Mesoporous MnO2 as enzyme immobilization host for amperometric glucose biosensor construction

Mesoporous MnO₂ (mesoMnO₂) is synthesized facilely through sol–gel process using nonionic surfactant polyxyethylene fatty alcohol (AEO₉) as template. Transmission electron microscopy (TEM) image and N₂ adsorption/desorption isotherm show that the obtained mesoMnO₂ material presents disordered porous structure and appropriate pore size suitable for the immobilization of glucose oxidase (GOx). An amperometric glucose biosensor based on GOx entrapped in mesoMnO₂ is fabricated, in which mesoMnO₂ also acts as a catalyst for the electrochemical oxidation of H₂O₂ produced by enzyme reaction. The biosensor shows fast and sensitive current response to glucose in the linear range of 0.0009–2.73 mM. The response time (t_95%) is less than 7 s. The sensitivity and detection limit are 24.2 μA cm⁻² mM⁻¹ and 1.8 × 10⁻⁷ M (S/N = 3), respectively. This indicates that mesoMnO₂ has promising application in enzyme immobilization and biosensor construction.     

Size dependence of SiO2 particles enhanced glucose biosensor

A wide size range of SiO₂ particles were synthesized and were used as enzyme immobilization carriers to fabricate glucose biosensors. The size of the particles was in the range of 17-520 nm. These biosensors could be operated under physiological conditions (0.1 M phosphate buffer, pH 7.2). Particle size could affect the performance of SiO₂ modified glucose biosensors drastically. The smaller particles had higher performance. The smallest SiO₂ modified biosensor could work well in the glucose concentration range of 0.02-10 mM with a correlation coefficient of 0.9993. Its sensitivity was 2.08 μA/mM and the detection limit was 1.5 μM glucose.     

Bicontinuous gyroidal mesoporous carbon matrix for facilitating protein electrochemical and bioelectrocatalytic performances

A strategy of protein-entrapment in bicontinuous gyroidal mesoporous carbon (BGMC) nanocomposite films is described. Herein, the quasi-reversible electron transfer of redox proteins (such as glucose oxidase and myoglobin) is probed and the associated biocatalytic activity is revealed. The apparent heterogeneous electron transfer rate constant of the immobilized glucose oxidase is up to 9.4 s⁻¹, much larger than those in carbon nanotubes and some conventional mesoporous carbons. The BGMC based glucose biosensor enables the determination of glucose at a potential of 0.6 V (vs. SCE). Its detection limit is 1.0 × 10⁻⁵ M (signal-to-noise ratio, S/N = 3), the linear response is up to 7.49 mM and the detection sensitivity is 52.5 nA mM⁻¹ Furthermore, a series of BGMCs with different pore sizes is designed and synthesized using sucrose or phenol formaldehyde resin to study the influences of pore sizes and carbon sources on the immobilization of redox proteins and on the heterogeneous electron transfer.     

Development of amperometric glucose biosensor through immobilizing enzyme in a Pt nanoparticles/mesoporous carbon matrix

Pt nanoparticles were deposited on mesoporous carbon material CMK-3. Glucose oxidase (GOx) was immobilized in the resulting Pt nanoparticles/mesoporous carbon (Pt/CMK-3) matrix, and then the mixture was cast on a glassy carbon electrode (GCE) using gelatin as a binder. The glucose biosensor exhibited excellent current response to glucose after cross-linking with glutaraldehyde. At 0.6V (vs. SCE) the response current was linear to glucose concentration in the range of 0.04-12.2mM. The response time (time for achieving 95% of the maximum current) was 15s and the detection limit (S/N=3) was 1 microM. The Michaelis-Menten constant (K(m)(app)) and the maximum current density (i(max)) were 10.8 mM and 908 microAcm(-2), respectively. The activation energy of the enzymatic reaction was estimated to be 22.54 kJ mol(-1). The biosensor showed good stability. It achieved the maximum response current at about 52 degrees C and retained 95.1% of its initial response current after being stored for 30 days. In addition, some fabrication and operation parameters for the biosensor were optimized in this work. The biosensor was used to monitor the glucose levels of serum samples after being covered with an extra Nafion film to improve its anti-interferent ability and satisfied results were obtained.     

Electrochemistry and biosensing of glucose oxidase based on mesoporous carbons with different spatially ordered dimensions

A strategy of protein entrapment within mesoporous carbon matrices is demonstrated to probe the electrochemistry of glucose oxidase. Large surface area and remarkable electro-catalytic properties of carbon mesoporous materials make them suitable candidates for high loading of protein molecules and the promotion of heterogeneous electron transfer. In this work, two kinds of mesoporous carbon nanocomposite films were designed and prepared with highly ordered two-dimensional (2D) and three-dimensional (3D) structures for the immobilization of glucose oxidase, in which the quasi-reversible electron transfer of the redox enzyme was probed, and the apparent heterogeneous electron transfer rate constants () are 3.9 and 4.2 s⁻¹, respectively. Furthermore, the associated biocatalytic activity was also revealed. Highly ordered 3D-mesoporous carbon material exhibited larger adsorption capacity for glucose oxidase and the immobilized enzymes retained a higher bioactivity compared with 2D-mesoporous carbons. The preparation of protein-entrapped mesoporous carbon nanocomposites expands the scope of carbon-based electrochemical devices and opens a new avenue for the development of biosensors.     

Immobilization of glucose oxidase on the films prepared by electrochemical copolymerization of pyrrole and 1-(2-carboxyethyl)pyrrole for glucose sensing

Glucose oxidase (GOx) was immobilized through amide linkages on the surfaces of the conducting polymer films prepared by electrochemical copolymerization of pyrrole (Py) and 1-(2-carboxyethyl)pyrrole (Py-COOH) for the purpose of fabricating GOx-immobilized electrodes for amperometric sensing of glucose. The conductivity of the copolymer film was in the range 10⁻⁸-10⁻³ S/cm and showed a tendency to decrease with increasing content of Py-COOH units in the copolymer. The amount of immobilized GOx increased significantly with increasing content of Py-COOH units in the copolymer film up to 30%, and showed a tendency to level off when the content of Py-COOH units became larger. The activity of immobilized GOx per area of the copolymer film decreased slightly with increasing content of Py-COOH units in the copolymer. Although the GOx-immobilized copolymer films gave the amperometric response to glucose depending on its concentration, the magnitude of the response to a given concentration was found to decrease with increasing content of Py-COOH units in the copolymer. The variation in the amperometric response was attributed to the difference in conductivity of the copolymer film. The appropriate content of Py-COOH units in the copolymer was considered to be 5% or less for the amperometric sensing of glucose with the GOx-immobilized copolymer film.     

An amperometric glucose biosensor constructed by immobilizing glucose oxidase on titanium-containing mesoporous composite material of no. 41 modified screen-printed electrodes

We have constructed a glucose biosensor by immobilizing glucose oxidase (GOD) on titanium-containing MCM-41 (Ti-MCM-41) modified screen-printed electrodes. The strategy of the sensing method is to monitor the extent of the decrease of the reduction current of O₂ upon adding glucose at a selected potential. The detection can be done at the applied potential of −0.50 V and can efficiently exclude the interference from commonly coexisted substances. The constructed sensor has a high sensitivity to glucose (5.4 mAM⁻¹ cm⁻²) and a linear response range of 0.10-10.0 mM. The detection limit is 0.04 mM at a signal-to-noise ratio of 3. The sensor also shows high stability and remains its catalytic activity up to 60 °C. The biocompatibility of Ti-MCM-41 means 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.     

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.     

Glucose biosensing based on the highly efficient immobilization of glucose oxidase on a Prussian blue modified nanostructured Au surface

We report on a novel glucose biosensor based on the immobilization of glucose oxidase (GOx) on a Prussian blue modified nanoporous gold surface. The amperometric glucose biosensor fabricated in this study exhibits a fast response and the very low detection limit of 2.5 μM glucose. The sensitivity of the biosensor was found to be very high, 177 μA/mM; the apparent Michaelis–Menten constant is calculated to be 2.1 mM. In addition, the biosensor has good reproducibility and remains stable over 60 days. The anti-interference ability of the biosensor was also assessed, showing little interference from possible interferents such as ascorbic acid (AA), acetaminophen (AP) and uric acid (UA).     

Ennoblement of stainless steel in the presence of glucose oxidase: nature and role of interfacial processes

The ennoblement of the free corrosion potential (E(corr)) of AISI 316L stainless steel which did not occur in synthetic fresh water (SFW), was observed after introduction of glucose oxidase (Gox) and glucose, or of hydrogen peroxide (H(2)O(2)). The composition of the surface was monitored using AFM and XPS, a detailed XPS analysis being based on the discrimination between oxygen of organic and inorganic nature proposed in a previous study. In H(2)O(2) medium, the main changes regarding the inorganic phase were the increase of the oxygen concentration in the passive film, the increase of the molar concentration ratio of oxidized species Fe(ox)/Cr(ox) and the growth of nanoparticles, presumably made of ferric oxide/hydroxide. In Gox medium, no significant changes were observed in both oxygen concentration and Fe(ox)/Cr(ox) ratio, but the density of colloidal particles decreased, indicating a dissolution of Fe oxide/hydroxide under the influence of gluconate. In contrast with H(2)O(2), in SFW and Gox the amount of organic compounds increased due to the accumulation of polysaccharides and proteins. The influence of glucose oxidase on the ennoblement of stainless steel is not due to indirect effects of H(2)O(2) through the change of surface composition. The E(corr) ennoblement seems to be directly due to the presence of H(2)O(2) and to the electrochemical behavior of H(2)O(2) and related oxygen species. This consideration is important for understanding and controlling microbial influenced corrosion.     

Characterization of gold nanoparticles electrochemically deposited on amine-functioned mesoporous silica films and electrocatalytic oxidation of glucose

This study reports the preparation and characterization of gold nanoparticles deposited on amine-functioned hexagonal mesoporous silica (NH₂–HSM) films and the electrocatalytic oxidation of glucose. Gold nanoparticles are fabricated by electrochemically reducing chloroauric acid on the surface of NH₂–HSM film, using potential step technology. The gold nanoparticles deposited have an average diameter of 80 nm and show high electroactivity. Prussian blue film can form easily on them while cycling the potential between −0.2 and 0.6 V (vs saturated calomel electrode) in single ferricyanide solution. The gold nanoparticles loading NH₂–HSM-film-coated glassy carbon electrode (Au–NH₂–HSM/GCE) shows strong catalysis to the oxidation of glucose, and according to the cathodic oxidation peak at about 0.16 V, the catalytic current is about 2.5 μA mM⁻¹. Under optimized conditions, the peak current of the cathodic oxidation peak is linear to the concentration of glucose in the range of 0.2 to 70 mM. The detection limit is estimated to be 0.1 mM. In addition, some electrochemical parameters about glucose oxidation are estimated.     

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.     

Synthesis and photocatalytic activity for water-splitting reaction of nanocrystalline mesoporous titania prepared by hydrothermal method

Nanocrystalline mesoporous TiO₂ was synthesized by hydrothermal method using titanium butoxide as starting material. XRD, SEM, and TEM analyses revealed that the synthesized TiO₂ had anatase structure with crystalline size of about 8 nm. Moreover, the synthesized titania possessed a narrow pore size distribution with average pore diameter and high specific surface area of 215 m²/g. The photocatalytic activity of synthesized TiO₂ was evaluated with photocatalytic H₂ production from water-splitting reaction. The photocatalytic activity of synthesized TiO₂ treated with appropriate calcination temperature was considerably higher than that of commercial TiO₂ (Ishihara ST-01). The utilization of mesoporous TiO₂ photocatalyst with high crystallinity of anatase phase promoted great H₂ production. Furthermore, the reaction temperature significantly influences the water-splitting reaction.     

Glucose biosensors based on the immobilization of copper oxide and glucose oxidase within a carbon paste matrix

The performance of amperometric glucose biosensors based on the dispersion of glucose oxidase (GOx) and copper oxide within a classical carbon (graphite) paste composite is reported in this work. Copper oxide promotes an excellent electrocatalytic activity towards the oxidation and reduction of hydrogen peroxide, allowing a large decrease in the oxidation and reduction overpotentials, as well as an important enhancement of the corresponding currents. Therefore, it is possible to perform the glucose biosensing at low potentials where there is no interference even in large excess of ascorbic acid, uric acid or acetaminophen. The influence of the copper oxide and glucose oxidase content in the paste on the analytical performance of the bioelectrode is discussed. The resulting biosensor shows a fast response, a linear relationship between current and glucose concentration up to 1.35 × 10⁻² M (2.43 g L⁻¹) and a detection limit of 2.0 × 10⁻⁵ M. The effect of the presence of the enzyme in the composite material on the dispersion of the copper oxide particles is also discussed.     

蜘蛛丝素和聚乙烯醇固定葡萄糖氧化酶 制备葡萄糖传感器

用蜘蛛丝素和聚乙烯醇的混合材料把葡萄糖氧化酶固定在氧电极表面,制成葡萄糖氧化酶电极。传感器对葡萄糖有灵敏的响应,平均响应时间为20s,电位变化值与葡萄糖浓度在3.0×10     

Thermal degradation of iron chelate complexes adsorbed on mesoporous silica and alumina

Nanometric Fe₂O₃ particles could be inserted inside the internal pore volume of SBA-15 mesoporous silica and mesoporous alumina supports, when Fe(III) chelates (EDTA, gluconate or citrate) were used as impregnating precursors. The oxidative degradation of the chelating anions was followed by combined TG-DTA. Strong chelate-SiOH interactions (case of bulky EDTA), favored by the mesopore curvature, yield sub-nanometric extremely well dispersed Fe₂O₃ particles preferentially located at the micropore mouths (confinement effect). Fe₂O₃ even more strongly interacts with alumina walls, generating either (Fe,Al)₂O₃ mixed phases or Fe-aluminate micro domains. These iron-based mesoporous alumina composites proved very active catalysts in total oxidation of phenol at ambient conditions, with extremely low iron leaching (0.2%).     

Monitoring of glucose and glutamate using enzyme microstructures and scanning electrochemical microscopy

Glucose oxidase and glutamate oxidase lines, with typical width of 100 µm, were patterned on gold surfaces using a micro-dispensing system, by shooting 100 pl droplets of the corresponding enzyme solutions. The probe of a scanning electrochemical microscope (SECM) was then carefully positioned in the close proximity of the enzyme microstructure and poised to + 600 mV vs. Ag/AgCl, KCl 0.1 M. The H₂O₂, generated by the enzyme lines at different concentrations of glucose and glutamate in the surrounding solution, was sequentially monitored. Reproducible calibration curves for glucose and glutamate were obtained in one single experiment, proving that the combination of enzyme microstructures with SECM can provide a new way of achieving multianalyte detection.     

Incorporation of Znq2 complexes into mesoporous silica and their transparent polymer luminescent nanocomposites

Znq₂-functionalized colloidal mesoporous silicas (Znq₂-CMS)/polymer transparent nanocomposites were prepared by in situ bulk polymerization. CMS nanoparticles or nanorods with hydroxyl-, mercapto- and sulfonic-functionalized interiors were obtained by different synthetic routes in the nanosize dimensions between 50 and 500 nm. The luminescent Znq₂ complex was successfully introduced in the pores of different mesoporous silicas by chemical adsorption as the driving force. The different internal circumstances of mesoporous silicas had an obvious effect on the luminescence and lifetime of Znq₂ complex. The transparent fluorescent nanocomposites were fabricated from different Znq₂-CMS and suitable monomers. The Znq₂-CMS were uniformly dispersed in the polymer matrix without evident aggregation. The photoluminescence properties of Znq₂-CMS in the transparent matrix exhibited a dependence on the inner surrounding of CMS due to the interaction between Znq₂-CMS and polymers. The maximum emission peak of the nanocomposites had a red-shift of 28 nm as compared to pure Znq₂-CMS.     

Growth of single crystalline dendritic Li2SiO3 arrays from LiNO3 and mesoporous SiO2

A solution based wet chemistry approach has been developed for synthesizing Li₂SiO₃ using LiNO₃ and mesoporous silica as starting materials at 550 °C. A reaction path where NO and O₂ are formed as side-products is proposed. The crystals synthesized exhibit dendritic growth where the as-prepared nanodendrite is a typical 1-fold nanodendrite composed of one several microns long and some tenth of nanometers wide trunk with small branches, which are several hundreds of nanometers long and up to 70 nm in diameter. The effect of the structure of the mesoporous silica for the final morphology is discussed.     

Glucose biosensors prepared by electropolymerization of p-chlorophenylamine with and without Nafion

Two different glucose biosensors for the amperometric determination of glucose, based on poly(p-chlorophenylamide) (PCPA) and bilayer film of PCPA and Nafion (PCPA/Nafion), are successfully developed. These two biosensors show linear amperometric responses to glucose ranging from 2.0×10⁻⁴ to 3.5×10⁻² mol l⁻¹ and 5.0×10⁻⁴ to 7.5×10⁻² mol l⁻¹, respectively, with the same correlation coefficient of 0.9988. Effects of polymerization potential and polymerization time on the performance of enzyme sensors are studied. It is found that PCPA, as a non-conducting polymer, can largely reduce the influence of electroactive interferents. Introduction of inner Nafion membrane not only further eliminates the influence of ascorbic acid on the sensor response but also increases electrode stability.