Response characteristics of the glucose-sensitive field-effect transistor. Computer simulation of the effect of gluconolactonase coimmobilization in a glucose oxidase membrane

The bienzyme system consisting of glucose oxidase and gluconolactonase was investigated using a conventional diffusion-kinetics model for an enzyme-modified field-effect transistor (FET) to clarify the effect of gluconolactonase coimmobilization in a glucose oxidase membrane on the steady-state response amplitude of a glucose sensor based on a FET. The model includes spontaneous and enzymatic hydrolysis reactions of d-glucono-δ-lactone and it elucidated the following experimental results: a glucose sensor with a membrane (about 1 μm in thickness) coimmobilizing these enzymes showed a sufficient response amplitude, whereas without coimmobilization of gluconolactonase no detectable response was observed up to 3 mM glucose; and the response amplitude depended strongly on the amount of lactonase in the membrane. The model also predicted an optimum enzyme ratio for coimmobilization in a membrane.     

Glucose sensor based on a field-effect transistor with a photolithographically patterned glucose oxidase membrane

A photopolymer solution consisting of polyvinylpyrrolidone and 2,5-bis(4′-azido-2′-sulfobenzal)cyclopentanone is used to make a patterned glucose oxidase membrane for a FET-glucose sensor by photolithography. A small patterned glucose oxidase membrane, 0.2 mm wide and 1 mm long, is made on the gate surface of an ISFET by developing a photocross-linked glucose oxidase membrane with aqueous 1–3% glutaraldehyde solution. The optimum composition of the enzyme/photopolymer solution is described. The sensor with the patterned membrane showed linear response to glucose concentration from 0.3 to 2.2 mM and useful response up to 5 mM.     

Fabrication of a non-enzymatic glucose sensor field-effect transistor based on vertically-oriented ZnO nanorods modified with Fe2O3

Herein, we report a non-enzymatic glucose sensor field-effect transistor (FET) based on vertically-oriented zinc oxide nanorods modified with iron oxide (Fe₂O₃-ZNRs). Compared with ZnO-based non-enzymatic glucose sensors, which show poor sensing performances, modification of ZnO with Fe₂O₃ dramatically enhances the sensing behavior of the fabricated non-enzymatic FET glucose sensor due to the excellent electrocatalytic nature of Fe₂O₃. The fabricated non-enzymatic FET sensor showed excellent catalytic activity for glucose detection under optimized conditions with a linear range up to 18 mM, detection limits down to ~ 12 μM, excellent selectivity, good reproducibility and long-term stability. Moreover, the fabricated FET sensor detected glucose in freshly drawn mouse whole blood and serum samples. The developed FET sensor has practical applications in real samples and the solution-based synthesis process is cost effective.     

Study on glucose oxidase fermentation coupled with membrane dialysis

The repression of glucose oxidase (GOD) biosynthesis by catabolites during fermentation can be alleviated through membrane dialysis fermentation (MDF). The results show that the volumetric enzyme productivity of MDF was two times higher than that of the control (fermentation without dialysis), and its total enzyme activity was increased by 30–50%. The operation conditions of MDF, such as pore size of the membrane, initiating time for membrane dialysis, and volume of dialysate used, were optimized. The content of amino acids and organic acids in the fermentation broth and the dialysate in the reservoir were assessed by amino acid analyzer and ionic chromatography, respectively. The relationship among the contents of pyruvic acid, gluconic acid, and enzyme activity during fermentation was analyzed quantitatively. Furthermore, the effect of membrane dialysis technology applied to the low-yield strain was found to be more effective than that applied to the high-yield strain.     

Amperometric biosensor with physically immobilized glucose oxidase on a PVA cryogel membrane

A new method of physically immobilizing a biomolecule of analytical interest in poly(vinyl alcohol) cryogels was developed to obtain suitable biosensors. An amperometric glucose sensor was constructed using glucose oxidase immobilized on membranes obtained by a freezing-thawing cyclic process. No chemical cross-linking agent was used. Sensor behaviour was evaluated electrochemically with a hydrogen peroxide electrode. The glucose content in standard solutions was determined and linear calibration curves in the 5 x 10(-5)-3 x 10(-3) mol 1(-1) range were obtained. Temperature and pH effects on the electrochemical response were described and kinetic parameters in the immobilized system were evaluated.     

Following a protein kinase activity using a field-effect transistor device

The specific phosphorylation of a peptide-functionalized ion-sensitive field-effect transistor device by casein kinase II in the presence of ATP enables the electronic readout of the protein kinase activity; treatment of the phosphorylated surface with alkaline phosphatase results in the regeneration of the active sensing surface.     

Air-assisted high-performance field-effect transistor with thin films of picene

A field-effect transistor (FET) with thin films of picene has been fabricated on SiO2 gate dielectric. The FET showed p-channel enhancement-type FET characteristics with the field-effect mobility, mu, of 1.1 cm2 V-1 s-1 and the on-off ratio of >10(5). This excellent device performance was realized under atmospheric conditions. The mu increased with an increase in temperature, and the FET performance was improved by exposure to air or O2 for a long time. This result implies that this device is an air (O2)-assisted FET. The FET characteristics are discussed on the basis of structural topography and the energy diagram of picene thin films.     

Biosensors for determination of glucose with glucose oxidase immobilized on an eggshell membrane

A glucose biosensor using an enzyme-immobilized eggshell membrane and oxygen electrode for glucose determination has been fabricated. Glucose oxidase was covalently immobilized on an eggshell membrane with glutaraldehyde as a cross-linking agent. The glucose biosensor was fabricated by positioning the enzyme-immobilized eggshell membrane on the surface of a dissolved oxygen sensor. The detection scheme was based on the depletion of dissolved oxygen content upon exposure to glucose solution and the decrease in the oxygen level was monitored and related to the glucose concentration. The effect of glutaraldehyde concentration, pH, phosphate buffer concentration and temperature on the response of the glucose biosensor has been studied in detail. Common matrix interferents such as ethanol, d-fructose, citric acid, sodium benzoate, sucrose and l-ascorbic acid did not give significant interference. The resulting sensor exhibited a fast response (100 s), high sensitivity (8.3409 mg L⁻¹ oxygen depletion/mmol L⁻¹ glucose) and good storage stability (85.2% of its initial sensitivity after 4 months). The linear response is 1.0×10⁻⁵ to 1.3×10⁻³ mol L⁻¹ glucose. The glucose content in real samples such as commercial glucose injection preparations and wines was determined, and the results were comparable to the values obtained from a commercial glucose assay kit based on a spectrophotometric method.     

Oxidation of glucose to gluconic acid by glucose oxidase in a membrane bioreactor

Glucose oxidase (GO) (EC 1.1.3.4) was used as catalyst for oxidizing glucose into gluconic acid utilizing a 10-mL Bioengineering Enzyme Membrane Reactor® or a 400-mL Millipore Stirred Ultrafiltration Cell (MSUC) coupled with a Millipore UF membrane (cutoff of 100 kDa) and operated for 12 h under an agitation of 100 rpm, pH 5.5, and 30°C. The effect of feeding rate (0.10, 0.15, or 0.20 min^?1), glucose (2.5 or 5.0 mM), and GO (1.0 or 2.0 mg/mL) concentrations on the catalysis were studied. A yield of about 75% was attained when the MSUC filled with 1.0 mg/mL of GO was fed with 2.5 mM glucose solution at a rate of 0.15 min^?1.     

Immobilization of glucose oxidase on ZnO nanorods decorated electrolyte-gated field effect transistor for glucose detection

In this paper, we report on growth of ZnO nanorods on the surface of gold interdigital electrodes and its implementation as a conductive n-type channel for the fabrication of a liquid-gated field effect transistor. Glucose oxidase was immobilized on the surface of the ZnO nanorods and the fabricated device was used as a four-electrode glucose biosensor. The resistance of the conductive channel was affected by addition of glucose. The applied bias voltage to the gate in the fabricated device affects the channel resistance in the same manner as the increase of enzymatic products during the glucose oxidation. Large effective area, good conductivity, and biocompatibility properties of ZnO nanorods are the key features in this highly sensitive and stable biosensor. Our measurements showed that the threshold voltage of transistor was about 0.75 V. The current increased in the presence of the glucose and exhibited a dynamic linear range with the logarithm of glucose concentration in the range between 0.01 and 5 mM. The detection limit was about 3.8 μM.     

Electrocatalytic sulfite biosensor with human sulfite oxidase co-immobilized with cytochrome c in a polyelectrolyte-containing multilayer

An efficient electrocatalytic biosensor for sulfite detection was developed by co-immobilizing sulfite oxidase and cytochrome c with polyaniline sulfonic acid in a layer-by-layer assembly. QCM, UV–Vis spectroscopy and cyclic voltammetry revealed increasing loading of electrochemically active protein with the formation of multilayers. The sensor operates reagentless at low working potential. A catalytic oxidation current was detected in the presence of sulfite at the modified gold electrode, polarized at +0.1 V (vs. Ag/AgCl 1 M KCl). The stability of the biosensor performance was characterized and optimized. A 17-bilayer electrode has a linear range between 1 and 60 μM sulfite with a sensitivity of 2.19 mA M⁻¹ sulfite and a response time of 2 min. The electrode retained a stable response for 3 days with a serial reproducibility of 3.8% and lost 20% of sensitivity after 5 days of operation. It is possible to store the sensor in a dry state for more than 2 months. The multilayer electrode was used for determination of sulfite in unspiked and spiked samples of red and white wine. The recovery and the specificity of the signals were evaluated for each sample. Figure Schematic of the bioelectrocatalytic sulfite sensor: sulfite oxidase (green) oxidizes sulfite to sulfate and transfers electrons via heme b ₅ to cyt c (red) and thence to the gold electrode     

Electrokinetic flow control in microfluidic chips using a field-effect transistor

A field-effect transistor is developed to control flow in microfluidic chips by modifying the surface charge condition. In this investigation, zeta potential at a particular location is altered locally by applying a gate voltage, while zeta potential at other locations is maintained at its original value. This non-uniform zeta potential results in a secondary electroosmotic flow in the lateral direction, which is used for flow control in microgeometries. Here, microchannel structures and field-effect transistors are formed on polydimethylsiloxane (PDMS) using soft lithography techniques, and a micro particle image velocimetry technique is used to obtain high resolution velocity distribution in the controlled region. The flow control is observed at relatively low gate voltage (less than 50 V), and this local flow control is primarily due to current leakage through the interface between PDMS and glass layers. A leakage capacitance model is introduced to estimate the modified zeta potential for the straight channel case, and excellent agreement is obtained between the predicted and experimental zeta potential results. This leakage-current based field-effect is then applied to a T-channel junction to control flow in the branch channel. Experiments show that the amount of discharge in the branch channel can be controlled by modulating gate voltage.     

An optical glucose biosensor based on glucose oxidase immobilized on a swim bladder membrane

An optical glucose biosensor using a swim bladder membrane as an enzyme immobilization platform and an oxygen-sensitive membrane as an optical oxygen transducer has been developed. During the enzymatic reaction, glucose is oxidized by glucose oxidase with a concomitant consumption of dissolved oxygen resulting in an increase in the fluorescence intensity of the optical oxygen transducer. The fluorescence intensity is directly related to the glucose concentration. The effects of pH, temperature, buffer concentration, and selectivity have been studied in detail. The immobilized enzyme retained 80% of its initial activity after being kept for more than 10 months at 4°C. The glucose biosensor has been successfully applied to the determination of glucose content in human blood serum and urine samples. Martin M.F. Choi was on sabbatical leave at The University of North Carolina at Chapel Hill from July 2004 to July 2005.     

Activated platinum electrodes as transducer for a glucose sensor using glucose oxidase in a photopolymer membrane

A planar platinum electrode was covered by a photopolymer membrane containing glucose oxidase (GOD) to construct an amperometric glucose sensor. The application of a photopolymer system in membrane formation gives the opportunity to manufacture cheap biosensors with good reproducibility by means of automated techniques and to miniaturise sensors using photolithography. The electrodes were pretreated mechanically and chemically resulting in a half-wave potential (E_1/2) of the H₂O₂ oxidation shifted towards more negative potentials. This shift allows the determination of glucose at a low working potential (300 mV vs. SCE) without addition of mediators. The important advantage of such applied potential decreasing lies in minimising the interference of oxidisable substances such as uric acid, bilirubin and paracetamol. The selectivity to ascorbic acid could also be proved without the application of additional protection layers. The glucose sensor developed has a high life-time, selectivity and sensitivity and a linear working concentration range from 0.05 up to 10 mmol/l of glucose. The sensor was used for the glucose determination in human serum samples with a very good correlation to a common photometric reference method. Received: 13 July 1996 / Revised: 11 September 1996 / Accepted: 14 September 1996     

A fully integrated graphene-polymer field-effect transistor biosensing device for on-site detection of glucose in human urine

Convenient and rapid self-measurement of the glucose level in the body is of great significance for diabetics to know their health conditions in time. In view of this, a polymer functionalized graphene field-effect transistor (P-GFET) portable biosensing device is demonstrated for glucose monitoring. The polymer is synthesized by acrylamide/3-acrylamidophenylboronic acid (AAPBA)/N, N-dimethylaminopropyl acrylamide. In the presence of glucose, the P-GFET shows Dirac point shifts and current changes as a result of the covalent bond between glucose and AAPBA in the synthesized polymer on graphene. The sensitivity of this P-GFET sensor can increase while the density of AAPBA in polymer increases. The used sensor could regain the detection capability after hydrochloric acid treatment due to the reversible reaction between polymer and glucose. In addition, the chemisorption interaction between polymer and glucose, which is stronger than physisorption interaction with other objects in urine, has been supported by the density functional theory study. The P-GFET shows high sensitivity of 822 μA1cm^?21mM^?1 with a limit of detection of 1.9 μM during human urine glucose monitoring. The sensor holds a detection range of 0.04–10 mM and good reusability over 20 times. With the customized portable real-time measurement capability in urine, our P-GFET sensor can offer advantages over current glucose detection methods.     

Use of glucose oxidase in a membrane reactor for gluconic acid production

This article aims at the evaluation of the catalytic performance of glucose oxidase (GO) (EC.1.1.3.4) for the glucose/gluconic acid conversion in the ultrafiltration cell type membrane reactor (MB-CSTR). The reactor was coupled with a Millipore ultrafiltration-membrane (cutoff of 100 kDa) and operated for 24 h under agitation of 100 rpm, pH 5.5, and 30 degrees C. The experimental conditions varied were the glucose concentration (2.5, 5.0, 10.0, 20.0, and 40.0 mM), the feeding rate (0.5, 1.0, 3.0, and 6.0/h), dissolved oxygen (8.0 and 16.0 mg/L), GO concentration (2.5, 5.0, 10.0, and 20.0 U(GO)/mL), and the glucose oxidase/catalase activity ratio (U(GO)/U(CAT))(1:0, 1:10, 1:20, and 1:30). A conversion yield of 80% and specific reaction rate of 40 x 10(-4) mmol/h x U(GO) were attained when the process was carried out under the following conditions: D =3.0/h, dissolved oxygen =16.0 mg/L, [G] =40 mM, and (U(GO)/U(CAT)) =1:20. A simplified model for explaining the inhibition of GO activity by hydrogen peroxide, formed during the glucose/gluconic acid conversion, was presented.     

Frequency response of the glucose sensor based on immobilized glucose oxidase membrane

Frequency response of the glucose sensor based on the immobilized glucose oxidase membrane was investigated experimentally by giving the sinusoidal change of glucose concentration to the glucose sensor and observing its output signal. Observed values of gains and phase lags of the frequency response of the glucose sensor followed the frequency response model of the first-order with dead time; The time constant and also the dead time were estimated and found to decrease as the amount of enzyme immobilized in the membrane increased and the thickness of the membrane decreased.

     

Fabrication of polymer Langmuir-Blodgett films containing regioregular poly(3-hexylthiophene) for application to field-effect transistor

Semiconducting thin films consisting of regioregular poly(3-hexylthiophene) (RR-PHT) and poly(N-dodecylacrylamide) (pDDA) were constructed by the Langmuir-Blodgett (LB) technique. A mixture of RR-PHT and pDDA spread from a chloroform solution on a water surface forms a stable monolayer, which can be transferred onto solid substrates by the LB method, yielding a well-defined polymer LB film. Surface morphology studies of the LB film indicate that the RR-PHT is dispersed uniformly throughout the surface. The polymer thin film was chemically doped by contacting with FeCl3 acetonitrile solution, and a conductivity of 5.6 S/cm was achieved. Further, the LB film was utilized as the semiconducting film in the field-effect transistor (FET), and mobilities of 2.2 x 10(-4) and 4.4 x 10(-4) cm2 V(-1) s(-1) were obtained by analyzing the saturated and linear regions of the current-voltage characteristic, respectively.     

Alginate beads containing pH-sensitive liposomes and glucose oxidase: glucose-sensitive release

Egg PC (EPC) liposomes bearing a copolymer of N-isopropylacrylamide, methacrylic acid, and octadecylacrylate (P(NIPAM-co-MAA-co-ODA)) were prepared as pH-sensitive liposomes. They were embedded in glucose oxidase (GOD)-immobilized alginate beads. The ratio of EPC/GOD/alginate in the beads was 7.8:1.0:140.4, and the beads were added to glucose solutions so that the concentration of GOD was 0.0068 mg/ml. The enzymatic activity of the immobilized GOD was one fifth to half of that of native enzyme. As the glucose concentration increased from 0 to 400 mg/dl, the degree of calcein release increased from 17% to 75%. The acidification induced by the enzymatic reaction would be responsible for the glucose-triggered release.     

PEG-modified glucose oxidase immobilized on a PVA cryogel membrane for amperometric biosensor applications

Poly(ethylene glycol)-modified glucose oxidase was immobilized in a poly(vinyl alcohol) cryogel membrane, obtained by a freezing-thawing cyclic process, to obtain a suitable amperometric glucose sensor. The covalent linkage between PEG and GOD molecule improved the physical immobilization of enzyme in the polymeric matrix, by decreasing its loss in time. Sensor behaviour was evaluated electrochemically with a hydrogen peroxide electrode. The glucose content in standard solutions was determined and linear calibration curves in the 5x10(-5)-5x10(-3) mol l(-1) range were obtained. The kinetic parameters in the immobilized system were evaluated and analytical characteristics of sensor, including stability and influence of pH and temperature, were determined.