possible with cyclic voltammetry or 0.3 µM using amperometry suggesting that edge plane pyrolytic graphite electrodes can conveniently replace carbon nanotube modified glassy carbon electrodes for biosensing applications with the relative advantages of reactivity, cost and simplicity of preparation. We advocate the routine use of edge plane and basal plane pyrolytic graphite electrodes in studies utilising carbon nanotubes particularly if ‘electrocatalytic’ properties are claimed for the latter.

Peptide nanotube-modified electrodes for enzyme-biosensor applications

Abstract: The fabrication and notably improved performance of composite electrodes based on modified self-assembled diphenylalanine peptide nanotubes is described. Peptide nanotubes were attached to gold electrodes, and we studied the resulting electrochemical behavior using cyclic voltammetry and chronoamperometry. The peptide nanotube-based electrodes demonstrated a direct and unmediated response to hydrogen peroxide and NADH at a potential of +0.4 V (vs SCE). This biosensor enables a sensitive determination of glucose by monitoring the hydrogen peroxide produced by an enzymatic reaction between the glucose oxidase attached to the peptide nanotubes and glucose. In addition, the marked electrocatalytic activity toward NADH enabled a sensitive detection of ethanol using ethanol dehydrogenase and NAD+. The peptide nanotube-based amperometric biosensor provides a potential new tool for sensitive biosensors and biomolecular diagnostics.

Cast Thin Film Biosensor Design Based on a Nafion Backbone, a Multiwalled Carbon Nanotube Conduit, and a Glucose Oxidase Function

Abstract: Novel electroanalytical sensing nanobiocomposite materials are reported. These materials are prepared by mixing multiwalled carbon nanotubes (MWNTs), a Nafion cation exchanger, and glucose oxidase (GOD) in appropriate amounts. The MWNTs are cylindrical with a diameter in the range 40−60 nm and with a length of up to several micrometers, and they provide electrical conductivity. Nafion acts as a polymer backbone to give stable and homogeneous cast thin films. Both MWNTs and Nafion provide negative functionalities to bind to positively charged redox enzymes such as glucose oxidase. The resulting biosensing composite material is inexpensive, reliable, and easy to use. The homogeneity of the MWNT−Nafion−GOD nanobiocomposite films was characterized by atomic force microscopy (AFM). Amperometric transducers fabricated with these materials were characterized electrochemically using cyclic voltammetry and amperometry in the presence of hydrogen peroxide and in the presence of glucose. Their linear response to hyd...

Poly(p-aminobenzene sulfonic acid)-modified glassy carbon electrode for simultaneous detection of dopamine and ascorbic acid

Abstract: A glassy carbon electrode (GCE) is modified with electropolymerized film of p-aminobenzene sulfonic acid (p-ABSA) in pH 70 acetate buffer solution (ABS) Cyclic voltammetry (CV), different pulse voltammetry (DPV) and amperometric curve were used to study the electrochemical properties of the polymer film The polymer film-modified electrode is used to electrochemically detect dopamine (DA) in the presence of ascorbic acid (AA) Polymer film showed excellent electrocatalytic activity for the oxidation of DA and AA The DA and AA anodic peak potential values at the modified electrode are 196 and −8 mV, respectively, which can be obtained from DPV recordings In pH 70 ABS, the anodic peak current increases linearly over three concentration intervals of DA, viz, 10 × 10−7–10 × 10−6, 10 × 10−6–10 × 10−5 and 10 × 10−5–10 × 10−4 mol l−1, with the correlation coefficient, 09984, 09973 and 09921, respectively, and the detection limit (S/N = 3) is 20 × 10−8 mol l−1 AA has no interference with the determination of DA because of the very distinct attracting interaction between DA cations and the negatively poly(p-ABSA) film The proposed method exhibits good recovery and reproducibility

Immobilization of glucose oxidase on gold nanoparticles modified Au electrode for the construction of biosensor

Abstract: A novel method to fabricate glucose biosensor was developed by immobilizing glucose oxidase (GOx) on gold nanoparticles, which had self-assembled on Au electrode modified with thiol-containing three-dimensional network of silica gel. The assembly process was followed and confirmed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), which indicated that the gold nanoparticles in the biosensing interface efficiently improved the electron transfer between analyte and electrode surface. The immobilized enzyme on the electrode surface exhibits excellent catalytic activities for the oxidation of glucose when soluble redox mediator ferrocenemethanol was present. The coverage of electrically wired active GOx ( Γ E 0 ) at the enzyme electrode surface was evaluated high to be 4.5 × 10 −12 mol cm −2 on the basis of kinetic models reported in literature. Moreover, this sensor exhibited fast amperometric response (3 s) to the mediated electrocatalyzed oxidation of glucose, and the catalytic current is proportional to the concentration of glucose up to 6 mM with a high sensitivity of 8.3 μA mM −1 cm −2 . The detection limit of the sensor was estimated to be 23 μM. In addition, the sensor has good reproducibility, and can remain stable over 60 days.

Method of determining analyte level using subcutaneous electrode

Abstract: A small diameter flexible electrode designed for subcutaneous in vivo amperometric monitoring of glucose is described. The electrode is designed to allow “one-point” in vivo calibration, i.e., to have zero output current at zero glucose concentration, even in the presence of other electroreactive species of serum or blood. The electrode is preferably three or four-layered, with the layers serially deposited within a recess upon the tip of a polyamide insulated gold wire. A first glucose concentration-to-current transducing layer is overcoated with an electrically insulating and glucose flux limiting layer (second layer) on which, optionally, an immobilized interference-eliminating horseradish peroxidase based film is deposited (third layer). An outer (fourth) layer is biocompatible.

Design of a subcutaneous implantable biochip for monitoring of glucose and lactate

Abstract: The design, fabrication, and in-vitro evaluation of an amperometric biochip that is designed for the continuous in vivo monitoring of physiological analytes is described. The 2 /spl times/4 /spl times/0.5 mm biochip contains two platinum working enzyme electrodes that adopt the microdisc array design to minimize diffusional limitations associated with enzyme kinetics. This configuration permits either dual analyte sensing or a differential response analytical methodology during amperometric detection of a single analyte. The working enzyme electrodes are complemented by a large area platinized platinum counter electrode and a silver reference electrode. The biorecognition layer of the working electrodes was fabricated from around 1.0-/spl mu/m-thick composite membrane of principally tetraethylene glycol (TEGDA) cross-linked poly(2-hydroxyethyl methacrylate) that also contained a derivatized polypyrrole component and a biomimetic methacrylate component with pendant phosphorylcholine groups. These two additional components were introduced to provide interference screening and in vivo biocompatibility, respectively. This composite membrane was used to immobilize glucose oxidase and lactate oxidase onto both planar and microdisc array electrode designs, which were then used to assay for in vitro glucose and lactate, respectively. The glucose biosensor exhibited a dynamic linear range of 0.10-13.0 mM glucose with a response time (t/sub 95/) of 50 s. The immobilized glucose oxidase within the hydrogel yielded a K/sub m(app)/ of 35 mM, not significantly different from that for the native, solution-borne enzyme (33 mM). The microdisc array biosensor displayed linearity for assayed lactate up to 90 mM, which represented a 30-fold increase in linear dynamic lactate range compared to the biosensor with the planar electrode configuration. Preliminary in vitro operational stability tests performed with the microdisc array lactate biosensor demonstrated retention of 80% initial biosensor response after five days of continuous operation in buffer under physiologic conditions of pH and temperature.

Amperometric detection in TMB/HRP-based assays.

Abstract: 3,3′,5,5′-Tetramethylbenzidine (TMB) is the most commonly used chromogen for horseradish peroxidase (HRP) and so its performance as an electrochemical substrate was evaluated. Measurements of HRP activity in solution were carried out by using an amperometric detector coupled to a flow injection analysis (FIA) system. The enzymatic product was easily detected at a potential of +0.1 V (vs. Ag-pseudoreference electrode) at a bare screen-printed electrode placed in a homemade electrochemical flow cell. A high flow rate (4.3 mL min−1) of 0.5 M H2SO4 was used to obtain repeatable signals and a short analysis time. The detection limit achieved after 15 min of incubation was 2×10−14 M of HRP. The applicability of the amperometric detector to ELISAs was demonstrated by using a commercially available kit for the quantification of interleukin-6 (IL-6) without modifying the kit manufacturer’s protocol or the reagents for this test.

Antioxidant Sensors Based on DNA-Modified Electrodes

Abstract: TiO2/ITO modified electrodes were developed to quantitatively photooxidize adsorbed ds-DNA and to study the effect of antioxidants as ds-DNA protecting agents TiO2 films are used for efficient ds-DNA immobilization, for ds-DNA oxidation through photogenerated hydroxyl radicals, and as electrodes for amperometric sensing The films, prepared by a sol−gel process, are deposited on ITO glass electrodes Damages occurring after ds-DNA oxidation by ROS are detected by adding MB as an intercalant probe and by monitoring the electrochemical reduction current of the intercalated redox probe The MB electrochemical signal is found to be sensitive enough to monitor ds-DNA structure changes, and the electrochemical sensor has been applied to the evaluation of the antioxidant properties of glutathione and gallic acid

Potentiometric enzyme electrode for urea determination using immobilized urease in poly(vinylferrocenium) film

Abstract: A new enzyme electrode for the determination of urea was developed by immobilizing urease in poly(vinylferrocenium) (PVF+) matrix. A PVF+ClO4− film was coated on Pt electrode at +0.7 V by electrooxidation of poly(vinylferrocene) in metylene chloride containing 0.1 M tetrabutylammonium perchlorate (TBAP). The enzyme modified electrode PVF+E− was prepared by anion-exchange in an enzyme solution in 1.0 mM phosphate buffer at pH 7.0. FTIR spectroscopy was used to identify PVF+ClO4−, and PVF+E−. UV spectroscopy was also used to prove the enzyme immobilization. The effects of polymeric film thickness, concentration of enzyme solution, immobilization time of the enzyme, pH and temperature of the medium, concentration of the buffer solution and possible interferents on the measured potential values were investigated. The potentiometric enzyme electrode developed in this study provided linearity to urea in the 5 × 10−5 to 1 × 10−1 M urea concentration range. The detection limit under the optimum working conditions was determined as 5 × 10−6 M for urea. The enzyme electrode was found to be stable for 24 days. The apparent Michaelis-Menten consant (KM app) value and the activation energy, Ea, of this immobilized enzyme system were found to be 4.48 × 10−5 M and 4.97 kcal mol−1 for urea, respectively.

Amperometric Detection of Morphine at Preheated Glassy Carbon Electrode Modified with Multiwall Carbon Nanotubes

Abstract: A highly sensitive and fast responding sensor for the determination of morphine is described. The multiwall carbon nanotubes immobilize on preheated glassy carbon electrode (5 min at 50 °C) by gently rubbing of electrode surface on a filter paper supporting the carbon nanotubes.The results indicated that carbon nanotubes(CNTs) modified glassy carbon electrode exhibited efficiently electrocatalytic oxidation for morphine with relatively high sensitivity, stability and long life. Under conditions of cyclic voltammetry, the potential for oxidation of morphine is lowered by approximately 100 mV and the current is enhanced significantly (10 times) in comparison to the bare glassy carbon electrode at wide pH range (2–9). The electrocatalytic behavior is further exploited as a sensitive detection scheme for morphine determination by hydrodynamic amperometry. Under the optimized conditions the calibration plots are linear in the concentration range 0.5–150 μM with the calculated detection limit (S/N=3) of 0.2 μM and sensitivity of 10 nA/μM and a relative standard deviation (RSD) of 2.5% (n=10). The amperometric response is extremely stable, with no loss in sensitivity over a continual 30 min operation. Such attractive ability of multiwall carbon nanotubes (MWCNTs) modified GC electrode, suggests great promise for a morphine amperometric sensor. Finally the ability of the modified electrode was evaluated for simultaneous determination of morphine and codeine.

Fabrication of Fe3O4 Nanoparticles Modified Electrode and Its Application for Voltammetric Sensing of Dopamine

Abstract: Magnetic nanoparticles of Fe3O4 approximately 5nm in size were synthesized and characterized by XRD and TEM. A novel gold electrode modified with Fe3O4 nanoparticles was then constructed and was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The modified electrode exhibited strong promoting effect and high stability toward the electrochemical oxidation of dopamine (DA), which gave reversible redox peaks with a formal potential of 0.192 V (vs. Ag/AgCl) electrode in pH 7.0 phosphate buffer solution (PB). The anodic peak currents (measured by constant potential amperometry) increased linearly with the concentration of dopamine in the range of 1.5×10−7 to 4.0×10−4 M. The detection limit (S/N=3) obtained was 3.0×10−8 M. The relative standard deviation (RSD) of 8 successive scans was 3.41% for 1.5×10−6 M DA. The interference of ascorbic acid (AA) could be eliminated efficiently. The proposed method showed excellent sensitivity and recovery.

Development of a lactate biosensor based on conducting copolymer bound lactate oxidase

Abstract: An amperometric enzyme electrode was developed for determination of lactate in serum. To prepare this electrode, commercial lactate oxidase from Pediococcus species has been immobilized through glutaraldehyde coupling onto polyaniline-co-fluoroaniline film deposited on an Indium tin oxide (ITO) coated glass plate. This plate acted as working electrode when combined with Pt electrode as counter electrode to the electrometer for the development of a biosensor. The method is based on generation of electrons from H 2 O 2 , which is formed from lactic acid by immobilized lactate oxidase. The concentration of lactic acid is directly proportional to the current measured. The enzyme electrode showed optimum response when operated at 42 °C in 0.05 M, sodium phosphate buffer pH 6.5 for 50 s. The biosensor showed a good performance with a linear response range from 0.1 to 5.5 mM/l. The minimum detection limit of the method is 0.1 mM/l and sensitivity of the sensor is 1.18 μA/mM/l lactate. This electrode was employed for determination of lactate in serum. The serum values in healthy and diseased persons were in the range 0.51–2.9 and 5.0–15.0 mM, respectively. The analytical recovery of added lactic acid was 71%. Within batch and between batch CV were