Showing papers on "Amperometry published in 2006"

Detection of MicroRNAs Using Electrocatalytic Nanoparticle Tags

Abstract: An ultrasensitive microRNA (miRNA) assay employing electrocatalytic nanoparticle tags to meet the need of miRNA expression analysis is described in this report. The assay utilizes an indium tin oxide electrode on which oligonucleotide capture probes are immobilized. After hybridization with periodate-treated miRNA, the nanoparticle tags, isoniazid-capped OsO2 nanoparticles, are brought to the electrode through a condensation reaction to chemically amplify the signal. The resulting electrode exhibits electrocatalytic activity toward the oxidation of hydrazine at −0.10 V, reducing the oxidation overpotential by as much as 900 mV. The effect of experimental variables on the amperometric response is investigated and optimized. A detection limit of 80 fmol/L in 2.5-μL droplets and a linear current−concentration relationship up to 200 pmol/L are obtained following a 60-min hybridization. Successful attempts are made in miRNA expression analysis of HeLa cells.

A novel hydrogen peroxide sensor based on horseradish peroxidase immobilized in DNA films on a gold electrode

Abstract: A novel third-generation hydrogen peroxide (H2O2) biosensor was developed by immobilizing horseradish peroxidase (HRP) on a biocompatible gold electrode modified with a well-ordered, self-assembled DNA film. Cysteamine was first self-assembled on a gold electrode to provide an interface for the assembly of DNA molecules. Then DNA was chemisorbed onto the self-assembled monolayers (SAMs) of cysteamine to form a network by controlling DNA concentration. The DNA-network film obtained provided a biocompatible microenvironment for enzyme molecules, greatly amplified the coverage of HRP molecules on the electrode surface, and most importantly could act as a charge carrier which facilitated the electron transfer between HRP and the electrode. Finally, HRP was adsorbed on the DNA-network film. The process of the biosensor construction was followed by atomic force microscopy (AFM). Voltammetric and time-based amperometric techniques were employed to characterize the properties of the biosensor derived. The enzyme electrode achieved 95% of the steady-state current within 2 s and had a 0.5 mu mol l(-1) detection limit of H2O2. Furthermore, the biosensor showed high sensitivity, good reproducibility, and excellent long-term stability.

Electrochemical multianalyte immunoassays using an array-based sensor.

Abstract: A novel amperometric biosensor for performing simultaneous electrochemical multianalyte immunoassays is described. The sensor consisted of eight iridium oxide sensing electrodes (0.78 mm2 each), an iridium counter electrode, and a Ag/AgCl reference electrode patterned on a glass substrate. Four different capture antibodies were immobilized on the sensing electrodes via adsorption. Quantification of proteins was achieved using an ELISA in which the electrochemical oxidation of enzyme-generated hydroquinone was measured. The spatial separation of the electrodes enabled simultaneous electrochemical immunoassays for multiple proteins to be conducted in a single assay without amperometric cross-talk between the electrodes. The simultaneous detection of goat IgG, mouse IgG, human IgG, and chicken IgY was demonstrated. The detection limit was 3 ng/mL for all analytes. The sensor had excellent precision (1.9‐8.2% interassay CV) and was comparable in performance to commercial single-analyte ELISAs. We anticipate t...

V-type nerve agent detection using a carbon nanotube-based amperometric enzyme electrode.

Abstract: An enzyme electrode for the detection of V-type nerve agents, VX (O-ethyl-S-2-diisopropylaminoethyl methylphosphonothioate) and R-VX (O-isobutyl-S-2-diethylaminoethyl methylphosphonothioate), is proposed. The principle of the new biosensor is based on the enzyme-catalyzed hydrolysis of the nerve agents and amperometric detection of the thiol-containing hydrolysis products at carbon nanotube-modified screen-printed electrodes. Demeton-S was used as a nerve agent mimic. 2-(Diethylamino)ethanethiol (DEAET) and 2-(dimethylamino)ethanethiol (DMAET), the thiol-containing hydrolysis product and hydrolysis product mimic of R-VX and VX, respectively, were monitored by exploiting the electrocatalytic activity of carbon nanotubes (CNT). As low as 2 μM DMAET and 0.8 μM DEAET were detected selectively at a low applied potential of 0.5 V vs Ag/AgCl at a CNT-modified mediator-free amperometric electrode. Further, the large surface area and the hydrophobicity of CNT was used to immobilize organophosphorus hydrolase mutan...

Electrochemical Nanoneedle Biosensor Based on Multiwall Carbon Nanotube

Abstract: We report the fabrication and analytical functions of a biosensor based on a nanoneedle consisting of a multiwall carbon nanotube attached to the end of an etched tungsten tip. The devised electrode is the smallest needle-type biosensor reported to date. The nanoneedles prepared in this work are 30 nm in diameter and 2−3 μm in length. Dopamine and glutamate, which are physiologically important neurotransmitters, were successfully detected using these nanoneedles. Bare nanoneedles detected dopamine in the range from 100 to 1000 μM by differential pulse voltammetry, and enzyme-modified nanoneedles were able to respond to glutamate in the 100−500 μM range by potentiostatic amperometry.

Electrochemical detection of arsenic(III) using iridium-implanted boron-doped diamond electrodes

Abstract: Iridium-modified, boron-doped diamond electrodes fabricated by an ion implantation method have been developed for electrochemical detection of arsenite (As(III)). Ir+ ions were implanted with an energy of 800 keV and a dose of 1015 ion cm-2. An annealing treatment at 850 °C for 45 min in H2 plasma (80 Torr) was required to rearrange metastable diamond produced by an implantation process. Characterization was investigated by SEM, AFM, Raman, and X-ray photoelectron spectroscopy. Cyclic voltammetry and flow injection analysis with amperometric detection were used to study the electrochemical reaction. The electrodes exhibited high catalytic activity toward As(III) oxidation with the detection limit (S/N = 3), sensitivity, and linearity of 20 nM (1.5 ppb), 93 nA μM-1 cm-2, and 0.999, respectively. The precision for 10 replicate determinations of 50 μM As(III) was 4.56% relative standard deviation. The advantageous properties of the electrodes were its inherent stability with a very low background current. Th...

Amperometric Glucose Biosensor Based on Entrapment of Glucose Oxidase in a Poly(3,4‐ethylenedioxythiophene) Film

Abstract: In this study, conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), is used as a matrix for the entrapment of glucose oxidase (GOD) and served as the working electrode for sensing glucose. The monomer, EDOT, is electropolymerized onto the platinum electrode by the cyclic voltammetric (CV) technique, scanned between 0.2 and 1.2 V (vs. Ag/AgCl/saturated KCl) in a phosphate buffer solution (PBS) containing GOD, which is entrapped into the PEDOT film simultaneously. The biosensor senses the reoxidative current of the mediator, ferricinium ions, with a constant applied potential of 0.35 V in the sensing system containing a phosphate buffer solution, ferricinium ions, and glucose. The indirect electrochemical method can efficiently reduce the sensing potential of the glucose. The sensing results show that the linear range of the calibration curve for the glucose concentration lies between 0.1 and 10.0 mM, which is a suitable level in the human body. Besides, the limit of detection and sensing sensitivity on glucose for the biosensor are 0.13 mM and 12.42 mA cm � 2 M � 1 , respectively. The response time of the biosensor, which is defined as the reaction current reaching 95% of the steady-state current, is about 4 – 10 s. In the aspects of interferences on ascorbic acid (AA) and uric acid (UA), the sensing currents increased about 9.7% and 39.1%, respectively, when compared to the sensing current of glucose. Moreover, the biosensor shows a good stability in which the sensing current of the electrode retains 80% of its original one over a period of 18 days.

Amperometric biosensor for hypoxanthine based on immobilized xanthine oxidase on nanocrystal gold–carbon paste electrodes

Abstract: The preparation and performance of a xanthine oxidase (XOD) biosensor, based on a carbon paste electrode (CPE) modified with electrodeposited gold nanoparticles (nAu), for the amperometric determination of hypoxanthine (Hx) is reported. Different XOD biosensor configurations were evaluated and compared with electrodes constructed by immobilizing XOD onto unmodified CPE and with biosensors prepared using glassy carbon electrodes and gold disk electrodes modified with electrodeposited gold. The XOD–nAu–CPE in which the enzyme was immobilized by cross-linking with glutaraldehyde (GA) and BSA exhibited the highest amperometric signal for Hx. Although Hx detection is usually carried out at potential values of around +600 mV versus Ag/AgCl, the GA–BSA–XOD–nAu–CPE allowed this detection to be carried out at 0.00 V, thus minimizing potential interferences from electrochemically oxidizable substances such as ascorbic acid. Experimental variables concerning the biosensor preparation were optimized. Calibration plots for Hx were constructed with the biosensor operating at +600 mV and at 0.00 V. The detection limit for Hx, 2.2 × 10 −7 mol l −1 , obtained using the latter potential value is similar to the best detection limits reported in the literature with other biosensor designs working at much more extreme potentials. The usefulness of the biosensor for the analysis of real samples was demonstrated by determining Hx in sardines and chicken meat.

On-chip amperometric measurement of quantal catecholamine release using transparent indium tin oxide electrodes.

Abstract: Carbon-fiber amperometry has been extensively used to monitor the time course of catecholamine release from cells as individual secretory granules discharge their contents during the process of quantal exocytosis, but microfabricated devices offer the promise of higher throughput. Here we report development of a microchip device that uses transparent indium tin oxide (ITO) electrodes to measure quantal exocytosis from cells in microfluidic channels. ITO films on a glass substrate were patterned as 20-mum-wide stripes using photolithography and wet etching and then coated with polylysine to facilitate cell adherence. Microfluidic channels (100 mum wide by 100 mum deep) were formed by molding poly(dimethylsiloxane) (PDMS) on photoresist and then reversibly sealing the PDMS slab to the ITO-glass substrate. Bovine adrenal chromaffin cells were loaded into the microfluidic channel and adhered to the ITO electrodes. Cells were stimulated to secrete by perfusing a depolarizing "high-K" solution while monitoring oxidation of catecholamines on the ITO electrode beneath the cell using amperometry. Amperometric spikes with charges ranging from 0.1 to 1.5 pC were recorded with a signal-to-noise ratio comparable to that of carbon-fiber electrodes. Further development of this approach will enable high-throughput measurement of quantal catecholamine release simultaneously with optical cell measurements such as fluorescence.

Novel lactate and pH biosensor for skin and sweat analysis based on single walled carbon nanotubes

Abstract: Carbon nanotubes (CNTs) were functionalized and employed in an electrochemical cell to serve as a biosensor to specifically detect either lactate or pH in an electrolyte solution of artificial sweat. They were functionalized with the carboxyl group ( COOH) to detect pH and the enzyme lactate oxidase (LOX) to detect lactate. All CNT samples were characterized to compare the electrodes before and after functionalization. Fourier transform infrared spectroscopy (FTIR) was used to verify the attachment of both COOH and LOX to the respective carbon nanotubes samples. Scanning electron microscopy (SEM) was used to examine the structure of the CNT–lactate electrode. Square wave voltammetry proved to be the best template to use to sense these target analytes. The functionalized CNT–COOH electrode displayed a linear response to pH 1–10, with a negative voltage shift corresponding to an increase in pH. Two types of lactate sensors were fabricated, both of which exhibited an increase in current corresponding to an increase in lactate concentration. The functionalized CNT–LOX on a glassy carbon electrode displayed an amperometric response in the range of 1–4 mM lactate. The CNT–LOX on a silicon/indium tin oxide (Si/ITO) substrate displayed an amperometric response in the range of 0.01–0.05 M lactate.

Amperometric aqueous sol–gel biosensor for low-potential stable choline detection at multi-wall carbon nanotube modified platinum electrode

Abstract: A novel amperometric biosensor based on the determination of H 2 O 2 liberated by the enzyme choline oxidase (ChOx) was fabricated by immobilization of ChOx into a sol–gel silicate film on the multi-wall carbon nanotubes (MWCNT) modified platinum electrode. Cyclic voltammetric results clearly showed that carbon nanotubes possess an excellent electrocatalytic activity towards the oxidation of H 2 O 2 at a low potential (0.16 V versus Ag/AgCl). The remarkable catalytic property of MWCNT was further exploited as a selective determination scheme for choline in the presence of some electroactive compounds. Experimental parameters of the choline sensor, such as applied potential, pH, and temperature were studied. The performance of the sensor showed sensitive determination of choline with a linear range from 5 × 10 −6 to 1 × 10 −4 M and a response time of less than 8 s. The detection limit of choline was determined to be about 1 × 10 −7 M. This biosensor was used to detect choline released from Lecithin by phospholipase D (PLD) in serum samples.

Amperometric third-generation hydrogen peroxide biosensor incorporating multiwall carbon nanotubes and hemoglobin

Abstract: An amperometric third-generation hydrogen peroxide biosensor was designed by immobilizing hemoglobin (Hb) on a glassy carbon electrode modified with multiwall carbon nanotubes (MWNT). The direct electron transfer of the Hb immobilized on the MWNT-modified electrode was observed. The formal potential of the immobilized Hb was −0.241 V versus Ag/AgCl (3 M NaCl) and the heterogeneous electron transfer rate constant was 0.58 s−1 in a 0.20 M acetate buffer solution (pH 5.4). The immobilized Hb exhibited excellent electrocatalytic activity to reduce hydrogen peroxide in the absence and presence of oxygen, which facilitated designing an amperometric third-generation biosensor for hydrogen peroxide. In the presence of oxygen, the response to hydrogen peroxide of the designed biosensor at a potential of −0.35 V was linear in the concentration range from 6.0 × 10−6 to 6.0 × 10−3 M, and the detection limit was 1.2 × 10−6 M. The relative standard deviation was 2.4% for nine successive assays at 1.0 × 10−5 M hydrogen peroxide. The designed biosensor was applied to the determination of hydrogen peroxide in pharmaceutical injections with high sensitivity and rapid response.

Cathodic detection of H2O2 using iodide-modified gold electrode in alkaline media.

Abstract: Oxidative chemisorption and cathodic stripping reductive desorption of iodide have been studied at a smooth polycrystalline gold (Au (poly)) electrode. Potential-dependent surface coverage of iodide has been controlled on the basis of its reductive desoprtion in 0.1 M KOH alkaline media and its quantitative oxidation to aqueous iodates in acidic media. The Au (poly) electrode surface catalyzes the decomposition of H2O2 to O2. Specific adsorption of iodide on the Au electrode inhibits fully the catalytic decomposition and electrochemical oxidation of H2O2 as well as the adsorption of unknown impurities and the oxidative degradation of the electrode surface by H2O2. A quantitative characterization/detection of H2O2 at the iodide-modified Au (poly) electrode in the alkaline media has, thus, been achieved. Performance of the electrode toward the detection of H2O2 with respect to response time and sensitivity as well as operational stability has been evaluated. It has a sensitivity of 0.272 mA cm-2 mM-1 in amp...

Hydrogen peroxide biosensor based on myoglobin/colloidal gold nanoparticles immobilized on glassy carbon electrode by a Nafion film

Abstract: A novel amperometric sensor of hydrogen peroxide was developed based on the immobilization of myoglobin (Mb) and colloidal gold nanoparticles (CGNs) on a glassy carbon electrode (GCE) by a Nafion film. The immobilized Mb displayed a pair of well-defined and nearly reversible cyclic voltammetric peaks with a formal potential (E°′) of −0.373 V in a 0.1 M phosphate buffer solution (PBS) of pH 6.9. The formal potential of the Mb heme Fe(III)/Fe(II) couple shifted linearly with pH with a slope of −49.6 mV/pH, indicating that the electron transfer is accompanied by single-proton transportation. The immobilized Mb exhibited excellent electrocatalytic response to the reduction of hydrogen peroxide, based on which an unmediated biosensor for hydrogen peroxide was achieved. The linear range for determination of hydrogen peroxide was from 1.5 × 10−6 to 9.0 × 10−5 M with a detection limit of 5.0 × 10−7 M at a signal-to-noise ratio of 3. The stability, repeatability and selectivity of the biosensor were also evaluated.

Vertically aligned carbon nanotube probes for monitoring blood cholesterol

Abstract: Detection of blood cholesterol is of great clinical significance. The amperometric detection technique was used for the enzymatic assay of total cholesterol. Multiwall carbon nanotubes (MWNTs), vertically aligned on a silicon platform, promote heterogeneous electron transfer between the enzyme and the working electrode. Surface modification of the MWNT with a biocompatible polymer, polyvinyl alcohol (PVA), converted the hydrophobic nanotube surface into a highly hydrophilic one, which facilitates efficient attachment of biomolecules. The fabricated working electrodes showed a linear relationship between cholesterol concentration and the output signal. The efficacy of the multiwall carbon nanotubes in promoting heterogeneous electron transfer was evident by distinct electrochemical peaks and higher signal-to-noise ratio as compared to the Au electrode with identical enzyme immobilization protocol. The selectivity of the cholesterol sensor in the presence of common interferents present in human blood, e.g. uric acid, ascorbic acid and glucose, is also reported.

Highly sensitive electrochemical detection of trace liquid peroxide explosives at a Prussian-blue ‘artificial-peroxidase’ modified electrode

Abstract: A highly sensitive electrochemical assay of the peroxide-based explosives triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD) at a Prussian-blue (PB) modified electrode is reported. The method involves photochemical degradation of the peroxide explosives and a low potential (0.0 V) electrocatalytic amperometric sensing of the generated hydrogen peroxide at the PB transducer and offers nanomolar detection limits following a short (15 s) irradiation times. The electrochemical sensing protocol should facilitate rapid field screening of peroxide explosives.