Enzyme-based biosensors applications

Since diamond is inactive for the oxidation and reduction reactions of H2O2, modification of the electrode is required to make diamond suitable for the enzyme-based biosensor application. Tatsuma, et al. [33] reported the use of heme peptide and horseradish peroxidase, types of redox enzymes, based on the direct electron transfer between the diamond electrode and the redox enzyme. Another promising approach is the deposition of metal nanoparticles that have catalytic activity for the H2O2 oxidation- reduction reaction. 

In recent years the electrochemistry of the enzyme membrane has been a subject of great interest due to its significance in both theories and practical applications to biosensors (i-5). Since the enzyme electrode was first proposed and prepared by Clark et al. (6) and Updike et al. (7), enzyme-based biosensors have become a widely interested research field. Research efforts have been directed toward improved designs of the electrode and the necessary membrane materials required for the proper operation of sensors. Different methods have been developed for immobilizing the enzyme on the electrode surface, such as covalent and adsorptive couplings (8-12) of the enzymes to the electrode surface, entrapment of the enzymes in the carbon paste mixture (13 etc. The entrapment of the enzyme into a conducting polymer has become an attractive method (14-22) because of the conducting nature of the polymer matrix and of the easy preparation procedure of the enzyme electrode. The entrapment of enzymes in the polypyrrole film provides a simple way of enzyme immobilization for the construction of a biosensor. It is known that the PPy-... 

Numerous enzyme-based biosensors have been commercialized in recent three decades, mostly for clinical and environmental applications.98... 

As can be seen from Eqs. (5), (2) and (3), the reaction of electrochemical enzyme-based biosensors relies on different mechanisms the right transport of substrate, co-substrate and products. For venous blood measurements or in vivo applications the proper transport of oxygen is not maintained. Therefore, new microgel formulation has to be used based on functionalised polymers. 

Applications in Clinical Analysis An example of the application of a potentiometric enzyme-based biosensor in clinical analysis is an automated monitor designed specifically to analyze blood samples at the bedside of palicnls. The i-STAT Portable Clinical Analyzer, shown in I igure 23-14a. is a handheld device capable of determining a broad range of clinically important analytes such as polas-... 

Application of poIy(AMFc) electrode. The poly(AMFc) modified electrode was used in the construction of a flavin enzyme-based biosensor. Fig. 3B shows the effect of pH on the response of the glucose electrode. This pH profile is similar to that reported in literature with a maximum at pH of around 5.5. A pH of 5.5 was therefore used for characterization of the electrode. 

In principle, enzyme-based biosensors have potential application in the agro-food analysis, within three main areas that are food safety, food quality, and process control. The term food safety involves the concept of the production and marketing of harmless food, monitoring the presence of contaminants, such as residues of pesticides, fertilizers, heavy metals, and other toxic organic compounds also used as additives. Food quality is related not only to safety but mainly to nutritional value and acceptability. Thus, in this context freshness, appearance, flavor, texture, and composition are food characteristics that have to be controlled. Moreover, enzyme biosensors allow the determination and quantification, on-line, of compounds of interest in process control, such as fermentation, sugar, alcohols contents, and so on. 

Liu, Y., Matharu, Z., Howland, M.C., Revzin, A., Simonian, A.L., 2012b. Affinity and enzyme-based biosensors recent advances and emerging applications in cell analysis and point-of-care testing. Analytical and Bioanalytical Chemistry 404, 1181-1196. 

A review of chemical sensors and arrays [6] focuses on conducting polymers as inherent receptors, the modification of conducting polymers with receptors, the use of conducting polymers as transducers as well as some applications in combinatorial and high-throughput assays. Fundamental aspects of redox-related conductivity and pH-sensitive conductivity are included, and applications to chemical- and enzyme-based biosensors are summarized based on analyte. A variety of detection methods (electrical, electrochemical, and optical) are surveyed. 

A very specialized application of enzyme-based biosensor arrays has been reported for the resolution of pesticide mixtures containing dichlorvos and methylparaoxon, with a three-element array and a flow injection system [41]. The screen-printed, amperometric electrode array was modified with three acetylcholinesterase enzyme variants, one from electric eel and two from Drosophila (fruit fly) mutants, and were used to measure signal inhibition in conjunction with an artificial neural network. Good results down to the low uM range of pesticide concentrations were reported. 

Surface plasmon resonance (SPR) is a method for measuring adsorption of materials onto planar (frequently gold or silver) surfaces or to the surface of metal nanoparticles. Surface plasmon resonance is observed when the frequency of photons matches the frequency of oscillation of the bound metal electrons. SPR can be used in a number of colour-based biosensor applications as well as lab-on-a chip sensors. SPR has been used to follow the rate of release of DNA III polymerase holo-enzyme following gap filling between Ozaki fragments where it was... 

Particularly attractive for numerous bioanalytical applications are colloidal metal (e.g., gold) and semiconductor quantum dot nanoparticles. The conductivity and catalytic properties of such systems have been employed for developing electrochemical gas sensors, electrochemical sensors based on molecular- or polymer-functionalized nanoparticle sensing interfaces, and for the construction of different biosensors including enzyme-based electrodes, immunosensors, and DNA sensors. Advances in the application of molecular and biomolecular functionalized metal, semiconductor, and magnetic particles for electroanalytical and bio-electroanalytical applications have been reviewed by Katz et al. [142]. 

There are also RMs which are prepared for a specific application and are used for validation of relevant methods. Cobbaert et al. (1999) made use of Ion Selective Electrode (ISE)-protein-based materials when evaluating a procedure which used an electrode with an enzyme-linked biosensor to determine glucose and lactate in blood. Chance et al. (1999) are involved with the diagnosis of inherited disorders in newborn children and they prepared a series of reference materials consisting of blood spotted onto filter paper and dried, from which amino-acids can be eluted and... 

Enzyme-based optical sensor applications will be further described in this book. They are still the most widespread optical biosensors but work is needed to overcome limitations such as shelf life, long term stability, in situ measurements, miniaturization, and the marketing of competitive devices. 

N.A. Chaniotakis, Enzyme stabilization strategies based on electrolytes and polyelectrolytes for biosensor applications. Anal. Bioanal. Chem. 378, 89-95 (2002). 

Chapters 1 to 5 deal with ionophore-based potentiometric sensors or ion-selective electrodes (ISEs). Chapters 6 to 11 cover voltammetric sensors and biosensors and their various applications. The third section (Chapter 12) is dedicated to gas analysis. Chapters 13 to 17 deal with enzyme based sensors. Chapters 18 to 22 are dedicated to immuno-sensors and genosensors. Chapters 23 to 29 cover thick and thin film based sensors and the final section (Chapters 30 to 38) is focused on novel trends in electrochemical sensor technologies based on electronic tongues, micro and nanotechnologies, nanomaterials, etc. 

This book on Electrochemical (Bio)Sensor Analysis, edited by S. Alegret and A. Merko< i, is an additional step to advance the field of rapid analysis. It presents advanced sensor developments as well as practical applications of electrochemical (bio)sensors in various fields in a single source. The book contains 38 chapters grouped into seven sections (a) Potentiometric sensors, (b) Yoltammetric (bio)sensors, (c) Gas sensors, (d) Enzyme based sensors, (e) Affinity biosensors, (f) Thick and thin film biosensors, and (g) Novel trends. This interdisciplinary book has contributions from well-known specialists in the field and will be a useful resource for professionals with an interest in the application of electrochemical (bio)sensors. 

Table 13.2 summarises the different approaches used to construct enzyme electrochemical biosensors for application to food analysis based on the different types of enzymes available. Generally, the main problems of many of the proposed amperometric devices have been poor selectivity due to high potential values required to monitor the enzyme reaction, and poor sensitivity. Typical interferences in food samples are reducing compounds, such as ascorbic acid, uric acid, bilirubin and acetaminophen. Electrocatalysts, redox mediators or a second enzyme coupled reaction have been used to overcome these problems (see Table 13.2), in order to achieve the required specifications in terms of selectivity and sensitivity. 

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