Determination of the intrinsic kinetic constants of immobilized glucose oxidase and catalase

Enzyme production ofd-gluconic acid and glucose oxidase: successful tales of cascade reactions

This review mainly focuses on the use of glucose oxidase in the production ofd-gluconic acid, which is a reactant of undoubtable interest in different industrial areas. As example of diverse enzymatic cascade reactions.

Coupling and Regulation of Porous Carriers Using Plasma and Amination to Improve the Catalytic Performance of Glucose Oxidase and Catalase

Multiple enzyme systems are being increasingly used for their high-efficiency and co-immobilization is a key technology to lower the cost and improve the stability of enzymes. In this study, poly glycidyl methacrylate (PGMA) spheres were synthesized using suspension polymerization, and were used as a support to co-immobilize glucose oxidase (GOx) and catalase (CAT). Surface modification was carried out via a combination of plasma and amination to promote the properties of the catalyzer. The co-immobilized enzymes showed a more extensive range of optimum pH and temperature from 5.5 to 7.5 and 25 to 40°C, respectively, compared to free enzymes. Furthermore, the maximum activity and protein adsorption quantity of the co-immobilized enzymes reached 25.98 U/g and 6.07 mg/g, respectively. The enzymatic activity of the co-immobilized enzymes was maintained at ~70% after storage for 5 days and at 82% after three consecutive cycles, indicating that the immobilized material could be applied industrially.

Common causes of glucose oxidase instability in in vivo biosensing: a brief review

Clinical management of diabetes must overcome the challenge of in vivo glucose sensors exhibiting lifetimes of only a few days. Limited sensor life originates from compromised enzyme stability of the sensing enzyme. Sensing enzymes degrade in the presence of low molecular weight materials (LMWM) and hydrogen peroxide in vivo. Sensing enzymes could be made to withstand these degradative effects by (1) stabilizing the microenvironment surrounding the sensing enzyme or (2) improving the structural stability of the sensing enzyme genetically. We review the degradative effect of LMWM and hydrogen peroxide on the sensing enzyme glucose oxidase (GOx). In addition, we examine advances in stabilizing GOx against degradation using hybrid silica gels and genetic engineering of GOx. We conclude molecularly engineered GOx combined with silica-based encapsulation provides an avenue for designing long-term in vivo sensor systems.

Function of an implanted tissue glucose sensor for more than 1 year in animals

An implantable sensor capable of long-term monitoring of tissue glucose concentrations by wireless telemetry has been developed for eventual application in people with diabetes. The sensor telemetry system functioned continuously while implanted in subcutaneous tissues of two pigs for a total of 222 and 520 days, respectively, with each animal in both nondiabetic and diabetic states. The sensor detects glucose via an enzyme electrode that is based on differential electrochemical oxygen detection, which reduces the sensitivity of the sensor to encapsulation by the body, variations in local microvascular perfusion, limited availability of tissue oxygen, and inactivation of the enzymes. After an initial 2-week stabilization period, the implanted sensors maintained stability of calibration for extended periods. The lag between blood and tissue glucose concentrations was 11.8 +/- 5.7 and 6.5 +/- 13.3 minutes (mean +/- standard deviation), respectively, for rising and falling blood glucose challenges. The lag resulted mainly from glucose mass transfer in the tissues, rather than the intrinsic response of the sensor, and showed no systematic change over implant test periods. These results represent a milestone in the translation of the sensor system to human applications.

Stable Flexible Electrodes With Enzyme Cluster Decorated Carbon Nanotubes for Glucose-Driven Power Source in Biosensing Applications

Over the years, implantable sensor technology has found many applications in healthcare. Research projects have aimed at improving power supply lifetime for longevity of an implanted sensor system. Miniature power sources, inspired from the biofuel cell principle, can utilize enzymes (proteins) as catalysts to produce energy from fuel(s) that are perennial in the human body. Bio-nanocatalytic hierarchical structures, clusters made of enzyme molecules, can be covalently linked to the electrode’s surface to provide better enzyme loading and sustained activity. Carbon nanotube base electrodes, with high surface area for direct electron transfer, and enzyme clusters can achieve efficient enzymatic redox reaction. A redox pair of such bioelectrodes can make up a power source with improved performance. In this study, we have investigated high throughput processes for coupling enzyme catalysts with power harvesting mechanisms via a screen printing process and solution processing. The process incorporates enzyme (glucosse oxidase and catalase) micro-/nanocluster immobilization on the surface of carboxylated (functionalized) carbon nanotubes with screen printed electrodes. The 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysulfosuccinimide amide linkage chemistries were used to bind the enzyme molecules to nanotube surface, and bis[sulfosuccinimidyl] suberate (BS3) was used as the cross-linker between enzymes. Optimized enzyme cross-linking was obtained after 25 min at room temperature with 0.07 mmol BS3/nmol of enzymes, with which 44% of enzymes were immobilized onto the surface of the bioelectrode with only 24% enzyme activity lost. A cell, redox pair of bioelectrodes, was tested under continuous operation. It was able to maintain most of the enzyme activity for 7 days before complete deactivation at 16 days. Thus, the power harvesting mechanism was able to produce power continuously for 7 days. The results were also analyzed to identify impeding factors such as competitive inhibition by reaction byproduct and cathode design, and methods to rectify them have been discussed. Coupling this new and improved nanobiopower cell with a product removal mechanism and enzyme mutagenesis should provide enzyme protection and longevity. This would bring the research one step closer to development of compatible implantable battery technology for medical applications.

Immobilized glucose oxidase in implantable glucose sensor technology

Glucose oxidase has had a central role in previous glucose sensing methods and is key to the development of certain new glucose sensors. The immobilized enzyme is specific for glucose and sufficiently long-lived for many sensor applications, but new glucose sensing applications may place increased demands on the enzyme.

In vitro and in vivo degradation of glucose oxidase enzyme used for an implantable glucose biosensor

BACKGROUND

The degradation of the glucose oxidase (GOD) enzyme, commonly used in the construction of glucose sensors has been of concern for scientists for decades. Many researchers have found that GOD deactivates over time, mostly due to H2O2 oxidation. This decay can lead to the eventual failure of the sensor. However, these findings are controversial, because other researchers did not find this degradation.

METHODS

The goal of this study was twofold. The first goal was to evaluate the in vitro and in vivo stability of two commercially available GOD enzymes and the second goal was to evaluate Nafion as a protective coating of GOD. Crosslinked GOD samples were sandwiched between two 10-microm pore polycarbonate membranes (Nafion coated or uncoated) and placed in custom designed Lexan chambers. Chambers were then exposed to a total of five different environments: Dulbecco's Modified Eagle Medium (DMEM) or phosphate buffered saline (PBS) with and without a 5.6-mM glucose concentration, as well as the subcutaneous in vivo environment of 12 rats. After a period of up to 4 weeks, chambers were retrieved, opened, and tested for enzyme activity using a three-electrode system.

RESULTS

Enzyme activity showed only a slight decrease when exposed to DMEM and PBS without glucose. A more dramatic decrease in activity was observed in enzymes exposed to PBS and DMEM with 5.6 mM glucose. The in vivo environment also caused a significant decrease in enzyme activity, but the decrease was lower than for the in vitro environment with glucose conditions.

CONCLUSION

The presence of glucose in vitro and in vivo led to the production of H2O2, suggesting this to be the main agent responsible for enzyme degradation. The use of a Nafion coating did not provide any additional protection.

Glucose monitoring: state of the art and future possibilities

This article reviews the development of glucose monitoring techniques and approaches during the last decade. The predominance of the electrochemical measuring principles reported in the literature makes them a focus of this work. Biosensors are still in the main stream of the research interest of most teams due to their high selectivity for glucose determination. Systematization and classification of the glucose monitoring principles and types of glucose sensors is shown. The review gives a brief description of the basic operational principles of the most popular types of glucose biosensors, providing an enhanced bibliography of the original works of the main groups in establishing or significantly contributing to the development of the particular type of glucose biosensor. Different design approaches are overviewed including needle-type sensors, sensors for chronical implantation and the combination of the glucose biosensors with microdialysis sampling technique. The authors approach for replacing of the spent enzyme and thus recharging the sensor in situ while implanted is widely discussed. This approach provides a way to increase the lifespan of the system and ultimately, it could lead to rare transcutaneous interventions for refilling of the implanted sensor.

Bioreactor applications of glucose oxidase covalently bonded on pHEMA membranes

Glucose oxidase was immobilized onto poly(2-hydroxyethyl methacrylate) membranes by covalent bonding through epichlorohydrin. The highest immobilization efficiency was found to be 17.4%. The Km values were 5.9 and 8.8 mM for free and bound enzymes, respectively, and the Vmax values were 0.071 and 0.067 mM/min for free and bound enzymes. When the medium was saturated with oxygen Km was not altered significantly but Vmax was. The optimum pHs for the free and bound enzyme were determined to be 5 and 6, respectively, and the optimum temperature was 30 degrees C for both forms. The inactivation constant for the bound enzyme was found to be 1.7 x 10(-4) min-1.

Immobilization of glucose oxidase: a comparison of entrapment and covalent bonding

Glucose oxidase was immobilized onto poly(2-hydroxyethyl methacrylate) (pHEMA) membranes by two methods: by covalent bonding through epichlorohydrin and by entrapment between pHEMA membranes. The highest immobilization efficiency was found to be 17.4% and 93.7% for the covalent bonding and entrapment, respectively. The Km values were 5.9 mmol dm-3, 8.8 mmol dm-3 and 12.4 mmol dm-3 for free, bound and entrapped enzyme, respectively. The Vmax values were 0.071 mmol dm-3 min-1, 0.067 mmol dm-3 min-1 and 0.056 mmol dm-3 min-1 for free, bound and entrapped enzyme. When the medium was saturated with oxygen, Km was not significantly altered but Vmax was. The optimum pH values for the free, covalently-bound and entrapped enzyme were determined to be 5, 6, and 7, respectively. The optimum temperature was 30 degrees C for free or covalently-bound enzyme but 35 degrees C for entrapped enzyme. The deactivation constant for bound enzyme was determined as 1.7 x 10(-4) min-1 and 6.9 x 10(-4) min-1 for the entrapped enzyme.

Dynamic concentration challenges for biosensor characterization

A method and apparatus are described for characterization of the steady state and dynamic response of biosensors. The apparatus produces a steady stream of homogeneously mixed analyte whose concentration can be fixed at discrete values or varied continuously. The device is ideally suited for continuously operated biosensors, but is also effective for biosensors that operate in discrete sampling modes. The system permits simultaneous testing of several sensors and determination of the accuracy, precision and repeatability of sensor response. The characteristics of this testing apparatus were validated with ferrocyanide and glucose as indicators. As an example of use of the apparatus, concentration ramps were created and used to complement conventional step changes for characterizing an implantable glucose sensor. The ramp rate can be adjusted easily by scaling the apparatus to simulate the rate of concentration change anticipated during actual monitoring situations.