Glucose enzyme electrode with extended linearity: Application to undiluted blood measurements

An enzyme electrodes is described for glucose determination in unstirred, undiluted whole blood. The system comprises an H₂O₂-detecting electrode upon which is placed a membrane laminate incorporating glucose oxidase. The external membrane was pretreated with methyltrichlorosilane. The electrode response was linearly dependent on glucose concentration up to 50 mmol l^?1 glucose, it had a decreased dependence on dissolved oxygen concentrations and gave response times of 30–90 s. Whole blood glucose measurements correlated well with a routine spectrophotometric method.     

Mediator-free amperometric determination of glucose based on direct electron transfer between glucose oxidase and an oxidized boron-doped diamond electrode

A mediator-free glucose biosensor, termed a “third-generation biosensor,” was fabricated by immobilizing glucose oxidase (GOD) directly onto an oxidized boron-doped diamond (BDD) electrode. The surface of the oxidized BDD electrode possesses carboxyl groups (as shown by Raman spectra) which covalently cross-link with GOD through glutaraldehyde. Glucose was determined in the absence of a mediator used to transfer electrons between the electrode and enzyme. O₂ has no effect on the electron transfer. The effects of experimental variables (applied potential, pH and cross-link time) were investigated in order to optimize the analytical performance of the amperometric detection method. The resulting biosensor exhibited fast amperometric response (less than 5 s) to glucose. The biosensor provided a linear response to glucose over the range 6.67×10⁻⁵ to 2×10⁻³ mol/L, with a detection limit of 2.31×10⁻⁵ mol/L. The lifetime, reproducibility and measurement repeatability were evaluated and satisfactory results were obtained.     

Chemically modified reticulated vitreous carbon electrode with immobilized enzyme as a detector in flow-injection determination of glucose

The construction and response of a chemically modified electrode in which glucose oxidase (E.C. 1.1.3.4) is covalently attached to the surface of reticulated vitreous carbon is reported. Hydrogen peroxide produced by the oxidation of glucose is consumed at the electrode suface, which is held at + 0.9 V vs. a saturated calomel reference electrode. The hydrodynamic and electrochemical properties of the reticulated vitreous carbon electrode substrate make the electrode attractive for use in flow systems. The current varies nonlinearly with glucose concentration throughout most of the range examined (10^?1?10^?4 M). At concentrations of 2.5–10 mM, response is approximately linear with concentration, with a sensitivity of about 400 nA mM^?1. Relative standard deviation for five sample at 10 mM^?1 is less than 2%.     

A coated-metal enzyme electrode for urea determinations

A potentiometric enzyme electrode is reported in which an enzyme immobilized in polyvinyl chloride is used to coat an antimony metal electrode to detect changes in pH when the electrode is immersed in a solution of the enzyme substrat. As an example, urea is determined in solution by using immobilized urease on an antimony electrode, giving a linear concentration range of 5.0 × 10^-4–1.0 × 10^-2 M urea with a slope of 44 mV per decade change in urea concentration. The response slope is stable for about 1 week, with response times in the range 1–2 min, but with absolute potential changes occurring from day to day.     

Glucose biosensor based on new carbon nanotube-gold-titania nano-composites modified glassy carbon electrode

In this paper, a novel biosensor was prepared by immobilizing glucose oxidase （GOx） on carbon nanotube-gold-titania nanocomposites （CNT/Au/TiO2） modified glassy carbon electrode （GCE）. SEM was initially used to investigate the surface morphology of CNT/Au/TiO2 nanocomposites modified GCE, indicating the formation of the nano-porous structure which could readily facilitate the attachment of GOx on the electrode surface. Cyclic voltammogram （CV） and electrochemical impedance spectrum （EIS） were further utilized to explore relevant electrochemical activity on CNT]Au/TiO2 nanocomposites modified GCE. The observations demonstrated that the immobilized GOx could efficiently execute its bioelectrocatalytic activity for the oxidation of glucose. The biosensor exhibited a wider linearity range from 0.1 mmol L-1 to 8 mmol L^-1 glucose with a detection limit of 0.077 mmol L^- 1.     

A rapid and easy procedure of biosensor fabrication by micro-encapsulation of enzyme in hydrophilic synthetic latex films. Application to the amperometric determination of glucose

Novel enzyme electrodes based on synthetic hydrophilic latex matrices are described for the detection of glucose. Glucose oxidase was immobilised through micro-encapsulation, by the simple adsorption of enzyme–latex suspensions on the surface of a platinum electrode. Two latex films functionalised by a hydroxy or a gluconamide group were used. The response of these biosensors to glucose additions was measured by potentiostating the modified electrodes at 0.6 V/SCE in order to oxidise the hydrogen peroxide generated by the enzymatic oxidation of glucose in the presence of dioxygen. The response of such electrodes was evaluated as a function of film thickness and temperature. The sensitivity for a two-layer latex-based biosensor was found to be 38.78 mA M⁻¹ cm⁻² with a response time of 3–5 s. Moreover, a marked improvement of the thermal stability of the biosensor was observed. Only at temperatures higher than 65°C the enzyme started to be denatured and being inactive.     

A specific enzyme electrode for urea

A truly specific, simple enzyme electrode is described for the assay of urea in blood serum. The sensor used is the newly developed air-gap electrode of R??i?ka and Hansen, and has advantages of speed of response and specificity over earlier enzyme electrodes for urea. Potassium, sodium and ammonium ions and other organic and inorganic species present in blood do not interfere. Linear curves are obtained from 2 · 10^-2M to 1 · 10^-4M urea with slopes close to Nernstian (about 0.90 pH/decade). Urea in blood was assayed with an accuracy of 2.2% and a precision of 2.0% with immobilized urease; only 3–5 min is required per assay. The electrode was used for a month and almost 500 assays with excellent results. Since the sensor never touches the sample solution, problems caused by blood components which block membrane pores are avoided.     

Determination of reducing sugars with a 2,4-dinitrophenolate-selective membrane electrode

A 2,4-dinitrophenolate-selective liquid-membrane electrode based on tetrapentylammonium dinitrophenolate dissolved in 2-nitrotoluene is described. The electrode exhibits rapid and near- Nernstian response to the activity of 2,4-dinitrophenolate anions in the range 3×10^?5 ?1×10^?2 M. The response is unaffected by pH in the range 7.5–12.5. The electrode has been successfully applied to the kinetic potentiometric determination of fructose, glucose and galactose at 60°C and of fructose in the presence of glucose and galactose at 30°C. The electrode can be used for the potentiometric determination of glucose and fructose after completion of the reaction with excess of 2,4-dinitrophenolate ions and of sucrose after acid hydrolysis. Mixtures of glucose, fructose and sucrose in aqueous solutions or honey samples can be determined by the proposed procedures with an average error of about 2%.     

A biocompatible needle-type glucose sensor based on platinum-electroplated carbon electrode

A biocompatible needle-type glucose sensor with a 3-electrode configuration was constructed. A platinum-electroplated carbon stick was used as the working electrode, Ag/AgCl as the reference electrode, and a disposable hypodermic needle made of stainless steel as the counter electrode. A Nafion membrane, an immobilized glucose oxidase (GOD) membrane, and a biocompatible membrane with diffusion-limiting effect were coated successively onto the working electrode. The sensor showed a rapid response (< 120 s in batch operation), good reproducibility (RE < 3%), good stability (over 36 h in control serum), a wide dynamic range (5-600 mg/dL glucose), and superior biocompatibility. It was used to determine glucose in serum. The data obtained from the sensor showed good agreement with that from a clinical autoanalyzer (R > 0.95).     

Development of glucose amperometric biosensor based on a novel attractive enzyme immobilization matrix: amino derivative of thiacalix[4]arene

Calixarenes and their derivatives may be a promising material for enzyme immobilization owing to their particular configuration, unique molecule recognition function and aggregation properties. In this paper, p-tert-butylthiacalix[4]arene tetra-amine (TC4TA) was first used as enzyme immobilization material. This attractive material was exploited for the mild immobilization of glucose oxidase (GOD) to develop glucose amperometric biosensor. GOD was strongly adsorbed on the TC4TA modified electrode to form TC4TA/GOD composite membrane. The adsorption mechanism was driven from the covalent bond between amino-group of TC4TA and carboxyl group of GOD and molecule recognition function of TC4TA. Amperometric detection of glucose was evaluated by holding the modified electrode at 0.60 V (versus SCE) to oxidize the hydrogen peroxide generated by the enzymatic reaction. The sensor (TC4TA/GOD) showed a relative fast response (response time was about 5 s), low detection limit (20 μM, S/N = 3), and high sensitivity (ca. 10.2 mA M⁻¹ cm⁻²) with a linear range of 0.08–10 mM of glucose, as well as a good operational and storage stability. In addition, optimization of the biosensor construction, the effects of the applied potential as well as common interfering compounds on the amperometric response of the sensor were investigated and discussed herein.     

Development of an amperometric glucose biosensor based on the immobilization of glucose oxidase in an ormosil-PVA matrix onto a Prussian Blue modified electrode

An amperometric glucose biosensor was developed based on the immobilization of glucose oxidase in the organically modified silicate (ormosil)-polyvinyl acetate (PVA) matrix onto a Prussian Blue (PB)-modified glassy carbon electrode. A higher stability PB-modified electrode was prepared by the electrochemical deposition of FeCl₃, K₃[Fe(CN)₆] and ethylenediamine tetraacetic acid (EDTA) under cyclic voltammetric (CV) conditions. The effects of the potential range of CV conditions, electrolyte cations, applied potential, pH, temperature and co-existing substances were investigated. The detection limit of the glucose biosensor was 8.1 μmol·L⁻¹ (S/N = 3) with a linear range from 20 μmol·L⁻¹ to 2 mmol·L⁻¹ (R = 0.9965). The biosensor presented a fast response and good selectivity. Additionally, excellent reproducibility and stability of the biosensor were observed. Supported by the National High Technical Development Project (863 project) Foundation (Grant No. 2006AA09Z160) and the National Natural Science Foundation of China (Grant No. 20775064)     

An enzyme electrode for the amperometric determination of glucose

An amperometric method utilizing a glucose electrode has been developed for the determination of blood glucose. The time of measurement is less than 12 s if a kinetic method is used and 1 min if a steady-state method is used. The long-term stability of the electrode is ca. 0.1% change from maximum response per day when stored at room temperature for over 10 months. The enzyme electrode determination of blood sugar compares favorably with commonly used methods with respect to accuracy, precision, and stability. The only reagent required for blood sugar determinations is a buffer solution. The electrode consists of a metallic sensing layer covered by a thin film of immobilized glucose oxidase held in place by means of cellophane. When poised at the correct potential, the current produced is proportional to the glucose concentration.     

An enzyme reactor electrode for urea determinations.

An enzyme reactor electrode system for the determination of urea is described. A buffer is pumped through an enzyme reactor (0.4 ml) containing urease immobilized with glutaraldehyde to glass. The effluent is mixed with sodium hydroxide pumped through a second channel and fed through an ammonia gas electrode. Samples are introduced via a third flow channel and mixed with the buffer. The conversion of urea to ammonia is quantitative for sample concentrations of less than 0.03 M for a flow rate of 40 ml h^-1. The reactor electrode shows a Nernstian slope of 57 mV/decade for 5·10^-5–3·10^-2 M urea. The response is independent of variations in the flow rate, enzyme activity or temperature of the reactor.     

Fluoride-selective electrode with internal redox reference electrode

The potential response of a symmetrical configuration in which the LaF₃-membrance is placed between two solutions is discussed. The electrode body provides contact with the inner surface of the fluoride membrane, with a solution containing Fe(CN) ₆ ^3– -Fe(CN) ₆ ^4– redox couple and a Pt wire as internal reference electrode. The electrode was examined in terms of potentialconcentration curves and potential-time response and shown to behave similarly to the commencal Orion fluoride electrode. The advantage of the proposed redox reference system is that the electrode has minimal drift immediately after assembly.     

Amperometric enzyme electrode for glucose determination based on poly(pyrrole-2-aminobenzoic acid)

Polymerization of pyrrole and 2-aminobenzoic acid has been investigated, and a functionalized stable film of poly(pyrrole-2-aminobenzoic acid) (PP2ABA) has been obtained electrochemically onto platinum electrode. Different cyclic voltammetric behavior is obtained for polypyrrole and PP2ABA during electrosynthesis. Fourier-transformed infrared spectrometry and surface-enhanced Raman spectrometry measurements on the two films have confirmed the presence of carboxylate group in the films. The enzyme, glucose oxidase, was covalently immobilized on a conducting PP2ABA film, and amperometric response was measured as a function of concentration of glucose at a potential of 0.7 V vs Ag/AgCl in 0.1 M phosphate buffer at pH 6.2. The effect of polymeric film thickness, pH, and possible interferents were investigated. The linear range of the calibration curve is from 3 to 40 mM with a sensitivity of 0.058 μA mM⁻¹ cm⁻² and a limit of detection of 0.5 mM. The apperent Mishaelis–Menten constant K _M is calculated to be 1 × 10⁻² mM, and the response time is 5 s.     

Preparation and characterization of Prussian blue nanowire array and bioapplication for glucose biosensing

Prussian blue nanowire array (PBNWA) was prepared via electrochemical deposition with polycarbonate membrane template for effective modification of glassy carbon electrode. The PBNWA electrode thus obtained was demonstrated to have high-catalytic activity for the electrochemical reduction of hydrogen peroxide in neutral media. This enabled the PBNWA electrode to show rapid response to H₂O₂ at a low potential of −0.1 V over a wide range of concentrations from 1 × 10⁻⁷ M to 5 × 10⁻² M with a high sensitivity of 183 μA mM⁻¹ cm⁻². Such a low-working potential also substantially improved the selectivity of the PBNWA electrode against most electroactive species such as ascorbic acid and uric acid in physiological media. A detection limit of 5 × 10⁻⁸ M was obtained using the PBNWA electrode for H₂O₂, which compared favorably with most electroanalysis procedures for H₂O₂. A biosensor toward glucose was then constructed with the PBNWA electrode as the basic electrode by crosslinking glucose oxidase (GOx). The glucose biosensor allowed rapid, selective and sensitive determination of glucose at −0.1 V. The amperometric response exhibited a linear correlation to glucose concentration through an expanded range from 2 × 10⁻⁶ M to 1 × 10⁻² M, and the response time and detection limit were determined to be 3 s and 1 μM, respectively.     

Amperometric determination of bonded glucose with an MnO(2) and glucose oxidase bulk-modified screen-printed electrode using flow-injection analysis

A screen-printed amperometric biosensor based on carbon ink double bulk-modified with MnO₂ as a mediator and glucose oxidase as a biocomponent was investigated for its ability to serve as a detector for bonded glucose in different compounds, such as cellobiose, saccharose, (-)-4-nitrophenyl-β-d-glucopyranoside, as well as in beer samples by flow-injection analysis (FIA). The biosensor could be operated under physiological conditions (0.1 M phosphate buffer, pH 7.5) and exhibited good reproducibility and stability. Bonded glucose was released with glucosidase in solution, and the free glucose was detected with the modified screen-printed electrode (SPE). The release of glucose by the aid of glucosidase from cellobiose, saccharose and (-)-4-nitrophenyl-β-d-glucopyranoside in solution showed that stoichiometric quantities of free glucose could be monitored in all three cases.The linear range of the amperometric response of the biosensor in the FIA-mode flow rate 0.2 mL min⁻¹, injection volume 0.25 mL, operation potential 0.48 V versus Ag/AgCl) extends from 11 to 13,900 μmol L⁻¹ glucose in free form. The limit of detection (3σ) is 1 μmol L⁻¹ glucose. A concentration of 100 μmol L⁻¹ yields a relative standard deviation of approximately 7% with five injections. These values correspond to the same concentrations of bonded glucose supposed that it is liberated quantitatively (incubation for 2 h with glucosidase).Bonded glucose could be determined in beer samples using the same assay. The results corresponded very well with the reference procedure.     

Electrocatalytic oxidation of glucose at a Ni-curcumin modified glassy carbon electrode

The electrocatalytic oxidation of glucose was investigated on a nickel-basedchemically modified electrode (Ni(II)-curcumin) prepared by electropolymerization of Ni-curcumin complex (curcumin=1,7-bis[4-hydroxy-3-methoxyphenyl]-1,6-heptadiene-3,5-dione) in alkaline solution. Reaction kinetic and mechanism were investigated by using cyclic voltammetry (CV) and chronoamperometry (CA) techniques and steady-state polarization measurements. Cyclic voltammetry studies indicated that in the presence of glucose the anodic peak current of surface redox mediator was increased, followed by decrease in the corresponding cathodic current. This indicates that glucose was oxidized at the surface of this modified electrode. The results were explained based on the concept of electrocatalytic reactions that occur in this chemically modified electrode. The diffusion coefficient of glucose and the rate constant of the catalytic oxidation of glucose were found to be 6.7×10⁻⁶ cm² s⁻¹ and 6.5×10³ M⁻¹ s⁻¹, respectively. It has shown that by using the Ni-curcumin modified electrode, glucose can be determined with good response and low detection limit.     

Immobilized Fullerene C60‐Enzyme‐Based Electrochemical Glucose Sensor

A mixed‐valence cluster of cobalt(II) hexacyanoferrate and fullerene C60‐enzyme‐based electrochemical glucose sensor was developed. A water insoluble fullerene C60‐glucose oxidase (C60‐GOD) was prepared and applied as an immobilized enzyme on a glassy carbon electrode with cobalt(II) hexacyanoferrate for analysis of glucose. The glucose in 0.1 M KCl/phosphate buffer solution at pH = 6 was measured with an applied electrode potential at 0.0 mV (vs Ag/AgCl reference electrode). The C60‐GOD‐based electrochemical glucose sensor exhibited efficient electro‐catalytic activity toward the liberated hydrogen peroxide and allowed cathodic detection of glucose. The C60‐GOD electrochemical glucose sensor also showed quite good selectivity to glucose with no interference from easily oxidizable biospecies, e.g. uric acid, ascorbic acid, cysteine, tyrosine, acetaminophen and galactose. The current of H₂O₂ reduced by cobalt(II) hexacyanoferrate was found to be proportional to the concentration of glucose in aqueous solutions. The immobilized C60‐GOD enzyme‐based glucose sensor exhibited a good linear response up to 8 mM glucose with a sensitivity of 5.60 × 10² nA/mM and a quite short response time of 5 sec. The C60‐GOD‐based glucose sensor also showed a good sensitivity with a detection limit of 1.6 × 10^‐6 M and a high reproducibility with a relative standard deviation (RSD) of 4.26%. Effects of pH and temperature on the responses of the immobilized C60‐GOD/cobalt(II) hexacyanoferrate‐based electrochemical glucose sensor were also studied and discussed.