Composite Transducers for Amperometric Biosensors. The Glucose Sensor

Enzyme Biosensors for Biomedical Applications: Strategies for Safeguarding Analytical Performances in Biological Fluids

Enzyme-based chemical biosensors are based on biological recognition. In order to operate, the enzymes must be available to catalyze a specific biochemical reaction and be stable under the normal operating conditions of the biosensor. Design of biosensors is based on knowledge about the target analyte, as well as the complexity of the matrix in which the analyte has to be quantified. This article reviews the problems resulting from the interaction of enzyme-based amperometric biosensors with complex biological matrices containing the target analyte(s). One of the most challenging disadvantages of amperometric enzyme-based biosensor detection is signal reduction from fouling agents and interference from chemicals present in the sample matrix. This article, therefore, investigates the principles of functioning of enzymatic biosensors, their analytical performance over time and the strategies used to optimize their performance. Moreover, the composition of biological fluids as a function of their interaction with biosensing will be presented.

Amperometric glucose biosensor utilizing FAD-dependent glucose dehydrogenase immobilized on nanocomposite electrode

Amperometric glucose biosensors utilizing commercially available FAD-dependent glucose dehydrogenases from two strains of Aspergillus species are described. Enzymes were immobilized on nanocomposite electrode consisting of multi-walled carbon nanotubes by entrapment between chitosan layers. Unlike the common glucose oxidase based biosensor, the presented biosensors appeared to be O(2)-independent. The optimal amount of enzymes, working potential and pH value of working media of the glucose biosensors were determined. The biosensor utilizing enzyme isolated from Aspergillus sp. showed linearity over the range from 50 to 960 μM and from 70 to 620 μM for enzyme from Aspergillus oryzae. The detection limits were 4.45 μM and 4.15 μM, respectively. The time of response was found to be 60 s. The biosensors showed excellent operational stability - no loss of sensitivity after 100 consecutive measurements and after the storage for 4 weeks at 4 °C in phosphate buffer solution. When biosensors were held in a dessicator at room temperature without use, they kept the same response ability at least after 6 months. Finally, the results obtained from measurements of beverages and wine samples were compared with those obtained with the enzymatic-spectrophotometric and standard HPLC methods, respectively. Good correlation between results in case of analysis of real samples and good analytical performance of presented glucose biosensor allows to use presented concept for mass production and commercial use.

Prospects of conducting polymers in biosensors

Applications of conducting polymers to biosensors have recently aroused much interest. This is because these molecular electronic materials offer control of different parameters such as polymer layer thickness, electrical properties and bio-reagent loading, etc. Moreover, conducting polymer based biosensors are likely to cater to the pressing requirements such as biocompatibility, possibility of in vivo sensing, continuous monitoring of drugs or metabolites, multi-parametric assays, miniaturization and high information density. This paper deals with the emerging trends in conducting polymer based biosensors during the last about 5 years.

Recent developments, characteristics, and potential applications of electrochemical biosensors

The objective of this study is to analyze the technical importance, performance, techniques, advantages, and disadvantages of the biosensors in general and of the electrochemical biosensors in particular. A product of reaction diffuses to the transducer in the first generation biosensors (based on Clark biosensors). The mediated biosensors or second generation biosensors use specific mediators between the reaction and the transducer to improve sensitivity. The second generation biosensors involve two steps: first, there is a redox reaction between enzyme and substrate that is reoxidized by the mediator, and eventually the mediator is oxidized by the electrode. No normal product or mediator diffusion is directly involved in the third generation biosensors, direct biosensors. Based on the type of transducer, current biosensors are divided into optical, mass, thermal, and electrochemical sensors. They are used in medical diagnostics, food quality controls, environmental monitoring, and other applications. These biosensors are also grouped under two broad categories of sensors: direct and indirect detection systems. Moreover, these systems could be further grouped into continuous or batch operation. Therefore, amperometric biosensors and their current applications are focused on more in detail since they are the most commonly used biosensors in monitoring and diagnosing tests in clinical analysis. Problems related to the commercialization of medical, environmental, and industrial biosensors as well as their performance characteristics, their competitiveness in comparison to the conventional analytical tools, and their costs determine the future development of these biosensors.

Glucose biosensor prepared by glucose oxidase encapsulated sol-gel and carbon-nanotube-modified basal plane pyrolytic graphite electrode

A new glucose biosensor has been fabricated by immobilizing glucose oxidase into a sol-gel composite at the surface of a basal plane pyrolytic graphite (bppg) electrode modified with multiwall carbon nanotube. First, the bppg electrode is subjected to abrasive immobilization of carbon nanotubes by gently rubbing the electrode surface on a filter paper supporting the carbon nanotubes. Second, the electrode surface is covered with a thin film of a sol-gel composite containing encapsulated glucose oxidase. The carbon nanotubes offer excellent electrocatalytic activity toward reduction and oxidation of hydrogen peroxide liberated in the enzymatic reaction between glucose oxidase and glucose, enabling sensitive determination of glucose. The amperometric detection of glucose is carried out at 0.3 V (vs saturated calomel electrode) in 0.05 M phosphate buffer solution (pH 7.4) with linear response range of 0.2-20 mM glucose, sensitivity of 196 nA/mM, and detection limit of 50 microM (S/N=3). The response time of the electrode is < 5s when it is stored dried at 4 degrees C, the sensor showed almost no change in the analytical performance after operation for 3 weeks. The present carbon nanotube sol-gel biocomposite glucose oxidase sensor showed excellent properties for the sensitive determination of glucose with good reproducibility, remarkable stability, and rapid response and in comparison to bulk modified composite biosensors the amounts of enzyme and carbon nanotube needed for electrode fabrication are dramatically decreased.

Amperometric detection of phenolic compounds by polypyrrole-based composite carbon paste electrodes

This contribution describes new composite carbon paste electrodes (CPEs) for the determination of phenolic compounds. The composite CPEs were prepared by in situ generation of polypyrrole (PPy) within a paste containing the enzyme polyphenol oxidase (PPO). The best paste composition (enzyme/pyrrole monomer/carbon particles/Nujol) was determined for a model enzyme, glucose oxidase (GOx) according to the enzymatic activity of the resulting electrodes and to the enzyme leakage from the paste during storage in phosphate buffer. The in situ electrogenerated PPy improves the enzyme immobilisation within the paste since practically no enzyme was lost in solution after 72 h of immersion. Moreover, the enzyme activity remains particularly stable under storage since the biocomposite structure conserves 80% of its activity after 1 month of storage. Following the optimisation of the paste composition, PPO-based carbon paste biosensors were prepared and presented excellent analytical properties toward catechol detection with a sensitivity of 4.7 A M(-1) cm(-2) and a response time lower than 20 s. The resulting biosensors were applied to the determination of polyphenolic compounds (e.g., epicatechin and ferulic acid).

Determination of β-d-glucose using flow injection analysis and composite-type amperometric tubular biosensors

An amperometric tubular cell involving composite biosensors for the determination of beta-d-glucose in a flow injection analysis (FIA) system is proposed. Diverse configurations and parameters are evaluated to improve the system's response. The configuration producing less noise resulted when the biosensor was located closer to the auxiliary electrode, which also required coupling both electrodes within the system under a continuous flow regime. Further, we report on the influence of the active area of the biosensor and of the flow rate used. Statistical analyses of the data revealed two regions with a linear response range for the determination of beta-d-glucose, with a detection limit of 4.7 x 10(-4) M and in the low concentration region a sensitivity of 17.46 +/- 0.12 microAM(-1). At the beta-d-glucose concentrations studied there was no evidence of enzymatic saturation. An increment on the ionic strength of the sample and carrier passing through the analysis system decreases its sensitivity. The reproducibility of the analytical system in terms of its standard deviation was 2.9% with a 95% confidence level, having a lifetime that lasted at least 100 days. beta-d-Glucose was determined in different commercial medical glucose-containing solutions, the experimental results are in good agreement with those reported by the manufacturer.

Composite Carbon Paste Biosensor for Phenolic Derivatives Based on in Situ Electrogenerated Polypyrrole Binder

Amperometric biosensors based on new composite carbon paste (CPE) electrodes have been designed for the determination of phenolic compounds. The composite CPEs were prepared by in situ generation of polypyrrole (PPy) within a paste containing the enzyme polyphenol oxidase (PPO). The best paste composition (enzyme/pyrrole monomer/carbon particles/Nujol) was determined for a model enzyme, glucose oxidase, according to the enzymatic activity of the resulting electrodes and to the enzyme leakage from the paste during storage in phosphate buffer. The in situ electrogenerated PPy enables improvement in enzyme immobilization within the paste since practically no enzyme was lost in solution after 72 h of immersion. Moreover, the enzyme activity remains particularly stable under storage since the biocomposite structure maintains 80% of its activity after 1-month storage. Following the optimization of the paste composition, PPO-based carbon paste biosensors were prepared and presented excellent analytical properties toward catechol detection with a sensitivity of 4.7 A M(-1) cm(-2) and a response time lower than 20 s. The resulting biosensors were finally applied to the determination of epicatechin and ferulic acid as flavonol and polyphenol model, respectively.

A glucose/hydrogen peroxide biofuel cell that uses oxidase and peroxidase as catalysts by composite bulk-modified bioelectrodes based on a solid binding matrix

An improved composite bulk-modified bioelectrode setup based on a solid binding matrix (SBM) has been used to develop a glucose/hydrogen peroxide biofuel cell. Fuel is combined through a catalytically promoted reaction with oxygen into and oxidized species and electricity. The present work explores the feasibility of a sugar-feed biofuel cell based on SBM technology. The biofuel cell that utilizes mediators as electron transporters from the glucose oxidation pathway of the enzyme directly to electrodes is considered in this work. The anode was a glucose oxidase (GOx, EC 1.1.3.4)/ferrocene-modified SBM/graphite composite electrode. The cathode was a horseradish peroxidase (HRP, EC 1.11.1.7)/ferrocene-modified SBM/graphite composite electrode. The composite transducer material was layered on a wide polymeric surface to obtain the biomodified electrodic elements, anodes and cathodes and were assembled into a biofuel cell using glucose and H(2)O(2) as the fuel substrate and the oxidizer. The electrochemical properties and the characteristics of single composite bioelectrodes are described. The open-circuit voltage of the cell was 0.22 V, and the power output of the cell was 0.15 microW/cm(2) at 0.021 V. The biofuel cell proved to be stable for an extended period of continuous work (30 days). The reproducibility of the biotransducers fabrication was also investigated. In addition, an application of presented biofuel cell, e.g. the use of hydrolyzed corn syrup as renewable biofuels, was discussed.

Amperometric Determination of Glucose with a Carbon Paste Biosensor

A simple glucose biosensor has been developed by bulk modification of a carbon paste electrode with glucose oxidase as a biocomponent and manganese dioxide as a mediator. The sensor was employed as amperometric detector in a flow-injection system at 21 °C in 0.2 M phosphate buffer (pH 7.5). At an applied working potential of 0.48 V vs Ag/AgCl and a flow rate of 0.2 ml min-1, the sensor exhibited well reproducible amperometric response to glucose. A linear relation between the peak current and the analyte concentration was found between 20 and 500 mg l-1 glucose with a detection limit (3σ) of 10.5 mg l-1 glucose. The sensor can be operated continuously for 12 h without any loss in the signal height and can be used for the determination of glucose in white wine samples.

Selective and sensitive biosensor for theophylline based on xanthine oxidase electrode

Milk and microbial xanthine oxidases (XOs) were used for the construction of amperometric enzyme electrodes. Substrate specificity differences of these enzymes were studied. Of the two enzymes, only the microbial XO was found to oxidize theophylline, but not theobromine and caffeine. The substrate specificity of microbial XO was affected by pH, where the optimum for xanthine was 5.5, while for theophylline it was in the range from 6.5 to 8.5. The theophylline biosensor showed a low detection limit of 2 x 10(-7) M and signal linearity up to 5 x 10(-5) M. The sensitivity of the microbial XO electrode to theophylline could be selectively eliminated by immersion in alkaline phosphate solution, thus allowing for the construction of a blank electrode for differential measurements. The feasibility of this approach has been demonstrated by the determination of free (unbound) and total theophylline in blood samples. The biosensor exhibited good operational (>6 h) and shelf (>3 months) stability when trehalose was used as a stabilizer of the biocatalytic layer.

A glucose oxidase electrode based on electropolymerized conducting polymer with polyanion-enzyme conjugated dopant

An enzyme immobilization method has been developed by electropolymerization chemistry of conducting polymer which results in a more effective and reproducible enzyme electrode. As a model system, in this study, glucose oxidase (GOD) was conjugated with a polyanion, poly(2-acrylamido-2-methylpropane sulfonic acid), via a poly(ethylene oxide) spacer to improve the efficiency of enzyme immobilization into a conducting polymer. GOD was successfully conjugated with a high conjugation yield of more than 90%, and its bioactivity was preserved. The resulting polyanion-GOD conjugate was used as a dopant for the electrochemical polymerization of pyrrole. Polypyrrole was effectively deposited on a Pt wire working electrode with the polyanion-GOD conjugate. The enzyme electrode responded to glucose concentrations of up to 20 mM with a sensitivity of 40 nA/mM at an applied potential of 0.4 V within a response time of 30 s. Although the response signal decreased at the low applied potential of 0.3 V, the enzyme electrode showed sensitive response signals of about 16 nA/mM up to 20 mM in glucose concentration. Under the deoxygenated condition, reduced but clear response current signal was obtained. The results show that the current signal response of the enzyme electrode to glucose concentration may be produced by mixed mechanisms.

Amperometric biosensors based on solid binding matrices applied in food quality monitoring

Solid binding matrix (SBM) based composite transducers have been used for development of series of multibiosensor systems applicable in various fields. Here we present two hybrid three-channel multibiosensors for simultaneous amperometric operation in food quality control, i.e. glucose/fructose/ethanol multibiosensor, based on glucose oxidase/fructose dehydrogenase/alcohol dehydrogenase surface-modified enzyme electrodes and L-lactate/L-malate/sulfite multibiosensor, based on L-lactate dehydrogenase/L-malate dehydrogenase/sulfite oxidase surface-modified enzyme electrodes. Different parameters have been studied in order to optimize the response of the multibiosensor systems. The multibiosensor showed a good sensitivity, linear range and storage stability. The multibiosensors were used for the determination of glucose, fructose, ethanol, L-lactate, L-malate and sulfite in samples of wine, resulting in a good agreement with data certified by the supplier. Comparison of various designs, surface-modified, bulk-modified and thick-cover, of SBM based biosensors is studied on the example of fructose biosensor.