Glucose sensor for flow injection analysis of serum glucose based on immobilization of glucose oxidase in titania sol-gel membrane

A novel amperometric glucose sensor was constructed by immobilizing glucose oxidase (GOD) in a titania sol-gel film, which was prepared with a vapor deposition method. The sol-gel film was uniform, porous and showed a very low mass transport barrier and a regular dense distribution of GOD. Titania sol-gel matrix retained the native structure and activity of entrapped enzyme and prevented the cracking of conventional sol-gel glasses and the leaking of enzyme out of the film. With ferrocenium as a mediator the glucose sensor exhibited a fast response, a wide linear range from 0.07 to 15 mM. It showed a good accuracy and high sensitivity as 7.2 microA cm(-2) mM(-1). The general interferences coexisted in blood except ascorbic acid did not affect glucose determination, and coating Nafion film on the sol-gel film could eliminate the interference from ascorbic acid. The serum glucose determination results obtained with a flow injection analysis (FIA) system showed an acceptable accuracy, a good reproducibility and stability and indicated the sensor could be used in FIA determination of glucose. The vapor deposition method could fabricate glucose sensor in batches with a very small amount of enzyme.     

Amperometric glucose biosensors based on layer-by-layer assembly of chitosan and glucose oxidase on the Prussian blue-modified gold electrode

A glucose biosensor based on layer-by-layer (LBL) self-assembling of chitosan and glucose oxidase (GOD) on a Prussian blue film was developed. First, Prussian blue was deposited on a cleaned gold electrode then chitosan and GOD were assembled alternately to construct a multilayer film. The resulting amperometric glucose biosensor exhibited a fast response time (within 10 s) and a linear calibration range from 6 μM to 1.6 mM with a detection limit of 3.1 μM glucose (s/n = 3). With the low operating potential, the biosensor showed little interference to the possible interferents, including ascorbic acid, acetaminophen and uric acid, indicating an excellent selectivity.     

Covalent conjugation of avidin with dye-doped silica nanopaticles and preparation of high density avidin nanoparticles as photostable bioprobes

A sensitive, selective and stable amperometric glucose biosensor employing novel PtPd bimetallic nanoparticles decorated on multi-walled carbon nanotubes (PtPd-MWCNTs) was investigated. PtPd-MWCNTs were prepared by a modified Watanabe method, and characterized by XRD and TEM. The biosensor was constructed by immobilizing the PtPd-MWCNTs catalysts in a Nafion film on a glassy carbon electrode. An inner Na?on film coating was used to eliminate common interferents such as uric acid, ascorbic acid and fructose. Finally, a highly porous surface with an orderly three-dimensional network enzyme layer (CS-GA-GOx) was fabricated by electrodeposition. The resulting biosensor exhibited a good response to glucose with a wide linear range (0.062-14.07 mM) and a low detection limit 0.031 mM. The biosensor also showed a short response time (within 5 s), and a high sensitivity (112 μA mM(-1)cm(-2)). The Michaelis-Menten constant (K(m)) was determined as 3.3 mM. In addition, the biosensor exhibited high reproducibility, good storage stability and satisfactory anti-interference ability. The applicability of the biosensor to actual serum sample analysis was also evaluated.     

Amperometric glucose biosensor based on adsorption of glucose oxidase at platinum nanoparticle-modified carbon nanotube electrode

A new amperometric biosensor, based on adsorption of glucose oxidase (GOD) at the platinum nanoparticle-modified carbon nanotube (CNT) electrode, is presented in this article. CNTs were grown directly on the graphite substrate. The resulting GOD/Pt/CNT electrode was covered by a thin layer of Nafion to avoid the loss of GOD in determination and to improve the anti-interferent ability. The morphologies and electrochemical performance of the CNT, Pt/CNT, and Nafion/GOD/Pt/CNT electrodes have been investigated by scanning electron microscopy, cyclic voltammetry, and amperometric methods. The excellent electrocatalytic activity and special three-dimensional structure of the enzyme electrode result in good characteristics such as a large determination range (0.1-13.5mM), a short response time (within 5s), a large current density (1.176 mA cm(-2)), and high sensitivity (91mA M(-1)cm(-2)) and stability (73.5% remains after 22 days). In addition, effects of pH value, applied potential, electrode construction, and electroactive interferents on the amperometric response of the sensor were investigated and discussed. The reproducibility and applicability to whole blood analysis of the enzyme electrode were also evaluated.     

A mediator-free glucose biosensor based on glucose oxidase/chitosan/α-zirconium phosphate ternary biocomposite

A novel glucose oxidase/chitosan/α-zirconium phosphate (GOD/chitosan/α-ZrP) ternary biocomposite was prepared by co-intercalating glucose oxidase (GOD) and chitosan into the interlayers of α-zirconium phosphate (α-ZrP) via a delamination–reassembly procedure. The results of X-ray diffraction, infrared spectroscopy, circular dichroism, and ultraviolet spectrum characterizations indicated not only the layered and hybrid structure of the GOD/chitosan/α-ZrP ternary biocomposite but also the recovered activity of the intercalated GOD improved by the co-intercalated chitosan. By depositing the GOD/chitosan/α-ZrP biocomposite film onto a glassy carbon electrode, the direct electrochemistry of the intercalated GOD was achieved with a fast electron transfer rate constant, k_s, of 7.48 ± 3.52 s⁻¹. Moreover, this GOD/chitosan/α-ZrP biocomposite modified electrode exhibited a sensitive response to glucose in the linear range of 0.25–8.0 mM (R = 0.9994, n = 14), with a determination limit of 0.076 mM.     

Amperometric glucose sensor based on coimmobilization of glucose oxidase and Poly(p-phenylenediamine) at a platinum microdisk electrode

A miniaturized glucose biosensor in which glucose oxidase (GOD) and poly(p-phenylenediamine) (poly-PPD) were coimmobilized at the surface of a platinum microdisk electrode was developed and used successfully for amperometric determination of glucose. The performance of sensors prepared at different monomer concentrations and polymerization potentials with different media was investigated in detail. It was found that similarly to poly(o-phenylenediamine) (poly-OPD), (poly-PPD) noticeably eliminated the electrochemical interference of ascorbic acid, uric acid, and l-cysteine. The amperometric response of glucose with the biosensor under optimal conditions exhibited a linear relationship in the range of 5.0 x 10(-5) to 3.0 x 10(-3) M with correlation coefficient 0.9995. According to the Michaelis-Menten equation, the apparent Michaelis constant for glucose and the maximum steady-state current density of the poly-PPD/GOD-modified microelectrode were 3.94 mM and 607.5 microA cm(-2), respectively. The current density of the sensor responding to glucose in the linear range can reach 160 microA cm(-2) mM(-1), which is far greater than that obtained using poly-OPD and poly(phenol) film. In addition, the stability of the sensor was examined over a 2-month period.     

Biosensor based on polyaniline-Prussian Blue/multi-walled carbon nanotubes hybrid composites

In this work, a novel route for fabrication polyaniline (PANI)-Prussian Blue (PB) hybrid composites is proposed by the spontaneous redox reaction in the FeCl(3)-K(3)[Fe(CN)(6)] and the aniline solution. With the introduction of multi-walled carbon nanotubes (MWNTs), the PANI-PB/MWNTs system shows synergy between the PANI-PB and MWNTs which amplified the H(2)O(2) sensitivity greatly. A linear range from 8 x1 0(-8) to 1 x 10(-5)M and a high sensitivity 508.1 8 microA microM cm(2) for H(2)O(2) detection are obtained. The composites also show good stability in neutral solution. A glucose biosensor was further constructed by immobilizing glucose oxidase (GOD) with Nafion and glutaraldehyde on the electrode surface. The performance factors influencing the resulted biosensor were studied in detail. The biosensor exhibits excellent response performance to glucose with the linear range from 1 to 11 mM and a detection limit of 0.01 mM. Furthermore, the biosensor shows rapid response, high sensitivity, good reproducibility, long-term stability and freedom of interference from other co-existing electroactive species.     

Fabrication of ultra-thin polypyrrole-glucose oxidase film from supporting electrolyte-free monomer solution for potentiometric biosensing of glucose

A simple electropolymerisation process is described for the fabrication of an ultra-thin ( approximately 55 nm) polypyrrole (PPy)-glucose oxidase (GOD) film in a supporting electrolyte-free monomer solution for potentiometric biosensing of glucose. The optimum conditions for growing the ultra-thin film include 0.1 M pyrrole, 55-110 U/ml GOD, an applied current density of 0.05 mA/cm(2) and an electrical charge of 25 mC/cm(2). Long-term storage of the biosensor in acetate buffer improved the sensitivity of the biosensor by a factor of approximately two. The biosensor can also be used repeatedly for over 2 months with little or no loss in sensitivity. The interference effect of ascorbic acid was successfully reduced by inclusion of an outer PPy-Cl layer.     

A noninterference polypyrrole glucose biosensor

In order to eliminate the interference of impurities, such as ascorbic acid, a noninterference polypyrrole glucose biosensor was constructed with a four-electrode cell consisting of a polypyrrole film electrode, a polypyrrole-glucose oxidase electrode, a counter electrode and a reference electrode. The pure catalytic current of glucose oxidase (GOD) can be obtained from the difference between response currents of two working electrodes with and without GOD. The effects of potential, pH and temperature on analytical performance of the glucose biosensor were discussed. The optimum pH and apparent activation energy of enzyme-catalyzed reaction are 5.5 and 25 kJ mol(-1), respectively. The response current of the biosensor increases linearly with the increasing glucose concentration from 0.005 to 20.0 mmol dm(-3). The results show the glucose biosensor with under 2% of relative deviation has good ability of anti-interference. The glucose biosensor was also characterized with FT-IR and UV-vis spectra.     

Reagentless glucose biosensor based on direct electron transfer of glucose oxidase immobilized on colloidal gold modified carbon paste electrode

The direct electrochemistry of glucose oxidase (GOD) adsorbed on a colloidal gold modified carbon paste electrode was investigated. The adsorbed GOD displayed a pair of redox peaks with a formal potential of -(449+/-1) mV in 0.1 M pH 5.0 phosphate buffer solution. The response showed a surface-controlled electrode process with an electron transfer rate constant of (38.9+/-5.3)/s determined in the scan rate range from 10 to 100 mV/s. GOD adsorbed on gold colloid nanoparticles maintained its bioactivity and stability. The immobilized GOD could electrocatalyze the reduction of dissolved oxygen and resulted in a great increase of the reduction peak current. Upon the addition of glucose, the reduction peak current decreased, which could be used for glucose detection with a high sensitivity (8.4 microA/mM), a linear range from 0.04 to 0.28 mM and a detection limit of 0.01 mM at a signal-to-noise ratio of 3sigma. The sensor could exclude the interference of commonly coexisted uric and ascorbic acid.     

Immobilization and direct electrochemistry of glucose oxidase on a tetragonal pyramid-shaped porous ZnO nanostructure for a glucose biosensor

A tetragonal pyramid-shaped porous ZnO (TPSP-ZnO) nanostructure is used for the immobilization, direct electrochemistry and biosensing of proteins. The prepared ZnO has a large surface area and good biocompatibility. Using glucose oxidase (GOD) as a model, this shaped ZnO is tested for immobilization of proteins and the construction of electrochemical biosensors with good electrochemical performances. The interaction between GOD and TPSP-ZnO is examined by using AFM, N(2) adsorption isotherms and electrochemical methods. The immobilized GOD at a TPSP-ZnO-modified glassy carbon electrode shows a good direct electrochemical behavior, which depends on the properties of the TPSP-ZnO. Based on a decrease of the electrocatalytic response of the reduced form of GOD to dissolved oxygen, the proposed biosensor exhibits a linear response to glucose concentrations ranging from 0.05 to 8.2mM with a detection limit of 0.01mM at an applied potential of -0.50V which has better biosensing properties than those from other morphological ZnO nanoparticles. The biosensor shows good stability, reproducibility, low interferences and can diagnose diabetes very fast and sensitively. Such the TPSP-ZnO nanostructure provides a good matrix for protein immobilization and biosensor preparation.     

Fabrication of bienzyme nanobiocomposite electrode using functionalized carbon nanotubes for biosensing applications

Mediated biosensors consisting of an oxidase and peroxidase (POx) have attracted increasing attention because of their wider applicability. This work presents a novel approach to fabricate nanobiocomposite bienzymatic biosensor based on functionalized multiwalled carbon nanotubes (MWNTs) with the aim of evaluating their ability as sensing elements in amperometric transducers. Electrochemical behavior of the bienzymatic nanobiocomposite biosensor is investigated by Faradaic impedance spectroscopy and cyclic voltammetry. The results indicate that glucose oxidase (GOD) and horseradish peroxidase (HRP) are strongly adsorbed on the surface of the thionin (TH) functionalized MWNTs and demonstrate a facile electron transfer between immobilized GOD/HRP and the electrode via the functionalized MWNTs in a Nafion film. The functionalized carbon nanotubes act as molecular wires to allow efficient electron transfer between the underlying electrode and the redox centres of enzymes through TH. Linear ranges for these electrodes are from 10 nM to 10 mM for glucose and 17 nM to 56 mM for hydrogen peroxide with the detection limit of 3 and 6 nM, respectively. A remarkable feature of the bienzyme electrode is the possibility to determine glucose and hydrogen peroxide at a very low applied potential where the noise level and interferences from other electroactive compounds are minimal. Performance of the biosensor is evaluated with respect to response time, detection limit, selectivity, temperature and pH as well as operating and storage stability.     

A contact lens with embedded sensor for monitoring tear glucose level

We report the design, construction, and testing of a contact lens with an integrated amperometric glucose sensor, proposing the possibility of in situ human health monitoring simply by wearing a contact lens. The glucose sensor was constructed by creating microstructures on a polymer substrate, which was subsequently shaped into a contact lens. Titania sol-gel film was applied to immobilize glucose oxidase, and Nafion? was used to decrease several potential interferences (ascorbic acid, lactate, and urea) present in the tear film. The sensor exhibits a fast response (20s), a high sensitivity (240 μA cm(-2) mM(-1)) and a good reproducibility after testing a number of sensors. It shows good linearity for the typical range of glucose concentrations in the tear film (0.1-0.6 mM), and acceptable accuracy in the presence of interfering agents. The sensor can attain a minimum detection of less than 0.01 mM glucose.     

Enhanced direct electrochemistry of glucose oxidase and biosensing for glucose via synergy effect of graphene and CdS nanocrystals

Integrating graphene-based composites with enzyme provides a potent strategy to enhance biosensor performance due to their unique physicochemical properties. Herein we report on the utilization of graphene-CdS (G-CdS) nanocomposite as a novel immobilization matrix for the enzymes, which glucose oxidase (GOD) was chosen as model enzyme. In comparison with the graphene sheet and CdS nanocrystal, G-CdS nanocomposite exhibited excellent electron transfer properties for GOD with the rate constant (k(s)) of 5.9 s(-1) due to the synergy effect of graphene sheet and CdS nanocrystals. Further, based on the decrease of the electrocatalytic response of the reduced form of GOD to dissolved oxygen, the obtained glucose biosensor displays satisfactory analytical performance over an acceptable linear range from 2.0 to 16 mM with a detection limit of 0.7 mM, and also prevents the effects of interfering species, which is suitable for glucose determination by real samples. These results mean that this immobilization matrix not only can be used for immobilizing GOD, but also can be extended to other enzymes and bioactive molecules, thus providing a promising platform for the development of biosensors.     

A glucose biosensor based on chitosan-glucose oxidase-gold nanoparticles biocomposite formed by one-step electrodeposition

An amperometric biosensor for the quantitative measurement of glucose is reported. The biosensor is based on a biocomposite that is homogeneous and easily prepared. This biocomposite is made of chitosan hydrogel, glucose oxidase, and gold nanoparticles by a direct and facile electrochemical deposition method under enzyme-friendly conditions. The resulting biocomposite provided a shelter for the enzyme to retain its bioactivity at considerably extreme conditions, and the decorated gold nanoparticles in the biocomposite offer excellent affinity to enzyme. The biosensor exhibited a rapid response (within 7s) and a linear calibration range from 5.0 microM to 2.4 mM with a detection limit of 2.7 microM for the detection of glucose. The combination of gold nanoparticles affinity and the promising feature of the biocomposite with the onestep nonmanual technique favor the sensitive determination of glucose with improved analytical capabilities.     

A glucose biosensor based on electrodeposition of palladium nanoparticles and glucose oxidase onto Nafion-solubilized carbon nanotube electrode

Electrodeposition was used for the co-deposition of glucose oxidase (GOx) enzymes and palladium nanoparticles onto a Nafion-solubilized carbon nanotube (CNT) film. The co-deposited Pd-GOx-Nafion CNT bioelectrode retains its biocatalytic activity and offers an efficient oxidation and reduction of the enzymatically liberated H2O2, allowing for fast and sensitive glucose quantification. The combination of Pd-GOx electrodeposition with Nafion-solubilized CNTs enhances the storage time and performance of the sensor. An extra Nafion coating was used to eliminate common interferents such as uric and ascorbic acids. The fabricated Pd-GOx-Nafion CNT glucose biosensor exhibits a linear response up to 12 mM glucose and a detection limit of 0.15 mM (S/N = 3).     

A metal dispersed sol-gel biocomposite amperometric glucose biosensor

A new glucose biosensor has been fabricated by immobilizing glucose oxidase into a copper dispersed sol-gel derived ceramic-graphite composite. The copper in the biocomposite offers excellent electrocatalytic activity towards the reduction (at -0.2 V) as well as oxidation (at +0.45 V) of hydrogen peroxide liberated in the enzymatic reaction enabling sensitive and selective determination of glucose. A linear response to glucose in the concentration range between 2.7 x 10(-5) to 4.0 x 10(-3) M with a correlation coefficient of 0.9987 and 4.0 x 10(-5) to 5.6 x 10(-3) M with a correlation coefficient of 0.9989 were observed with the electrocatalytic reduction and oxidation, respectively. Ascorbic acid and uric acid did not interfere with the glucose measurement during catalytic reduction at -0.2 V, a Nafion membrane was used to eliminate these interferences during the electrocatalytic oxidation at +0.45 V. The combination of copper catalysis and the promising feature of sol-gel biocomposite favor the sensitive and selective determination of glucose with improved analytical capabilities.     

Direct electrochemistry and electrocatalysis of glucose oxidase immobilized on glassy carbon electrode modified by Nafion and ordered mesoporous silica-SBA-15

In this paper, it was found that glucose oxidase (GOD) has been stably immobilized on glassy carbon electrode modified by ordered mesoporous silica-SBA-15 and Nafion. The sorption behavior of GOD immobilized on SBA-15 matrix was characterized by transmission electron microscopy (TEM), ultraviolet–visible (UV–vis), FTIR, respectively, which demonstrated that SBA-15 can facilitate the electron exchange between the electroactive center of GOD and electrode. The direct electrochemistry and electrocatalysis behavior of GOD on modified electrode were characterized by cyclic voltammogram (CV) which indicated that GOD immobilized on Nafion and SBA-15 matrices displays direct, nearly reversible and surface-controlled redox reaction with an enhanced electron transfer rate constant of 3.89 s⁻¹ in 0.1 M phosphate buffer solution (PBS) (pH 7.12). Furthermore, it was also discovered that, in the absence of O₂, GOD immobilized on Nafion and SBA-15 matrices can produce a wide linear response to glucose in the positive potential range. Thus, Nafion/GOD-SBA-15/GC electrode is hopeful to be used in the third non-mediator's glucose biosensor. In addition, GOD immobilized on SBA-15 and Nafion matrices possesses an excellent bioelectrocatalytic activity for the reduction of O₂. The Nafion/GOD-SBA-15/GC electrode can be utilized as the cathode in biofuel cell.     

Direct electrochemistry of glucose oxidase and biosensing for glucose based on boron-doped carbon nanotubes modified electrode

Due to their unique physicochemical properties, doped carbon nanotubes are now extremely attractive and important nanomaterials in bioanalytical applications. In this work, selecting glucose oxidase (GOD) as a model enzyme, we investigated the direct electrochemistry of GOD based on the B-doped carbon nanotubes/glassy carbon (BCNTs/GC) electrode with cyclic voltammetry. A pair of well-defined, quasi-reversible redox peaks of the immobilized GOD was observed at the BCNTs based enzyme electrode in 0.1M phosphate buffer solution (pH 6.98) by direct electron transfer between the protein and the electrode. As a new platform in glucose analysis, the new glucose biosensor based on the BCNTs/GC electrode has a sensitivity of 111.57 microA mM(-1)cm(-2), a linear range from 0.05 to 0.3mM and a detection limit of 0.01mM (S/N=3). Furthermore, the BCNTs modified electrode exhibits good stability and excellent anti-interferent ability to the commonly co-existed uric acid and ascorbic acid. These indicate that boron-doped carbon nanotubes are the good candidate material for the direct electrochemistry of the redox-active enzyme and the construction of the related enzyme biosensors.     

Simultaneous determination of the monoamine neurotransmitters and glucose in rat brain by microdialysis sampling coupled with liquid chromatography-dual electrochemical detector

A new type of chemically modified electrode based ring-disk electrode as the dual electrochemical detector (DECD) for high-performance liquid chromatography (HPLC) to simultaneously determine the monoamine neurotransmitters and glucose is described. The ring electrode was modified with an ion-exchange polymer-overoxidized polypyrrole (OPPy) and the disk electrode was modified with nano Au colloid and glucose oxidase (GOD). The electrochemical behaviors of dopamine (DA) and ascorbic acid (AA) at the OPPy chemically modified electrode (CME) were investigated by differential pulse voltammetry (DPV). It was found that the CME could permeate dopamine cations and repelled the ascorbate anions, which could be used to determine the monoamine neurotransmitters and avoid the interference of AA. The electrochemical behavior of glucose at the Nafion/GOD-Au colloid/GC CME was investigated by amperometry and flow injection analysis (FIA). It was found that the sensitivity of the CME increased apparently in determination of glucose. In order to obtain better separation and current responses of the analytes in HPLC-DECD, several operational parameters have been investigated. Under the optimum conditions, the method showed good stability and reproducibility. The application of this method coupled with microdialysis sampling for in vivo simultaneous determination of monoamine neurotransmitters and glucose in rat brain was satisfactory.